fix(core): preserve relatedRequestId 0 in debounce guard

[kiranmagic7]

What changed

• Treat relatedRequestId as present unless it is undefined when deciding whether a notification can be debounced.
• Add a regression test for two same-tick debounced notifications with relatedRequestId: 0.
• Add a patch changeset for @modelcontextprotocol/core.

Why

0 is a valid MCP/JSON-RPC request id. The previous truthiness check treated relatedRequestId: 0 as absent, so simple request-associated notifications could be coalesced by the debounce path while non-zero ids were sent immediately.

Fixes #2117.

Tests

• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts -t "relatedRequestId 0" — passes
• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts — 151 tests pass
• pnpm --filter @modelcontextprotocol/core test — 553 tests pass
• pnpm --filter @modelcontextprotocol/core typecheck — passes
• pnpm --filter @modelcontextprotocol/core lint — passes
• pnpm changeset status --since origin/main — reports @modelcontextprotocol/core patch bump

Compatibility / risk

Small behavior fix only: notifications already associated with non-zero request ids bypass debounce; this makes request id 0 follow the same path. Notifications without a related request id remain debounced as before.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6da1da1

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

This PR includes changesets to release 1 package

Name	Type
@modelcontextprotocol/core	Patch

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

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commit: 6da1da1

[kiranmagic7]

Rebased this on current main (head 5d11cba3). Local verification after the rebase:

• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts -t "relatedRequestId 0" - 1 passed
• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts - 151 passed
• pnpm --filter @modelcontextprotocol/core test - 553 passed
• pnpm --filter @modelcontextprotocol/core typecheck - passed
• pnpm --filter @modelcontextprotocol/core lint - passed
• pnpm changeset status --since origin/main - reports @modelcontextprotocol/core patch bump

GitHub checks have now completed successfully on the refreshed head.

[kiranmagic7]

Rebased this on current main and resolved the packages/core/src/shared/protocol.ts conflict. Latest head is 2b6b644c0dc92f7bc47d59b25f5f31b934459ee1.

Local verification after the rebase:

pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts -t "relatedRequestId 0"
PASS: 1 file, 1 test

pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts
PASS: 1 file, 31 tests

pnpm --filter @modelcontextprotocol/core test
PASS: 20 files, 368 tests

pnpm --filter @modelcontextprotocol/core typecheck
PASS

pnpm --filter @modelcontextprotocol/core lint
PASS

pnpm changeset status --since origin/main
PASS: reports @modelcontextprotocol/core patch bump

git diff --check origin/main...HEAD
PASS

GitHub now reports the branch as mergeable again; checks are running on the refreshed head.

[kiranmagic7]

Friendly follow-up: this still looks ready for maintainer/code-owner review. Latest head 2b6b644c0dc92f7bc47d59b25f5f31b934459ee1 is mergeable from the PR view, all 13 GitHub checks are passing, and the focused relatedRequestId 0 regression verification is in the previous update. Happy to adjust anything maintainers want changed.

[kiranmagic7]

Rebased this on current main and refreshed the branch. Latest head is 72f0af98.

Local verification after the rebase:

pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts -t "relatedRequestId 0"
PASS: 1 file, 1 test

pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts
PASS: 1 file, 31 tests

pnpm --filter @modelcontextprotocol/core test
PASS: 22 files, 464 tests

pnpm --filter @modelcontextprotocol/core typecheck
PASS

pnpm --filter @modelcontextprotocol/core lint
PASS

pnpm changeset status --since origin/main
PASS: reports @modelcontextprotocol/core patch bump

git diff --check origin/main...HEAD
PASS

GitHub checks should restart on the refreshed head.

[kiranmagic7]

Rebased this on current main and refreshed the branch. Latest head is 6da1da1f.

Local verification after the rebase:

pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts -t "relatedRequestId 0"
PASS: 1 file, 1 test

pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts
PASS: 1 file, 31 tests

pnpm --filter @modelcontextprotocol/core test
PASS: 23 files, 474 tests

pnpm --filter @modelcontextprotocol/core typecheck
PASS

pnpm --filter @modelcontextprotocol/core lint
PASS

pnpm changeset status --since origin/main
PASS: reports @modelcontextprotocol/core patch bump

git diff --check origin/main...HEAD
PASS

GitHub checks should restart on the refreshed head.