fix(server): support extension subscription notifications

[SnowSky1]

Summary

• preserve extension-namespaced keys in subscriptions/listen filters and acknowledgements
• add a generic ServerNotifier.extension() event path filtered by the requested extension key
• cover io.modelcontextprotocol/tasks / notifications/tasks through schema, event-bus, and createMcpHandler tests

Fixes #2569.

Validation

• core schema tests: 3/3
• server focused tests: 25/25
• full pre-push hook: build, lint, and typecheck

Stack note

This draft currently includes #2592 as its first commit because that baseline fix is required for the repository pre-push lint gate. I will rebase this PR onto main after #2592 lands so this diff contains only the extension-subscription commit.

[changeset-bot]

🦋 Changeset detected

Latest commit: 7b63522

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

This PR includes changesets to release 6 packages

Name	Type
@modelcontextprotocol/server	Patch
@modelcontextprotocol/core	Patch
@modelcontextprotocol/client	Patch
@modelcontextprotocol/core-internal	Patch
@modelcontextprotocol/server-legacy	Patch
@modelcontextprotocol/codemod	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/client@2593

@modelcontextprotocol/codemod

npm i https://pkg.pr.new/@modelcontextprotocol/codemod@2593

@modelcontextprotocol/core

npm i https://pkg.pr.new/@modelcontextprotocol/core@2593

@modelcontextprotocol/server

npm i https://pkg.pr.new/@modelcontextprotocol/server@2593

@modelcontextprotocol/server-legacy

npm i https://pkg.pr.new/@modelcontextprotocol/server-legacy@2593

@modelcontextprotocol/express

npm i https://pkg.pr.new/@modelcontextprotocol/express@2593

@modelcontextprotocol/fastify

npm i https://pkg.pr.new/@modelcontextprotocol/fastify@2593

@modelcontextprotocol/hono

npm i https://pkg.pr.new/@modelcontextprotocol/hono@2593

@modelcontextprotocol/node

npm i https://pkg.pr.new/@modelcontextprotocol/node@2593

commit: 7b63522