diff --git a/AGENTS.md b/AGENTS.md
index a414e40d..de787654 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -7,4 +7,4 @@
   - Before providing a Staging preview URL, request `/api/microcosm/staging/runs` for the selected country and confirm that the JSON response reports the repository as available. Checking only the HTTP status is insufficient because the route can return HTTP 200 with `available: false`. Treat 401, 403, the 404 response Hugging Face may return for an unauthorized private repository, and any `available: false` response as a failed launch.
 - When investigating a discrepant Microcosm calibration target, follow [the shared investigation workflow](docs/ai/workflows/investigate-microcosm-target.md) and its linked role-specific reviews.
 - Before starting the application for Cross-dataset work, configure exactly one DIR or URL artifact location for each country you will use, as described in [the Cross-dataset application configuration](docs/cross-dataset-api.md#configure-the-application).
-- Adding a Microcosm country is one entry in `frontend/lib/microcosm/countries.ts`; pages are gated by the registration's capabilities and the release artifact's `country` block, never by country code (see [the spec-driven countries note](docs/spec-driven-countries.md)).
+- Adding a Microcosm country is one entry in `frontend/packages/calibration-tree/src/countries.ts`; pages are gated by the registration's capabilities and the release artifact's `country` block, never by country code (see [the spec-driven countries note](docs/spec-driven-countries.md)).
diff --git a/CLAUDE.md b/CLAUDE.md
index e8b7c29a..d2891d09 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -2,4 +2,4 @@
 
 - When investigating a discrepant Microcosm calibration target, follow [the shared investigation workflow](docs/ai/workflows/investigate-microcosm-target.md) and its linked role-specific reviews.
 - Before starting the application for Cross-dataset work, configure exactly one DIR or URL artifact location for each country you will use, as described in [the Cross-dataset application configuration](docs/cross-dataset-api.md#configure-the-application).
-- Adding a Microcosm country is one entry in `frontend/lib/microcosm/countries.ts`; pages are gated by the registration's capabilities and the release artifact's `country` block, never by country code (see [the spec-driven countries note](docs/spec-driven-countries.md)).
+- Adding a Microcosm country is one entry in `frontend/packages/calibration-tree/src/countries.ts`; pages are gated by the registration's capabilities and the release artifact's `country` block, never by country code (see [the spec-driven countries note](docs/spec-driven-countries.md)).
diff --git a/README.md b/README.md
index bbdf607c..c6fe1fe0 100644
--- a/README.md
+++ b/README.md
@@ -204,7 +204,7 @@ with `POPULACE_UK_STAGING_HF_REPO` or `POPULACE_UK_STAGING_HF_REVISION`. Never
 use a `NEXT_PUBLIC_` variable for a private-repository credential.
 
 The staging contract fixtures under
-`frontend/lib/microcosm/fixtures/staging-contract/` are byte-identical copies
+`frontend/packages/calibration-tree/src/fixtures/staging-contract/` are byte-identical copies
 of Microcosm's canonical producer fixtures. The consumer tests pin each
 version's `SHA256SUMS` digest and verify every listed file. A contract change
 must update the canonical Microcosm fixture, its digest manifest, this copy,
diff --git a/docs/calibration-tree-artifacts.md b/docs/calibration-tree-artifacts.md
index 390f2a59..240245dc 100644
--- a/docs/calibration-tree-artifacts.md
+++ b/docs/calibration-tree-artifacts.md
@@ -4,6 +4,23 @@ The calibration explorer reads precomputed schema-6 JSON from private Vercel
 Blob storage. The browser does not download calibration diagnostics or rebuild
 the hierarchy. Schemas 1 through 5 are unsupported.
 
+## Code
+
+The builder, the schema-6 types, parsers and serializers, the Blob I/O, the
+release and staging readers the builder reads from, and the publisher
+(`src/publish-calibration-tree.ts`, run by `bun run publish:calibration-tree`)
+live in the `@policyengine/calibration-tree` workspace package at
+`frontend/packages/calibration-tree/`. The dashboard imports it through its
+subpath exports, such as `@policyengine/calibration-tree/calibration-tree-bundle`.
+The package imports only its own modules, Node built-ins and `@vercel/blob`,
+and its boundary test enforces that.
+
+`src/fixtures/calibration-tree-golden.json` records the exact bytes the builder
+writes for representative US and UK release and staging inputs, the
+comparisons between them, and the manifest. The golden tests require every
+change to reproduce it. Regenerate it only for an intended output change, as
+`src/test-support/calibration-tree-golden-cases.ts` describes.
+
 ## Required Blob folder schema
 
 ```text
@@ -355,7 +372,8 @@ fails publication and therefore fails the GitHub Actions job.
 
 ## Verification
 
-Run from `frontend/`:
+Run from `frontend/`; `bun test` includes the package's tests and
+`bun run lint` also typechecks the package:
 
 ```sh
 bun test
@@ -363,6 +381,9 @@ bun run lint
 bun run build
 ```
 
+To check the package on its own, run `bun test` and `bun run typecheck` from
+`frontend/packages/calibration-tree/`.
+
 Then verify that:
 
 1. The manifest and all parts declare schema 6.
diff --git a/docs/spec-driven-countries.md b/docs/spec-driven-countries.md
index 7680c713..b285d73c 100644
--- a/docs/spec-driven-countries.md
+++ b/docs/spec-driven-countries.md
@@ -24,7 +24,7 @@ contract: they are served only by `/microcosm/datasets` from
 
 ## Code-owned metadata that remains
 
-`COUNTRY_REGISTRY` in `frontend/lib/microcosm/countries.ts` is the only required
+`COUNTRY_REGISTRY` in `frontend/packages/calibration-tree/src/countries.ts` is the only required
 registration point: country unions and parsers, selector lists, dataset and
 national-geography labels, public/private link behavior, and page gating read
 the registration or the artifact `country` block. Overview and target-browser
@@ -73,10 +73,10 @@ production tables.
 ### Country
 
 `release_manifest.country` is read by `releaseCountry` in
-`frontend/lib/microcosm/latest-artifact.ts` and served as `country` on the
+`frontend/packages/calibration-tree/src/latest-artifact.ts` and served as `country` on the
 overview summary and the target-diagnostics page (client type
 `MicrocosmArtifactCountry`). Registration lives in
-`frontend/lib/microcosm/countries.ts`; adding a country is one entry there.
+`frontend/packages/calibration-tree/src/countries.ts`; adding a country is one entry there.
 
 ```json
 {
diff --git a/frontend/app/api/microcosm/builds/route.ts b/frontend/app/api/microcosm/builds/route.ts
index 5dfbd34d..0e06f6b9 100644
--- a/frontend/app/api/microcosm/builds/route.ts
+++ b/frontend/app/api/microcosm/builds/route.ts
@@ -2,7 +2,7 @@ import { NextResponse } from "next/server";
 
 import { parseBuildSource } from "@/lib/microcosm/build-source";
 import { loadBuildRuns } from "@/lib/microcosm/build-runs";
-import { parseCountry, scrub } from "@/lib/microcosm/latest-artifact";
+import { parseCountry, scrub } from "@policyengine/calibration-tree/latest-artifact";
 
 export const dynamic = "force-dynamic";
 export const revalidate = 0;
diff --git a/frontend/app/api/microcosm/builds/run/route.ts b/frontend/app/api/microcosm/builds/run/route.ts
index d6c1250e..cf80ae7a 100644
--- a/frontend/app/api/microcosm/builds/run/route.ts
+++ b/frontend/app/api/microcosm/builds/run/route.ts
@@ -2,7 +2,7 @@ import { NextResponse } from "next/server";
 
 import { parseBuildSource } from "@/lib/microcosm/build-source";
 import { loadBuildRun } from "@/lib/microcosm/build-runs";
-import { parseCountry, scrub } from "@/lib/microcosm/latest-artifact";
+import { parseCountry, scrub } from "@policyengine/calibration-tree/latest-artifact";
 
 export const dynamic = "force-dynamic";
 export const revalidate = 0;
diff --git a/frontend/app/api/microcosm/compare/route.ts b/frontend/app/api/microcosm/compare/route.ts
index bc6fa558..5083fb65 100644
--- a/frontend/app/api/microcosm/compare/route.ts
+++ b/frontend/app/api/microcosm/compare/route.ts
@@ -6,7 +6,7 @@ import {
   loadPointerReleaseId,
   parseCountry,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 export const revalidate = 21_600;
 export const runtime = "nodejs";
diff --git a/frontend/app/api/microcosm/comparison-tree/route.test.ts b/frontend/app/api/microcosm/comparison-tree/route.test.ts
index 4cf1fe9c..c0658c2d 100644
--- a/frontend/app/api/microcosm/comparison-tree/route.test.ts
+++ b/frontend/app/api/microcosm/comparison-tree/route.test.ts
@@ -4,7 +4,7 @@ import { gzipSync } from "node:zlib";
 import {
   calibrationComparisonBuildArtifactId,
   calibrationComparisonPairArtifactId,
-} from "@/lib/microcosm/calibration-comparison-bundle";
+} from "@policyengine/calibration-tree/calibration-comparison-bundle";
 import {
   createCalibrationComparisonTreeHandler,
   type CalibrationComparisonTreeRouteDependencies,
diff --git a/frontend/app/api/microcosm/comparison-tree/route.ts b/frontend/app/api/microcosm/comparison-tree/route.ts
index d1692fe1..2001f26d 100644
--- a/frontend/app/api/microcosm/comparison-tree/route.ts
+++ b/frontend/app/api/microcosm/comparison-tree/route.ts
@@ -1,24 +1,24 @@
 import { NextResponse } from "next/server";
 
 import { withBasePath } from "@/lib/base-path";
-import { ensureCalibrationComparison } from "@/lib/microcosm/calibration-comparison-blob";
+import { ensureCalibrationComparison } from "@policyengine/calibration-tree/calibration-comparison-blob";
 import {
   calibrationComparisonBuildArtifactId,
   calibrationComparisonPairArtifactId,
-} from "@/lib/microcosm/calibration-comparison-bundle";
-import { getCalibrationTreeBlob } from "@/lib/microcosm/calibration-tree-blob";
+} from "@policyengine/calibration-tree/calibration-comparison-bundle";
+import { getCalibrationTreeBlob } from "@policyengine/calibration-tree/calibration-tree-blob";
 import { immutableCalibrationTreePartResponse } from "@/lib/microcosm/calibration-tree-http";
 import {
   isCalibrationTreePart,
   isSha256,
   type CalibrationTreePart,
-} from "@/lib/microcosm/calibration-tree-artifact";
+} from "@policyengine/calibration-tree/calibration-tree-artifact";
 import {
   isCountry,
   selectableCountries,
   type MicrocosmCountry,
-} from "@/lib/microcosm/countries";
-import type { TargetChangeMode } from "@/lib/microcosm/target-change";
+} from "@policyengine/calibration-tree/countries";
+import type { TargetChangeMode } from "@policyengine/calibration-tree/target-change";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
diff --git a/frontend/app/api/microcosm/comparison-tree/target-detail/route.test.ts b/frontend/app/api/microcosm/comparison-tree/target-detail/route.test.ts
index 465c6184..37c1e541 100644
--- a/frontend/app/api/microcosm/comparison-tree/target-detail/route.test.ts
+++ b/frontend/app/api/microcosm/comparison-tree/target-detail/route.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from "bun:test";
 
-import type { CalibrationTreeComparisonTargetDetailResponse } from "@/lib/microcosm/calibration-tree-artifact";
+import type { CalibrationTreeComparisonTargetDetailResponse } from "@policyengine/calibration-tree/calibration-tree-artifact";
 import {
   createCalibrationComparisonTargetDetailHandler,
   type CalibrationComparisonTargetDetailRouteDependencies,
diff --git a/frontend/app/api/microcosm/comparison-tree/target-detail/route.ts b/frontend/app/api/microcosm/comparison-tree/target-detail/route.ts
index a078c0dc..e42b3d11 100644
--- a/frontend/app/api/microcosm/comparison-tree/target-detail/route.ts
+++ b/frontend/app/api/microcosm/comparison-tree/target-detail/route.ts
@@ -1,12 +1,12 @@
 import { NextResponse } from "next/server";
 
-import { loadCalibrationComparisonTargetDetail } from "@/lib/microcosm/calibration-comparison-blob";
-import { isSha256 } from "@/lib/microcosm/calibration-tree-artifact";
+import { loadCalibrationComparisonTargetDetail } from "@policyengine/calibration-tree/calibration-comparison-blob";
+import { isSha256 } from "@policyengine/calibration-tree/calibration-tree-artifact";
 import {
   isCountry,
   selectableCountries,
   type MicrocosmCountry,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
diff --git a/frontend/app/api/microcosm/cross-dataset/route.ts b/frontend/app/api/microcosm/cross-dataset/route.ts
index 10ec163f..924f10d3 100644
--- a/frontend/app/api/microcosm/cross-dataset/route.ts
+++ b/frontend/app/api/microcosm/cross-dataset/route.ts
@@ -3,7 +3,7 @@ import { NextResponse } from "next/server";
 import { ArtifactError } from "@/lib/cross-dataset/artifact";
 import { crossDatasetApiResponse } from "@/lib/cross-dataset/query";
 import { configuredCrossDatasetReader } from "@/lib/cross-dataset/source";
-import { parseCountry } from "@/lib/microcosm/latest-artifact";
+import { parseCountry } from "@policyengine/calibration-tree/latest-artifact";
 
 export const revalidate = 300;
 export const runtime = "nodejs";
diff --git a/frontend/app/api/microcosm/releases/route.ts b/frontend/app/api/microcosm/releases/route.ts
index 53336b66..1a1b1c05 100644
--- a/frontend/app/api/microcosm/releases/route.ts
+++ b/frontend/app/api/microcosm/releases/route.ts
@@ -5,7 +5,7 @@ import {
   loadReleases,
   parseCountry,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 export const revalidate = 60;
 
diff --git a/frontend/app/api/microcosm/route.ts b/frontend/app/api/microcosm/route.ts
index e734c9e8..e9401726 100644
--- a/frontend/app/api/microcosm/route.ts
+++ b/frontend/app/api/microcosm/route.ts
@@ -11,7 +11,7 @@ import {
   parseCountry,
   microcosmRepo,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 export const revalidate = 21_600;
 export const runtime = "nodejs";
diff --git a/frontend/app/api/microcosm/staging/compare/route.ts b/frontend/app/api/microcosm/staging/compare/route.ts
index df8ef2d9..f5ba57a3 100644
--- a/frontend/app/api/microcosm/staging/compare/route.ts
+++ b/frontend/app/api/microcosm/staging/compare/route.ts
@@ -1,12 +1,12 @@
 import { NextResponse } from "next/server";
 
-import { hasCapability } from "@/lib/microcosm/countries";
+import { hasCapability } from "@policyengine/calibration-tree/countries";
 import {
   loadPointerReleaseId,
   parseCountry,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
-import { loadStagingComparison } from "@/lib/microcosm/staging-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
+import { loadStagingComparison } from "@policyengine/calibration-tree/staging-artifact";
 
 export const dynamic = "force-dynamic";
 export const revalidate = 0;
diff --git a/frontend/app/api/microcosm/staging/run/route.ts b/frontend/app/api/microcosm/staging/run/route.ts
index 586e2827..0c01d4cf 100644
--- a/frontend/app/api/microcosm/staging/run/route.ts
+++ b/frontend/app/api/microcosm/staging/run/route.ts
@@ -1,8 +1,8 @@
 import { NextResponse } from "next/server";
 
-import { hasCapability } from "@/lib/microcosm/countries";
-import { parseCountry, scrub } from "@/lib/microcosm/latest-artifact";
-import { loadStagingRun } from "@/lib/microcosm/staging-artifact";
+import { hasCapability } from "@policyengine/calibration-tree/countries";
+import { parseCountry, scrub } from "@policyengine/calibration-tree/latest-artifact";
+import { loadStagingRun } from "@policyengine/calibration-tree/staging-artifact";
 
 export const dynamic = "force-dynamic";
 export const revalidate = 0;
diff --git a/frontend/app/api/microcosm/staging/runs/route.ts b/frontend/app/api/microcosm/staging/runs/route.ts
index 2a1def49..418fc4db 100644
--- a/frontend/app/api/microcosm/staging/runs/route.ts
+++ b/frontend/app/api/microcosm/staging/runs/route.ts
@@ -1,7 +1,7 @@
 import { NextResponse } from "next/server";
 
-import { loadStagingRuns } from "@/lib/microcosm/staging-artifact";
-import { parseCountry, scrub } from "@/lib/microcosm/latest-artifact";
+import { loadStagingRuns } from "@policyengine/calibration-tree/staging-artifact";
+import { parseCountry, scrub } from "@policyengine/calibration-tree/latest-artifact";
 
 export const dynamic = "force-dynamic";
 export const revalidate = 0;
diff --git a/frontend/app/api/microcosm/staging/target-change-tree/route.ts b/frontend/app/api/microcosm/staging/target-change-tree/route.ts
index 5dd51949..b4ab3afe 100644
--- a/frontend/app/api/microcosm/staging/target-change-tree/route.ts
+++ b/frontend/app/api/microcosm/staging/target-change-tree/route.ts
@@ -5,13 +5,13 @@ import {
   classifyApiError,
   parseCountry,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
-import { isSha256 } from "@/lib/microcosm/calibration-tree-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
+import { isSha256 } from "@policyengine/calibration-tree/calibration-tree-artifact";
 import {
   loadStagingTargetChangeDataset,
   loadStagingTargetChangeDatasetFromBuild,
-} from "@/lib/microcosm/staging-artifact";
-import type { TargetChangeMode } from "@/lib/microcosm/target-change";
+} from "@policyengine/calibration-tree/staging-artifact";
+import type { TargetChangeMode } from "@policyengine/calibration-tree/target-change";
 import { buildTargetChangeTree } from "@/lib/microcosm/target-change-tree";
 
 export const dynamic = "force-dynamic";
diff --git a/frontend/app/api/microcosm/staging/target-diagnostics/route.ts b/frontend/app/api/microcosm/staging/target-diagnostics/route.ts
index 8da6e8b2..80254929 100644
--- a/frontend/app/api/microcosm/staging/target-diagnostics/route.ts
+++ b/frontend/app/api/microcosm/staging/target-diagnostics/route.ts
@@ -1,8 +1,8 @@
 import { NextResponse } from "next/server";
 
-import { hasCapability } from "@/lib/microcosm/countries";
-import { parseCountry, scrub } from "@/lib/microcosm/latest-artifact";
-import { loadStagingTargetDiagnostics } from "@/lib/microcosm/staging-artifact";
+import { hasCapability } from "@policyengine/calibration-tree/countries";
+import { parseCountry, scrub } from "@policyengine/calibration-tree/latest-artifact";
+import { loadStagingTargetDiagnostics } from "@policyengine/calibration-tree/staging-artifact";
 
 export const dynamic = "force-dynamic";
 export const revalidate = 0;
diff --git a/frontend/app/api/microcosm/staging/target-tree/route.ts b/frontend/app/api/microcosm/staging/target-tree/route.ts
index 4dae4471..748a113c 100644
--- a/frontend/app/api/microcosm/staging/target-tree/route.ts
+++ b/frontend/app/api/microcosm/staging/target-tree/route.ts
@@ -1,9 +1,9 @@
 import { NextResponse } from "next/server";
 
-import { buildCalibrationTree, type CalibrationTreeTarget } from "@/lib/microcosm/calibration-tree";
+import { buildCalibrationTree, type CalibrationTreeTarget } from "@policyengine/calibration-tree/calibration-tree";
 import { calibrationTreeRequestState } from "@/lib/microcosm/calibration-tree-request";
-import { classifyApiError, parseCountry, scrub } from "@/lib/microcosm/latest-artifact";
-import { loadStagingCalibration } from "@/lib/microcosm/staging-artifact";
+import { classifyApiError, parseCountry, scrub } from "@policyengine/calibration-tree/latest-artifact";
+import { loadStagingCalibration } from "@policyengine/calibration-tree/staging-artifact";
 
 export const dynamic = "force-dynamic";
 export const revalidate = 0;
diff --git a/frontend/app/api/microcosm/target-diagnostics/route.ts b/frontend/app/api/microcosm/target-diagnostics/route.ts
index 45b49265..aef1ebda 100644
--- a/frontend/app/api/microcosm/target-diagnostics/route.ts
+++ b/frontend/app/api/microcosm/target-diagnostics/route.ts
@@ -6,7 +6,7 @@ import {
   loadRelease,
   parseCountry,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 export const revalidate = 21_600;
 export const runtime = "nodejs";
diff --git a/frontend/app/api/microcosm/target-investigation/route.ts b/frontend/app/api/microcosm/target-investigation/route.ts
index f6446f82..3690a728 100644
--- a/frontend/app/api/microcosm/target-investigation/route.ts
+++ b/frontend/app/api/microcosm/target-investigation/route.ts
@@ -6,7 +6,7 @@ import {
   loadRelease,
   parseCountry,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 export const revalidate = 21_600;
 
diff --git a/frontend/app/api/microcosm/target-treemap/route.ts b/frontend/app/api/microcosm/target-treemap/route.ts
index db910387..3e4e0d94 100644
--- a/frontend/app/api/microcosm/target-treemap/route.ts
+++ b/frontend/app/api/microcosm/target-treemap/route.ts
@@ -6,7 +6,7 @@ import {
   parseCountry,
   microcosmTargetTreemap,
   scrub,
-} from "@/lib/microcosm/latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 export const revalidate = 21_600;
 export const runtime = "nodejs";
diff --git a/frontend/app/api/microcosm/tree-manifest/route.test.ts b/frontend/app/api/microcosm/tree-manifest/route.test.ts
index f27ed8aa..99f096d3 100644
--- a/frontend/app/api/microcosm/tree-manifest/route.test.ts
+++ b/frontend/app/api/microcosm/tree-manifest/route.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from "bun:test";
 
-import { emptyCalibrationTreeManifest, withCalibrationTreeManifestEntry } from "@/lib/microcosm/calibration-tree-manifest";
+import { emptyCalibrationTreeManifest, withCalibrationTreeManifestEntry } from "@policyengine/calibration-tree/calibration-tree-manifest";
 import { createCalibrationTreeManifestHandler } from "./route";
 
 test("manifest API returns one country's current immutable release identity", async () => {
diff --git a/frontend/app/api/microcosm/tree-manifest/route.ts b/frontend/app/api/microcosm/tree-manifest/route.ts
index bfc79e68..efeb6ff9 100644
--- a/frontend/app/api/microcosm/tree-manifest/route.ts
+++ b/frontend/app/api/microcosm/tree-manifest/route.ts
@@ -1,11 +1,11 @@
 import { NextResponse } from "next/server";
 
-import { readCalibrationTreeManifest } from "@/lib/microcosm/calibration-tree-blob";
-import { calibrationTreeCountryManifest } from "@/lib/microcosm/calibration-tree-manifest";
+import { readCalibrationTreeManifest } from "@policyengine/calibration-tree/calibration-tree-blob";
+import { calibrationTreeCountryManifest } from "@policyengine/calibration-tree/calibration-tree-manifest";
 import {
   isCountry,
   selectableCountries,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
diff --git a/frontend/app/api/microcosm/tree/route.ts b/frontend/app/api/microcosm/tree/route.ts
index 8a6e64a6..02e1d0fc 100644
--- a/frontend/app/api/microcosm/tree/route.ts
+++ b/frontend/app/api/microcosm/tree/route.ts
@@ -1,19 +1,19 @@
 import { NextResponse } from "next/server";
 
 import { withBasePath } from "@/lib/base-path";
-import { getCalibrationTreeBlob } from "@/lib/microcosm/calibration-tree-blob";
+import { getCalibrationTreeBlob } from "@policyengine/calibration-tree/calibration-tree-blob";
 import { immutableCalibrationTreePartResponse } from "@/lib/microcosm/calibration-tree-http";
 import {
   isCalibrationTreePart,
   isSha256,
   type CalibrationTreePart,
-} from "@/lib/microcosm/calibration-tree-artifact";
-import { resolveCalibrationRelease } from "@/lib/microcosm/calibration-release-locator";
+} from "@policyengine/calibration-tree/calibration-tree-artifact";
+import { resolveCalibrationRelease } from "@policyengine/calibration-tree/calibration-release-locator";
 import {
   isCountry,
   selectableCountries,
   type MicrocosmCountry,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
diff --git a/frontend/app/api/microcosm/variable/route.ts b/frontend/app/api/microcosm/variable/route.ts
index b32a43bf..4e10e052 100644
--- a/frontend/app/api/microcosm/variable/route.ts
+++ b/frontend/app/api/microcosm/variable/route.ts
@@ -4,7 +4,7 @@ import { promisify } from "node:util";
 
 import { NextResponse } from "next/server";
 
-import { microcosmRepo, scrub } from "@/lib/microcosm/latest-artifact";
+import { microcosmRepo, scrub } from "@policyengine/calibration-tree/latest-artifact";
 import {
   HOSTED_US_RELEASE,
   reviewedVariableRelease,
diff --git a/frontend/app/microcosm/page.tsx b/frontend/app/microcosm/page.tsx
index 9314538d..1e8e6245 100644
--- a/frontend/app/microcosm/page.tsx
+++ b/frontend/app/microcosm/page.tsx
@@ -1,7 +1,7 @@
 import { AppShell } from "@/components/layout/app-shell";
 import { MicrocosmOverviewView } from "@/components/microcosm/microcosm-overview-view";
 import { publishedReleaseSelection } from "@/lib/microcosm/calibration-selection";
-import { parseCountry } from "@/lib/microcosm/countries";
+import { parseCountry } from "@policyengine/calibration-tree/countries";
 
 interface MicrocosmOverviewPageProps {
   searchParams?: Promise<Record<string, string | string[] | undefined>>;
diff --git a/frontend/app/microcosm/targets/page.tsx b/frontend/app/microcosm/targets/page.tsx
index a3d2e99c..5d46b1a6 100644
--- a/frontend/app/microcosm/targets/page.tsx
+++ b/frontend/app/microcosm/targets/page.tsx
@@ -1,7 +1,7 @@
 import { AppShell } from "@/components/layout/app-shell";
 import { MicrocosmTargetsView } from "@/components/microcosm/microcosm-targets-view";
 import { publishedReleaseSelection } from "@/lib/microcosm/calibration-selection";
-import { parseCountry } from "@/lib/microcosm/countries";
+import { parseCountry } from "@policyengine/calibration-tree/countries";
 
 interface MicrocosmTargetsPageProps {
   searchParams?: Promise<Record<string, string | string[] | undefined>>;
diff --git a/frontend/bun.lock b/frontend/bun.lock
index a664d676..b1329105 100644
--- a/frontend/bun.lock
+++ b/frontend/bun.lock
@@ -5,6 +5,7 @@
     "": {
       "name": "calibration-diagnostics-frontend",
       "dependencies": {
+        "@policyengine/calibration-tree": "workspace:*",
         "@policyengine/ui-kit": "^0.9.0",
         "@tanstack/react-query": "^5.84.0",
         "@tanstack/react-query-devtools": "^5.83.0",
@@ -31,6 +32,17 @@
         "typescript": "^5.8.0",
       },
     },
+    "packages/calibration-tree": {
+      "name": "@policyengine/calibration-tree",
+      "version": "0.1.0",
+      "dependencies": {
+        "@vercel/blob": "^2.6.1",
+      },
+      "devDependencies": {
+        "@types/bun": "^1.3.14",
+        "typescript": "^5.8.0",
+      },
+    },
   },
   "packages": {
     "@alloc/quick-lru": ["@alloc/quick-lru@5.2.0", "", {}, "sha512-UrcABB+4bUrFABwbluTIBErXwvbsU/V7TZWfmbgJfbkwiBuziS9gxdODUyuiecfdGQ85jglMW6juS3+z5TsKLw=="],
@@ -125,6 +137,8 @@
 
     "@next/swc-win32-x64-msvc": ["@next/swc-win32-x64-msvc@16.2.6", "", { "os": "win32", "cpu": "x64" }, "sha512-F0+4i0h9J6C4eE3EAPWsoCk7UW/dbzOjyzxY0qnDUOYFu6FFmdZ6l97/XdV3/Nz3VYyO7UWjyEJUXkGqcoXfMA=="],
 
+    "@policyengine/calibration-tree": ["@policyengine/calibration-tree@workspace:packages/calibration-tree"],
+
     "@policyengine/ui-kit": ["@policyengine/ui-kit@0.9.1", "", { "dependencies": { "class-variance-authority": "^0.7.1", "clsx": "^2.1.1", "cmdk": "^1.1.1", "d3-geo": "^3.1.0", "dayjs": "^1.11.13", "lucide-react": "^0.577.0", "radix-ui": "^1.4.3", "tailwind-merge": "^3.5.0", "tw-animate-css": "^1.4.0" }, "peerDependencies": { "react": ">=19", "react-dom": ">=19", "recharts": ">=2.12" } }, "sha512-wigj/WodytMGqW8n02IKda2uYVxzBE3iDqzRweDJn+4VZQqb02rCf1TBqsM9WGslkPAetavjAoQrBCVnGZQEKQ=="],
 
     "@radix-ui/number": ["@radix-ui/number@1.1.1", "", {}, "sha512-MkKCwxlXTgz6CFoJx3pCwn07GKp36+aZyu/u2Ln2VrA5DcdyCZkASEDBTd8x5whTQQL5CiYf4prXKLcgQdv29g=="],
diff --git a/frontend/bunfig.toml b/frontend/bunfig.toml
index 8755352e..27f7bdaa 100644
--- a/frontend/bunfig.toml
+++ b/frontend/bunfig.toml
@@ -1,2 +1,7 @@
+[install]
+# Keep the hoisted node_modules layout that Next.js and Vercel build against.
+# Bun otherwise installs a project with workspaces using its isolated linker.
+linker = "hoisted"
+
 [test]
 preload = ["./test/setup.ts"]
diff --git a/frontend/components/layout/country-context.tsx b/frontend/components/layout/country-context.tsx
index 4e8d4a4b..868f4fde 100644
--- a/frontend/components/layout/country-context.tsx
+++ b/frontend/components/layout/country-context.tsx
@@ -13,7 +13,7 @@ import {
   DEFAULT_COUNTRY,
   isCountry,
   type MicrocosmCountry,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 export type Country = MicrocosmCountry;
 
diff --git a/frontend/components/layout/mobile-nav.tsx b/frontend/components/layout/mobile-nav.tsx
index fb432aa7..09feab9d 100644
--- a/frontend/components/layout/mobile-nav.tsx
+++ b/frontend/components/layout/mobile-nav.tsx
@@ -5,7 +5,7 @@ import { useEffect, useId, useRef, useState } from "react";
 
 import { useCountry } from "@/components/layout/country-context";
 import { activeNavItem, navGroupsForCountry } from "@/components/layout/nav-items";
-import { countryRegistration } from "@/lib/microcosm/countries";
+import { countryRegistration } from "@policyengine/calibration-tree/countries";
 
 import { NavSidebar } from "./nav-sidebar";
 
diff --git a/frontend/components/layout/nav-items.test.ts b/frontend/components/layout/nav-items.test.ts
index 57bcc391..e1aef082 100644
--- a/frontend/components/layout/nav-items.test.ts
+++ b/frontend/components/layout/nav-items.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from "bun:test";
 
-import { hasCapability, selectableCountries } from "@/lib/microcosm/countries";
+import { hasCapability, selectableCountries } from "@policyengine/calibration-tree/countries";
 
 import {
   activeNavItem,
diff --git a/frontend/components/layout/nav-items.ts b/frontend/components/layout/nav-items.ts
index 34b97396..67117a34 100644
--- a/frontend/components/layout/nav-items.ts
+++ b/frontend/components/layout/nav-items.ts
@@ -2,7 +2,7 @@ import type { Country } from "@/components/layout/country-context";
 import {
   countryCapabilities,
   type CountryCapability,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 // A page is shown when the country (or the release artifact, which can narrow
 // a registration) serves its capability. Pages that run on country-specific
diff --git a/frontend/components/layout/nav-sidebar.tsx b/frontend/components/layout/nav-sidebar.tsx
index 1e15d76b..acb1b6b0 100644
--- a/frontend/components/layout/nav-sidebar.tsx
+++ b/frontend/components/layout/nav-sidebar.tsx
@@ -13,7 +13,7 @@ import {
 import {
   countryRegistration,
   selectableCountries,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 export function NavSidebar({ onNavigate }: { onNavigate?: () => void } = {}) {
   const pathname = usePathname();
diff --git a/frontend/components/microcosm/calibration-explorer-filter-menu.tsx b/frontend/components/microcosm/calibration-explorer-filter-menu.tsx
index 9c381faf..d77f0016 100644
--- a/frontend/components/microcosm/calibration-explorer-filter-menu.tsx
+++ b/frontend/components/microcosm/calibration-explorer-filter-menu.tsx
@@ -7,8 +7,8 @@ import {
   type ComparisonFit,
   type ExplorerFilters,
   type ExplorerState,
-} from "@/lib/microcosm/calibration-explorer";
-import type { CalibrationTreeResponse } from "@/lib/microcosm/calibration-tree";
+} from "@policyengine/calibration-tree/calibration-explorer";
+import type { CalibrationTreeResponse } from "@policyengine/calibration-tree/calibration-tree";
 
 const FIT_BAND_LABELS: Record<string, string> = {
   "0_5": "0–5%",
diff --git a/frontend/components/microcosm/calibration-explorer-map.tsx b/frontend/components/microcosm/calibration-explorer-map.tsx
index 5c50e14b..485251f2 100644
--- a/frontend/components/microcosm/calibration-explorer-map.tsx
+++ b/frontend/components/microcosm/calibration-explorer-map.tsx
@@ -43,14 +43,14 @@ import {
   explorerReducer,
   type ExplorerBreakdown,
   type ExplorerState,
-} from "@/lib/microcosm/calibration-explorer";
+} from "@policyengine/calibration-tree/calibration-explorer";
 import { prefetchCalibrationDescendants } from "@/lib/microcosm/calibration-prefetch";
 import {
   type CalibrationTreeGroup,
   type CalibrationTreeNode,
   type CalibrationTreeResponse,
   type CalibrationTreeSizeMode,
-} from "@/lib/microcosm/calibration-tree";
+} from "@policyengine/calibration-tree/calibration-tree";
 import {
   condenseCalibrationTreemap,
   expandedGroupsForNode,
diff --git a/frontend/components/microcosm/calibration-explorer-view.test.ts b/frontend/components/microcosm/calibration-explorer-view.test.ts
index 8baaecf5..00467077 100644
--- a/frontend/components/microcosm/calibration-explorer-view.test.ts
+++ b/frontend/components/microcosm/calibration-explorer-view.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test";
 
-import type { ExplorerState } from "../../lib/microcosm/calibration-explorer";
+import type { ExplorerState } from "@policyengine/calibration-tree/calibration-explorer";
 import {
   EXPLORER_MAP_VERTICAL_PADDING,
   explorerBreadcrumbs,
diff --git a/frontend/components/microcosm/calibration-explorer-view.ts b/frontend/components/microcosm/calibration-explorer-view.ts
index f45dd8bd..6dc4dfde 100644
--- a/frontend/components/microcosm/calibration-explorer-view.ts
+++ b/frontend/components/microcosm/calibration-explorer-view.ts
@@ -1,14 +1,14 @@
 import type {
   ExplorerPath,
   ExplorerState,
-} from "@/lib/microcosm/calibration-explorer";
+} from "@policyengine/calibration-tree/calibration-explorer";
 import {
   type CalibrationTreeMetrics,
   type CalibrationTreeNode,
   type CalibrationTreeSizeMode,
-} from "@/lib/microcosm/calibration-tree";
-import { canonicalLabel, programLabel } from "@/lib/microcosm/program-label";
-import { sourceLabel } from "@/lib/microcosm/source-label";
+} from "@policyengine/calibration-tree/calibration-tree";
+import { canonicalLabel, programLabel } from "@policyengine/calibration-tree/program-label";
+import { sourceLabel } from "@policyengine/calibration-tree/source-label";
 
 export const EXPLORER_MAP_VERTICAL_PADDING = 10;
 
diff --git a/frontend/components/microcosm/microcosm-staging-view.tsx b/frontend/components/microcosm/microcosm-staging-view.tsx
index d48a502a..17879880 100644
--- a/frontend/components/microcosm/microcosm-staging-view.tsx
+++ b/frontend/components/microcosm/microcosm-staging-view.tsx
@@ -39,7 +39,7 @@ import {
   type MicrocosmStagingRunResponse,
   type MicrocosmStagingRunSummary,
 } from "@/lib/api/hooks/use-microcosm";
-import { countryRegistration, hasCapability } from "@/lib/microcosm/countries";
+import { countryRegistration, hasCapability } from "@policyengine/calibration-tree/countries";
 import {
   formatStagingCurrentStatus,
   formatStagingStatus,
diff --git a/frontend/components/microcosm/microcosm-target-detail.tsx b/frontend/components/microcosm/microcosm-target-detail.tsx
index 4e2c0f81..06d5d428 100644
--- a/frontend/components/microcosm/microcosm-target-detail.tsx
+++ b/frontend/components/microcosm/microcosm-target-detail.tsx
@@ -9,8 +9,8 @@ import {
   type MicrocosmTargetRow,
 } from "@/lib/api/hooks/use-microcosm";
 import { chronicleSourceEntryUrl } from "@/lib/microcosm/chronicle-entry-url";
-import { canonicalLabel } from "@/lib/microcosm/program-label";
-import { sourceLabel } from "@/lib/microcosm/source-label";
+import { canonicalLabel } from "@policyengine/calibration-tree/program-label";
+import { sourceLabel } from "@policyengine/calibration-tree/source-label";
 import { usStateName } from "@/lib/microcosm/us-state-names";
 
 interface DisplayDimension {
diff --git a/frontend/components/microcosm/microcosm-targets-view.tsx b/frontend/components/microcosm/microcosm-targets-view.tsx
index 2f5c353d..cc21740d 100644
--- a/frontend/components/microcosm/microcosm-targets-view.tsx
+++ b/frontend/components/microcosm/microcosm-targets-view.tsx
@@ -17,7 +17,7 @@ import { PageHeader } from "@/components/shared/page-header";
 import { SectionCard } from "@/components/shared/section-card";
 import { ToolbarSelect } from "@/components/shared/toolbar-select";
 import { MicrocosmTargetDetail } from "@/components/microcosm/microcosm-target-detail";
-import { sourceLabel } from "@/lib/microcosm/source-label";
+import { sourceLabel } from "@policyengine/calibration-tree/source-label";
 import {
   releaseSelectOptions,
   useMicrocosmReleases,
diff --git a/frontend/components/microcosm/staging-target-change-map.tsx b/frontend/components/microcosm/staging-target-change-map.tsx
index 942f947e..2e0f5173 100644
--- a/frontend/components/microcosm/staging-target-change-map.tsx
+++ b/frontend/components/microcosm/staging-target-change-map.tsx
@@ -29,18 +29,18 @@ import {
   createExplorerFilters,
   createExplorerState,
   explorerReducer,
-} from "@/lib/microcosm/calibration-explorer";
+} from "@policyengine/calibration-tree/calibration-explorer";
 import type {
   CalibrationTreeGroup,
   CalibrationTreeMetrics,
-} from "@/lib/microcosm/calibration-tree";
+} from "@policyengine/calibration-tree/calibration-tree";
 import {
   condenseCalibrationTreemapByMetric,
   expandedGroupsForNode,
   type CalibrationTreemapGroup,
   type CalibrationTreemapNode,
 } from "@/lib/microcosm/calibration-treemap-layout";
-import type { TargetChangeMode } from "@/lib/microcosm/target-change";
+import type { TargetChangeMode } from "@policyengine/calibration-tree/target-change";
 import type { TargetChangeTreeResponse } from "@/lib/microcosm/target-change-tree";
 import {
   formatTargetChange,
diff --git a/frontend/components/microcosm/staging-target-detail-presentation.test.ts b/frontend/components/microcosm/staging-target-detail-presentation.test.ts
index c7561ca3..d0a4a1e1 100644
--- a/frontend/components/microcosm/staging-target-detail-presentation.test.ts
+++ b/frontend/components/microcosm/staging-target-detail-presentation.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from "bun:test";
 
-import type { TargetChangeRow } from "@/lib/microcosm/target-change";
+import type { TargetChangeRow } from "@policyengine/calibration-tree/target-change";
 import { stagingTargetDetailPresentation } from "./staging-target-detail-presentation";
 
 const TARGET_CHANGE: TargetChangeRow = {
diff --git a/frontend/components/microcosm/staging-target-detail-presentation.ts b/frontend/components/microcosm/staging-target-detail-presentation.ts
index bc1ed857..27a06a37 100644
--- a/frontend/components/microcosm/staging-target-detail-presentation.ts
+++ b/frontend/components/microcosm/staging-target-detail-presentation.ts
@@ -6,7 +6,7 @@ import {
   type MicrocosmTargetErrorSummary,
 } from "@/components/microcosm/microcosm-target-detail";
 import type { MicrocosmTargetRow } from "@/lib/api/hooks/use-microcosm";
-import type { TargetChangeRow } from "@/lib/microcosm/target-change";
+import type { TargetChangeRow } from "@policyengine/calibration-tree/target-change";
 import { formatTargetChange } from "@/lib/microcosm/target-change-visualization";
 
 export interface StagingTargetDetailPresentation {
diff --git a/frontend/lib/api/hooks/use-microcosm.test.ts b/frontend/lib/api/hooks/use-microcosm.test.ts
index 69f67702..2b0928a3 100644
--- a/frontend/lib/api/hooks/use-microcosm.test.ts
+++ b/frontend/lib/api/hooks/use-microcosm.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from "bun:test";
 
-import { createExplorerState } from "@/lib/microcosm/calibration-explorer";
+import { createExplorerState } from "@policyengine/calibration-tree/calibration-explorer";
 
 import {
   fetchCalibrationTreePartsConcurrently,
diff --git a/frontend/lib/api/hooks/use-microcosm.ts b/frontend/lib/api/hooks/use-microcosm.ts
index 46df32fd..675c1227 100644
--- a/frontend/lib/api/hooks/use-microcosm.ts
+++ b/frontend/lib/api/hooks/use-microcosm.ts
@@ -17,8 +17,8 @@ import {
 import { withBasePath } from "@/lib/base-path";
 import type { BuildRunSource } from "@/lib/microcosm/build-monitor";
 import type { BuildRunResponse, BuildRunsResponse } from "@/lib/microcosm/build-runs";
-import type { ExplorerState } from "@/lib/microcosm/calibration-explorer";
-import type { CalibrationTreeResponse } from "@/lib/microcosm/calibration-tree";
+import type { ExplorerState } from "@policyengine/calibration-tree/calibration-explorer";
+import type { CalibrationTreeResponse } from "@policyengine/calibration-tree/calibration-tree";
 import {
   calibrationTreeResponseFromBundle,
   calibrationTreeTargetDetailSelection,
@@ -34,12 +34,12 @@ import {
   type CalibrationTreeTargetDetailsArtifact,
   type CalibrationTreeTargetSummaryArtifact,
   type CalibrationTreeTierArtifact,
-} from "@/lib/microcosm/calibration-tree-artifact";
-import type { CalibrationProvenance } from "@/lib/microcosm/target-loss-attribution";
+} from "@policyengine/calibration-tree/calibration-tree-artifact";
+import type { CalibrationProvenance } from "@policyengine/calibration-tree/target-loss-attribution";
 import type {
   TargetChangeMode,
   TargetChangeRow,
-} from "@/lib/microcosm/target-change";
+} from "@policyengine/calibration-tree/target-change";
 import type {
   TargetChangeTreeApiResponse,
   TargetChangeTreeResponse,
@@ -49,7 +49,7 @@ import {
   hasCapability,
   type CountryCapability,
   type RepositoryVisibility,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 import { apiGet } from "../client";
 
 export interface MicrocosmGates {
diff --git a/frontend/lib/cross-dataset/fact-presentation.ts b/frontend/lib/cross-dataset/fact-presentation.ts
index 09a1f0b4..cfb07b57 100644
--- a/frontend/lib/cross-dataset/fact-presentation.ts
+++ b/frontend/lib/cross-dataset/fact-presentation.ts
@@ -4,9 +4,9 @@ import type {
   SourceSummary,
 } from "./artifact";
 import type { Country } from "@/components/layout/country-context";
-import { DEFAULT_COUNTRY, isCountry } from "@/lib/microcosm/countries";
+import { DEFAULT_COUNTRY, isCountry } from "@policyengine/calibration-tree/countries";
 import { sourceDisplayLabel } from "./presentation";
-import { sourceAuthorityLabel } from "../source-labels";
+import { sourceAuthorityLabel } from "@policyengine/calibration-tree/source-labels";
 
 export interface FactCatalogParams {
   country: Country;
diff --git a/frontend/lib/cross-dataset/source.ts b/frontend/lib/cross-dataset/source.ts
index a027c738..0c849958 100644
--- a/frontend/lib/cross-dataset/source.ts
+++ b/frontend/lib/cross-dataset/source.ts
@@ -6,7 +6,7 @@ import {
   DEFAULT_COUNTRY,
   countryRegistration,
   type MicrocosmCountry,
-} from "../microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 interface CountryArtifactConfig {
   countryCode: string;
diff --git a/frontend/lib/microcosm/build-monitor.test.ts b/frontend/lib/microcosm/build-monitor.test.ts
index f9db4e9c..828c241c 100644
--- a/frontend/lib/microcosm/build-monitor.test.ts
+++ b/frontend/lib/microcosm/build-monitor.test.ts
@@ -27,7 +27,7 @@ import {
   parseStagingEvents,
   parseStagingManifest,
   parseStagingProgress,
-} from "./staging-contract";
+} from "@policyengine/calibration-tree/staging-contract";
 
 const T0 = Date.parse("2026-09-26T10:00:00Z");
 const min = (n: number) => n * 60_000;
@@ -1001,7 +1001,19 @@ describe("solver passes inside calibration", () => {
 });
 
 describe("version 3 outcomes", () => {
-  const FIXTURES = join(import.meta.dir, "fixtures", "staging-contract", "v3");
+  // The staging contract fixtures live beside the contract parser in the
+  // calibration tree package.
+  const FIXTURES = join(
+    import.meta.dir,
+    "..",
+    "..",
+    "packages",
+    "calibration-tree",
+    "src",
+    "fixtures",
+    "staging-contract",
+    "v3",
+  );
   const fixtureText = (path: string) => readFileSync(join(FIXTURES, path)).toString();
   const fixtureJson = (path: string) => JSON.parse(fixtureText(path)) as Record<string, unknown>;
 
diff --git a/frontend/lib/microcosm/build-runs.ts b/frontend/lib/microcosm/build-runs.ts
index 79d2fd1c..b8812efb 100644
--- a/frontend/lib/microcosm/build-runs.ts
+++ b/frontend/lib/microcosm/build-runs.ts
@@ -23,7 +23,7 @@ import {
 import {
   hasCapability,
   type MicrocosmCountry,
-} from "@/lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 import {
   discoverLocalRuns,
   loadLocalRunDocuments,
@@ -33,7 +33,7 @@ import {
 import {
   loadStagingRuns,
   loadStagingRunTelemetry,
-} from "@/lib/microcosm/staging-artifact";
+} from "@policyengine/calibration-tree/staging-artifact";
 import {
   collectorConfigured,
   loadCollectorRun,
diff --git a/frontend/lib/microcosm/calibration-prefetch.test.ts b/frontend/lib/microcosm/calibration-prefetch.test.ts
index 2ac80b17..f9da57b2 100644
--- a/frontend/lib/microcosm/calibration-prefetch.test.ts
+++ b/frontend/lib/microcosm/calibration-prefetch.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test";
 
-import { createExplorerState, type ExplorerState } from "./calibration-explorer";
+import { createExplorerState, type ExplorerState } from "@policyengine/calibration-tree/calibration-explorer";
 import {
   prefetchCalibrationDescendants,
   type CalibrationTreeFetcher,
@@ -8,7 +8,7 @@ import {
 import type {
   CalibrationTreeNode,
   CalibrationTreeResponse,
-} from "./calibration-tree";
+} from "@policyengine/calibration-tree/calibration-tree";
 
 const EMPTY_METRICS = {
   nTargets: 0,
diff --git a/frontend/lib/microcosm/calibration-prefetch.ts b/frontend/lib/microcosm/calibration-prefetch.ts
index 2a25d8e2..a52a432b 100644
--- a/frontend/lib/microcosm/calibration-prefetch.ts
+++ b/frontend/lib/microcosm/calibration-prefetch.ts
@@ -1,8 +1,8 @@
 import {
   nextLevelExplorerStates,
   type ExplorerState,
-} from "./calibration-explorer";
-import type { CalibrationTreeResponse } from "./calibration-tree";
+} from "@policyengine/calibration-tree/calibration-explorer";
+import type { CalibrationTreeResponse } from "@policyengine/calibration-tree/calibration-tree";
 
 export type CalibrationTreeFetcher = (
   state: ExplorerState,
diff --git a/frontend/lib/microcosm/calibration-tree-http.ts b/frontend/lib/microcosm/calibration-tree-http.ts
index ddd36e43..23b31f54 100644
--- a/frontend/lib/microcosm/calibration-tree-http.ts
+++ b/frontend/lib/microcosm/calibration-tree-http.ts
@@ -1,7 +1,7 @@
 import type { GetBlobResult } from "@vercel/blob";
 import { NextResponse } from "next/server";
 
-import { calibrationTreeBlobText } from "./calibration-tree-blob";
+import { calibrationTreeBlobText } from "@policyengine/calibration-tree/calibration-tree-blob";
 
 function acceptsGzip(request: Request): boolean {
   return (request.headers.get("accept-encoding") ?? "")
diff --git a/frontend/lib/microcosm/calibration-tree-request.ts b/frontend/lib/microcosm/calibration-tree-request.ts
index fa9c3a99..50dcad86 100644
--- a/frontend/lib/microcosm/calibration-tree-request.ts
+++ b/frontend/lib/microcosm/calibration-tree-request.ts
@@ -5,7 +5,7 @@ import {
   type CalibrationStatus,
   type ComparisonFit,
   type FitBand,
-} from "./calibration-explorer";
+} from "@policyengine/calibration-tree/calibration-explorer";
 
 const CALIBRATION_STATUSES = new Set<CalibrationStatus>([
   "included",
diff --git a/frontend/lib/microcosm/calibration-treemap-layout.test.ts b/frontend/lib/microcosm/calibration-treemap-layout.test.ts
index 480d6868..005981be 100644
--- a/frontend/lib/microcosm/calibration-treemap-layout.test.ts
+++ b/frontend/lib/microcosm/calibration-treemap-layout.test.ts
@@ -4,7 +4,7 @@ import type {
   CalibrationTreeGroup,
   CalibrationTreeMetrics,
   CalibrationTreeNode,
-} from "./calibration-tree";
+} from "@policyengine/calibration-tree/calibration-tree";
 import {
   condenseCalibrationTreemap,
   expandedGroupsForNode,
diff --git a/frontend/lib/microcosm/calibration-treemap-layout.ts b/frontend/lib/microcosm/calibration-treemap-layout.ts
index c97a8081..b7ef0dd5 100644
--- a/frontend/lib/microcosm/calibration-treemap-layout.ts
+++ b/frontend/lib/microcosm/calibration-treemap-layout.ts
@@ -1,11 +1,11 @@
-import type { ExplorerNodeSelection } from "./calibration-explorer";
+import type { ExplorerNodeSelection } from "@policyengine/calibration-tree/calibration-explorer";
 import type {
   CalibrationTreeGroup,
   CalibrationTreeMetrics,
   CalibrationTreeNode,
   CalibrationTreeSizeMode,
   CalibrationTreeTarget,
-} from "./calibration-tree";
+} from "@policyengine/calibration-tree/calibration-tree";
 
 // Keep these aligned with the original calibration map. They represent roughly
 // a 51px square for groups and a 28px square for nodes.
diff --git a/frontend/lib/microcosm/countries.ts b/frontend/lib/microcosm/countries.ts
index a57253d5..1d8d5144 100644
--- a/frontend/lib/microcosm/countries.ts
+++ b/frontend/lib/microcosm/countries.ts
@@ -1,241 +1,5 @@
-// Country registry for the Microcosm dashboard: the one place a country is
-// registered. Adding a country is one entry here; everything else (selectors,
-// navigation, repository resolution, national geography, link behaviour) reads
-// the registration or the release artifact's typed `country` block.
-//
-// Isomorphic: imported by client components and API routes alike, so it must
-// not import server-only modules or read `process.env`. Repository resolvers
-// accept an explicit environment object from server-side callers.
-
-export const COUNTRY_CAPABILITIES = [
-  "calibration",
-  "targets",
-  "compare",
-  "cross_dataset",
-  "staging",
-  "model_coverage",
-  "pipeline",
-  "variables",
-  "external_checks",
-] as const;
-export type CountryCapability = (typeof COUNTRY_CAPABILITIES)[number];
-
-export type RepositoryVisibility = "public" | "private";
-
-export type RepositoryEnvironment = Readonly<
-  Record<string, string | undefined>
->;
-
-export interface ResolvedRepository {
-  repo: string;
-  revision: string;
-}
-
-export interface CountryRegistration {
-  // Default HF dataset repository and revision (the server may override both
-  // through the deployment variables named in repo_env / revision_env).
-  repo: string;
-  revision: string;
-  repo_env?: string;
-  revision_env?: string;
-  // Country display name ("United States").
-  label: string;
-  // Sidebar dataset line ("Microcosm US").
-  dataset_label: string;
-  // National geography label and id (null when the id is unknown).
-  geography: string;
-  geography_id: string | null;
-  visibility: RepositoryVisibility;
-  capabilities: readonly CountryCapability[];
-  // Optional staging telemetry repository. A staging-capable country must
-  // declare this instead of inheriting another country's repository.
-  staging?: {
-    repo: string;
-    revision: string;
-    repo_env?: string;
-    revision_env?: string;
-    token_env?: string;
-  };
-  // Other jurisdiction codes a cross-dataset bundle may use for this country.
-  jurisdiction_aliases?: readonly string[];
-  // Conformance-only registration: a valid country that is never listed in
-  // selectors or alert allowlists.
-  fixture?: true;
-}
-
-const ALL_CAPABILITIES: readonly CountryCapability[] = COUNTRY_CAPABILITIES;
-
-const CALIBRATION_CAPABILITIES: readonly CountryCapability[] = [
-  "calibration",
-  "targets",
-  "compare",
-  "cross_dataset",
-];
-
-// Deprecated upstream identifiers: Microcosm's published HF repositories and
-// deployment variables still use the former Populace names.
-export const COUNTRY_REGISTRY = {
-  us: {
-    repo: "policyengine/populace-us",
-    revision: "main",
-    repo_env: "POPULACE_HF_REPO",
-    label: "United States",
-    dataset_label: "Microcosm US",
-    geography: "United States",
-    geography_id: "0100000US",
-    visibility: "public",
-    capabilities: ALL_CAPABILITIES,
-    staging: {
-      // Deprecated upstream identifier: the US staging publisher still uses
-      // the former Populace repository and deployment-variable names.
-      repo: "policyengine/populace-us-staging",
-      revision: "main",
-      repo_env: "POPULACE_STAGING_HF_REPO",
-      revision_env: "POPULACE_STAGING_HF_REVISION",
-    },
-  },
-  uk: {
-    repo: "policyengine/populace-uk-private",
-    revision: "main",
-    repo_env: "POPULACE_UK_HF_REPO",
-    revision_env: "POPULACE_UK_HF_REVISION",
-    label: "United Kingdom",
-    dataset_label: "Microcosm UK",
-    geography: "United Kingdom",
-    geography_id: null,
-    visibility: "private",
-    capabilities: [...CALIBRATION_CAPABILITIES, "staging"],
-    staging: {
-      repo: "policyengine/populace-uk-staging",
-      revision: "main",
-      repo_env: "POPULACE_UK_STAGING_HF_REPO",
-      revision_env: "POPULACE_UK_STAGING_HF_REVISION",
-      token_env: "POPULACE_UK_STAGING_HF_TOKEN",
-    },
-    jurisdiction_aliases: ["GB"],
-  },
-  be: {
-    repo: "policyengine/populace-be-private",
-    revision: "main",
-    repo_env: "POPULACE_BE_HF_REPO",
-    revision_env: "POPULACE_BE_HF_REVISION",
-    label: "Belgium",
-    dataset_label: "Microcosm Belgium",
-    geography: "Belgium",
-    geography_id: null,
-    visibility: "private",
-    capabilities: CALIBRATION_CAPABILITIES,
-  },
-  // Synthetic repository used only by the third-country conformance fixture.
-  zz: {
-    repo: "policyengine/microcosm-zz-fixture",
-    revision: "main",
-    label: "Zedland",
-    dataset_label: "Microcosm ZZ",
-    geography: "Zedland",
-    geography_id: null,
-    visibility: "private",
-    capabilities: ["calibration", "targets", "compare"],
-    fixture: true,
-  },
-  // Synthetic non-US staging registration. It verifies that staging artifact
-  // resolution is country-scoped without exposing an unfinished country in
-  // selectors or treating its fixture repository as a published dataset.
-  am: {
-    repo: "policyengine/microcosm-am-fixture",
-    revision: "main",
-    label: "Armenia",
-    dataset_label: "Microcosm Armenia",
-    geography: "Armenia",
-    geography_id: null,
-    visibility: "private",
-    capabilities: ["calibration", "targets", "compare", "staging"],
-    staging: {
-      repo: "policyengine/microcosm-am-staging-fixture",
-      revision: "main",
-    },
-    fixture: true,
-  },
-} satisfies Record<string, CountryRegistration>;
-
-export type MicrocosmCountry = keyof typeof COUNTRY_REGISTRY;
-
-export const DEFAULT_COUNTRY: MicrocosmCountry = "us";
-
-const COUNTRY_CODES = Object.keys(COUNTRY_REGISTRY) as MicrocosmCountry[];
-
-export function isCountry(value: string | null | undefined): value is MicrocosmCountry {
-  return value != null && Object.hasOwn(COUNTRY_REGISTRY, value);
-}
-
-export function parseCountry(value: string | null | undefined): MicrocosmCountry {
-  return isCountry(value) ? value : DEFAULT_COUNTRY;
-}
-
-export function countryRegistration(country: MicrocosmCountry): CountryRegistration {
-  return COUNTRY_REGISTRY[country];
-}
-
-// Countries offered in selectors, in registry order; fixtures are excluded.
-export function selectableCountries(): MicrocosmCountry[] {
-  return COUNTRY_CODES.filter((country) => !countryRegistration(country).fixture);
-}
-
-export function countryCapabilities(country: MicrocosmCountry): readonly CountryCapability[] {
-  return COUNTRY_REGISTRY[country].capabilities;
-}
-
-export function hasCapability(country: MicrocosmCountry, capability: CountryCapability): boolean {
-  return countryCapabilities(country).includes(capability);
-}
-
-function configuredValue(
-  environment: RepositoryEnvironment,
-  variableName: string | undefined,
-  fallback: string,
-): string {
-  return (variableName ? environment[variableName] : undefined) ?? fallback;
-}
-
-export function resolveRegisteredRepository(
-  country: MicrocosmCountry,
-  environment: RepositoryEnvironment,
-): ResolvedRepository {
-  const registration = countryRegistration(country);
-  return {
-    repo: configuredValue(
-      environment,
-      registration.repo_env,
-      registration.repo,
-    ),
-    revision: configuredValue(
-      environment,
-      registration.revision_env,
-      registration.revision,
-    ),
-  };
-}
-
-export function resolveRegisteredStagingRepository(
-  country: MicrocosmCountry,
-  environment: RepositoryEnvironment,
-): ResolvedRepository | null {
-  const registration = countryRegistration(country);
-  if (!hasCapability(country, "staging") || !registration.staging) return null;
-  return {
-    repo: configuredValue(
-      environment,
-      registration.staging.repo_env,
-      registration.staging.repo,
-    ),
-    revision: configuredValue(
-      environment,
-      registration.staging.revision_env,
-      registration.staging.revision,
-    ),
-  };
-}
-
-export function isCountryCapability(value: unknown): value is CountryCapability {
-  return typeof value === "string" && (COUNTRY_CAPABILITIES as readonly string[]).includes(value);
-}
+// Former location of the country registry, kept as a compatibility
+// re-export for code that has not yet moved to the package path. The
+// registry lives in @policyengine/calibration-tree/countries; import it from
+// there.
+export * from "@policyengine/calibration-tree/countries";
diff --git a/frontend/lib/microcosm/hf-webhook-config.ts b/frontend/lib/microcosm/hf-webhook-config.ts
index 1a359b0e..60fe8000 100644
--- a/frontend/lib/microcosm/hf-webhook-config.ts
+++ b/frontend/lib/microcosm/hf-webhook-config.ts
@@ -4,7 +4,7 @@ import {
   selectableCountries,
   type MicrocosmCountry,
   type RepositoryEnvironment,
-} from "./countries";
+} from "@policyengine/calibration-tree/countries";
 
 export interface WebhookRepositoryRegistration {
   country: MicrocosmCountry;
diff --git a/frontend/lib/microcosm/hf-webhook-handler.ts b/frontend/lib/microcosm/hf-webhook-handler.ts
index d6b552ab..156cbfc7 100644
--- a/frontend/lib/microcosm/hf-webhook-handler.ts
+++ b/frontend/lib/microcosm/hf-webhook-handler.ts
@@ -4,7 +4,7 @@ import { NextResponse } from "next/server";
 
 import { postReleaseAlert } from "@/lib/slack";
 
-import type { MicrocosmCountry } from "./countries";
+import type { MicrocosmCountry } from "@policyengine/calibration-tree/countries";
 import type { HfWebhookConfig } from "./hf-webhook-config";
 
 interface UpdatedRef {
diff --git a/frontend/lib/microcosm/local-build-runs.ts b/frontend/lib/microcosm/local-build-runs.ts
index 2a8b412f..86963cf6 100644
--- a/frontend/lib/microcosm/local-build-runs.ts
+++ b/frontend/lib/microcosm/local-build-runs.ts
@@ -8,7 +8,7 @@ import {
   parseStagingManifest,
   parseStagingProgress,
   validateStagingRunConsistency,
-} from "@/lib/microcosm/staging-contract";
+} from "@policyengine/calibration-tree/staging-contract";
 
 // Local build runs: the `runs/<run_id>/` telemetry folders a Microcosm build
 // writes on the machine it runs on (the US release writes them under
diff --git a/frontend/lib/microcosm/presentation.ts b/frontend/lib/microcosm/presentation.ts
index d74c78bf..7bdf5e07 100644
--- a/frontend/lib/microcosm/presentation.ts
+++ b/frontend/lib/microcosm/presentation.ts
@@ -1,4 +1,4 @@
-import type { MicrocosmCountry } from "./countries";
+import type { MicrocosmCountry } from "@policyengine/calibration-tree/countries";
 
 export interface MicrocosmPresentationSlots {
   overview_intro?: string;
diff --git a/frontend/lib/microcosm/production-release.test.ts b/frontend/lib/microcosm/production-release.test.ts
index 875617a6..1a59f04c 100644
--- a/frontend/lib/microcosm/production-release.test.ts
+++ b/frontend/lib/microcosm/production-release.test.ts
@@ -7,7 +7,7 @@ import {
 import {
   hfResolveUrl,
   microcosmRevision,
-} from "./latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 test("dashboard discovery follows the repository branch while variable calculation stays pinned", () => {
   expect(microcosmRevision("us")).toBe("main");
diff --git a/frontend/lib/microcosm/reviewed-repository-import.fixture.ts b/frontend/lib/microcosm/reviewed-repository-import.fixture.ts
index f97a8c99..c62cb82b 100644
--- a/frontend/lib/microcosm/reviewed-repository-import.fixture.ts
+++ b/frontend/lib/microcosm/reviewed-repository-import.fixture.ts
@@ -9,7 +9,7 @@ import {
   microcosmCountryGeography,
   microcosmRepo,
   microcosmRevision,
-} from "./latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 import { IncompatibleProductionReleaseError } from "./production-release";
 
 // Collecting page data imports every route, so one country's refused selection
diff --git a/frontend/lib/microcosm/reviewed-repository-import.test.ts b/frontend/lib/microcosm/reviewed-repository-import.test.ts
index 3148fa89..cac9d6f7 100644
--- a/frontend/lib/microcosm/reviewed-repository-import.test.ts
+++ b/frontend/lib/microcosm/reviewed-repository-import.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from "bun:test";
 
-import { COUNTRY_REGISTRY } from "./countries";
+import { COUNTRY_REGISTRY } from "@policyengine/calibration-tree/countries";
 
 // A US-only data-selection conflict must fail US reads only. Asserting it while
 // building the repository table would throw during module import instead, taking
diff --git a/frontend/lib/microcosm/source-attribution.ts b/frontend/lib/microcosm/source-attribution.ts
index 2130a80c..d8d9761b 100644
--- a/frontend/lib/microcosm/source-attribution.ts
+++ b/frontend/lib/microcosm/source-attribution.ts
@@ -2,7 +2,7 @@ import {
   countryRegistration,
   type MicrocosmCountry,
   type RepositoryVisibility,
-} from "./countries";
+} from "@policyengine/calibration-tree/countries";
 
 export interface MicrocosmSourceAttribution {
   label: string;
diff --git a/frontend/lib/microcosm/target-change-tree.test.ts b/frontend/lib/microcosm/target-change-tree.test.ts
index 1189c9b6..f3cd529f 100644
--- a/frontend/lib/microcosm/target-change-tree.test.ts
+++ b/frontend/lib/microcosm/target-change-tree.test.ts
@@ -3,9 +3,9 @@ import { describe, expect, test } from "bun:test";
 import {
   createExplorerState,
   type ExplorerState,
-} from "./calibration-explorer";
-import type { Calibration } from "./latest-artifact";
-import { buildTargetChangeDataset } from "./target-change";
+} from "@policyengine/calibration-tree/calibration-explorer";
+import type { Calibration } from "@policyengine/calibration-tree/latest-artifact";
+import { buildTargetChangeDataset } from "@policyengine/calibration-tree/target-change";
 import { buildTargetChangeTree } from "./target-change-tree";
 
 interface RowInput {
diff --git a/frontend/lib/microcosm/target-change-tree.ts b/frontend/lib/microcosm/target-change-tree.ts
index 32c2f437..e8b0c8ef 100644
--- a/frontend/lib/microcosm/target-change-tree.ts
+++ b/frontend/lib/microcosm/target-change-tree.ts
@@ -1,9 +1,9 @@
-import type { ExplorerState } from "./calibration-explorer";
+import type { ExplorerState } from "@policyengine/calibration-tree/calibration-explorer";
 import {
   buildCalibrationTree,
   type CalibrationTreeResponse,
   type CalibrationTreeTarget,
-} from "./calibration-tree";
+} from "@policyengine/calibration-tree/calibration-tree";
 import {
   targetChangeForMode,
   type TargetChangeAttributionSide,
@@ -12,8 +12,8 @@ import {
   type TargetChangeMode,
   type TargetChangeRow,
   type TargetChangeSummary,
-} from "./target-change";
-import type { TargetMatchingSummary } from "./target-surface-matcher";
+} from "@policyengine/calibration-tree/target-change";
+import type { TargetMatchingSummary } from "@policyengine/calibration-tree/target-surface-matcher";
 
 export interface TargetChangeTreeResponse extends CalibrationTreeResponse {
   available: boolean;
diff --git a/frontend/lib/microcosm/target-change-visualization.test.ts b/frontend/lib/microcosm/target-change-visualization.test.ts
index 4033d962..e8bb44ba 100644
--- a/frontend/lib/microcosm/target-change-visualization.test.ts
+++ b/frontend/lib/microcosm/target-change-visualization.test.ts
@@ -3,8 +3,8 @@ import { describe, expect, test } from "bun:test";
 import type {
   CalibrationTreeGroup,
   CalibrationTreeMetrics,
-} from "./calibration-tree";
-import type { TargetChangeRow } from "./target-change";
+} from "@policyengine/calibration-tree/calibration-tree";
+import type { TargetChangeRow } from "@policyengine/calibration-tree/target-change";
 import {
   formatTargetChange,
   targetChangeDetailValues,
diff --git a/frontend/lib/microcosm/target-change-visualization.ts b/frontend/lib/microcosm/target-change-visualization.ts
index 99bd2e20..9899038c 100644
--- a/frontend/lib/microcosm/target-change-visualization.ts
+++ b/frontend/lib/microcosm/target-change-visualization.ts
@@ -2,12 +2,12 @@ import type { Placed } from "@/lib/treemap/squarify";
 import type {
   CalibrationTreeChangeMetrics,
   CalibrationTreeGroup,
-} from "./calibration-tree";
+} from "@policyengine/calibration-tree/calibration-tree";
 import { aggregateCalibrationTreeMetrics } from "./calibration-treemap-layout";
 import type {
   TargetChangeMode,
   TargetChangeRow,
-} from "./target-change";
+} from "@policyengine/calibration-tree/target-change";
 
 export type TargetChangeDirection = "increase" | "reduction";
 
diff --git a/frontend/lib/microcosm/target-matching-presentation.ts b/frontend/lib/microcosm/target-matching-presentation.ts
index 614e3b8e..c0ead2b2 100644
--- a/frontend/lib/microcosm/target-matching-presentation.ts
+++ b/frontend/lib/microcosm/target-matching-presentation.ts
@@ -1,8 +1,8 @@
-import type { TargetMatchKind } from "./target-surface-matcher";
+import type { TargetMatchKind } from "@policyengine/calibration-tree/target-surface-matcher";
 import type {
   TargetRepresentation,
   TargetRowRepresentation,
-} from "./target-representation";
+} from "@policyengine/calibration-tree/target-representation";
 
 export function targetRepresentationLabel(
   representation: TargetRepresentation | TargetRowRepresentation,
diff --git a/frontend/lib/microcosm/third-country-conformance.test.ts b/frontend/lib/microcosm/third-country-conformance.test.ts
index f99a8532..19274d23 100644
--- a/frontend/lib/microcosm/third-country-conformance.test.ts
+++ b/frontend/lib/microcosm/third-country-conformance.test.ts
@@ -2,8 +2,8 @@ import { describe, expect, test } from "bun:test";
 
 import { isCountry as isClientCountry } from "@/components/layout/country-context";
 import { navGroupsForCountry } from "@/components/layout/nav-items";
-import { countryCapabilities, selectableCountries } from "@/lib/microcosm/countries";
-import { sourceAuthorityLabel } from "@/lib/source-labels";
+import { countryCapabilities, selectableCountries } from "@policyengine/calibration-tree/countries";
+import { sourceAuthorityLabel } from "@policyengine/calibration-tree/source-labels";
 
 import diagnosticsFixture from "./fixtures/zz-release/calibration_diagnostics.json";
 import releaseManifestFixture from "./fixtures/zz-release/release_manifest.json";
@@ -17,7 +17,7 @@ import {
   microcosmRevision,
   microcosmTargetTreemap,
   parseCountry,
-} from "./latest-artifact";
+} from "@policyengine/calibration-tree/latest-artifact";
 
 const COUNTRY = "zz" as const;
 const RELEASE_ID = "microcosm-zz-2026-conformance";
diff --git a/frontend/lib/slack.ts b/frontend/lib/slack.ts
index f0d97e2c..156bef2b 100644
--- a/frontend/lib/slack.ts
+++ b/frontend/lib/slack.ts
@@ -1,4 +1,4 @@
-import type { MicrocosmCountry } from "@/lib/microcosm/latest-artifact";
+import type { MicrocosmCountry } from "@policyengine/calibration-tree/latest-artifact";
 
 const DASHBOARD_URL = "https://microcosm.institute/calibration/dashboard/microcosm";
 
diff --git a/frontend/package.json b/frontend/package.json
index c76942ef..faabd39d 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -3,16 +3,20 @@
   "version": "0.1.0",
   "private": true,
   "type": "module",
+  "workspaces": [
+    "packages/*"
+  ],
   "scripts": {
     "dev": "node scripts/dev.mjs",
     "build": "next build",
     "start": "next start",
-    "lint": "tsc --noEmit",
-    "publish:calibration-tree": "bun run scripts/publish-calibration-tree.ts",
+    "lint": "tsc --noEmit && tsc --noEmit -p packages/calibration-tree",
+    "publish:calibration-tree": "bun run packages/calibration-tree/src/publish-calibration-tree.ts",
     "test:dev-port": "node --test scripts/available-port.node-test.mjs",
     "replay:build-run": "bun run scripts/replay-build-run.ts"
   },
   "dependencies": {
+    "@policyengine/calibration-tree": "workspace:*",
     "@policyengine/ui-kit": "^0.9.0",
     "@tanstack/react-query": "^5.84.0",
     "@tanstack/react-query-devtools": "^5.83.0",
diff --git a/frontend/packages/calibration-tree/package.json b/frontend/packages/calibration-tree/package.json
new file mode 100644
index 00000000..76a6b871
--- /dev/null
+++ b/frontend/packages/calibration-tree/package.json
@@ -0,0 +1,51 @@
+{
+  "name": "@policyengine/calibration-tree",
+  "version": "0.1.0",
+  "description": "Builds, validates, reads and publishes Microcosm calibration tree artifacts (tree schema 6), with the release and staging readers they are built from.",
+  "private": true,
+  "type": "module",
+  "exports": {
+    "./calibration-build-comparison": "./src/calibration-build-comparison.ts",
+    "./calibration-comparison-blob": "./src/calibration-comparison-blob.ts",
+    "./calibration-comparison-bundle": "./src/calibration-comparison-bundle.ts",
+    "./calibration-explorer": "./src/calibration-explorer.ts",
+    "./calibration-release-locator": "./src/calibration-release-locator.ts",
+    "./calibration-tree": "./src/calibration-tree.ts",
+    "./calibration-tree-artifact": "./src/calibration-tree-artifact.ts",
+    "./calibration-tree-blob": "./src/calibration-tree-blob.ts",
+    "./calibration-tree-bundle": "./src/calibration-tree-bundle.ts",
+    "./calibration-tree-manifest": "./src/calibration-tree-manifest.ts",
+    "./chronicle-metadata": "./src/chronicle-metadata.ts",
+    "./countries": "./src/countries.ts",
+    "./hierarchy-target-reader": "./src/hierarchy-target-reader.ts",
+    "./historical-weight-summary": "./src/historical-weight-summary.ts",
+    "./latest-artifact": "./src/latest-artifact.ts",
+    "./legacy-target-reader": "./src/legacy-target-reader.ts",
+    "./program-label": "./src/program-label.ts",
+    "./publish-calibration-tree": "./src/publish-calibration-tree.ts",
+    "./reforms": "./src/reforms.ts",
+    "./source-label": "./src/source-label.ts",
+    "./source-labels": "./src/source-labels.ts",
+    "./staging-artifact": "./src/staging-artifact.ts",
+    "./staging-contract": "./src/staging-contract.ts",
+    "./structured-dimension-reader": "./src/structured-dimension-reader.ts",
+    "./structured-target-reader": "./src/structured-target-reader.ts",
+    "./target-change": "./src/target-change.ts",
+    "./target-loss-attribution": "./src/target-loss-attribution.ts",
+    "./target-loss-attribution-manifest": "./src/target-loss-attribution-manifest.ts",
+    "./target-representation": "./src/target-representation.ts",
+    "./target-surface-matcher": "./src/target-surface-matcher.ts"
+  },
+  "scripts": {
+    "publish:calibration-tree": "bun run src/publish-calibration-tree.ts",
+    "test": "bun test",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@vercel/blob": "^2.6.1"
+  },
+  "devDependencies": {
+    "@types/bun": "^1.3.14",
+    "typescript": "^5.8.0"
+  }
+}
diff --git a/frontend/lib/microcosm/calibration-build-comparison.test.ts b/frontend/packages/calibration-tree/src/calibration-build-comparison.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-build-comparison.test.ts
rename to frontend/packages/calibration-tree/src/calibration-build-comparison.test.ts
diff --git a/frontend/lib/microcosm/calibration-build-comparison.ts b/frontend/packages/calibration-tree/src/calibration-build-comparison.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-build-comparison.ts
rename to frontend/packages/calibration-tree/src/calibration-build-comparison.ts
diff --git a/frontend/lib/microcosm/calibration-comparison-blob.test.ts b/frontend/packages/calibration-tree/src/calibration-comparison-blob.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-comparison-blob.test.ts
rename to frontend/packages/calibration-tree/src/calibration-comparison-blob.test.ts
diff --git a/frontend/lib/microcosm/calibration-comparison-blob.ts b/frontend/packages/calibration-tree/src/calibration-comparison-blob.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-comparison-blob.ts
rename to frontend/packages/calibration-tree/src/calibration-comparison-blob.ts
diff --git a/frontend/lib/microcosm/calibration-comparison-bundle.test.ts b/frontend/packages/calibration-tree/src/calibration-comparison-bundle.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-comparison-bundle.test.ts
rename to frontend/packages/calibration-tree/src/calibration-comparison-bundle.test.ts
diff --git a/frontend/lib/microcosm/calibration-comparison-bundle.ts b/frontend/packages/calibration-tree/src/calibration-comparison-bundle.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-comparison-bundle.ts
rename to frontend/packages/calibration-tree/src/calibration-comparison-bundle.ts
diff --git a/frontend/lib/microcosm/calibration-explorer.test.ts b/frontend/packages/calibration-tree/src/calibration-explorer.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-explorer.test.ts
rename to frontend/packages/calibration-tree/src/calibration-explorer.test.ts
diff --git a/frontend/lib/microcosm/calibration-explorer.ts b/frontend/packages/calibration-tree/src/calibration-explorer.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-explorer.ts
rename to frontend/packages/calibration-tree/src/calibration-explorer.ts
diff --git a/frontend/lib/microcosm/calibration-release-locator.test.ts b/frontend/packages/calibration-tree/src/calibration-release-locator.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-release-locator.test.ts
rename to frontend/packages/calibration-tree/src/calibration-release-locator.test.ts
diff --git a/frontend/lib/microcosm/calibration-release-locator.ts b/frontend/packages/calibration-tree/src/calibration-release-locator.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-release-locator.ts
rename to frontend/packages/calibration-tree/src/calibration-release-locator.ts
diff --git a/frontend/lib/microcosm/calibration-tree-artifact.test.ts b/frontend/packages/calibration-tree/src/calibration-tree-artifact.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree-artifact.test.ts
rename to frontend/packages/calibration-tree/src/calibration-tree-artifact.test.ts
diff --git a/frontend/lib/microcosm/calibration-tree-artifact.ts b/frontend/packages/calibration-tree/src/calibration-tree-artifact.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree-artifact.ts
rename to frontend/packages/calibration-tree/src/calibration-tree-artifact.ts
diff --git a/frontend/lib/microcosm/calibration-tree-blob.test.ts b/frontend/packages/calibration-tree/src/calibration-tree-blob.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree-blob.test.ts
rename to frontend/packages/calibration-tree/src/calibration-tree-blob.test.ts
diff --git a/frontend/lib/microcosm/calibration-tree-blob.ts b/frontend/packages/calibration-tree/src/calibration-tree-blob.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree-blob.ts
rename to frontend/packages/calibration-tree/src/calibration-tree-blob.ts
diff --git a/frontend/lib/microcosm/calibration-tree-bundle.ts b/frontend/packages/calibration-tree/src/calibration-tree-bundle.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree-bundle.ts
rename to frontend/packages/calibration-tree/src/calibration-tree-bundle.ts
diff --git a/frontend/packages/calibration-tree/src/calibration-tree-golden.test.ts b/frontend/packages/calibration-tree/src/calibration-tree-golden.test.ts
new file mode 100644
index 00000000..5f53f011
--- /dev/null
+++ b/frontend/packages/calibration-tree/src/calibration-tree-golden.test.ts
@@ -0,0 +1,91 @@
+import { expect, test } from "bun:test";
+
+import recordedGoldens from "./fixtures/calibration-tree-golden.json";
+import {
+  GOLDEN_COMPARISON_CASES,
+  GOLDEN_SOURCE_CASES,
+  GZIP_HEADER_WITHOUT_OS,
+  goldenComparisonRecord,
+  goldenManifestRecord,
+  goldenSourceBuild,
+  goldenSourceRecord,
+  type CalibrationTreeGoldenRecord,
+  type GoldenComparisonCaseName,
+  type GoldenSourceCaseName,
+} from "./test-support/calibration-tree-golden-cases";
+
+// The record was produced by the builder before it moved into its own
+// package. Every case must reproduce it exactly: paths, raw JSON digests and
+// sizes, gzip sizes, deflate streams, build ids, and reader responses.
+const recorded = recordedGoldens as CalibrationTreeGoldenRecord;
+
+// The US release has 5,659 targets; building and validating its bundle
+// gzips about 40 MB three times. The limit is generous so the suite also
+// passes on a heavily loaded machine.
+const BUILD_TIMEOUT_MS = 300_000;
+
+const SOURCE_DESCRIPTIONS: Record<GoldenSourceCaseName, string> = {
+  "us-release": "a US legacy release",
+  "uk-release": "a UK schema 8 hierarchy release",
+  "uk-release-loss-attribution": "a UK release with target loss attribution",
+  "be-release": "a Belgium release",
+  "us-staging": "a US version 1 staging run",
+  "uk-staging": "a UK version 2 staging run",
+  "uk-staging-staged-bundle": "a UK staging run read from its staged dataset bundle",
+};
+
+const COMPARISON_DESCRIPTIONS: Record<GoldenComparisonCaseName, string> = {
+  "us-comparison": "a US release-to-staging comparison",
+  "uk-comparison": "a UK release-to-staging comparison",
+};
+
+for (const name of GOLDEN_SOURCE_CASES) {
+  test(
+    `${SOURCE_DESCRIPTIONS[name]} reproduces its recorded tree bundle and reader responses`,
+    async () => {
+      expect(await goldenSourceRecord(name)).toEqual(recorded.sources[name]);
+    },
+    BUILD_TIMEOUT_MS,
+  );
+}
+
+for (const name of GOLDEN_COMPARISON_CASES) {
+  test(
+    `${COMPARISON_DESCRIPTIONS[name]} reproduces its recorded bundles and target detail`,
+    async () => {
+      expect(await goldenComparisonRecord(name)).toEqual(recorded.comparisons[name]);
+    },
+    BUILD_TIMEOUT_MS,
+  );
+}
+
+test(
+  "the tree manifest for every recorded build reproduces its recorded bytes",
+  async () => {
+    expect(await goldenManifestRecord()).toEqual(recorded.manifest);
+  },
+  BUILD_TIMEOUT_MS,
+);
+
+test(
+  "every recorded part is gzip with the fixed header ahead of its recorded deflate stream",
+  async () => {
+    for (const name of GOLDEN_SOURCE_CASES) {
+      const { bundle } = await goldenSourceBuild(name);
+      for (const file of bundle.files) {
+        expect([...file.compressed.subarray(0, GZIP_HEADER_WITHOUT_OS.length)])
+          .toEqual(GZIP_HEADER_WITHOUT_OS);
+      }
+    }
+  },
+  BUILD_TIMEOUT_MS,
+);
+
+test("the recorded US release spans several target-summary and target-detail shards", () => {
+  const parts = recorded.sources["us-release"].files.map((file) => file.part);
+  expect(parts.filter((part) => part.startsWith("target-summary-")).length)
+    .toBeGreaterThan(1);
+  expect(parts.filter((part) => part.startsWith("target-details-")).length)
+    .toBeGreaterThan(1);
+  expect(parts.filter((part) => part.startsWith("tier-")).length).toBeGreaterThan(1);
+});
diff --git a/frontend/lib/microcosm/calibration-tree-manifest.test.ts b/frontend/packages/calibration-tree/src/calibration-tree-manifest.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree-manifest.test.ts
rename to frontend/packages/calibration-tree/src/calibration-tree-manifest.test.ts
diff --git a/frontend/lib/microcosm/calibration-tree-manifest.ts b/frontend/packages/calibration-tree/src/calibration-tree-manifest.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree-manifest.ts
rename to frontend/packages/calibration-tree/src/calibration-tree-manifest.ts
diff --git a/frontend/lib/microcosm/calibration-tree.test.ts b/frontend/packages/calibration-tree/src/calibration-tree.test.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree.test.ts
rename to frontend/packages/calibration-tree/src/calibration-tree.test.ts
diff --git a/frontend/lib/microcosm/calibration-tree.ts b/frontend/packages/calibration-tree/src/calibration-tree.ts
similarity index 100%
rename from frontend/lib/microcosm/calibration-tree.ts
rename to frontend/packages/calibration-tree/src/calibration-tree.ts
diff --git a/frontend/lib/microcosm/chronicle-metadata.test.ts b/frontend/packages/calibration-tree/src/chronicle-metadata.test.ts
similarity index 100%
rename from frontend/lib/microcosm/chronicle-metadata.test.ts
rename to frontend/packages/calibration-tree/src/chronicle-metadata.test.ts
diff --git a/frontend/lib/microcosm/chronicle-metadata.ts b/frontend/packages/calibration-tree/src/chronicle-metadata.ts
similarity index 100%
rename from frontend/lib/microcosm/chronicle-metadata.ts
rename to frontend/packages/calibration-tree/src/chronicle-metadata.ts
diff --git a/frontend/lib/microcosm/countries.test.ts b/frontend/packages/calibration-tree/src/countries.test.ts
similarity index 100%
rename from frontend/lib/microcosm/countries.test.ts
rename to frontend/packages/calibration-tree/src/countries.test.ts
diff --git a/frontend/packages/calibration-tree/src/countries.ts b/frontend/packages/calibration-tree/src/countries.ts
new file mode 100644
index 00000000..a57253d5
--- /dev/null
+++ b/frontend/packages/calibration-tree/src/countries.ts
@@ -0,0 +1,241 @@
+// Country registry for the Microcosm dashboard: the one place a country is
+// registered. Adding a country is one entry here; everything else (selectors,
+// navigation, repository resolution, national geography, link behaviour) reads
+// the registration or the release artifact's typed `country` block.
+//
+// Isomorphic: imported by client components and API routes alike, so it must
+// not import server-only modules or read `process.env`. Repository resolvers
+// accept an explicit environment object from server-side callers.
+
+export const COUNTRY_CAPABILITIES = [
+  "calibration",
+  "targets",
+  "compare",
+  "cross_dataset",
+  "staging",
+  "model_coverage",
+  "pipeline",
+  "variables",
+  "external_checks",
+] as const;
+export type CountryCapability = (typeof COUNTRY_CAPABILITIES)[number];
+
+export type RepositoryVisibility = "public" | "private";
+
+export type RepositoryEnvironment = Readonly<
+  Record<string, string | undefined>
+>;
+
+export interface ResolvedRepository {
+  repo: string;
+  revision: string;
+}
+
+export interface CountryRegistration {
+  // Default HF dataset repository and revision (the server may override both
+  // through the deployment variables named in repo_env / revision_env).
+  repo: string;
+  revision: string;
+  repo_env?: string;
+  revision_env?: string;
+  // Country display name ("United States").
+  label: string;
+  // Sidebar dataset line ("Microcosm US").
+  dataset_label: string;
+  // National geography label and id (null when the id is unknown).
+  geography: string;
+  geography_id: string | null;
+  visibility: RepositoryVisibility;
+  capabilities: readonly CountryCapability[];
+  // Optional staging telemetry repository. A staging-capable country must
+  // declare this instead of inheriting another country's repository.
+  staging?: {
+    repo: string;
+    revision: string;
+    repo_env?: string;
+    revision_env?: string;
+    token_env?: string;
+  };
+  // Other jurisdiction codes a cross-dataset bundle may use for this country.
+  jurisdiction_aliases?: readonly string[];
+  // Conformance-only registration: a valid country that is never listed in
+  // selectors or alert allowlists.
+  fixture?: true;
+}
+
+const ALL_CAPABILITIES: readonly CountryCapability[] = COUNTRY_CAPABILITIES;
+
+const CALIBRATION_CAPABILITIES: readonly CountryCapability[] = [
+  "calibration",
+  "targets",
+  "compare",
+  "cross_dataset",
+];
+
+// Deprecated upstream identifiers: Microcosm's published HF repositories and
+// deployment variables still use the former Populace names.
+export const COUNTRY_REGISTRY = {
+  us: {
+    repo: "policyengine/populace-us",
+    revision: "main",
+    repo_env: "POPULACE_HF_REPO",
+    label: "United States",
+    dataset_label: "Microcosm US",
+    geography: "United States",
+    geography_id: "0100000US",
+    visibility: "public",
+    capabilities: ALL_CAPABILITIES,
+    staging: {
+      // Deprecated upstream identifier: the US staging publisher still uses
+      // the former Populace repository and deployment-variable names.
+      repo: "policyengine/populace-us-staging",
+      revision: "main",
+      repo_env: "POPULACE_STAGING_HF_REPO",
+      revision_env: "POPULACE_STAGING_HF_REVISION",
+    },
+  },
+  uk: {
+    repo: "policyengine/populace-uk-private",
+    revision: "main",
+    repo_env: "POPULACE_UK_HF_REPO",
+    revision_env: "POPULACE_UK_HF_REVISION",
+    label: "United Kingdom",
+    dataset_label: "Microcosm UK",
+    geography: "United Kingdom",
+    geography_id: null,
+    visibility: "private",
+    capabilities: [...CALIBRATION_CAPABILITIES, "staging"],
+    staging: {
+      repo: "policyengine/populace-uk-staging",
+      revision: "main",
+      repo_env: "POPULACE_UK_STAGING_HF_REPO",
+      revision_env: "POPULACE_UK_STAGING_HF_REVISION",
+      token_env: "POPULACE_UK_STAGING_HF_TOKEN",
+    },
+    jurisdiction_aliases: ["GB"],
+  },
+  be: {
+    repo: "policyengine/populace-be-private",
+    revision: "main",
+    repo_env: "POPULACE_BE_HF_REPO",
+    revision_env: "POPULACE_BE_HF_REVISION",
+    label: "Belgium",
+    dataset_label: "Microcosm Belgium",
+    geography: "Belgium",
+    geography_id: null,
+    visibility: "private",
+    capabilities: CALIBRATION_CAPABILITIES,
+  },
+  // Synthetic repository used only by the third-country conformance fixture.
+  zz: {
+    repo: "policyengine/microcosm-zz-fixture",
+    revision: "main",
+    label: "Zedland",
+    dataset_label: "Microcosm ZZ",
+    geography: "Zedland",
+    geography_id: null,
+    visibility: "private",
+    capabilities: ["calibration", "targets", "compare"],
+    fixture: true,
+  },
+  // Synthetic non-US staging registration. It verifies that staging artifact
+  // resolution is country-scoped without exposing an unfinished country in
+  // selectors or treating its fixture repository as a published dataset.
+  am: {
+    repo: "policyengine/microcosm-am-fixture",
+    revision: "main",
+    label: "Armenia",
+    dataset_label: "Microcosm Armenia",
+    geography: "Armenia",
+    geography_id: null,
+    visibility: "private",
+    capabilities: ["calibration", "targets", "compare", "staging"],
+    staging: {
+      repo: "policyengine/microcosm-am-staging-fixture",
+      revision: "main",
+    },
+    fixture: true,
+  },
+} satisfies Record<string, CountryRegistration>;
+
+export type MicrocosmCountry = keyof typeof COUNTRY_REGISTRY;
+
+export const DEFAULT_COUNTRY: MicrocosmCountry = "us";
+
+const COUNTRY_CODES = Object.keys(COUNTRY_REGISTRY) as MicrocosmCountry[];
+
+export function isCountry(value: string | null | undefined): value is MicrocosmCountry {
+  return value != null && Object.hasOwn(COUNTRY_REGISTRY, value);
+}
+
+export function parseCountry(value: string | null | undefined): MicrocosmCountry {
+  return isCountry(value) ? value : DEFAULT_COUNTRY;
+}
+
+export function countryRegistration(country: MicrocosmCountry): CountryRegistration {
+  return COUNTRY_REGISTRY[country];
+}
+
+// Countries offered in selectors, in registry order; fixtures are excluded.
+export function selectableCountries(): MicrocosmCountry[] {
+  return COUNTRY_CODES.filter((country) => !countryRegistration(country).fixture);
+}
+
+export function countryCapabilities(country: MicrocosmCountry): readonly CountryCapability[] {
+  return COUNTRY_REGISTRY[country].capabilities;
+}
+
+export function hasCapability(country: MicrocosmCountry, capability: CountryCapability): boolean {
+  return countryCapabilities(country).includes(capability);
+}
+
+function configuredValue(
+  environment: RepositoryEnvironment,
+  variableName: string | undefined,
+  fallback: string,
+): string {
+  return (variableName ? environment[variableName] : undefined) ?? fallback;
+}
+
+export function resolveRegisteredRepository(
+  country: MicrocosmCountry,
+  environment: RepositoryEnvironment,
+): ResolvedRepository {
+  const registration = countryRegistration(country);
+  return {
+    repo: configuredValue(
+      environment,
+      registration.repo_env,
+      registration.repo,
+    ),
+    revision: configuredValue(
+      environment,
+      registration.revision_env,
+      registration.revision,
+    ),
+  };
+}
+
+export function resolveRegisteredStagingRepository(
+  country: MicrocosmCountry,
+  environment: RepositoryEnvironment,
+): ResolvedRepository | null {
+  const registration = countryRegistration(country);
+  if (!hasCapability(country, "staging") || !registration.staging) return null;
+  return {
+    repo: configuredValue(
+      environment,
+      registration.staging.repo_env,
+      registration.staging.repo,
+    ),
+    revision: configuredValue(
+      environment,
+      registration.staging.revision_env,
+      registration.staging.revision,
+    ),
+  };
+}
+
+export function isCountryCapability(value: unknown): value is CountryCapability {
+  return typeof value === "string" && (COUNTRY_CAPABILITIES as readonly string[]).includes(value);
+}
diff --git a/frontend/lib/microcosm/fixtures/be-release/calibration_diagnostics.json b/frontend/packages/calibration-tree/src/fixtures/be-release/calibration_diagnostics.json
similarity index 100%
rename from frontend/lib/microcosm/fixtures/be-release/calibration_diagnostics.json
rename to frontend/packages/calibration-tree/src/fixtures/be-release/calibration_diagnostics.json
diff --git a/frontend/lib/microcosm/fixtures/be-release/release_manifest.json b/frontend/packages/calibration-tree/src/fixtures/be-release/release_manifest.json
similarity index 100%
rename from frontend/lib/microcosm/fixtures/be-release/release_manifest.json
rename to frontend/packages/calibration-tree/src/fixtures/be-release/release_manifest.json
diff --git a/frontend/packages/calibration-tree/src/fixtures/calibration-tree-golden.json b/frontend/packages/calibration-tree/src/fixtures/calibration-tree-golden.json
new file mode 100644
index 00000000..a4d719e4
--- /dev/null
+++ b/frontend/packages/calibration-tree/src/fixtures/calibration-tree-golden.json
@@ -0,0 +1,742 @@
+{
+  "schemaVersion": 6,
+  "sources": {
+    "us-release": {
+      "buildArtifactId": "a66bd48af3da1089ab48225245a8549c3adbf2f2a13d0c922f75eabace014887",
+      "files": [
+        {
+          "part": "filter-index",
+          "path": "calibration-trees/us/a66bd48af3da1089ab48225245a8549c3adbf2f2a13d0c922f75eabace014887/filter-index.json.gz",
+          "sha256": "6a741042b02bddfbfa1c481f9d4a20e8a8cdd4d2cbe80bf2c9fe8d9f977ed51a",
+          "rawBytes": 138229,
+          "gzipBytes": 33527,
+          "deflateSha256": "1ca1078eb8f427e9abb1322cb06e956c8d9f81980c467b223ccb89610f2b4055"
+        },
+        {
+          "part": "target-summary-0001",
+          "path": "calibration-trees/us/a66bd48af3da1089ab48225245a8549c3adbf2f2a13d0c922f75eabace014887/target-summary-0001.json.gz",
+          "sha256": "9cfc348ae34a3f8b140e938d55701ad5eb3e853611c74869fdf90477f4a5164a",
+          "rawBytes": 7998998,
+          "gzipBytes": 291909,
+          "deflateSha256": "9334f9fa5c1ae6058acb88fbd70b73c17074db82104ad2251a89a24b5a4a8eff"
+        },
+        {
+          "part": "target-summary-0002",
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v2/calibration/runs/uk-calibration-v2-fixture/events.ndjson b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v2/calibration/runs/uk-calibration-v2-fixture/events.ndjson
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v2/completed-spine/runs/uk-spine-v2-fixture/events.ndjson b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v2/completed-spine/runs/uk-spine-v2-fixture/events.ndjson
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v2/completed-spine/runs/uk-spine-v2-fixture/progress.json b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v2/completed-spine/runs/uk-spine-v2-fixture/progress.json
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similarity index 100%
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v2/failed/runs/uk-failed-v2-fixture/events.ndjson b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v2/failed/runs/uk-failed-v2-fixture/events.ndjson
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v2/failed/runs/uk-failed-v2-fixture/progress.json b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v2/failed/runs/uk-failed-v2-fixture/progress.json
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v2/failed/runs/uk-failed-v2-fixture/run_manifest.json b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v2/failed/runs/uk-failed-v2-fixture/run_manifest.json
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v3/SHA256SUMS b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v3/SHA256SUMS
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v3/blocked/runs/uk-blocked-v3-fixture/events.ndjson b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v3/blocked/runs/uk-blocked-v3-fixture/events.ndjson
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diff --git a/frontend/lib/microcosm/fixtures/staging-contract/v3/calibration/runs/uk-calibration-v3-fixture/events.ndjson b/frontend/packages/calibration-tree/src/fixtures/staging-contract/v3/calibration/runs/uk-calibration-v3-fixture/events.ndjson
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rename from frontend/lib/microcosm/fixtures/target-loss-attribution/malformed-partial.json
rename to frontend/packages/calibration-tree/src/fixtures/target-loss-attribution/malformed-partial.json
diff --git a/frontend/lib/microcosm/fixtures/target-loss-attribution/unavailable-warning.json b/frontend/packages/calibration-tree/src/fixtures/target-loss-attribution/unavailable-warning.json
similarity index 100%
rename from frontend/lib/microcosm/fixtures/target-loss-attribution/unavailable-warning.json
rename to frontend/packages/calibration-tree/src/fixtures/target-loss-attribution/unavailable-warning.json
diff --git a/frontend/lib/microcosm/fixtures/target-loss-attribution/valid-unequal-custom-scales.json b/frontend/packages/calibration-tree/src/fixtures/target-loss-attribution/valid-unequal-custom-scales.json
similarity index 100%
rename from frontend/lib/microcosm/fixtures/target-loss-attribution/valid-unequal-custom-scales.json
rename to frontend/packages/calibration-tree/src/fixtures/target-loss-attribution/valid-unequal-custom-scales.json
diff --git a/frontend/lib/microcosm/fixtures/target-loss-attribution/valid-uniform.json b/frontend/packages/calibration-tree/src/fixtures/target-loss-attribution/valid-uniform.json
similarity index 100%
rename from frontend/lib/microcosm/fixtures/target-loss-attribution/valid-uniform.json
rename to frontend/packages/calibration-tree/src/fixtures/target-loss-attribution/valid-uniform.json
diff --git a/frontend/lib/microcosm/fixtures/us-legacy-target-identities.json.gz b/frontend/packages/calibration-tree/src/fixtures/us-legacy-target-identities.json.gz
similarity index 100%
rename from frontend/lib/microcosm/fixtures/us-legacy-target-identities.json.gz
rename to frontend/packages/calibration-tree/src/fixtures/us-legacy-target-identities.json.gz
diff --git a/frontend/lib/microcosm/hierarchy-target-reader.test.ts b/frontend/packages/calibration-tree/src/hierarchy-target-reader.test.ts
similarity index 100%
rename from frontend/lib/microcosm/hierarchy-target-reader.test.ts
rename to frontend/packages/calibration-tree/src/hierarchy-target-reader.test.ts
diff --git a/frontend/lib/microcosm/hierarchy-target-reader.ts b/frontend/packages/calibration-tree/src/hierarchy-target-reader.ts
similarity index 100%
rename from frontend/lib/microcosm/hierarchy-target-reader.ts
rename to frontend/packages/calibration-tree/src/hierarchy-target-reader.ts
diff --git a/frontend/lib/microcosm/historical-weight-summary.test.ts b/frontend/packages/calibration-tree/src/historical-weight-summary.test.ts
similarity index 100%
rename from frontend/lib/microcosm/historical-weight-summary.test.ts
rename to frontend/packages/calibration-tree/src/historical-weight-summary.test.ts
diff --git a/frontend/lib/microcosm/historical-weight-summary.ts b/frontend/packages/calibration-tree/src/historical-weight-summary.ts
similarity index 100%
rename from frontend/lib/microcosm/historical-weight-summary.ts
rename to frontend/packages/calibration-tree/src/historical-weight-summary.ts
diff --git a/frontend/lib/microcosm/latest-artifact.test.ts b/frontend/packages/calibration-tree/src/latest-artifact.test.ts
similarity index 100%
rename from frontend/lib/microcosm/latest-artifact.test.ts
rename to frontend/packages/calibration-tree/src/latest-artifact.test.ts
diff --git a/frontend/lib/microcosm/latest-artifact.ts b/frontend/packages/calibration-tree/src/latest-artifact.ts
similarity index 99%
rename from frontend/lib/microcosm/latest-artifact.ts
rename to frontend/packages/calibration-tree/src/latest-artifact.ts
index b0ba929b..692006b4 100644
--- a/frontend/lib/microcosm/latest-artifact.ts
+++ b/frontend/packages/calibration-tree/src/latest-artifact.ts
@@ -8,7 +8,7 @@ import { basename, join } from "node:path";
 
 import { createHash } from "node:crypto";
 
-import { sourceAuthorityLabel } from "@/lib/source-labels";
+import { sourceAuthorityLabel } from "./source-labels";
 
 import { normalizeChronicleMetadata } from "./chronicle-metadata";
 import {
diff --git a/frontend/lib/microcosm/legacy-target-reader.ts b/frontend/packages/calibration-tree/src/legacy-target-reader.ts
similarity index 100%
rename from frontend/lib/microcosm/legacy-target-reader.ts
rename to frontend/packages/calibration-tree/src/legacy-target-reader.ts
diff --git a/frontend/lib/microcosm/legacy-target-regression.test.ts b/frontend/packages/calibration-tree/src/legacy-target-regression.test.ts
similarity index 100%
rename from frontend/lib/microcosm/legacy-target-regression.test.ts
rename to frontend/packages/calibration-tree/src/legacy-target-regression.test.ts
diff --git a/frontend/packages/calibration-tree/src/package-boundary.test.ts b/frontend/packages/calibration-tree/src/package-boundary.test.ts
new file mode 100644
index 00000000..7d6846ac
--- /dev/null
+++ b/frontend/packages/calibration-tree/src/package-boundary.test.ts
@@ -0,0 +1,128 @@
+// The package must stay self-contained so it can leave the dashboard's
+// repository: its modules import only each other, Node built-ins and the
+// dependencies its manifest declares, never the dashboard's `@/` aliases,
+// Next.js or `server-only`. Consumers reach it only through its exports.
+import { Glob } from "bun";
+import { expect, test } from "bun:test";
+import { existsSync, readFileSync, statSync } from "node:fs";
+import { builtinModules } from "node:module";
+import { basename, dirname, join, relative, resolve } from "node:path";
+
+const PACKAGE_ROOT = resolve(import.meta.dir, "..");
+const SOURCE_ROOT = join(PACKAGE_ROOT, "src");
+// Bun lists its own modules (`bun`, `bun:test`, ...) among the built-ins.
+const NODE_BUILTINS = new Set(builtinModules.filter((name) => !name.startsWith("bun")));
+
+interface PackageManifest {
+  name: string;
+  exports: Record<string, string>;
+  dependencies?: Record<string, string>;
+  devDependencies?: Record<string, string>;
+}
+
+function packageManifest(): PackageManifest {
+  return JSON.parse(readFileSync(join(PACKAGE_ROOT, "package.json"), "utf8"));
+}
+
+function sourceFiles(): string[] {
+  return [...new Glob("**/*.ts").scanSync({ cwd: SOURCE_ROOT })].sort();
+}
+
+// Tests and their support code may also use the test runner, the package's
+// own entry points and its development dependencies.
+function isTestCode(relativePath: string): boolean {
+  return relativePath.endsWith(".test.ts") || relativePath.startsWith("test-support/");
+}
+
+function importSpecifiers(source: string): string[] {
+  const patterns = [
+    /(?:^|\n)\s*(?:import|export)\s[^;]*?\sfrom\s+["']([^"']+)["']/g,
+    /(?:^|\n)\s*import\s+["']([^"']+)["']/g,
+    /\bimport\(\s*["']([^"']+)["']\s*\)/g,
+    /\bmock\.module\(\s*["']([^"']+)["']/g,
+  ];
+  return patterns.flatMap((pattern) =>
+    [...source.matchAll(pattern)].map((match) => match[1])
+  );
+}
+
+function packageName(specifier: string): string {
+  const segments = specifier.split("/");
+  return specifier.startsWith("@") ? segments.slice(0, 2).join("/") : segments[0];
+}
+
+function resolvesInsidePackage(fromFile: string, specifier: string): boolean {
+  const base = resolve(dirname(fromFile), specifier);
+  if (relative(PACKAGE_ROOT, base).startsWith("..")) return false;
+  return [base, `${base}.ts`, join(base, "index.ts")].some(
+    (candidate) => existsSync(candidate) && statSync(candidate).isFile(),
+  );
+}
+
+function importViolation(
+  relativePath: string,
+  specifier: string,
+  manifest: PackageManifest,
+): string | null {
+  const file = join(SOURCE_ROOT, relativePath);
+  const testCode = isTestCode(relativePath);
+  if (specifier.startsWith(".")) {
+    return resolvesInsidePackage(file, specifier) ? null : "does not resolve inside the package";
+  }
+  if (specifier === "bun" || specifier.startsWith("bun:")) {
+    return testCode ? null : "is test-runner code outside a test";
+  }
+  if (specifier.startsWith("node:")) {
+    return NODE_BUILTINS.has(specifier.slice("node:".length)) ? null : "is not a Node built-in";
+  }
+  if (NODE_BUILTINS.has(specifier)) return "must use the node: prefix";
+  if (specifier.startsWith("@/")) return "is a dashboard path alias";
+  if (packageName(specifier) === manifest.name) {
+    if (!testCode) return "is a self-reference; package modules import each other relatively";
+    return `./${specifier.slice(manifest.name.length + 1)}` in manifest.exports
+      ? null
+      : "is not a package export";
+  }
+  const declared = {
+    ...manifest.dependencies,
+    ...(testCode ? manifest.devDependencies : {}),
+  };
+  return packageName(specifier) in declared ? null : "is not a declared dependency";
+}
+
+test("package modules import only package files, Node built-ins and declared dependencies", () => {
+  const manifest = packageManifest();
+  const violations = sourceFiles().flatMap((relativePath) =>
+    importSpecifiers(readFileSync(join(SOURCE_ROOT, relativePath), "utf8")).flatMap((specifier) => {
+      const violation = importViolation(relativePath, specifier, manifest);
+      return violation ? [`${relativePath}: "${specifier}" ${violation}`] : [];
+    })
+  );
+
+  expect(violations).toEqual([]);
+});
+
+test("every package export resolves to a package module", () => {
+  const manifest = packageManifest();
+  const unresolved = Object.entries(manifest.exports).flatMap(([subpath, target]) => {
+    const file = resolve(PACKAGE_ROOT, target);
+    const valid =
+      subpath === `./${basename(target, ".ts")}` &&
+      !relative(SOURCE_ROOT, file).startsWith("..") &&
+      existsSync(file);
+    return valid ? [] : [`${subpath} -> ${target}`];
+  });
+
+  expect(Object.keys(manifest.exports).length).toBeGreaterThan(0);
+  expect(unresolved).toEqual([]);
+});
+
+test("every package module is exported", () => {
+  const manifest = packageManifest();
+  const exportedTargets = new Set(Object.values(manifest.exports));
+  const unexported = sourceFiles()
+    .filter((relativePath) => !isTestCode(relativePath))
+    .filter((relativePath) => !exportedTargets.has(`./src/${relativePath}`));
+
+  expect(unexported).toEqual([]);
+});
diff --git a/frontend/lib/microcosm/program-label.test.ts b/frontend/packages/calibration-tree/src/program-label.test.ts
similarity index 100%
rename from frontend/lib/microcosm/program-label.test.ts
rename to frontend/packages/calibration-tree/src/program-label.test.ts
diff --git a/frontend/lib/microcosm/program-label.ts b/frontend/packages/calibration-tree/src/program-label.ts
similarity index 100%
rename from frontend/lib/microcosm/program-label.ts
rename to frontend/packages/calibration-tree/src/program-label.ts
diff --git a/frontend/packages/calibration-tree/src/publish-calibration-tree-golden.test.ts b/frontend/packages/calibration-tree/src/publish-calibration-tree-golden.test.ts
new file mode 100644
index 00000000..8f1cf64d
--- /dev/null
+++ b/frontend/packages/calibration-tree/src/publish-calibration-tree-golden.test.ts
@@ -0,0 +1,176 @@
+import { afterEach, expect, test } from "bun:test";
+
+import recordedGoldens from "./fixtures/calibration-tree-golden.json";
+import {
+  emptyCalibrationTreeManifest,
+  withCalibrationTreeManifestEntry,
+  type CalibrationTreeManifestEntry,
+} from "@policyengine/calibration-tree/calibration-tree-manifest";
+import { COUNTRY_REGISTRY } from "@policyengine/calibration-tree/countries";
+import {
+  goldenReleaseInputs,
+  withRegisteredRepositories,
+  type CalibrationTreeGoldenRecord,
+  type GoldenReleaseInput,
+} from "./test-support/calibration-tree-golden-cases";
+import {
+  reconcileReleaseBuilds,
+  type CalibrationManifestStore,
+} from "@policyengine/calibration-tree/publish-calibration-tree";
+
+// A repair rebuilds a published release whose index went missing and refuses
+// any rebuilt index whose digest differs from the manifest entry. Seeding the
+// entry with the recorded build id and index digest therefore proves, through
+// the publisher's own Hugging Face reads and source hashing, that it rebuilds
+// the recorded index byte for byte.
+const recorded = recordedGoldens as CalibrationTreeGoldenRecord;
+const MAIN_REVISION_SHA = "0123456789abcdef0123456789abcdef01234567";
+// Generous, so the suite also passes on a heavily loaded machine.
+const BUILD_TIMEOUT_MS = 300_000;
+const originalFetch = globalThis.fetch;
+
+afterEach(() => {
+  globalThis.fetch = originalFetch;
+});
+
+type ReleaseCaseName = keyof ReturnType<typeof goldenReleaseInputs>;
+
+// The dataset repository as the publisher reads it: one tagged release at
+// its commit, which `latest.json` on the main branch also names.
+function huggingFaceReleaseRepository(release: GoldenReleaseInput): typeof fetch {
+  const repo = COUNTRY_REGISTRY[release.country].repo;
+  const api = `https://huggingface.co/api/datasets/${repo}`;
+  const resolveUrl = (revision: string, path: string) =>
+    `https://huggingface.co/datasets/${repo}/resolve/${revision}/${path}`;
+  const prefix = `releases/${release.releaseId}`;
+  const publishedFiles = new Map<string, string>([
+    ["calibration_diagnostics.json", release.diagnosticsText],
+    ...(release.releaseManifestText == null
+      ? []
+      : [["release_manifest.json", release.releaseManifestText] as [string, string]]),
+  ]);
+  const responses = new Map<string, () => Response>([
+    [
+      `${api}/tree/main/releases?recursive=true`,
+      () => Response.json([...publishedFiles.keys()].map((name) => ({
+        type: "file",
+        path: `${prefix}/${name}`,
+      }))),
+    ],
+    [
+      `${api}/refs`,
+      () => Response.json({
+        tags: [{ name: release.releaseId, targetCommit: release.hfCommitSha }],
+      }),
+    ],
+    [`${api}/revision/main`, () => Response.json({ sha: MAIN_REVISION_SHA })],
+    [`${api}/revision/${release.releaseId}`, () => Response.json({ sha: release.hfCommitSha })],
+    [
+      resolveUrl(MAIN_REVISION_SHA, "latest.json"),
+      () => Response.json({ release_id: release.releaseId }),
+    ],
+  ]);
+  for (const [name, text] of publishedFiles) {
+    responses.set(resolveUrl(release.hfCommitSha, `${prefix}/${name}`), () => new Response(text));
+    responses.set(resolveUrl("main", `${prefix}/${name}`), () => new Response(text));
+  }
+  return (async (input: string | URL | Request) => {
+    const url = String(input);
+    const respond = responses.get(url);
+    if (respond) return respond();
+    if (url.startsWith(resolveUrl(release.hfCommitSha, `${prefix}/`))) {
+      return new Response(null, { status: 404 });
+    }
+    throw new Error(`Unexpected Hugging Face request ${url}`);
+  }) as typeof fetch;
+}
+
+function recordedReleaseEntry(
+  release: GoldenReleaseInput,
+  name: ReleaseCaseName,
+): CalibrationTreeManifestEntry {
+  const record = recorded.sources[name];
+  const index = record.files.find((file) => file.part === "index");
+  if (!index) throw new Error(`The ${name} record has no index.`);
+  return {
+    buildArtifactId: record.buildArtifactId,
+    kind: "release",
+    sourceId: release.releaseId,
+    label: release.releaseId,
+    releaseId: release.releaseId,
+    stagingRunId: null,
+    hfRepo: COUNTRY_REGISTRY[release.country].repo,
+    hfCommitSha: release.hfCommitSha,
+    treeSchemaVersion: 6,
+    indexSha256: index.sha256,
+    indexBytes: index.rawBytes,
+    createdAt: release.publishedAt,
+    updatedAt: release.publishedAt,
+  };
+}
+
+// A published release whose stored index has gone missing.
+function storeMissingIndex(
+  release: GoldenReleaseInput,
+  entry: CalibrationTreeManifestEntry,
+): CalibrationManifestStore {
+  return {
+    readManifest: async () => withCalibrationTreeManifestEntry(
+      emptyCalibrationTreeManifest(),
+      release.country,
+      entry,
+      true,
+    ),
+    listBlobs: async () => new Map(),
+    audit: async () => ({
+      complete: false,
+      repairable: true,
+      reasons: ["index is missing"],
+      index: null,
+    }),
+    updateManifest: async () => {
+      throw new Error("A dry run must not write the manifest.");
+    },
+  };
+}
+
+const RELEASE_DESCRIPTIONS: Record<"us-release" | "uk-release" | "be-release", string> = {
+  "us-release": "US legacy",
+  "uk-release": "UK hierarchy",
+  "be-release": "Belgium",
+};
+
+for (const [name, description] of Object.entries(RELEASE_DESCRIPTIONS) as Array<
+  [keyof typeof RELEASE_DESCRIPTIONS, string]
+>) {
+  test(
+    `a dry-run repair of the recorded ${description} release rebuilds its recorded index`,
+    async () => {
+      const release = goldenReleaseInputs()[name];
+      const entry = recordedReleaseEntry(release, name);
+      globalThis.fetch = huggingFaceReleaseRepository(release);
+
+      const report = await withRegisteredRepositories(() =>
+        reconcileReleaseBuilds(release.country, "unused-blob-token", true, storeMissingIndex(release, entry))
+      );
+
+      expect(report.outcomes).toEqual([{
+        sourceId: release.releaseId,
+        status: "repaired",
+        buildArtifactId: recorded.sources[name].buildArtifactId,
+        reason: "Dry run; no Blob writes performed.",
+      }]);
+    },
+    BUILD_TIMEOUT_MS,
+  );
+}
+
+test("a repair refuses a rebuilt index that differs from the recorded digest", async () => {
+  const release = goldenReleaseInputs()["uk-release"];
+  const entry = { ...recordedReleaseEntry(release, "uk-release"), indexSha256: "0".repeat(64) };
+  globalThis.fetch = huggingFaceReleaseRepository(release);
+
+  await expect(withRegisteredRepositories(() =>
+    reconcileReleaseBuilds(release.country, "unused-blob-token", true, storeMissingIndex(release, entry))
+  )).rejects.toThrow("Rebuilt calibration index differs from immutable manifest entry");
+});
diff --git a/frontend/scripts/publish-calibration-tree.test.ts b/frontend/packages/calibration-tree/src/publish-calibration-tree.test.ts
similarity index 99%
rename from frontend/scripts/publish-calibration-tree.test.ts
rename to frontend/packages/calibration-tree/src/publish-calibration-tree.test.ts
index edbaa457..ce10d492 100644
--- a/frontend/scripts/publish-calibration-tree.test.ts
+++ b/frontend/packages/calibration-tree/src/publish-calibration-tree.test.ts
@@ -15,7 +15,7 @@ import {
   withCalibrationTreeManifestEntry,
   type CalibrationTreeManifest,
   type CalibrationTreeManifestEntry,
-} from "../lib/microcosm/calibration-tree-manifest";
+} from "./calibration-tree-manifest";
 
 const originalFetch = globalThis.fetch;
 
diff --git a/frontend/scripts/publish-calibration-tree.ts b/frontend/packages/calibration-tree/src/publish-calibration-tree.ts
similarity index 98%
rename from frontend/scripts/publish-calibration-tree.ts
rename to frontend/packages/calibration-tree/src/publish-calibration-tree.ts
index 7530e634..30e2d71b 100644
--- a/frontend/scripts/publish-calibration-tree.ts
+++ b/frontend/packages/calibration-tree/src/publish-calibration-tree.ts
@@ -1,11 +1,11 @@
 import {
   CALIBRATION_TREE_SCHEMA_VERSION,
   type CalibrationTreeSourceArtifact,
-} from "../lib/microcosm/calibration-tree-artifact";
+} from "./calibration-tree-artifact";
 import {
   buildCalibrationTreeBundle,
   type CalibrationTreeBundleFile,
-} from "../lib/microcosm/calibration-tree-bundle";
+} from "./calibration-tree-bundle";
 import {
   auditCalibrationTreeBuild,
   listCalibrationTreeBlobs,
@@ -13,12 +13,12 @@ import {
   updateCalibrationTreeManifest,
   uploadCalibrationTreeBundle,
   type CalibrationTreeBuildAudit,
-} from "../lib/microcosm/calibration-tree-blob";
+} from "./calibration-tree-blob";
 import type { ListBlobResultBlob } from "@vercel/blob";
 import type {
   CalibrationTreeManifest,
   CalibrationTreeManifestEntry,
-} from "../lib/microcosm/calibration-tree-manifest";
+} from "./calibration-tree-manifest";
 import { createHash } from "node:crypto";
 import {
   CalibrationReleaseNotFoundError,
@@ -26,24 +26,24 @@ import {
   resolveHfReleaseDirectorySha,
   resolveHfRepositoryCommitPublishedAt,
   resolveHfRevisionSha,
-} from "../lib/microcosm/calibration-release-locator";
+} from "./calibration-release-locator";
 import {
   isCountry,
   selectableCountries,
   type MicrocosmCountry,
-} from "../lib/microcosm/countries";
+} from "./countries";
 import {
   buildCalibration,
   loadReleases,
   microcosmRepo,
   microcosmRevision,
-} from "../lib/microcosm/latest-artifact";
+} from "./latest-artifact";
 import {
   loadStagingRuns,
   resolveStagingCalibrationSource,
   resolveStagingRevisionSha,
   stagingRepository,
-} from "../lib/microcosm/staging-artifact";
+} from "./staging-artifact";
 
 type JsonObject = Record<string, unknown>;
 
diff --git a/frontend/lib/microcosm/reforms.test.ts b/frontend/packages/calibration-tree/src/reforms.test.ts
similarity index 100%
rename from frontend/lib/microcosm/reforms.test.ts
rename to frontend/packages/calibration-tree/src/reforms.test.ts
diff --git a/frontend/lib/microcosm/reforms.ts b/frontend/packages/calibration-tree/src/reforms.ts
similarity index 100%
rename from frontend/lib/microcosm/reforms.ts
rename to frontend/packages/calibration-tree/src/reforms.ts
diff --git a/frontend/lib/microcosm/source-label.test.ts b/frontend/packages/calibration-tree/src/source-label.test.ts
similarity index 100%
rename from frontend/lib/microcosm/source-label.test.ts
rename to frontend/packages/calibration-tree/src/source-label.test.ts
diff --git a/frontend/lib/microcosm/source-label.ts b/frontend/packages/calibration-tree/src/source-label.ts
similarity index 61%
rename from frontend/lib/microcosm/source-label.ts
rename to frontend/packages/calibration-tree/src/source-label.ts
index 9823a7d5..ebe8d75d 100644
--- a/frontend/lib/microcosm/source-label.ts
+++ b/frontend/packages/calibration-tree/src/source-label.ts
@@ -1,4 +1,4 @@
-import { sourceAuthorityLabel } from "@/lib/source-labels";
+import { sourceAuthorityLabel } from "./source-labels";
 
 export function sourceLabel(source: string): string {
   return sourceAuthorityLabel(source);
diff --git a/frontend/lib/source-labels.test.ts b/frontend/packages/calibration-tree/src/source-labels.test.ts
similarity index 100%
rename from frontend/lib/source-labels.test.ts
rename to frontend/packages/calibration-tree/src/source-labels.test.ts
diff --git a/frontend/lib/source-labels.ts b/frontend/packages/calibration-tree/src/source-labels.ts
similarity index 100%
rename from frontend/lib/source-labels.ts
rename to frontend/packages/calibration-tree/src/source-labels.ts
diff --git a/frontend/lib/microcosm/staging-artifact.test.ts b/frontend/packages/calibration-tree/src/staging-artifact.test.ts
similarity index 100%
rename from frontend/lib/microcosm/staging-artifact.test.ts
rename to frontend/packages/calibration-tree/src/staging-artifact.test.ts
diff --git a/frontend/lib/microcosm/staging-artifact.ts b/frontend/packages/calibration-tree/src/staging-artifact.ts
similarity index 98%
rename from frontend/lib/microcosm/staging-artifact.ts
rename to frontend/packages/calibration-tree/src/staging-artifact.ts
index 84163369..5663eb85 100644
--- a/frontend/lib/microcosm/staging-artifact.ts
+++ b/frontend/packages/calibration-tree/src/staging-artifact.ts
@@ -13,24 +13,24 @@ import {
   loadRelease,
   microcosmCountryGeography,
   microcosmRepo,
-} from "@/lib/microcosm/latest-artifact";
-import type { CalibrationTreeSourceArtifact } from "@/lib/microcosm/calibration-tree-artifact";
+} from "./latest-artifact";
+import type { CalibrationTreeSourceArtifact } from "./calibration-tree-artifact";
 import {
   countryRegistration,
   resolveRegisteredStagingRepository,
   type RepositoryEnvironment,
   type ResolvedRepository,
-} from "@/lib/microcosm/countries";
+} from "./countries";
 import {
   type ReformValidation,
   buildReformValidation,
-} from "@/lib/microcosm/reforms";
+} from "./reforms";
 import {
   buildTargetChangeDataset,
   type TargetChangeDataset,
-} from "@/lib/microcosm/target-change";
-import { buildTargetChangeDatasetFromSummaryAndCalibration } from "@/lib/microcosm/calibration-build-comparison";
-import { loadCalibrationComparisonSource } from "@/lib/microcosm/calibration-comparison-blob";
+} from "./target-change";
+import { buildTargetChangeDatasetFromSummaryAndCalibration } from "./calibration-build-comparison";
+import { loadCalibrationComparisonSource } from "./calibration-comparison-blob";
 import {
   IncompatibleStagingDataError,
   isStructuredStagingDocument,
@@ -41,7 +41,7 @@ import {
   parseStagingRunIndex,
   validateStagingRunConsistency,
   type StagingSchemaVersion,
-} from "@/lib/microcosm/staging-contract";
+} from "./staging-contract";
 
 type JsonObject = Record<string, unknown>;
 
diff --git a/frontend/lib/microcosm/staging-contract.test.ts b/frontend/packages/calibration-tree/src/staging-contract.test.ts
similarity index 100%
rename from frontend/lib/microcosm/staging-contract.test.ts
rename to frontend/packages/calibration-tree/src/staging-contract.test.ts
diff --git a/frontend/lib/microcosm/staging-contract.ts b/frontend/packages/calibration-tree/src/staging-contract.ts
similarity index 100%
rename from frontend/lib/microcosm/staging-contract.ts
rename to frontend/packages/calibration-tree/src/staging-contract.ts
diff --git a/frontend/lib/microcosm/structured-dimension-reader.test.ts b/frontend/packages/calibration-tree/src/structured-dimension-reader.test.ts
similarity index 100%
rename from frontend/lib/microcosm/structured-dimension-reader.test.ts
rename to frontend/packages/calibration-tree/src/structured-dimension-reader.test.ts
diff --git a/frontend/lib/microcosm/structured-dimension-reader.ts b/frontend/packages/calibration-tree/src/structured-dimension-reader.ts
similarity index 100%
rename from frontend/lib/microcosm/structured-dimension-reader.ts
rename to frontend/packages/calibration-tree/src/structured-dimension-reader.ts
diff --git a/frontend/lib/microcosm/structured-target-reader.ts b/frontend/packages/calibration-tree/src/structured-target-reader.ts
similarity index 100%
rename from frontend/lib/microcosm/structured-target-reader.ts
rename to frontend/packages/calibration-tree/src/structured-target-reader.ts
diff --git a/frontend/lib/microcosm/target-change.test.ts b/frontend/packages/calibration-tree/src/target-change.test.ts
similarity index 100%
rename from frontend/lib/microcosm/target-change.test.ts
rename to frontend/packages/calibration-tree/src/target-change.test.ts
diff --git a/frontend/lib/microcosm/target-change.ts b/frontend/packages/calibration-tree/src/target-change.ts
similarity index 100%
rename from frontend/lib/microcosm/target-change.ts
rename to frontend/packages/calibration-tree/src/target-change.ts
diff --git a/frontend/lib/microcosm/target-loss-attribution-manifest.ts b/frontend/packages/calibration-tree/src/target-loss-attribution-manifest.ts
similarity index 100%
rename from frontend/lib/microcosm/target-loss-attribution-manifest.ts
rename to frontend/packages/calibration-tree/src/target-loss-attribution-manifest.ts
diff --git a/frontend/lib/microcosm/target-loss-attribution.test.ts b/frontend/packages/calibration-tree/src/target-loss-attribution.test.ts
similarity index 100%
rename from frontend/lib/microcosm/target-loss-attribution.test.ts
rename to frontend/packages/calibration-tree/src/target-loss-attribution.test.ts
diff --git a/frontend/lib/microcosm/target-loss-attribution.ts b/frontend/packages/calibration-tree/src/target-loss-attribution.ts
similarity index 100%
rename from frontend/lib/microcosm/target-loss-attribution.ts
rename to frontend/packages/calibration-tree/src/target-loss-attribution.ts
diff --git a/frontend/lib/microcosm/target-representation.test.ts b/frontend/packages/calibration-tree/src/target-representation.test.ts
similarity index 100%
rename from frontend/lib/microcosm/target-representation.test.ts
rename to frontend/packages/calibration-tree/src/target-representation.test.ts
diff --git a/frontend/lib/microcosm/target-representation.ts b/frontend/packages/calibration-tree/src/target-representation.ts
similarity index 100%
rename from frontend/lib/microcosm/target-representation.ts
rename to frontend/packages/calibration-tree/src/target-representation.ts
diff --git a/frontend/lib/microcosm/target-surface-matcher.test.ts b/frontend/packages/calibration-tree/src/target-surface-matcher.test.ts
similarity index 100%
rename from frontend/lib/microcosm/target-surface-matcher.test.ts
rename to frontend/packages/calibration-tree/src/target-surface-matcher.test.ts
diff --git a/frontend/lib/microcosm/target-surface-matcher.ts b/frontend/packages/calibration-tree/src/target-surface-matcher.ts
similarity index 100%
rename from frontend/lib/microcosm/target-surface-matcher.ts
rename to frontend/packages/calibration-tree/src/target-surface-matcher.ts
diff --git a/frontend/packages/calibration-tree/src/test-support/calibration-tree-golden-cases.ts b/frontend/packages/calibration-tree/src/test-support/calibration-tree-golden-cases.ts
new file mode 100644
index 00000000..0a7b0b93
--- /dev/null
+++ b/frontend/packages/calibration-tree/src/test-support/calibration-tree-golden-cases.ts
@@ -0,0 +1,952 @@
+// Golden calibration tree cases: representative builder inputs (US and UK,
+// releases and staging runs, and comparisons between them) assembled from the
+// fixtures the module tests already use, and a record of everything the
+// builder writes for them. The record reduces each written part to its path,
+// raw JSON digest and size, gzip size and deflate-stream digest, and adds the
+// build ids, the manifest bytes, and what the readers return from the
+// written bytes.
+//
+// fixtures/calibration-tree-golden.json is that record as produced by the
+// builder before it moved into this package; the golden tests require the
+// builder to reproduce it exactly. The cases import the builder through the
+// package's public entry points. Regenerate the record only for an intended
+// output change, from the package directory:
+//
+//   bun run src/test-support/calibration-tree-golden-cases.ts
+import { createHash } from "node:crypto";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+import { gunzipSync } from "node:zlib";
+
+import {
+  loadCalibrationComparisonSource,
+  loadCalibrationComparisonTargetDetail,
+} from "@policyengine/calibration-tree/calibration-comparison-blob";
+import { buildCalibrationComparisonBundles } from "@policyengine/calibration-tree/calibration-comparison-bundle";
+import { createExplorerState, type ExplorerState } from "@policyengine/calibration-tree/calibration-explorer";
+import {
+  CALIBRATION_TREE_SCHEMA_VERSION,
+  calibrationTreePartPath,
+  calibrationTreeResponseFromBundle,
+  calibrationTreeTargetsFromSummaries,
+  parseCalibrationTreeIndex,
+  parseCalibrationTreePart,
+  type CalibrationTreeFilterIndexArtifact,
+  type CalibrationTreeSourceArtifact,
+  type CalibrationTreeTargetDetailsArtifact,
+  type CalibrationTreeTargetSummaryArtifact,
+  type CalibrationTreeTierArtifact,
+} from "@policyengine/calibration-tree/calibration-tree-artifact";
+import type { getCalibrationTreeBlob } from "@policyengine/calibration-tree/calibration-tree-blob";
+import {
+  buildCalibrationTreeBundle,
+  type CalibrationTreeBundle,
+  type CalibrationTreeBundleFile,
+} from "@policyengine/calibration-tree/calibration-tree-bundle";
+import {
+  emptyCalibrationTreeManifest,
+  serializeCalibrationTreeManifest,
+  withCalibrationTreeManifestEntry,
+  type CalibrationTreeManifestEntry,
+} from "@policyengine/calibration-tree/calibration-tree-manifest";
+import {
+  COUNTRY_REGISTRY,
+  type CountryRegistration,
+  type MicrocosmCountry,
+} from "@policyengine/calibration-tree/countries";
+import {
+  UK_LOCAL_CALIBRATION_DIR_ENV,
+  buildCalibration,
+  microcosmRepo,
+  type Calibration,
+} from "@policyengine/calibration-tree/latest-artifact";
+import {
+  resolveStagingCalibrationSource,
+  stagingRepository,
+} from "@policyengine/calibration-tree/staging-artifact";
+import {
+  TARGET_LOSS_BASIS_HASH_ALGORITHM,
+  TARGET_LOSS_FORMULA,
+  targetLossBasisHash,
+} from "@policyengine/calibration-tree/target-loss-attribution";
+
+type JsonObject = Record<string, unknown>;
+
+const FIXTURES = join(import.meta.dir, "..", "fixtures");
+export const CALIBRATION_TREE_GOLDEN_RECORD_PATH = join(FIXTURES, "calibration-tree-golden.json");
+
+// gzipSync writes a fixed ten-byte header: magic, deflate, no flags, zero
+// mtime, maximum-compression flag, then the operating-system byte, which
+// zlib sets per platform (3 on Linux, 19 on macOS). Everything after it is
+// the deflate stream and the CRC-32 and size trailer.
+export const GZIP_HEADER_WITHOUT_OS = [0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02];
+const GZIP_HEADER_BYTES = 10;
+
+export interface GoldenFileRecord {
+  part: string;
+  path: string;
+  sha256: string;
+  rawBytes: number;
+  gzipBytes: number;
+  deflateSha256: string;
+}
+
+export interface GoldenBundleRecord {
+  buildArtifactId: string;
+  files: GoldenFileRecord[];
+}
+
+export interface GoldenSourceRecord extends GoldenBundleRecord {
+  readers: {
+    programRootSha256: string;
+    geographyRootSha256: string;
+  };
+}
+
+export interface GoldenComparisonRecord {
+  pairArtifactId: string;
+  reported: GoldenBundleRecord;
+  shared: GoldenBundleRecord;
+  firstTargetDetailSha256: string;
+}
+
+export const GOLDEN_SOURCE_CASES = [
+  "us-release",
+  "uk-release",
+  "uk-release-loss-attribution",
+  "be-release",
+  "us-staging",
+  "uk-staging",
+  "uk-staging-staged-bundle",
+] as const;
+export type GoldenSourceCaseName = (typeof GOLDEN_SOURCE_CASES)[number];
+
+export const GOLDEN_COMPARISON_CASES = ["us-comparison", "uk-comparison"] as const;
+export type GoldenComparisonCaseName = (typeof GOLDEN_COMPARISON_CASES)[number];
+
+export interface CalibrationTreeGoldenRecord {
+  schemaVersion: typeof CALIBRATION_TREE_SCHEMA_VERSION;
+  sources: Record<GoldenSourceCaseName, GoldenSourceRecord>;
+  comparisons: Record<GoldenComparisonCaseName, GoldenComparisonRecord>;
+  manifest: { sha256: string; rawBytes: number };
+}
+
+export interface GoldenReleaseInput {
+  country: MicrocosmCountry;
+  releaseId: string;
+  hfCommitSha: string;
+  publishedAt: string;
+  diagnosticsText: string;
+  releaseManifestText: string | null;
+}
+
+interface GoldenSourceBuild {
+  country: MicrocosmCountry;
+  bundle: CalibrationTreeBundle;
+  manifestEntry: CalibrationTreeManifestEntry;
+}
+
+function sha256Text(value: string): string {
+  return createHash("sha256").update(value, "utf8").digest("hex");
+}
+
+function sha256Bytes(value: Uint8Array): string {
+  return createHash("sha256").update(value).digest("hex");
+}
+
+function fixtureText(relativePath: string): string {
+  return readFileSync(join(FIXTURES, relativePath), "utf8");
+}
+
+function compressedFixtureText(relativePath: string): string {
+  return gunzipSync(readFileSync(join(FIXTURES, relativePath))).toString("utf8");
+}
+
+// --- Inputs ---------------------------------------------------------------
+
+const US_RELEASE_ID = "populace-us-2024-buildp-sparse-rmloss100-cae8640-20260728T011454Z";
+const UK_RELEASE_ID = "microcosm-uk-2024-25-national-golden";
+const UK_LOSS_ATTRIBUTION_RELEASE_ID = "microcosm-uk-2024-25-loss-attribution-golden";
+const BE_RELEASE_ID = "microcosm-be-2024-national-golden";
+
+const US_STAGING_RUN_ID = "us-calibration-golden-20260930T120000Z";
+const UK_STAGING_RUN_ID = "uk-calibration-golden-20261002T231556Z";
+const UK_STAGED_BUNDLE_RUN_ID = "uk-frs-calibration-attempt-20261003T081500Z-golden";
+
+const US_STAGING_REVISION = "5c2a9e1d7b3f4a6c8e0d2b4f6a8c0e2d4b6f8a0c";
+const UK_STAGING_REVISION = "8e4b2d6f0a1c3e5a7c9e1b3d5f7a9c1e3b5d7f9a";
+const UK_STAGED_BUNDLE_REVISION = "40439a3f8d241cd361bb693488b42e7258623a00";
+
+// Assign each identity-only legacy target a deterministic target and
+// estimates, so the tree carries real fit bands and errors.
+function withLegacyValues(targets: JsonObject[]): JsonObject[] {
+  return targets.map((target, targetIndex) => {
+    const targetValue = 1_000 * (1 + (targetIndex % 97));
+    return {
+      ...target,
+      target: targetValue,
+      initial_estimate: targetValue * (1 + ((targetIndex % 31) - 15) / 50),
+      final_estimate: targetValue * (1 + ((targetIndex % 23) - 11) / 100),
+    };
+  });
+}
+
+// Attach the weighted target-error attribution Microcosm reports from
+// diagnostics schema 6 on: provided weights and scales, each target's capped
+// scaled error and loss contribution, and the basis digest the reader
+// verifies. Comparisons are built only between builds that report it.
+function withReportedLossAttribution(diagnostics: JsonObject): JsonObject {
+  const cap = 1;
+  const weighted = (diagnostics.targets as JsonObject[]).map((target, targetIndex) => ({
+    ...target,
+    name: String(target.name),
+    target: Number(target.target),
+    final_estimate: Number(target.final_estimate),
+    target_loss_weight: 1 + (targetIndex % 4),
+    target_loss_scale: Math.max(Math.abs(Number(target.target)), 1),
+  }));
+  const totalWeight = weighted.reduce((sum, target) => sum + target.target_loss_weight, 0);
+  const targets = weighted.map((target) => {
+    const cappedError = Math.min(
+      Math.abs(target.final_estimate - target.target) / target.target_loss_scale,
+      cap,
+    );
+    const share = target.target_loss_weight / totalWeight;
+    return {
+      ...target,
+      target_loss_weight_share: share,
+      final_capped_scaled_error: cappedError,
+      final_loss_contribution: share * cappedError,
+    };
+  });
+  return {
+    ...diagnostics,
+    final_loss: targets.reduce((sum, target) => sum + target.final_loss_contribution, 0),
+    diagnostic_warnings: [],
+    target_loss_basis: {
+      formula: TARGET_LOSS_FORMULA,
+      cap,
+      target_count: targets.length,
+      total_target_weight: totalWeight,
+      weight_kind: "provided",
+      scale_kind: "provided",
+      hash_algorithm: TARGET_LOSS_BASIS_HASH_ALGORITHM,
+      sha256: targetLossBasisHash(targets.map((target) => ({
+        name: target.name,
+        target_loss_weight: target.target_loss_weight,
+        target_loss_scale: target.target_loss_scale,
+      }))),
+    },
+    targets,
+  };
+}
+
+function usLegacyTargets(): JsonObject[] {
+  const fixture = JSON.parse(compressedFixtureText("us-legacy-target-identities.json.gz")) as {
+    targets: JsonObject[];
+  };
+  return withLegacyValues(fixture.targets);
+}
+
+// Schema 6 keeps the legacy target reader and adds reported attribution.
+function usReleaseDiagnostics(): JsonObject {
+  return withReportedLossAttribution({ schema_version: 6, targets: usLegacyTargets() });
+}
+
+// The four structured UK geographies and two receipts lines used by the
+// schema 7 and schema 8 reader tests.
+const UK_GEOGRAPHIES = [
+  { id: "K02000001", label: "United Kingdom" },
+  { id: "K03000001", label: "Great Britain" },
+  { id: "E92000001", label: "England" },
+  { id: "S92000003", label: "Scotland" },
+];
+const UK_RECEIPT_LINES = [
+  { id: "income_tax", label: "Income tax receipts" },
+  { id: "national_insurance", label: "National insurance contributions" },
+];
+
+function ukHierarchyTarget(options: {
+  name: string;
+  provider: { id: string; label: string };
+  category: { id: string; label: string };
+  geography: { id: string; label: string };
+  dimension: { id: string; label: string } | null;
+  targetLabel: string;
+  target: number;
+  initialEstimate: number;
+  finalEstimate: number;
+}): JsonObject {
+  return {
+    name: `${options.name}@2025`,
+    target_name: options.name,
+    source: `${options.provider.label} citation`,
+    target: options.target,
+    initial_estimate: options.initialEstimate,
+    final_estimate: options.finalEstimate,
+    hierarchy: {
+      provider: options.provider,
+      category: { ...options.category, provider_id: options.provider.id },
+      geography: { ...options.geography, level: "country" },
+      dimensions: options.dimension
+        ? [{
+            id: `${options.category.id}_line`,
+            label: "Economic and fiscal outlook line",
+            value_id: options.dimension.id,
+            value_label: options.dimension.label,
+          }]
+        : [],
+      target: { id: options.name, label: options.targetLabel },
+    },
+  };
+}
+
+function ukHierarchyTargets(): JsonObject[] {
+  const obr = { id: "obr", label: "Office for Budget Responsibility" };
+  const ons = { id: "ons", label: "Office for National Statistics" };
+  const receipts = { id: "obr.efo_receipts", label: "Economic and fiscal outlook receipts" };
+  const population = { id: "ons.population", label: "Population estimates" };
+  const targets: JsonObject[] = [];
+  UK_GEOGRAPHIES.forEach((geography, geographyIndex) => {
+    UK_RECEIPT_LINES.forEach((line, lineIndex) => {
+      const targetValue = 1_000 * (geographyIndex + 1) + 250 * lineIndex;
+      targets.push(ukHierarchyTarget({
+        name: `obr.${line.id}.${geography.id}`,
+        provider: obr,
+        category: receipts,
+        geography,
+        dimension: line,
+        targetLabel: `${line.label}, ${geography.label}`,
+        target: targetValue,
+        initialEstimate: targetValue * 0.9,
+        finalEstimate: targetValue * (1 + 0.004 * (geographyIndex - lineIndex)),
+      }));
+    });
+    const populationValue = 5_000_000 * (geographyIndex + 1);
+    targets.push(ukHierarchyTarget({
+      name: `ons.population.${geography.id}`,
+      provider: ons,
+      category: population,
+      geography,
+      dimension: null,
+      targetLabel: `Population, ${geography.label}`,
+      target: populationValue,
+      initialEstimate: populationValue * 1.08,
+      finalEstimate: populationValue * (1 - 0.0000001 * geographyIndex),
+    }));
+  });
+  return targets;
+}
+
+function ukHierarchyDiagnostics(targets: JsonObject[]): JsonObject {
+  return withReportedLossAttribution({ schema_version: 8, release_id: UK_RELEASE_ID, targets });
+}
+
+// The candidate a later staging run would produce: every receipts estimate
+// moves, Scotland's population target is dropped and Wales's is added.
+function ukStagingTargets(): JsonObject[] {
+  const moved: JsonObject[] = ukHierarchyTargets()
+    .filter((target) => target.target_name !== "ons.population.S92000003")
+    .map((target, targetIndex) => ({
+      ...target,
+      final_estimate: Number(target.final_estimate) * (1 + 0.01 * ((targetIndex % 5) - 2)),
+    }));
+  const wales = { id: "W92000004", label: "Wales" };
+  moved.push(ukHierarchyTarget({
+    name: `ons.population.${wales.id}`,
+    provider: { id: "ons", label: "Office for National Statistics" },
+    category: { id: "ons.population", label: "Population estimates" },
+    geography: wales,
+    dimension: null,
+    targetLabel: `Population, ${wales.label}`,
+    target: 3_100_000,
+    initialEstimate: 3_200_000,
+    finalEstimate: 3_099_000,
+  }));
+  return moved;
+}
+
+// The candidate a later US staging run would produce: the first 1,500
+// release targets, every estimate moved.
+function usStagingDiagnostics(): JsonObject {
+  const targets = usLegacyTargets().slice(0, 1_500).map((target, targetIndex) => ({
+    ...target,
+    final_estimate: Number(target.final_estimate) * (1 + 0.003 * ((targetIndex % 7) - 3)),
+  }));
+  return withReportedLossAttribution({ schema_version: 6, targets });
+}
+
+export function goldenReleaseInputs(): Record<
+  "us-release" | "uk-release" | "uk-release-loss-attribution" | "be-release",
+  GoldenReleaseInput
+> {
+  return {
+    "us-release": {
+      country: "us",
+      releaseId: US_RELEASE_ID,
+      hfCommitSha: "7d3e1f0a9b8c7d6e5f4a3b2c1d0e9f8a7b6c5d4e",
+      publishedAt: "2026-07-28T01:14:54.000Z",
+      diagnosticsText: JSON.stringify(usReleaseDiagnostics()),
+      releaseManifestText: null,
+    },
+    "uk-release": {
+      country: "uk",
+      releaseId: UK_RELEASE_ID,
+      hfCommitSha: "f3a5c7e9b1d3f5a7c9e1b3d5f7a9c1e3b5d7f9a1",
+      publishedAt: "2026-10-04T18:57:22.000Z",
+      diagnosticsText: JSON.stringify(ukHierarchyDiagnostics(ukHierarchyTargets())),
+      releaseManifestText: JSON.stringify({ country: { code: "uk" } }),
+    },
+    "uk-release-loss-attribution": {
+      country: "uk",
+      releaseId: UK_LOSS_ATTRIBUTION_RELEASE_ID,
+      hfCommitSha: "a9c1e3b5d7f9a1c3e5b7d9f1a3c5e7b9d1f3a5c7",
+      publishedAt: "2026-10-06T09:30:00.000Z",
+      diagnosticsText: fixtureText("target-loss-attribution/valid-uniform.json"),
+      releaseManifestText: null,
+    },
+    "be-release": {
+      country: "be",
+      releaseId: BE_RELEASE_ID,
+      hfCommitSha: "b2d4f6a8c0e2b4d6f8a0c2e4b6d8f0a2c4e6b8d0",
+      publishedAt: "2026-09-16T12:00:00.000Z",
+      diagnosticsText: fixtureText("be-release/calibration_diagnostics.json"),
+      releaseManifestText: fixtureText("be-release/release_manifest.json"),
+    },
+  };
+}
+
+// --- Builder, as the publisher drives it -----------------------------------
+
+function bundleComparison(calibration: Calibration) {
+  return {
+    releaseId: calibration.release_id,
+    calibrationProvenance: calibration.calibration_provenance,
+    status: calibration.target_loss_attribution.status,
+    aggregate: calibration.target_loss_attribution.aggregate,
+    cap: calibration.target_loss_attribution.cap,
+    basisIdentifier: calibration.target_loss_attribution.basis_identifier,
+    targetRepresentation: calibration.target_schema.target_representation,
+  };
+}
+
+function indexFile(bundle: CalibrationTreeBundle): CalibrationTreeBundleFile {
+  const file = bundle.files.find((candidate) => candidate.part === "index");
+  if (!file) throw new Error("Calibration tree bundle has no index.");
+  return file;
+}
+
+// Repository overrides and the UK local-run directory change which inputs
+// the builder reads; the record uses each country's registered defaults.
+function repositoryEnvironmentNames(): string[] {
+  const names = new Set<string>([UK_LOCAL_CALIBRATION_DIR_ENV]);
+  for (const registration of Object.values(COUNTRY_REGISTRY) as CountryRegistration[]) {
+    for (const name of [
+      registration.repo_env,
+      registration.revision_env,
+      registration.staging?.repo_env,
+      registration.staging?.revision_env,
+    ]) {
+      if (name) names.add(name);
+    }
+  }
+  return [...names];
+}
+
+export async function withRegisteredRepositories<Result>(
+  operation: () => Promise<Result>,
+): Promise<Result> {
+  const saved = new Map(repositoryEnvironmentNames().map((name) => [name, process.env[name]]));
+  for (const name of saved.keys()) delete process.env[name];
+  try {
+    return await operation();
+  } finally {
+    for (const [name, value] of saved) {
+      if (value == null) delete process.env[name];
+      else process.env[name] = value;
+    }
+  }
+}
+
+async function withHuggingFaceFiles<Result>(
+  files: Map<string, string>,
+  operation: () => Promise<Result>,
+): Promise<Result> {
+  const originalFetch = globalThis.fetch;
+  globalThis.fetch = (async (input: string | URL | Request) => {
+    const body = files.get(String(input));
+    return body == null
+      ? new Response(null, { status: 404 })
+      : new Response(body, { headers: { "Content-Type": "application/json" } });
+  }) as typeof fetch;
+  try {
+    return await operation();
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+}
+
+function buildReleaseSource(input: GoldenReleaseInput): GoldenSourceBuild {
+  const prefix = `releases/${input.releaseId}`;
+  const diagnostics = {
+    json: JSON.parse(input.diagnosticsText) as JsonObject,
+    source: {
+      path: `${prefix}/calibration_diagnostics.json`,
+      sha256: sha256Text(input.diagnosticsText),
+    } satisfies CalibrationTreeSourceArtifact,
+  };
+  const releaseManifest = input.releaseManifestText == null
+    ? null
+    : {
+        json: JSON.parse(input.releaseManifestText) as JsonObject,
+        source: {
+          path: `${prefix}/release_manifest.json`,
+          sha256: sha256Text(input.releaseManifestText),
+        } satisfies CalibrationTreeSourceArtifact,
+      };
+  const calibration = buildCalibration(
+    diagnostics.json,
+    input.releaseId,
+    null,
+    {},
+    releaseManifest?.json ?? {},
+    {},
+    input.country,
+    "huggingface_immutable",
+    diagnostics.source.sha256,
+    input.hfCommitSha,
+  );
+  const bundle = buildCalibrationTreeBundle({
+    country: input.country,
+    createdAt: input.publishedAt,
+    releaseId: input.releaseId,
+    hfRepo: microcosmRepo(input.country),
+    hfCommitSha: input.hfCommitSha,
+    sourceArtifacts: {
+      calibrationDiagnostics: diagnostics.source,
+      buildManifest: null,
+      releaseManifest: releaseManifest?.source ?? null,
+      demographics: null,
+    },
+    rows: calibration.rows,
+    calibrationProvenance: calibration.calibration_provenance,
+    lossAttributionAvailable: calibration.target_loss_attribution.status !== "unavailable",
+    comparison: bundleComparison(calibration),
+  });
+  const build = bundle.index.build;
+  const index = indexFile(bundle);
+  return {
+    country: input.country,
+    bundle,
+    manifestEntry: {
+      buildArtifactId: build.buildArtifactId,
+      kind: "release",
+      sourceId: build.sourceId,
+      label: build.label,
+      releaseId: input.releaseId,
+      stagingRunId: null,
+      hfRepo: microcosmRepo(input.country),
+      hfCommitSha: input.hfCommitSha,
+      treeSchemaVersion: CALIBRATION_TREE_SCHEMA_VERSION,
+      indexSha256: index.sha256,
+      indexBytes: index.rawBytes,
+      createdAt: build.createdAt,
+      updatedAt: build.createdAt,
+    },
+  };
+}
+
+async function buildStagingSource(options: {
+  country: MicrocosmCountry;
+  runId: string;
+  revisionSha: string;
+  files: Map<string, string>;
+}): Promise<GoldenSourceBuild> {
+  const repository = stagingRepository(options.country);
+  if (!repository) throw new Error(`Staging is not configured for ${options.country}.`);
+  const source = await withHuggingFaceFiles(options.files, () =>
+    resolveStagingCalibrationSource(options.runId, 0, options.country, options.revisionSha)
+  );
+  if (!source) throw new Error(`Staging run ${options.runId} has no calibration diagnostics.`);
+  const { calibration } = source;
+  const bundle = buildCalibrationTreeBundle({
+    country: options.country,
+    buildKind: "staging",
+    sourceId: options.runId,
+    label: source.candidateReleaseId,
+    createdAt: source.updatedAt,
+    releaseId: source.candidateReleaseId,
+    hfRepo: repository.repo,
+    hfCommitSha: options.revisionSha,
+    sourceArtifacts: { ...source.sourceArtifacts, demographics: null },
+    rows: calibration.rows,
+    calibrationProvenance: calibration.calibration_provenance,
+    lossAttributionAvailable: calibration.target_loss_attribution.status !== "unavailable",
+    comparison: bundleComparison(calibration),
+  });
+  const index = indexFile(bundle);
+  return {
+    country: options.country,
+    bundle,
+    manifestEntry: {
+      buildArtifactId: bundle.index.buildArtifactId,
+      kind: "staging",
+      sourceId: options.runId,
+      label: source.candidateReleaseId,
+      releaseId: null,
+      stagingRunId: options.runId,
+      hfRepo: repository.repo,
+      hfCommitSha: options.revisionSha,
+      treeSchemaVersion: CALIBRATION_TREE_SCHEMA_VERSION,
+      indexSha256: index.sha256,
+      indexBytes: index.rawBytes,
+      createdAt: source.updatedAt,
+      updatedAt: source.updatedAt,
+    },
+  };
+}
+
+function stagingFileUrl(country: MicrocosmCountry, revision: string, path: string): string {
+  return `https://huggingface.co/datasets/${stagingRepository(country)!.repo}/resolve/${revision}/${path}`;
+}
+
+// A version 1 run: progress names the candidate and the diagnostics sit at
+// the legacy run path.
+function usVersion1StagingFiles(): Map<string, string> {
+  const runId = US_STAGING_RUN_ID;
+  const url = (path: string) => stagingFileUrl("us", US_STAGING_REVISION, `runs/${runId}/${path}`);
+  return new Map([
+    [url("progress.json"), JSON.stringify({
+      schema_version: 1,
+      run_id: runId,
+      candidate_release_id: "populace-us-2024-golden-candidate",
+      updated_at: "2026-09-30T12:00:00+00:00",
+    })],
+    [url("run_manifest.json"), JSON.stringify({ schema_version: 1, run_id: runId })],
+    [url("calibration_diagnostics.json"), JSON.stringify(usStagingDiagnostics())],
+  ]);
+}
+
+function version2RunManifest(
+  runId: string,
+  updatedAt: string,
+  artifacts: JsonObject[],
+): JsonObject {
+  return {
+    schema_name: "microcosm.staging.run-manifest",
+    schema_version: 2,
+    run_id: runId,
+    country_code: "GB",
+    operation_id: "uk_national_calibration",
+    pipeline: { id: "uk_national_calibration", version: "2026.09" },
+    candidate_id: `${runId}-candidate`,
+    release_id: null,
+    run_kind: "calibration",
+    non_release: true,
+    started_at: "2026-10-02T20:00:00+00:00",
+    updated_at: updatedAt,
+    status: "completed",
+    current_stage: "complete",
+    sample: { mode: "full" },
+    delivery: {
+      contract_version: 2,
+      enabled: true,
+      mode: "local_only",
+      run_id: runId,
+      configured_repository: null,
+      upload_attempts: 0,
+      upload_successes: 0,
+      read_back: "not_requested",
+      last_error_code: null,
+      opt_out_reason: null,
+    },
+    artifacts,
+    failure: null,
+    paths: {
+      progress: `runs/${runId}/progress.json`,
+      events: `runs/${runId}/events.ndjson`,
+      calibration_progress: null,
+    },
+  };
+}
+
+// A version 2 run that uploaded its diagnostics with its telemetry.
+function ukVersion2StagingFiles(): Map<string, string> {
+  const runId = UK_STAGING_RUN_ID;
+  const diagnosticsText = JSON.stringify(ukHierarchyDiagnostics(ukStagingTargets()));
+  const manifest = version2RunManifest(runId, "2026-10-02T23:15:56+00:00", [{
+    logical_name: "calibration_diagnostics",
+    artifact_kind: "aggregate_diagnostics",
+    contract_relative_path: "artifacts/calibration_diagnostics.json",
+    media_type: "application/json",
+    sha256: sha256Text(diagnosticsText),
+    classification: "aggregate",
+  }]);
+  const url = (path: string) => stagingFileUrl("uk", UK_STAGING_REVISION, `runs/${runId}/${path}`);
+  return new Map([
+    [url("run_manifest.json"), JSON.stringify(manifest)],
+    [url("artifacts/calibration_diagnostics.json"), diagnosticsText],
+  ]);
+}
+
+// A version 2 run whose diagnostics travel in its staged dataset bundle in
+// the release repository, located by the staged-dataset receipt.
+function ukStagedBundleStagingFiles(): Map<string, string> {
+  const runId = UK_STAGED_BUNDLE_RUN_ID;
+  const diagnosticsText = JSON.stringify(ukHierarchyDiagnostics(ukStagingTargets()));
+  const releaseRepository = COUNTRY_REGISTRY.uk.repo;
+  const receiptText = JSON.stringify({
+    contract_version: 1,
+    run_id: runId,
+    status: "uploaded",
+    mode: "local_and_remote",
+    repository: releaseRepository,
+    prefix: `staged/${runId}`,
+    revision: UK_STAGED_BUNDLE_REVISION,
+    error_code: null,
+    opt_out_reason: null,
+    files: {
+      "calibration_diagnostics.json": {
+        bytes: Buffer.byteLength(diagnosticsText, "utf8"),
+        sha256: sha256Text(diagnosticsText),
+      },
+      "microcosm_uk_2024_25.h5": { bytes: 1, sha256: "0".repeat(64) },
+    },
+  });
+  const manifest = version2RunManifest(runId, "2026-10-03T08:30:00+00:00", [{
+    logical_name: "staged_dataset",
+    artifact_kind: "build_metadata",
+    contract_relative_path: "artifacts/staged_dataset.json",
+    media_type: "application/json",
+    sha256: sha256Text(receiptText),
+    classification: "non_row_level",
+  }]);
+  const url = (path: string) => stagingFileUrl("uk", UK_STAGING_REVISION, `runs/${runId}/${path}`);
+  return new Map([
+    [url("run_manifest.json"), JSON.stringify(manifest)],
+    [url("artifacts/staged_dataset.json"), receiptText],
+    [
+      `https://huggingface.co/datasets/${releaseRepository}/resolve/${UK_STAGED_BUNDLE_REVISION}/staged/${runId}/calibration_diagnostics.json`,
+      diagnosticsText,
+    ],
+  ]);
+}
+
+const sourceBuilds = new Map<GoldenSourceCaseName, Promise<GoldenSourceBuild>>();
+
+function buildSourceCase(name: GoldenSourceCaseName): Promise<GoldenSourceBuild> {
+  return withRegisteredRepositories(async () => {
+    switch (name) {
+      case "us-release":
+      case "uk-release":
+      case "uk-release-loss-attribution":
+      case "be-release":
+        return buildReleaseSource(goldenReleaseInputs()[name]);
+      case "us-staging":
+        return buildStagingSource({
+          country: "us",
+          runId: US_STAGING_RUN_ID,
+          revisionSha: US_STAGING_REVISION,
+          files: usVersion1StagingFiles(),
+        });
+      case "uk-staging":
+        return buildStagingSource({
+          country: "uk",
+          runId: UK_STAGING_RUN_ID,
+          revisionSha: UK_STAGING_REVISION,
+          files: ukVersion2StagingFiles(),
+        });
+      case "uk-staging-staged-bundle":
+        return buildStagingSource({
+          country: "uk",
+          runId: UK_STAGED_BUNDLE_RUN_ID,
+          revisionSha: UK_STAGING_REVISION,
+          files: ukStagedBundleStagingFiles(),
+        });
+    }
+  });
+}
+
+export function goldenSourceBuild(name: GoldenSourceCaseName): Promise<GoldenSourceBuild> {
+  let build = sourceBuilds.get(name);
+  if (!build) {
+    build = buildSourceCase(name);
+    sourceBuilds.set(name, build);
+  }
+  return build;
+}
+
+// --- Record ---------------------------------------------------------------
+
+function fileRecord(file: CalibrationTreeBundleFile): GoldenFileRecord {
+  return {
+    part: file.part,
+    path: file.path,
+    sha256: file.sha256,
+    rawBytes: file.rawBytes,
+    gzipBytes: file.gzipBytes,
+    deflateSha256: sha256Bytes(file.compressed.subarray(GZIP_HEADER_BYTES)),
+  };
+}
+
+export function bundleRecord(bundle: CalibrationTreeBundle): GoldenBundleRecord {
+  return {
+    buildArtifactId: bundle.index.buildArtifactId,
+    files: bundle.files.map(fileRecord),
+  };
+}
+
+// Stored bundle files by Blob path, served the way the Blob client returns them.
+type StoredFiles = Map<string, Uint8Array>;
+
+function storeBundle(storedFiles: StoredFiles, bundle: CalibrationTreeBundle): void {
+  for (const file of bundle.files) storedFiles.set(file.path, file.compressed);
+}
+
+function storedJson(storedFiles: StoredFiles, path: string): unknown {
+  const compressed = storedFiles.get(path);
+  if (!compressed) throw new Error(`Stored calibration tree file ${path} is missing.`);
+  return JSON.parse(gunzipSync(compressed).toString("utf8"));
+}
+
+function storedBlobReader(storedFiles: StoredFiles): typeof getCalibrationTreeBlob {
+  return (async (options: Parameters<typeof getCalibrationTreeBlob>[0]) => {
+    const path = calibrationTreePartPath(options.country, options.buildArtifactId, options.part);
+    const compressed = storedFiles.get(path);
+    if (!compressed) return null;
+    return {
+      statusCode: 200 as const,
+      stream: new Blob([new Uint8Array(compressed)]).stream(),
+      headers: new Headers(),
+      blob: {
+        url: `https://blob.example/${path}`,
+        downloadUrl: `https://blob.example/${path}?download=1`,
+        pathname: path,
+        contentDisposition: "inline",
+        cacheControl: "public, max-age=31536000",
+        uploadedAt: new Date("2026-10-15T00:00:00.000Z"),
+        etag: `"${sha256Bytes(compressed)}"`,
+        contentType: "application/gzip",
+        size: compressed.byteLength,
+      },
+    };
+  }) as typeof getCalibrationTreeBlob;
+}
+
+// The explorer's root responses, read back from the stored bytes the way the
+// dashboard loads a published tree.
+function readerRecord(bundle: CalibrationTreeBundle): GoldenSourceRecord["readers"] {
+  const storedFiles: StoredFiles = new Map();
+  storeBundle(storedFiles, bundle);
+  const index = parseCalibrationTreeIndex(
+    storedJson(storedFiles, calibrationTreePartPath(bundle.index.country, bundle.index.buildArtifactId, "index")),
+  );
+  const part = (descriptor: { part: Parameters<typeof parseCalibrationTreePart>[1]; path: string }) =>
+    parseCalibrationTreePart(storedJson(storedFiles, descriptor.path), descriptor.part);
+  const loaded = {
+    index,
+    tiers: index.parts.tiers.map((descriptor) => part(descriptor) as CalibrationTreeTierArtifact),
+    filterIndex: part(index.parts.filterIndex) as CalibrationTreeFilterIndexArtifact,
+    targetSummaries: calibrationTreeTargetsFromSummaries(
+      index,
+      index.parts.targetSummaries.map(
+        (descriptor) => part(descriptor) as CalibrationTreeTargetSummaryArtifact,
+      ),
+    ),
+    targetDetailShard: index.parts.targetDetails[0]
+      ? part(index.parts.targetDetails[0]) as CalibrationTreeTargetDetailsArtifact
+      : undefined,
+  };
+  const rootResponse = (breakdown: ExplorerState["breakdown"]) =>
+    sha256Text(JSON.stringify(
+      calibrationTreeResponseFromBundle(loaded, { ...createExplorerState(), breakdown }),
+    ));
+  return {
+    programRootSha256: rootResponse("program"),
+    geographyRootSha256: rootResponse("geography"),
+  };
+}
+
+export async function goldenSourceRecord(name: GoldenSourceCaseName): Promise<GoldenSourceRecord> {
+  const { bundle } = await goldenSourceBuild(name);
+  return { ...bundleRecord(bundle), readers: readerRecord(bundle) };
+}
+
+const COMPARISON_SOURCES: Record<
+  GoldenComparisonCaseName,
+  { current: GoldenSourceCaseName; candidate: GoldenSourceCaseName }
+> = {
+  "us-comparison": { current: "us-release", candidate: "us-staging" },
+  "uk-comparison": { current: "uk-release", candidate: "uk-staging" },
+};
+
+// Comparisons are built the way the dashboard builds them lazily: both
+// sources are read back from their stored bytes.
+export async function goldenComparisonRecord(
+  name: GoldenComparisonCaseName,
+): Promise<GoldenComparisonRecord> {
+  const [current, candidate] = await Promise.all([
+    goldenSourceBuild(COMPARISON_SOURCES[name].current),
+    goldenSourceBuild(COMPARISON_SOURCES[name].candidate),
+  ]);
+  const storedFiles: StoredFiles = new Map();
+  storeBundle(storedFiles, current.bundle);
+  storeBundle(storedFiles, candidate.bundle);
+  const getBlob = storedBlobReader(storedFiles);
+  const country = current.country;
+  const bundles = buildCalibrationComparisonBundles(
+    await loadCalibrationComparisonSource(country, current.bundle.index.buildArtifactId, getBlob),
+    await loadCalibrationComparisonSource(country, candidate.bundle.index.buildArtifactId, getBlob),
+  );
+  storeBundle(storedFiles, bundles.reported);
+  storeBundle(storedFiles, bundles.shared);
+  const firstTargetDetail = await loadCalibrationComparisonTargetDetail({
+    country,
+    buildArtifactId: bundles.reported.index.buildArtifactId,
+    targetOrdinal: 0,
+    getBlob,
+  });
+  return {
+    pairArtifactId: bundles.pairArtifactId,
+    reported: bundleRecord(bundles.reported),
+    shared: bundleRecord(bundles.shared),
+    firstTargetDetailSha256: sha256Text(JSON.stringify(firstTargetDetail)),
+  };
+}
+
+// The manifest the publisher would hold after publishing every recorded
+// source, latest release per country first.
+export async function goldenManifestRecord(): Promise<CalibrationTreeGoldenRecord["manifest"]> {
+  let manifest = emptyCalibrationTreeManifest();
+  const latestReleases = new Set<GoldenSourceCaseName>(["us-release", "uk-release", "be-release"]);
+  for (const name of GOLDEN_SOURCE_CASES) {
+    const { country, manifestEntry } = await goldenSourceBuild(name);
+    manifest = withCalibrationTreeManifestEntry(
+      manifest,
+      country,
+      manifestEntry,
+      latestReleases.has(name),
+    );
+  }
+  const serialized = serializeCalibrationTreeManifest(manifest);
+  return { sha256: sha256Text(serialized), rawBytes: Buffer.byteLength(serialized, "utf8") };
+}
+
+export async function recordCalibrationTreeGoldens(): Promise<CalibrationTreeGoldenRecord> {
+  const sources = {} as CalibrationTreeGoldenRecord["sources"];
+  for (const name of GOLDEN_SOURCE_CASES) sources[name] = await goldenSourceRecord(name);
+  const comparisons = {} as CalibrationTreeGoldenRecord["comparisons"];
+  for (const name of GOLDEN_COMPARISON_CASES) comparisons[name] = await goldenComparisonRecord(name);
+  return {
+    schemaVersion: CALIBRATION_TREE_SCHEMA_VERSION,
+    sources,
+    comparisons,
+    manifest: await goldenManifestRecord(),
+  };
+}
+
+if (import.meta.main) {
+  const record = await recordCalibrationTreeGoldens();
+  await Bun.write(CALIBRATION_TREE_GOLDEN_RECORD_PATH, `${JSON.stringify(record, null, 2)}\n`);
+  console.log(`Recorded ${CALIBRATION_TREE_GOLDEN_RECORD_PATH}`);
+}
diff --git a/frontend/lib/microcosm/treemap.test.ts b/frontend/packages/calibration-tree/src/treemap.test.ts
similarity index 100%
rename from frontend/lib/microcosm/treemap.test.ts
rename to frontend/packages/calibration-tree/src/treemap.test.ts
diff --git a/frontend/packages/calibration-tree/tsconfig.json b/frontend/packages/calibration-tree/tsconfig.json
new file mode 100644
index 00000000..af017ab0
--- /dev/null
+++ b/frontend/packages/calibration-tree/tsconfig.json
@@ -0,0 +1,16 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["ESNext", "DOM"],
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "types": ["bun"],
+    "strict": true,
+    "noEmit": true,
+    "skipLibCheck": true,
+    "isolatedModules": true,
+    "esModuleInterop": true,
+    "resolveJsonModule": true
+  },
+  "include": ["src/**/*.ts", "types/**/*.d.ts"]
+}
diff --git a/frontend/packages/calibration-tree/types/next-fetch-cache.d.ts b/frontend/packages/calibration-tree/types/next-fetch-cache.d.ts
new file mode 100644
index 00000000..77060ce2
--- /dev/null
+++ b/frontend/packages/calibration-tree/types/next-fetch-cache.d.ts
@@ -0,0 +1,8 @@
+// The dashboard calls the release and staging readers inside Next.js, whose
+// fetch reads a `next.revalidate` hint to cache Hugging Face responses; Bun
+// ignores the field. Next.js declares it on RequestInit for the dashboard.
+// This declaration mirrors Next's NextFetchRequestConfig and is seen only by
+// the package's own typecheck, so the package typechecks without Next.js.
+interface RequestInit {
+  next?: { revalidate?: number | false; tags?: string[] } | undefined;
+}
diff --git a/frontend/scripts/calibration-deployment-smoke.test.ts b/frontend/scripts/calibration-deployment-smoke.test.ts
index 35b85aea..86723d4c 100644
--- a/frontend/scripts/calibration-deployment-smoke.test.ts
+++ b/frontend/scripts/calibration-deployment-smoke.test.ts
@@ -1,7 +1,7 @@
 import { expect, spyOn, test } from "bun:test";
 
 import { verifyCalibrationDeployment } from "./calibration-deployment-smoke";
-import { hasCapability, selectableCountries } from "../lib/microcosm/countries";
+import { hasCapability, selectableCountries } from "@policyengine/calibration-tree/countries";
 
 type Fetcher = (url: string | URL, init?: RequestInit) => Promise<Response>;
 const noSleep = async (_milliseconds: number) => {};
diff --git a/frontend/scripts/calibration-deployment-smoke.ts b/frontend/scripts/calibration-deployment-smoke.ts
index b303de39..6b8a456f 100644
--- a/frontend/scripts/calibration-deployment-smoke.ts
+++ b/frontend/scripts/calibration-deployment-smoke.ts
@@ -4,7 +4,7 @@ import {
   hasCapability,
   selectableCountries,
   type MicrocosmCountry,
-} from "../lib/microcosm/countries";
+} from "@policyengine/calibration-tree/countries";
 
 type JsonObject = Record<string, unknown>;
 type Fetcher = (url: string | URL, init?: RequestInit) => Promise<Response>;
diff --git a/frontend/tsconfig.json b/frontend/tsconfig.json
index 3f8f96b4..de2774dc 100644
--- a/frontend/tsconfig.json
+++ b/frontend/tsconfig.json
@@ -19,5 +19,5 @@
     }
   },
   "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts", ".next/dev/types/**/*.ts"],
-  "exclude": ["node_modules"]
+  "exclude": ["node_modules", "packages"]
 }