feat(compat): add deprecated flat ctx.* getters + RequestHandlerExtra type alias

[felixweinberger]

Part of the v2 backwards-compatibility series — see reviewer guide.

v2 nested handler-context fields (extra.signal → ctx.mcpReq.signal, extra.authInfo → ctx.http?.authInfo). This adds non-optional @deprecated getters at the old flat locations.

Motivation and Context

v2 nested handler-context fields (extra.signal → ctx.mcpReq.signal, extra.authInfo → ctx.http?.authInfo). This adds non-optional @deprecated getters at the old flat locations.

v1 vs v2 pattern & evidence

v1 pattern:

`async (req, extra) => { extra.signal; extra.sendNotification(...); extra.taskStore }`

v2-native:

`async (req, ctx) => { ctx.mcpReq.signal; ctx.mcpReq.notify(...); ctx.task?.store }`

Evidence: GitHub code search: ~1,180 files use extra.signal/extra.sendNotification.

How Has This Been Tested?

• packages/core/test/shared/protocol.compat.test.ts — getter equivalence + warn-once
• Integration: validated bump-only against 5 OSS repos via the v2-bc-integration validation branch
• pnpm typecheck:all && pnpm lint:all && pnpm test:all green

Breaking Changes

None — additive @deprecated shim. Removed in v3.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added or updated documentation as needed

Additional context

Stacks on: C1

[changeset-bot]

🦋 Changeset detected

Latest commit: ef84a4a

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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