MCP tools/list stays under 40 KB, and a test holds it there #3366

Measured 2026-10-20: tools/list on production's /mcp answered 58,599 bytes, about 15k tokens that every harness session pays before it does anything.

Done:

• [ ] A test calls tools/list and fails when the JSON is over 40,000 bytes, naming the five longest descriptions.
• [ ] Descriptions in src/http/mcp.ts are cut until it passes. Each keeps its first sentence of intent and the facts an agent needs to call the tool correctly. Repeated explanations move to here (the manifest tool) and are referred to by name.
• [ ] test/mcp.test.ts and the plugin tool-name test still pass. No tool is removed or renamed.

Files: src/http/mcp.ts, test/mcp-size.test.ts. Risk: an agent loses guidance it relied on. Check each cut against the tool's tests. Builder: quill or scout.

Parked by the crew: the check stayed red through 2 automatic tries (pull #3389 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.