Move the MCP server into Rust, hosted by the app and yaak mcp

[gschier]

Replaces the @yaak/mcp-server plugin with crates/yaak-mcp on rmcp 3.5, PR 4 of the Yaak Proxy plan (proxy tools come in 4b).

• yaak-mcp: the plugin's 15 tools, same names, input schemas and output text, written against an McpHost trait. Stdio transport, and streamable HTTP that requires Authorization: Bearer <token>.
• CLI: yaak mcp serves stdio with the CLI's own queries and send path. -e and --cookie-jar act as the active environment and jar; toasts go to stderr.
• App: serves 127.0.0.1:64343/mcp while the new mcpServerEnabled setting is on (default off), starting and stopping when it changes. The token is generated on first start and kept in key_values. The plugin's send handler is now send_http_request_in_window, shared with MCP.
• Settings > Agents (hidden on the web through a new agents platform capability): the Yaak CLI with status, install prompt, and agent skill; the app's MCP server toggle and token; and Connect an agent, with setup for Claude Code, Codex, Cursor, VS Code, and other MCP clients through the CLI or the app. The menu's Install CLI item opens this tab.
• The local model-event loop in models_ext.rs moved to its own thread. It blocks in recv(), so as a runtime task it parked a worker, and anything spawned from it (the settings sync) sat in that worker's LIFO slot until a later spawn pushed it out.
• Plugin: deprecation toast and README note. Not removed, plugin API unchanged.

Differences from the plugin: list_workspaces drops the internal _label and lists a workspace open in two windows once; send_http_request JSON keys come out alphabetical (it still returns metadata only, no body, as before). Old mcp-remote configs need the header now. With the plugin still installed, the built-in server can't bind 64343 and says so in a toast.

Tests

cargo test -p yaak-mcp -p yaak-cli: per-tool tests on the CLI host against a temp DB through an rmcp client (the plugin's five send cases included), end-to-end tests spawning yaak mcp (including one where an MCP send's environment and cookie jar reach response.* and cookie.value), and an HTTP auth test (401 without or with a wrong token, 404 off /mcp).

Claude Code → yaak mcp (stdio)

> list_workspaces {}                       < [{"id":"wk_5o2qcrAHCL","name":"MCP Demo"}]
> list_http_requests {"workspaceId":...}   < [{"model":"http_request","id":"rq_yVyUXzUoqU","name":"Hello",...}]
> send_http_request {"id":"rq_yVyUXzUoqU"} < {"model":"http_response","status":200,"contentLength":42,"elapsed":12,...}
> create_folder {"name":"Smoke Tests"}     < {"model":"folder","id":"fl_4yjmyWaM8Q",...}
> create_http_request {"name":"Echo","method":"POST","folderId":"fl_4yjmyWaM8Q","bodyType":"application/json","body":{"text":"{\"ok\": true}"},...}
                                           < {"model":"http_request","id":"rq_gwtcEoSX7D",...}

Claude Code → app via mcp-remote (token redacted)

> list_workspaces {}                       < [{"id":"wk_m9Q74jFJUs","name":"App MCP Demo"}]
> get_environment_id {}                    < No environment selected
> list_http_requests {}                    < [{"id":"rq_R9wAYFqiDb","name":"Hello",...}]
> send_http_request {"id":"rq_R9wAYFqiDb"} < {"status":200,"contentLength":42,"elapsed":54,...}
> show_toast {"message":"Hello from Claude Code over MCP","color":"success"}
                                           < ✓ Toast shown: "Hello from Claude Code over MCP"

In the app, one tick of the setting starts the listener and one untick stops it (app log), and the sent request shows its saved 200 in the sidebar.

[greptile-apps]

Confidence Score: 5/5

[High impact] The PR appears safe to merge; the latest change fixes the web menu issue without introducing a new failure.

Summary

Moves MCP tools into Rust, served through yaak mcp over stdio or through the app over authenticated localhost HTTP.

• Yaak's MCP tools now run from a shared Rust server.
• The Yaak CLI serves MCP tools through yaak mcp.
• The desktop app can host an authenticated MCP server on localhost.
• Settings > Agents shows how to connect AI clients to Yaak.
• The app handles local model updates on a separate thread.
• The old MCP plugin now directs users to Yaak's built-in server.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  Agent[AI agent] -->|stdio| CLI[yaak mcp]
  Agent -->|HTTP with bearer token| App[App MCP server]
  CLI --> Tools[Shared Rust MCP tools]
  App --> Tools
  Tools --> Host[McpHost]
  Host --> Data[Workspace data and request sends]

Loading

_{Reviews (3) · Last reviewed commit: "Hide the Install CLI menu item where age..." · Reviewed by Greptile}

[gschier]

@greptileai review

[gschier]

@greptileai review