codemode: add durable MCP elicitation approvals example

[mattzcarey]

Summary

• add an example-only, server-side MCP implementation built with a plain Agent, persistent WorkerTransport, and createMcpHandler
• expose exactly two tools: search({ code }) for read-only Portal catalog discovery and execute({ code }) for durable operation execution
• derive catalog metadata and executable portal.<operation>() methods from one dynamic PortalConnector, with collision and reserved-name checks
• translate operation-level requiresApproval pauses into form-mode MCP elicitation, then approve/replay or reject without exposing a model-callable approval tool
• use the already released runtime.tool().execute({ code }, undefined) API for both tools; this PR contains no Codemode package or SDK changes

The framework-neutral runtime.execute(), runtime.search(), and runtime.describe() convenience APIs have moved to the independent #1969.

Search and execute isolation

• search exposes only portal.tools() from the Portal connector. It returns JavaScript-safe names, raw upstream names, schemas, and approval policy, and removes completed searches from the durable audit history.
• execute exposes callable portal.<operation>() methods but not portal.tools().
• codemode remains reserved for runtime primitives.

Approval flow

1. Generated code reaches a protected Portal operation.
2. The durable runtime records its exact method and arguments, pauses the execution, and ends the Dynamic Worker pass.
3. The MCP handler sends elicitation/create on the originating tools/call stream.
4. Acceptance calls runtime.approve() and resumes through abort-and-replay; decline or cancel calls runtime.reject().
5. Clients without form-mode elicitation support fail closed.

The demo policy allows listing and commenting while requiring approval to create issues or merge requests.

Validation

• pnpm install --frozen-lockfile — passed
• pnpm --filter @cloudflare/agents-codemode-mcp-approvals-example test — 13 passed
• pnpm --filter @cloudflare/codemode test — 376 passed
• pnpm run build — 25 projects passed
• pnpm run check — exports, format, lint, and all 118 TypeScript projects passed
• pnpm exec nx affected -t test --base=origin/main --parallel=1 — 20 affected projects passed
• pnpm --dir examples/codemode-mcp-approvals exec wrangler deploy --dry-run --outdir /tmp/codemode-mcp-approvals-dry-run — bundled successfully

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