ASNT-98: Serve the agent bridge as an MCP server #110

Overview

An agent using the loopback bridge today spends every call on a shell round-trip: read the endpoint file, sed the token out, hand-quote JSON. stage_findings is the worst of it, and hand-quoting is what produced the malformed_request seen in live testing.

The seven methods are already granular and chainable. Adding more, smaller ones would mean more shell round-trips, not fewer. Fix the invocation, not the granularity.

Do not rewrite the transport. crates/app/src/agent_bridge.rs and the ai::agent contract stay as they are — tested, and documented in AGENTS.md as the language-neutral route any runtime can use. Add a thin MCP adapter in front that forwards to the loopback HTTP already running.

Scope

Target the 2026-07-28 MCP spec (current as of 2026-08-15; previous was 2025-11-25). That revision works in qrate's favour:

• Stateless core — initialize/initialized handshake removed, Mcp-Session-Id and protocol-level sessions removed. Every request is self-describing, which matches the bridge's existing one-request → one-answer → closed-socket shape. No session machinery to build.
• Client identity — _meta carries io.modelcontextprotocol/clientInfo (name + version) per request. A real replacement for the X-Agent header the Agent panel uses; keep X-Agent for raw HTTP callers, prefer clientInfo when present.
• Tool schemas — tools/list stops an agent guessing at parameter shapes. Biggest single win.
• Cacheable lists — ttlMs / cacheScope on list responses.
• Routing headers — Mcp-Method / Mcp-Name on tools/list and tools/call.
• server/discover for optional capability discovery.

Do not implement: Roots, Sampling and Logging (deprecated); legacy HTTP+SSE transport (deprecated, 12-month offramp); MRTR elicitation/sampling (qrate needs none). Extensions (MCP Apps, Tasks) are out of scope — qrate's calls are fast and synchronous.

Task Details

• One MCP tool per existing method, schemas generated from the ai::agent types.
• Stdio JSON-RPC as the transport an agent runtime registers.
• No new dependency: serde_json is already in the tree and the repo hand-rolls its HTTP; hand-roll the MCP subset rather than pull an SDK in for tools/list + tools/call.
• A feature-lifecycle policy now guarantees ≥12 months between deprecation and removal, so pinning to 2026-07-28 is safe.

Definition of Done

An agent registers one MCP server, then reviews an open project and stages findings without invoking a shell, and every call still appears in the Agent panel with a real client name.

Estimate

Medium

Type

Feature request

Blocks #? (ASNT-92, Pi agent harness and terminal UX) — with MCP in place the terminal stops being how an agent talks to qrate and becomes only how you watch one run.

Notion: https://app.notion.com/p/3bd21d32b13b81bb8a09fd0e4449d7de