feat(client): allow async tool output validators (#2971)

[karaaslanz]

Summary

• Allow the client-only jsonSchemaValidator option to provide an async getValidator(schema) and/or an async validation callback.
• Await compilation before tools/call, converting rejected compilation into the existing per-tool InvalidParams error, and await validation before inspecting valid.
• Preserve the shared synchronous validator interface and fromJsonSchema/server contract. Explicit per-call toolDefinition continues to compile in isolation.
• Add four focused client tests covering async compilation + validation, compilation rejection, validation mismatch and explicit-definition isolation; include a client changeset.

Refs #2971. Related #2998 modifies lazy validator-cache compilation and must be considered when integrating this change.

Verification

• git diff --check: PASS.
• Exact patched-source probe on Windows Node 24 + TypeScript 5.9.3: syntax transpilation of modified source/test, sync control, async compile/validate, cached reuse, rejection/mismatch: PASS. This is a focused source-backed test, not the full SDK suite.
• Full pnpm install / Vitest / package typecheck: NOT RUN successfully. The filtered install aborted with ERR_PNPM_BAD_PACKAGE_JSON: local node_modules/.pnpm/js-yaml@4.1.1/.../package.json contained NUL bytes. A direct typecheck was consequently blocked by missing workspace dependencies. No environment cleanup was attempted.

Opening as a draft so reviewers can confirm the client-only API scope and #2998 interaction before a ready-for-review declaration.

[changeset-bot]

🦋 Changeset detected

Latest commit: 71ee58c

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

This PR includes changesets to release 6 packages

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

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commit: 71ee58c