MCP TypeScript SDK requestId 0 cancellation candidate

[serejaris]

Upstream

• Issue: requestId 0 is silently dropped by _oncancel, making the first request from every Protocol uncancellable modelcontextprotocol/typescript-sdk#2115
• Watch note: watch/ai-native-frameworks-scouting-2026-05-27-cycle-21.md

Status

COMMENT-FIRST / candidate.

Six-subagent cycle 21 found this as the only new candidate not clearly duplicate-covered, assigned, or already occupied.

Parent gate:

• upstream issue is open;
• no assignee;
• no labels;
• PR search for 2115 OR _oncancel OR oncancel OR requestId 0 OR cancellation resource leak returned empty;
• repo contribution guide asks contributors to comment before starting work to avoid duplicate effort.

Regression card

Contract: cancellation notifications must abort the matching in-flight request even when requestId is 0.

Expected pre-fix failure: a cancellation notification with params.requestId = 0 does not abort the stored controller.

Expected post-fix pass: the controller for request id 0 is aborted with the provided reason.

Likely patch surface:

• packages/core/src/shared/protocol.ts
• _oncancel

Likely test surface:

• protocol cancellation tests under packages/core

Next action

Post upstream test-plan comment and wait for maintainer signal / assignment before coding.

[serejaris]

Cycle 22 follow-up: status changed to WATCH / duplicate-race.

Parent live gate corrected the cycle 21 duplicate result. modelcontextprotocol/typescript-sdk#2115 now has two exact competing PRs:

• fix: handle cancelled notifications for request id zero modelcontextprotocol/typescript-sdk#2116
• fix: handle cancellation for request id zero modelcontextprotocol/typescript-sdk#2138

Both are open, mergeable, review required, have green checks in the live view, change packages/core/src/shared/protocol.ts, add regression coverage in packages/core/test/shared/protocol.test.ts, and add a changeset for @modelcontextprotocol/core.

Decision: no upstream PR/comment from us. Our prior upstream test-plan comment is historical only. Unblock event: maintainer merges/closes #2116/#2138 or explicitly asks for an alternative fix/tests; repeat duplicate gate before any new upstream action.

Internal watch note: watch/ai-native-frameworks-scouting-2026-05-27-cycle-22.md.

[serejaris]

MCP TS #2115 duplicate-race refresh, 2026-05-27 23:11 UTC

• 6 read-only subagents + parent live gates + 3-role critique completed.
• Issue #2115 remains open/unassigned/no labels; our upstream test-plan comment is historical only.
• Exact competing PRs remain open: #2116 and #2138 are non-draft, MERGEABLE/BLOCKED/REVIEW_REQUIRED, with visible green checks, changesets, and regression tests for the requestId: 0 cancellation path.
• #2138 is the freshest duplicate lane by update time and validation envelope; this is not an upstream selection/approval signal.
• Decision remains WATCH / duplicate-race. No upstream comment/PR/ping. Re-open actionability only if both exact PRs close unmerged, maintainers ask for evidence/implementation, CI regresses, or a new uncovered edge appears.

Watch note updated locally; bundled commit follows after diff checks.

[serejaris]

MCP TS #2115 duplicate-race refresh, 2026-05-27 23:37 UTC

• 6 read-only roles + parent live gates + 3-role critique completed.
• Upstream #2115 remains open/unassigned/no labels; our upstream test-plan comment remains historical only, with no new maintainer direction.
• Exact competing PRs remain open: #2116 and #2138 are non-draft, MERGEABLE/BLOCKED/REVIEW_REQUIRED, with green visible checks, patch changesets for @modelcontextprotocol/core, and regression coverage for requestId: 0.
• Adjacent relatedRequestId: 0 PRs (#2120/#2135/#2141) are separate #2117/debounce context, not a new #2115 gap.
• Decision remains WATCH / duplicate-race. Upstream actions: 0. Re-open actionability only if both exact PRs close unmerged, maintainers ask for alternative evidence/implementation, CI regresses, a new uncovered edge appears, or one exact PR merges and the internal watch should close as absorbed.