refactor(mcp): type getReviewFeedbackItem with its producer's return type (#tech-debt)

[selfcontained]

What

McpRequestContext.getReviewFeedbackItem (apps/server/src/shared/mcp/server.ts) was declared Promise<Record<string, unknown> | null>. Its only producer, getFeedbackItemForAgent (agents/reviews.ts:576, wired via server/mcp-review-handlers.ts:272), returns (ReviewFeedbackItemRecord & { reviewId: number; messages: ReviewThreadMessageRecord[] }) | null. This PR declares that exact type — one declaration, both types already imported (the sibling listReviewFeedback uses them).

Why it's debt

The index-signature type let the consumer read any key as unknown without the compiler knowing the real shape. The sole consumer, dispatch_review_get_feedback (shared/mcp/persona-interaction-tools.ts), only null-checks the item and serialises it (jsonText(item), structuredContent: { item }), registers no outputSchema, and indexes no keys — so narrowing is type-only; no runtime object changes. The test mock in test/persona-interaction-tools.test.ts is cast as never and is unaffected.

Verification

• pnpm run check green; pnpm run test green (server 187 passed/1 skipped, web 133, extension 9).
• Compiler probe (consumer side): adding void item.notARealField; in the tool handler → TS2339 with this change; compiles silently on HEAD.
• Producer side is NOT protected by this change, deliberately: making the handler return { bogus: 1 } still compiles, because routes/mcp.ts types all ~37 mcp* route deps as unknown and hands them over via as Parameters<typeof handleMcpRequest>[3]. Typing just mcpGetReviewFeedbackItem would make it the one typed dep of 37; that whole family is queued as its own backlog entry.
• Local E2E: git-dependent specs (worktree, base-branch, callable-jobs Cmd+K launch with useWorktree: true) fail on this host because its Homebrew git is missing git-core, so git clone of a local bare repo falls through to the unlicensed Xcode git-upload-pack shim — reproducible outside the suite with a bare git clone. Non-git specs pass (agent-surfaces:680 known flake passed on re-run). Diff emits no JS change; relying on CI E2E.

Next

Next debt run: the 10th since the #1060 audit → a broad audit, including the new routes/mcp.ts unknown route-deps entry.

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