[effect-bot]

Adds a duplex variant to ChildProcess additionalFds, so a sidecar can run a request/response protocol over one inherited descriptor.

const handle = yield* ChildProcess.make("sidecar", [], {
  additionalFds: { fd3: { type: "duplex" } }
})
// write with handle.getInputFd(3), read with handle.getOutputFd(3)

Changes

• AdditionalFdConfig gets { type: "duplex", stream?, sink? }. ChildProcessHandle keeps its shape: getInputFd and getOutputFd both work on a duplex fd, so other spawner implementations are unaffected. DenoChildProcessSpawner already rejects additionalFds.
• NodeChildProcessSpawner wires the read stream and the write sink to the same child.stdio[fd] socket and sets allowHalfOpen = true on it, so the parent can still write after the child half-closes. When the input sink completes it calls end(), as input fds and stdin already do. On POSIX this is a real shutdown(SHUT_WR).
• Additional-fd output adapters retain the first error from setup onward and check it when reading starts. A duplex write failure no longer emits an uncaught error, and a delayed reader receives a mapped PlatformError instead of hanging.
• pipeTo(..., { to: "fdN" }) no longer replaces a duplex target with { type: "input" }. The target stays duplex and the piped stream becomes its input.
• The JSDoc for additionalFds, PipeToOptions.to and the handle getters describes the platform support below.

Platform support (as documented)

• Linux evidence: Effect's Node spawner is validated by the suite below. Separate raw node:child_process compatibility probes under Node.js and Deno verified same-fd request/response and half-close in both directions; those Deno probes did not validate Effect's spawner. Native DenoChildProcessSpawner still rejects additionalFds.
• Expected, not verified: the same behavior on macOS, because it uses the same POSIX socket-pair path in libuv, Deno and Bun. Request/response on Windows is also expected, because libuv and Deno create a duplex named pipe.
• Not supported: half-close on Windows, because named pipes have no write-side shutdown. Half-close on Bun is also unsupported, because Bun's end() closes the whole socket. The docs tell users to keep the input open until every response has been read.
• Unverified: extra fds with Bun on Windows.
• Child side: use new net.Socket({ fd }) in Node.js and Deno. Deno children can't use node:fs on the raw fd, and Bun children can't use net.Socket on it.

Tests

The final shared spawner suite adds two focused regressions:

1. Same-fd request/response after pipeTo ends its input, covering duplex-target preservation and parent half-close on POSIX.
2. A write failure before reading starts, checking the mapped write failure, absence of an uncaught exception, and mapped failure for a delayed reader rather than a hang.

Validation

At 1ba3ef7ef on Linux / Node 26.8.2:

• pnpm vitest --run for packages/platform/node-shared/test, packages/effect/test/process and DenoChildProcessSpawner.test.ts: 202 passed. The native Deno spawner tests do not establish duplex support there.
• pnpm lint and pnpm check: clean.
• Both retained duplex tests passed in three repeated runs; the reviewer independently ran the full Node spawner file: 80/80 passed.

Earlier validation also passed pnpm jsdocs --check and the doctests for the two changed modules (8 passed). A separate manual check under Node and Bun confirmed that an unused duplex write side does not hold exitCode or the event loop open after the child exits. No macOS or Windows execution was performed.

Closes #8902
Closes EFF-1844

[changeset-bot]

🦋 Changeset detected

Latest commit: f1ec011

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

This PR includes changesets to release 32 packages

Name	Type
effect	Patch
@effect/platform-node-shared	Patch
@effect/opentelemetry	Patch
@effect/vitest	Patch
@effect/ai-anthropic	Patch
@effect/ai-cloudflare	Patch
@effect/ai-openai-compat	Patch
@effect/ai-openai	Patch
@effect/ai-openrouter	Patch
@effect/ai-typesafe	Patch
@effect/atom-react	Patch
@effect/atom-solid	Patch
@effect/atom-vue	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-deno	Patch
@effect/platform-node	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-pglite	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-node	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/docgen	Patch
@effect/doctest	Patch
@effect/openapi-generator	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

[github-actions]

Bundle Size Analysis

Generated from PR build output; treat the content below as untrusted.

File Name	Current Size	Previous Size	Difference
arbitrary-combinators.ts	38.79 KB	38.79 KB	0.00 KB (0.00%)
basic.ts	7.06 KB	7.06 KB	0.00 KB (0.00%)
batching.ts	10.14 KB	10.14 KB	0.00 KB (0.00%)
brand.ts	6.73 KB	6.73 KB	0.00 KB (0.00%)
cache.ts	10.89 KB	10.89 KB	0.00 KB (0.00%)
config.ts	22.27 KB	22.27 KB	0.00 KB (0.00%)
differ.ts	21.34 KB	21.34 KB	0.00 KB (0.00%)
http-client.ts	22.67 KB	22.67 KB	0.00 KB (0.00%)
http-router.ts	34.05 KB	34.05 KB	0.00 KB (0.00%)
logger.ts	11.22 KB	11.22 KB	0.00 KB (0.00%)
metric.ts	9.03 KB	9.03 KB	0.00 KB (0.00%)
optic.ts	6.96 KB	6.96 KB	0.00 KB (0.00%)
pubsub.ts	15.18 KB	15.18 KB	0.00 KB (0.00%)
queue.ts	12.13 KB	12.13 KB	0.00 KB (0.00%)
schedule.ts	11.22 KB	11.22 KB	0.00 KB (0.00%)
schema-bigdecimal.ts	13.76 KB	13.76 KB	0.00 KB (0.00%)
schema-binary.ts	40.00 KB	40.00 KB	0.00 KB (0.00%)
schema-class.ts	21.09 KB	21.09 KB	0.00 KB (0.00%)
schema-fromJsonSchemaDocument.ts	32.10 KB	32.10 KB	0.00 KB (0.00%)
schema-representation-roundtrip.ts	27.31 KB	27.31 KB	0.00 KB (0.00%)
schema-string-transformation.ts	14.49 KB	14.49 KB	0.00 KB (0.00%)
schema-string.ts	12.02 KB	12.02 KB	0.00 KB (0.00%)
schema-template-literal.ts	16.09 KB	16.09 KB	0.00 KB (0.00%)
schema-toArbitrary.ts	38.32 KB	38.32 KB	0.00 KB (0.00%)
schema-toCodeDocument.ts	25.30 KB	25.30 KB	0.00 KB (0.00%)
schema-toCodecJson.ts	20.26 KB	20.26 KB	0.00 KB (0.00%)
schema-toEquivalence.ts	20.45 KB	20.45 KB	0.00 KB (0.00%)
schema-toFormatter.ts	20.57 KB	20.57 KB	0.00 KB (0.00%)
schema-toJsonSchemaDocument.ts	25.03 KB	25.03 KB	0.00 KB (0.00%)
schema-toRepresentation.ts	20.55 KB	20.55 KB	0.00 KB (0.00%)
schema.ts	20.31 KB	20.31 KB	0.00 KB (0.00%)
stm.ts	13.24 KB	13.24 KB	0.00 KB (0.00%)
stream.ts	9.99 KB	9.99 KB	0.00 KB (0.00%)

[tim-smart]

This could use Effect.suspend instead