fix(platform): return 499 instead of 503 when client disconnects during nested fiber execution

[wewelll]

Summary

Fixes #5968

• Fix causeResponse to pre-compute whether clientAbortFiberId exists anywhere in the cause tree before traversing individual interrupt nodes
• When a client disconnects and the cause tree contains multiple interrupt entries, the server now correctly returns 499 instead of 503

The Bug

In causeResponse, the original code checked cause.fiberId === clientAbortFiberId on each interrupt node during Cause.reduce traversal. This fails when the cause tree has a structure like:

Sequential(Interrupt(parentFiberId), Interrupt(clientAbortFiberId))

Because Cause.reduce visits the left branch first, it encounters parentFiberId before clientAbortFiberId and incorrectly returns 503.

The Fix

Pre-compute whether clientAbortFiberId exists anywhere in the cause tree using Cause.interruptors() before entering the reduce loop:

const isClientAbort = HashSet.has(Cause.interruptors(cause), clientAbortFiberId)

Then use this flag when handling interrupt nodes instead of checking the individual node's fiber ID.

Test

The test constructs a synthetic cause that mimics the problematic structure:

const parentFiberId = yield* Effect.fiberId
const childInterrupt = Cause.interrupt(parentFiberId)
const clientAbortInterrupt = Cause.interrupt(HttpServerError.clientAbortFiberId)
const cause = Cause.sequential(childInterrupt, clientAbortInterrupt)
const [response] = yield* HttpServerError.causeResponse(cause)
expect(response.status).toEqual(499)

Note: Effect's runtime properly propagates interrupt IDs to child fibers, so real HTTP tests with nested fibers don't reproduce this specific cause structure. The synthetic test directly exercises causeResponse with the problematic cause tree.

[changeset-bot]

🦋 Changeset detected

Latest commit: d14743b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 31 packages

Name	Type
@effect/platform	Patch
@effect/cli	Patch
@effect/cluster	Patch
@effect/experimental	Patch
@effect/opentelemetry	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-node-shared	Patch
@effect/platform-node	Patch
@effect/rpc	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-drizzle	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-node	Patch
@effect/sql	Patch
@effect/workflow	Patch
@effect/ai	Patch
@effect/ai-amazon-bedrock	Patch
@effect/ai-anthropic	Patch
@effect/ai-google	Patch
@effect/ai-openai	Patch
@effect/ai-openrouter	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/sql-kysely	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR