Fix unknown MCP cancellation suppresses a later reused request ID

[fubhy]

Summary

Every valid cancellation ID is inserted into cancelledRequests before active-request existence is known. The next Exit for the same client and typed ID is deleted from that set and discarded, including a later unrelated request that reuses X.

Important

This PR starts with focused failing reproduction tests. Add the implementation fix to this same branch; CI is expected to fail until that fix is included.

Unknown MCP cancellation suppresses a later reused request ID

Module: packages/effect/src/unstable/ai/McpServer.ts
Audit ID: relsem-mcp-stale-cancel-id
Severity / confidence: medium / high

What happens

Every valid cancellation ID is inserted into cancelledRequests before active-request existence is known. The next Exit for the same client and typed ID is deleted from that set and discarded, including a later unrelated request that reuses X.

Why it happens

The owning implementation diverges from relation unstable-services-004.

Expected behavior

MCP cancellation for an unknown request identifier is ignored; suppression applies only to the response of the matching active cancelled request.

Relevant implementation

These links and excerpts are pinned to audit base b206fa5d7655c1634c9993410a9203f6616a5ca2.

• packages/effect/src/unstable/ai/McpServer.ts:670

View problematic code at packages/effect/src/unstable/ai/McpServer.ts:670

              if (request.tag === "notifications/cancelled") {

View exact lines on GitHub

Reproduction

pnpm --filter effect test --run test/unstable/ai/McpServer/v2025_06_18.test.ts -t "SHOULD allow a later request to reuse an unknown cancelled identifier"

Observed failure: Independently rerun; failed at the intended semantic assertion.

Implementation handoff

The initial reproduction tests on this branch are the regression specification for the implementation fix that should follow in this PR.

1. Start with the pinned implementation excerpts and the Why it happens analysis above.
2. Change the implementation so it satisfies the stated Expected behavior; do not weaken or remove the reproduction assertions.
3. Run the focused reproduction command(s) and confirm the observed failures become passing tests:

pnpm --filter effect test --run test/unstable/ai/McpServer/v2025_06_18.test.ts -t "SHOULD allow a later request to reuse an unknown cancelled identifier"

4. Run the affected package's existing tests, then the repository lint and type checks before requesting review.

Audit provenance

• Audit base: b206fa5d7655c1634c9993410a9203f6616a5ca2
• Reproduction base: b206fa5d7655c1634c9993410a9203f6616a5ca2
• Findings: relsem-mcp-stale-cancel-id
• Initial patch: focused reproduction tests; implementation fix pending

Closes EFF-563

[changeset-bot]

🦋 Changeset detected

Latest commit: fb61bff

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

This PR includes changesets to release 30 packages

Name	Type
effect	Patch
@effect/ai-anthropic	Patch
@effect/ai-openai	Patch
@effect/ai-openai-compat	Patch
@effect/ai-openrouter	Patch
@effect/atom-react	Patch
@effect/atom-solid	Patch
@effect/atom-vue	Patch
@effect/docgen	Patch
@effect/doctest	Patch
@effect/openapi-generator	Patch
@effect/opentelemetry	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-deno	Patch
@effect/platform-node	Patch
@effect/platform-node-shared	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/vitest	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

[pullfrog]

no API key found — this repo is configured to use moonshotai/kimi-k2.7-code, which needs MOONSHOT_API_KEY, but the runner has no key for it.

To fix: add the key as a GitHub Actions secret (referenced from your workflow's env: block) or as a Pullfrog secret in the console — or switch this repo to a different model (free models need no key).

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  ^{｜ ⚠️ this action is pinned to a commit SHA, which freezes the cleanup step — switch to @v0 or keep the SHA fresh with Dependabot ｜ Rerun failed job ➔ ｜ View workflow run ｜ via Pullfrog ｜ Using Kimi K2 (free via Pullfrog for OSS) ｜ 𝕏}

[pullfrog]

✅ No new issues found.

Reviewed changes

• Added a changeset describing the MCP cancellation fix.
• Fixed McpServer cancellation by tracking active request IDs per client and only honoring notifications/cancelled when the target ID is currently active, preventing unknown cancellation IDs from suppressing later requests that reuse the same ID.
• Added regression tests for reusing an unknown cancelled identifier and for ignoring cancellation of an already-completed request identifier.

  ^{｜ ⚠️ this action is pinned to a commit SHA, which freezes the cleanup step — switch to @v0 or keep the SHA fresh with Dependabot ｜ View workflow run ｜ Using Kimi K2 (free via Pullfrog for OSS) ｜ 𝕏}

[github-actions]

Bundle Size Analysis

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

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