Give each request its own execution stack build

[RhysSullivan]

Problem

Concurrent API requests could share one database provider build, so a request could use — and lose — a connection owned by another request.

Every request gets its own database connection: opened when the request fiber's scope opens, closed when it closes. But makeExecutionStackMiddleware captures the boot fiber's context once at layer-construction time and re-applies it to every request with Effect.provideContext. A captured context also carries Effect's CurrentMemoMap, and the merge lets the boot map overwrite the fresh per-request map the host installed.

The per-request Effect.provide(stackLayer) then memoized its build in that boot map, which every in-flight request in the isolate shares. Sequential requests still rebuilt — the memo entry is refcounted by observer and drops to zero when the request scope closes — so only overlapping requests were affected. Three concurrent requests produced one stack build, leaving two of them operating a database handle owned by a third.

Two consequences follow. On Workers, the borrowing request performs I/O on a socket belonging to a different request. And when the owning request finishes, its scope finalizer ends the connection, so the borrower's next query — typically the read after a slow outbound call — fails on a connection that is already gone.

Fix

The stack is built with a request-local memoization scope (Effect.provide(stackLayer, { local: true })) at both branches, so overlapping requests each build their own stack over their own connection. The captured context keeps doing the one job it exists for: carrying the boot-scoped services the per-request body needs.

{ local: true } rather than stripping the memo map out of the captured context: it states the invariant at the call site that depends on it, it is the documented meaning of the option, and it does not depend on which memoization map happens to be ambient — so it holds for both cloud (which combines a request-scoped DB layer) and self-host (which does not).

Two other per-request provider builds run under a captured context for the same stated reason — closing over the per-request socket — and had the same defect: the account provider and the admin-users provider. Both are fixed the same way. The fixed-executor middleware captures a context too, but provides only pre-built values and never builds a layer per request, so it is unaffected.

Testing

apps/cloud/src/api.request-scope.node.test.ts gains three regressions that stand the real middleware up over authenticated requests and per-request in-memory databases, so the stack layer actually builds:

• three concurrent requests produce three stack builds
• every request's stack is built over its own database handle, never another's
• read, slow await, read again: the request that is still running holds an open connection of its own while the faster overlapping request has already ended and released its own

All three fail against the unfixed code — one build for three requests, a single handle backing every request, and an inverted release order where the slow request's own connection is released while it keeps working on the fast request's. All pass after the change, over five consecutive runs of the file.

bun run typecheck is green. Cloud e2e storage-error-report-shape and connections-credentials pass unchanged.

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Torn down — the PR is closed.

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