Add high-level MCP operation interceptor seam

[khandrew1]

What changed

• adds SDK-derived McpRequestMethod and AroundMcpRequest public types
• adds ServerOptions.aroundMcpRequest for the high-level McpServer
• places the seam around the seven tool/resource/prompt primitive operations
• keeps routing and input validation before interception, with output validation, projection, cache hints, and protocol validation after it
• keeps low-level Server.setRequestHandler() behavior unchanged

Why

Frameworks need a supported way to add operation middleware without replacing SDK-owned handlers, duplicating dispatch, parsing HTTP responses, or reaching into private registries. The existing low-level handler wrapper is outside the high-level validation and projection boundaries, so it cannot provide those guarantees.

This PR is intentionally stacked on #2501 because the consuming framework already depends on that coordinated 2026-07-28 preview.

Closes #2507.

Validation

• pnpm --filter @modelcontextprotocol/server typecheck
• server lint and Prettier
• server build and declaration generation
• full server test suite: 42 files, 453 tests
• full pre-push build, typecheck, and lint hooks

[changeset-bot]

🦋 Changeset detected

Latest commit: 5c6f3df

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

This PR includes changesets to release 10 packages

Name	Type
@modelcontextprotocol/server	Minor
@modelcontextprotocol/express	Major
@modelcontextprotocol/fastify	Major
@modelcontextprotocol/hono	Major
@modelcontextprotocol/node	Major
@modelcontextprotocol/core	Minor
@modelcontextprotocol/client	Minor
@modelcontextprotocol/server-legacy	Minor
@modelcontextprotocol/codemod	Minor
@modelcontextprotocol/core-internal	Patch

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commit: 5c6f3df

[khandrew1]

auto slop pr, sorry