feat: migrate to MCP SDK v2, add you-answer tool, and bump deps

[EdwardIrby]

Summary

Full upgrade of the DX toolkit packages: migrate from the @modelcontextprotocol/sdk monolith to the v2 split packages, add the new you-answer tool to the consumer surface, and bump dependencies (including the AI SDK ecosystem majors).

1. MCP SDK v2 migration (drop @modelcontextprotocol/sdk)

The v2 SDK splits the monolith into @modelcontextprotocol/client and @modelcontextprotocol/server (docs).

• mcp → client + server (stdio bridge)
• cli → client; @modelcontextprotocol/server added as a dev dep for the test MCP mock
• api → client (dep) + server (dev, test mocks); the bundle build now externalizes @modelcontextprotocol/client
• scripts (update-api-schemas.ts, classify-api-schema-change.ts) → v2 client
• ai-sdk-plugin: removed the vestigial SDK dep (its @ai-sdk/mcp adapter has its own MCP client and never needed it)
• langchain: removed the direct SDK dep; @langchain/mcp-adapters resolves its own v1 SDK transitively (the only remaining @modelcontextprotocol/sdk in bun.lock is that transitive dep — expected)
• Removed @modelcontextprotocol/inspector entirely (dev dep, inspector script, mcp-inspector.json)

Test mocks were rewritten to the v2 high-level server API (McpServer + registerTool + fromJsonSchema + createMcpHandler), since v2 folds HTTP handling into createMcpHandler and no longer ships a webStandardStreamableHttp subpath.

2. Add you-answer

• CLI contract regenerated to 7 tools (surfaceVersion 2026.08.20): you-answer, you-balance, you-contents, you-discover, you-finance, you-research, you-search. you-eco stays excluded; you-finance remains opt-in via ?tools=.
• API typed surface expanded to all 7 known tools. The schema generator now fetches via ?tools=<all known> so you-finance (served via a separate route, not the server default) is included.
• createYouApi now defaults a no-scope connection to advertising every known tool (?tools=<all known>), so the typed surface is truthful — every KnownToolName is callable on a default connection, including you-finance. A profile still scopes the set without an explicit ?tools= override.
• Fixed a pre-existing generator bug surfaced by you-discover: objectSchemaToType now unions the additionalProperties type with explicit property types so primitives (e.g. string) stay assignable to the index signature (you-discover's referrals).

3. Dependency bumps

• Tier 3 (majors): @ai-sdk/mcp ^2, ai peer/dev ^7, @ai-sdk/anthropic ^4 (ai-sdk-plugin)
• Tier 2 (minor): @langchain/mcp-adapters, langchain, @langchain/core, @langchain/langgraph, @langchain/anthropic, zod, @biomejs/biome

4. Docs

Updated the mcp/api/ai-sdk-plugin/langchain READMEs and docs/PERFORMANCE.md for you-answer and the new api default behavior.

Notes

• No connection pooling was added. The hosted You.com MCP server is stateless (legacy: 'stateless', responseMode: 'json'), so the stale-session resilience that motivated the pooled client pattern elsewhere doesn't apply; the adapter packages delegate connection management to @ai-sdk/mcp / @langchain/mcp-adapters.
• Versions are intentionally not hand-bumped in this branch. The publish workflows take an explicit bump input (the breaking SDK v2 line and the ai peer 6→7 bump warrant a major for the affected packages at release time).
• classify-api-schema-change.ts still tracks its narrower curated 3-tool set (it pre-dated this change and excluded you-balance even when the generator tracked 4). Expanding it is a separate drift-classification decision.

Validation

• bun run check — all 5 packages pass (biome + tsc + format-package)
• bun test — 67/67 pass
• bun run build — all 5 packages build
• bun scripts/update-api-schemas.ts --check — no schema drift vs. the live server

[factory-droid]

Droid finished @EdwardIrby's task —— View job

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Code Review Complete

Review status: Approved — no high-confidence issues found.

Clean MCP SDK v2 migration (import swaps to @modelcontextprotocol/client + @modelcontextprotocol/server) with a correct objectSchemaToType fix that unions additionalProperties types with explicit property types, and a well-tested createYouApi default that advertises all known tools. Parallel code review and a dedicated security review both found no high-confidence issues. The classify-api-schema-change.ts narrower 3-tool set is a pre-existing, author-documented intentional drift that this PR does not regress.

[factory-droid]

Droid finished @EdwardIrby's task —— View job

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Code Review Complete

Review status: Approved — no high-confidence issues found.

Clean MCP SDK v2 migration (import swaps to @modelcontextprotocol/client + @modelcontextprotocol/server) with a correct objectSchemaToType fix that unions additionalProperties types with explicit property types, and a well-tested createYouApi default that advertises all known tools. Parallel code review and a dedicated security review both found no high-confidence issues. The classify-api-schema-change.ts narrower 3-tool set is a pre-existing, author-documented intentional drift that this PR does not regress. The single P2 candidate about the classifier knownTools mismatch was validated and rejected as a pre-existing, author-acknowledged condition not introduced by this PR.