[ID01 F03] Desktop integration: expose Digital Thread project-control tools in the active Codex host #22

Problem

In the current Codex host session, Digital Thread project-control tools are not exposed as first-class tools. The agent must use the repository loopback CLI despite the registered MCP surface being available.

Evidence

• The active session catalogue has no Casys project-control tools.
• scripts/probes/mcp-call.ts implements the loopback client for http://127.0.0.1:3020/mcp.

Impact

The normal engineering loop is less discoverable and loses typed host affordances.

Acceptance criteria

• Establish whether the Desktop host can discover and expose the local Digital Thread MCP safely.
• If supported, expose the registered read and project-control tools with their exact schemas.
• Keep provider selection, runtime arguments, and Workbench mutation authority unavailable to the host integration.
• Make absence or connection failure explicit.
• Verify one read-only project call end to end on the packaged host.

Fact-check scope

ID01 F03; source and session inspection on 2026-09-09.

Evidence limit: Verified for this Codex host/session only; does not establish behavior on another host or authorize changing Codex globally.

The registered project_snapshot read succeeded through the existing CLI during this audit. This issue concerns host integration and discoverability, not a broken MCP endpoint. It is distinct from viewer-selection handoff in #6.