fix(app): reserve chat request slots during MCP discovery - #62564

Issue for this PR

Closes #53049

Type of change

• Bug fix

What does this PR do?

Classifies /api/command, /api/mcp and their nested routes through the existing slow-request share in request-queue-machine.ts. The queue keeps four slots and at most two slow requests, so a session read can start while MCP or command catalogs are still waiting on server startup or discovery. Current priorities, concurrency limits, deadlines, cancellation and retry behaviour are unchanged.

This is the current-dev port of #53050, which the automated age/reaction cleanup closed on 2026-11-04. That closure was not a review result. Base: 21bf6b493b76efcf3769ade999f05163760d61af.

How did you verify your code works?

• bun test --config /dev/null ./src/runtime/server/request-queue-machine.test.ts ./src/runtime/server/request-queue.test.ts from packages/app: 22 passed, 0 failed, 82 assertions. The transport case holds two catalogs and asserts a session read is dispatched before the third catalog.
• bun run typecheck in packages/app: no type errors in 2,332 files.
• bun run lint:changed: 0 problems in the 3 changed files.
• Native pre-push lint && typecheck gate passed.
• The exact-head upstream workflows on the previous head were action_required for fork runs, not failed tests. Full CI on this head is not claimed green while GitHub requires maintainer approval.

Not claimed: a full Desktop reproduction of the intermittent timeout. This is a queue-classification change with a loopback/transport regression, not a root-cause proof of every slow request.

Screenshots / recordings

No visual control changed.

Visual

<svg xmlns="http://www.w3.org/2000/svg" width="240" height="72" viewBox="0 0 240 72">
  <style>@media(prefers-reduced-motion:no-preference){.chat{animation:pass 2s infinite}}@keyframes pass{0%,100%{opacity:.5}50%{opacity:1}}</style>
  <g fill="none" stroke="currentColor"><rect x="8" y="12" width="48" height="48" rx="6"/><rect x="66" y="12" width="48" height="48" rx="6"/><rect x="124" y="12" width="108" height="48" rx="6" class="chat"/></g>
  <g fill="currentColor" font-family="sans-serif" font-size="10" text-anchor="middle"><text x="32" y="40">MCP</text><text x="90" y="40">MCP</text><text x="178" y="40">Chat can continue</text></g>
</svg>

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

Added by the opencode bot (AI-generated).

Related: #59526