diff --git a/packages/prompt-variance/src/index.ts b/packages/prompt-variance/src/index.ts
index b46dd9fe4..c535243e2 100644
--- a/packages/prompt-variance/src/index.ts
+++ b/packages/prompt-variance/src/index.ts
@@ -10,3 +10,16 @@ export {
   type PromptVarianceFamily,
   type PromptVarianceRow,
 } from "./rows.js";
+
+// Astra tool-evasion residual (CL-9027): forensics on the repro trace showed
+// evasion, not waste — the gpt-6-astra leaf re-issues the same effective tool
+// call with trivial argument deltas (path prefix, default offset/limit,
+// padding whitespace), so no exact tool fingerprint repeats 3x and the shared
+// threshold guard stays silent. This forbids that specific variation
+// (muse-rule precedent, CL-7869); no signature normalization ships in
+// first-party code. Named export rather than a family row: it travels the
+// ModelFamilyPolicy.promptResidual seam, composed over the gpt narrate note.
+export const astraResidual: string =
+  "Tool discipline (gpt-6-astra worker):\n" +
+  "- Never re-issue a tool call that repeats a prior call with only trivial argument changes (path prefix, offset, limit, whitespace).\n" +
+  "- Never re-read a file you have already read this session.";
diff --git a/src/agent/model-family-policy.test.ts b/src/agent/model-family-policy.test.ts
index 789bfd0c0..b800e2805 100644
--- a/src/agent/model-family-policy.test.ts
+++ b/src/agent/model-family-policy.test.ts
@@ -200,4 +200,200 @@ describe("resolveModelFamilyPolicy", () => {
     expect(gpt.toolDisciplineRules).toBeUndefined();
     expect(gpt.advertisedToolDeny).toEqual([]);
   });
+
+  describe("astra repro trace (CL-9027)", () => {
+    // Minimal failing session-trace fixture: 8 consecutive tool-only turns
+    // from a gpt-6-astra leaf (tool names + args + result sizes per turn).
+    // Fingerprint and repeat-count semantics mirror
+    // scripts/tool-fingerprint-forensics.ts (stableJson exact signatures,
+    // largest exact-repeat count per period 1-6): the shared threshold guard
+    // fires only on exact repeats, so a loop that varies trivial argument
+    // details escapes it. That is evasion, not threshold-tolerated waste —
+    // and the Step-3 residual forbids exactly this variation. The
+    // near-identical grouping below is test-only forensics; no signature
+    // normalization ships in first-party code.
+    interface ReproTurn {
+      tool: string;
+      args: Record<string, unknown>;
+      resultTokens: number;
+    }
+    const ASTRA_REPRO_TRACE: readonly ReproTurn[] = [
+      {
+        tool: "read",
+        args: { path: "src/agent/prompts.ts" },
+        resultTokens: 3200,
+      },
+      {
+        tool: "read",
+        args: { path: "./src/agent/prompts.ts" },
+        resultTokens: 3200,
+      },
+      {
+        tool: "read",
+        args: { path: "src/agent/prompts.ts", offset: 1 },
+        resultTokens: 3180,
+      },
+      {
+        tool: "grep",
+        args: { pattern: "narrate", path: "src/agent" },
+        resultTokens: 420,
+      },
+      {
+        tool: "read",
+        args: { path: "src/agent/prompts.ts" },
+        resultTokens: 3200,
+      },
+      {
+        tool: "grep",
+        args: { pattern: "narrate ", path: "src/agent" },
+        resultTokens: 420,
+      },
+      {
+        tool: "read",
+        args: { path: "./src/agent/prompts.ts", limit: 2000 },
+        resultTokens: 3200,
+      },
+      {
+        tool: "read",
+        args: { path: "src/agent/prompts.ts", offset: 0 },
+        resultTokens: 3200,
+      },
+    ];
+
+    function stableJson(value: unknown): string {
+      if (value === null || typeof value !== "object")
+        return JSON.stringify(value);
+      if (Array.isArray(value)) return `[${value.map(stableJson).join(",")}]`;
+      const obj = value as Record<string, unknown>;
+      const keys = Object.keys(obj).sort();
+      return `{${keys.map((k) => `${JSON.stringify(k)}:${stableJson(obj[k])}`).join(",")}}`;
+    }
+
+    function fingerprint(turn: ReproTurn): string {
+      return `${turn.tool}:${stableJson(turn.args)}`;
+    }
+
+    function maxExactRepeats(fps: readonly string[]): number {
+      let best = 1;
+      for (let period = 1; period <= 6; period++) {
+        for (let end = 1; end <= fps.length; end++) {
+          const prefix = fps.slice(0, end);
+          let i = prefix.length - 1;
+          let j = i - period;
+          let matched = 0;
+          while (j >= 0 && prefix[i] === prefix[j]) {
+            matched++;
+            i--;
+            j--;
+          }
+          const reps = Math.floor((matched + period) / period);
+          if (reps > best) best = reps;
+        }
+      }
+      return best;
+    }
+
+    function evasionKey(turn: ReproTurn): string {
+      const args = { ...turn.args };
+      // The trivial deltas this trace varies: a leading ./ prefix, default
+      // offset/limit values, and padding whitespace.
+      if (typeof args.path === "string")
+        args.path = args.path.replace(/^\.\//, "");
+      if (args.offset === 0 || args.offset === 1) delete args.offset;
+      if (typeof args.limit === "number") delete args.limit;
+      if (typeof args.pattern === "string") args.pattern = args.pattern.trim();
+      return `${turn.tool}:${stableJson(args)}`;
+    }
+
+    function classifyAstraTrace(trace: readonly ReproTurn[]): string {
+      if (maxExactRepeats(trace.map(fingerprint)) >= 3) return "waste";
+      const groups = new Map<string, number>();
+      for (const turn of trace) {
+        const key = evasionKey(turn);
+        groups.set(key, (groups.get(key) ?? 0) + 1);
+      }
+      return Math.max(...groups.values()) >= 3 ? "evasion" : "waste";
+    }
+
+    test("classifies as evasion: no exact repeat trips the shared guard", () => {
+      expect(ASTRA_REPRO_TRACE).toHaveLength(8);
+      expect(maxExactRepeats(ASTRA_REPRO_TRACE.map(fingerprint))).toBeLessThan(
+        3,
+      );
+      expect(classifyAstraTrace(ASTRA_REPRO_TRACE)).toBe("evasion");
+    });
+
+    test("pins the offending pattern and the wasted turn/token delta", () => {
+      const groups = new Map<string, number>();
+      for (const turn of ASTRA_REPRO_TRACE) {
+        const key = evasionKey(turn);
+        groups.set(key, (groups.get(key) ?? 0) + 1);
+      }
+      // Six re-reads of one file plus two re-greps of one pattern, each run
+      // differing only by a trivial argument delta.
+      expect(groups.get('read:{"path":"src/agent/prompts.ts"}')).toBe(6);
+      expect(groups.get('grep:{"path":"src/agent","pattern":"narrate"}')).toBe(
+        2,
+      );
+      const wastedTokens = ASTRA_REPRO_TRACE.reduce(
+        (sum, turn) => sum + turn.resultTokens,
+        0,
+      );
+      expect(wastedTokens).toBe(20020);
+    });
+  });
+
+  test("astra resolves to astra with the composed residual; thresholds stay default (CL-9027)", () => {
+    const base = resolveModelFamilyPolicy({
+      providerName: "unknown-provider",
+      model: "unknown-model",
+    });
+    const gpt = resolveModelFamilyPolicy({
+      providerName: "openai",
+      model: "gpt-5.6",
+    });
+    for (const orchestrator of [false, true]) {
+      const astra = resolveModelFamilyPolicy({
+        providerName: "codex/default",
+        model: "gpt-6-astra",
+        orchestrator,
+      });
+      expect(astra.family).toBe("astra");
+      // Keeps the gpt narrate nudge and adds the evasion-specific rules.
+      expect(astra.promptResidual).toContain(
+        "Narrate before tools (GPT worker):",
+      );
+      expect(astra.promptResidual).toContain("trivial argument changes");
+      expect(astra.promptResidual).not.toBe(gpt.promptResidual);
+      // Evasion earns a forbidding residual, not tighter thresholds.
+      expect(astra.toolOnlyTurnNudgeAt).toBe(base.toolOnlyTurnNudgeAt);
+      expect(astra.subAgentStallTimeoutMs).toBe(base.subAgentStallTimeoutMs);
+      expect(astra.applyGrokFinishBias).toBe(false);
+      expect(astra.toolDisciplineRules).toBeUndefined();
+      expect(astra.advertisedToolDeny).toEqual([]);
+    }
+  });
+
+  test("sol and generic gpt stay gpt with the byte-identical narrate residual", () => {
+    const generic = resolveModelFamilyPolicy({
+      providerName: "openai",
+      model: "gpt-5.6",
+    });
+    for (const model of [
+      "gpt-5.6-sol",
+      "gpt-5.5",
+      "gpt-5.6-luna",
+      "gpt-5.6-terra",
+    ] as const) {
+      for (const orchestrator of [false, true]) {
+        const policy = resolveModelFamilyPolicy({
+          providerName: "codex/default",
+          model,
+          orchestrator,
+        });
+        expect(policy.family).toBe("gpt");
+        expect(policy.promptResidual).toBe(generic.promptResidual);
+      }
+    }
+  });
 });
diff --git a/src/agent/model-family-policy.ts b/src/agent/model-family-policy.ts
index ca0ad69f0..5301e8bed 100644
--- a/src/agent/model-family-policy.ts
+++ b/src/agent/model-family-policy.ts
@@ -3,6 +3,7 @@ import {
   type ModelFamily,
 } from "../subagent/provider-family.js";
 import {
+  astraResidual,
   claudeRow,
   gptRow,
   grokRow,
@@ -164,9 +165,12 @@ const CLAUDE_POLICY: Omit<ModelFamilyPolicy, "family"> = {
 // Deliberately not manage_tasks ceremony — that is CL-7769, not this text.
 // The text lives here (policy owns data); buildGptNarrateBeforeToolsNote
 // (prompts.ts) returns it verbatim so the prompt carries exactly one copy.
-// Served cells (astra/sol/terra/…) are never named here — CL-8265
-// characterizes them later. Single-sourced from the versioned
-// prompt-variance package (CL-8269); the name stays for existing importers.
+// Served cells (sol/terra/…) are never named here — CL-8265 characterizes
+// them later. Astra is the one exception: forensics (CL-9027) showed the
+// gpt-6-astra cell evading the shared threshold guard via trivial argument
+// deltas, so it carries its own residual below. Single-sourced from the
+// versioned prompt-variance package (CL-8269); the name stays for existing
+// importers.
 export const GPT_NARRATE_BEFORE_TOOLS_NOTE = gptRow.residual;
 
 // GPT (Codex / gpt-*) thresholds are provisional: we have no eval
@@ -181,6 +185,21 @@ const GPT_POLICY: Omit<ModelFamilyPolicy, "family"> = {
   promptResidual: GPT_NARRATE_BEFORE_TOOLS_NOTE,
 };
 
+// Astra (served gpt-6-astra cell) is GPT plus the evasion residual. Forensics
+// on the repro trace (see model-family-policy.test.ts) classified the loop as
+// evasion — near-identical re-issued calls whose trivial argument deltas keep
+// every exact fingerprint under the shared threshold — so the residual forbids
+// that specific variation (muse-rule precedent, CL-7869) instead of tightening
+// thresholds: toolOnlyTurnNudgeAt stays at the permissive default. No
+// signature normalization ships in first-party code.
+export const ASTRA_PROMPT_RESIDUAL = `${GPT_NARRATE_BEFORE_TOOLS_NOTE}\n${astraResidual}`;
+
+const ASTRA_POLICY: Omit<ModelFamilyPolicy, "family"> = {
+  ...GPT_POLICY,
+  // Like gpt, primary and leaf alike: no orchestrator carve-out.
+  promptResidual: ASTRA_PROMPT_RESIDUAL,
+};
+
 export function resolveModelFamilyPolicy(input: {
   providerName: string;
   model?: string;
@@ -217,6 +236,10 @@ export function resolveModelFamilyPolicy(input: {
     case "gpt":
       // Primary and leaf alike: no orchestrator carve-out.
       return { family, ...GPT_POLICY };
+    case "astra":
+      // Primary and leaf alike, like gpt: no orchestrator carve-out. Generic
+      // gpt prompts are byte-identical — only astra carries the residual.
+      return { family, ...ASTRA_POLICY };
     default:
       return { family: "default", ...DEFAULT_POLICY };
   }
diff --git a/src/subagent/provider-family.test.ts b/src/subagent/provider-family.test.ts
index 4970d8f34..0eae482d3 100644
--- a/src/subagent/provider-family.test.ts
+++ b/src/subagent/provider-family.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "bun:test";
 import {
   detectModelFamily,
+  isAstraLeafProvider,
   isClaudeLeafProvider,
   isGptProvider,
   isKimiLeafProvider,
@@ -229,16 +230,23 @@ describe("isGptProvider (CL-8310)", () => {
     ).toBe(true);
   });
 
-  test("covers every in-tree codex catalog model without naming cells", () => {
-    // No terra/sol/astra special-casing: every served codex id resolves via
-    // the generic codex-provider / gpt-* match, so future cells ride along.
+  test("astra branches to its own family; other cells ride the generic gpt match", () => {
+    // CL-9027 reverses the no-special-casing rule for astra only: the
+    // gpt-6-astra cell doom-loops, so it resolves to the astra family while
+    // sol/terra/luna and generic gpt ids keep the generic gpt match.
     for (const model of CODEX_DEFAULT_MODELS) {
       expect(isGptProvider({ providerName: "codex/default", model })).toBe(
         true,
       );
-      expect(detectModelFamily({ providerName: "codex/default", model })).toBe(
-        "gpt",
-      );
+      const family = detectModelFamily({
+        providerName: "codex/default",
+        model,
+      });
+      if (model.toLowerCase().startsWith("gpt-6-astra")) {
+        expect(family).toBe("astra");
+      } else {
+        expect(family).toBe("gpt");
+      }
     }
   });
 
@@ -264,3 +272,49 @@ describe("isGptProvider (CL-8310)", () => {
     expect(isGptProvider({ providerName: "anthropic" })).toBe(false);
   });
 });
+
+describe("isAstraLeafProvider (CL-9027)", () => {
+  test("matches the served gpt-6-astra cell id on any provider", () => {
+    expect(
+      isAstraLeafProvider({
+        providerName: "codex/default",
+        model: "gpt-6-astra",
+      }),
+    ).toBe(true);
+    expect(
+      isAstraLeafProvider({
+        providerName: "openai-compat",
+        model: "GPT-6-ASTRA",
+      }),
+    ).toBe(true);
+    expect(
+      detectModelFamily({
+        providerName: "codex/default",
+        model: "gpt-6-astra",
+      }),
+    ).toBe("astra");
+  });
+
+  test("rejects sol, generic gpt, and other families", () => {
+    for (const input of [
+      { providerName: "codex/default", model: "gpt-5.6-sol" },
+      { providerName: "codex/default", model: "gpt-5.6-terra" },
+      { providerName: "codex/default", model: "gpt-5.6-luna" },
+      { providerName: "openai", model: "gpt-5.6" },
+      { providerName: "codex", model: "gpt-5.1" },
+      { providerName: "xai/default", model: "grok-4.6" },
+      { providerName: "anthropic", model: "claude-sonnet-4" },
+    ] as const) {
+      expect(isAstraLeafProvider(input)).toBe(false);
+    }
+    expect(
+      detectModelFamily({
+        providerName: "codex/default",
+        model: "gpt-5.6-sol",
+      }),
+    ).toBe("gpt");
+    expect(
+      detectModelFamily({ providerName: "openai", model: "gpt-5.6" }),
+    ).toBe("gpt");
+  });
+});
diff --git a/src/subagent/provider-family.ts b/src/subagent/provider-family.ts
index c1ac21076..8a42497e4 100644
--- a/src/subagent/provider-family.ts
+++ b/src/subagent/provider-family.ts
@@ -50,12 +50,26 @@ export function isClaudeLeafProvider(input: {
   return false;
 }
 
+/**
+ * True when the model id is the served gpt-6-astra cell. Forensics (CL-9027)
+ * showed that cell doom-looping via trivial argument deltas, so it resolves
+ * to its own family with an evasion-specific residual; other served cells
+ * (sol/terra/luna) keep riding the generic gpt match below.
+ */
+export function isAstraLeafProvider(input: {
+  providerName: string;
+  model?: string;
+}): boolean {
+  return input.model !== undefined && /^gpt-6-astra/i.test(input.model.trim());
+}
+
 /**
  * True when the inference path is the GPT family: a Codex provider name
  * (codex/ OAuth profiles, the codex-responses adapter, bare codex) or a
- * gpt-* model id on any provider. Served codex cells (astra/sol/terra/luna)
+ * gpt-* model id on any provider. Served codex cells (sol/terra/luna)
  * all match the generic gpt-* model shape — never name them here; CL-8265
- * characterizes cells later.
+ * characterizes cells later. Astra is the one exception: it branches to its
+ * own family in detectModelFamily below (CL-9027).
  */
 export function isGptProvider(input: {
   providerName: string;
@@ -76,6 +90,7 @@ export type ModelFamily =
   | "muse"
   | "claude"
   | "gpt"
+  | "astra"
   | "default";
 
 /**
@@ -92,6 +107,7 @@ export function detectModelFamily(input: {
   if (isKimiLeafProvider(input)) return "kimi";
   if (isMuseSparkLeafProvider(input)) return "muse";
   if (isClaudeLeafProvider(input)) return "claude";
+  if (isAstraLeafProvider(input)) return "astra";
   if (isGptProvider(input)) return "gpt";
   return "default";
 }