fix: keep related request id zero from debouncing

[he-yufeng]

Summary

• treat numeric relatedRequestId: 0 as present when deciding whether a notification can be debounced
• add regression coverage so related notifications for request id zero are sent immediately instead of being coalesced
• add a patch changeset for @modelcontextprotocol/core

Fixes #2117

To verify

• corepack pnpm --filter @modelcontextprotocol/core test -- --run packages/core/test/shared/protocol.test.ts
• corepack pnpm --filter @modelcontextprotocol/core typecheck
• corepack pnpm --filter @modelcontextprotocol/core lint
• git diff --check origin/main..HEAD

The pre-push hook also passed the repo typecheck/build/lint tasks.

[changeset-bot]

🦋 Changeset detected

Latest commit: 9d5481d

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

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

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/client

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/client@2120

@modelcontextprotocol/codemod

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/codemod@2120

@modelcontextprotocol/server

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server@2120

@modelcontextprotocol/server-legacy

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/server-legacy@2120

@modelcontextprotocol/express

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/express@2120

@modelcontextprotocol/fastify

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/fastify@2120

@modelcontextprotocol/hono

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/hono@2120

@modelcontextprotocol/node

npm i https://pkg.pr.new/modelcontextprotocol/typescript-sdk/@modelcontextprotocol/node@2120

commit: 9d5481d

[he-yufeng]

Rebased this on the latest main and re-ran the focused checks locally:

• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts -t "relatedRequestId 0"
• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts
• pnpm --filter @modelcontextprotocol/core run typecheck
• pnpm --filter @modelcontextprotocol/core run lint
• pre-push hook: pnpm -r typecheck, pnpm -r build, pnpm sync:snippets --check, pnpm -r lint

[he-yufeng]

Rebased this on the latest main and re-ran the focused/core checks locally:

• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts -t "relatedRequestId 0"
• pnpm --filter @modelcontextprotocol/core exec vitest run test/shared/protocol.test.ts
• pnpm --filter @modelcontextprotocol/core run typecheck
• pnpm --filter @modelcontextprotocol/core run lint
• git diff --check upstream/main..HEAD
• pre-push hook: pnpm -r typecheck, pnpm -r build, pnpm sync:snippets --check, pnpm -r lint

[he-yufeng]

Rebased this branch on current main, resolved the conflict in the debounce guard, and force-pushed 9d5481dc.

The resolved change keeps the current API shape and only makes the related request check explicit, so relatedRequestId: 0 is treated as present instead of being debounced away.

Validated locally:

• pnpm changeset status --since origin/main (@modelcontextprotocol/core patch)
• 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 (31 passed)
• pnpm --filter @modelcontextprotocol/core typecheck
• pnpm --filter @modelcontextprotocol/core lint
• git diff --check origin/main..HEAD

The pre-push hook also completed the repo-wide build, typecheck, and lint steps successfully.