[FabioHAraujo]

Stacked on #109 (MCP server); the base becomes main once #109 merges.

MCP clients (Claude Desktop, Claude Code, Cursor) launch local servers as a process and talk over stdio. lownotes-mcp is that process: it relays between the client's stdio and the running LowNotes.

The bridge

• Binary: src-tauri/src/bin/lownotes-mcp.rs, a console binary. It calls mcp_bridge::run() in the library, so it shares the endpoint and credential code with the app. default-run = "lownotes" keeps cargo run and tauri dev on the app.
• Token: read from the OS credential store through the reference in settings.json, without writing the file. When MCP is off, or the app has not created a token yet, the bridge says so instead.
• Windows endpoint check: pipe names are machine-wide, so before sending the token the bridge checks that the process serving the pipe runs as the same user (GetNamedPipeServerProcessId, then the process token's SID).
• Unix: the socket sits in a folder only the user can enter, so no extra check is needed.
• Relay: after the OK handshake, bytes are copied both ways, flushing every chunk to stdout. The bridge exits when either side closes.
• When LowNotes cannot be reached: the bridge answers the client's first request with a JSON-RPC error that says why, then exits with code 1. The possible reasons are: app not open, MCP off, token refused, endpoint owned by another user, credential store unavailable, or too many clients.
• Logs: stderr through tracing, at warn by default (LOWNOTES_LOG overrides it). No note content or token.

Shipping

• Tauri bundles src/bin/* next to the app, so the NSIS/MSI installers, the .app, and the .deb, .rpm and AppImage packages include it.
• release.yml:
  • the Windows portable zip and the Linux portable tarball carry lownotes-mcp;
  • the per-architecture macOS jobs upload both binaries, and the universal job runs lipo on each before tauri bundle;
  • the Arch package (PKGBUILD.ci and the AUR template) installs /usr/bin/lownotes-mcp with its own checksum.
• bundle.yml checks that the debug .deb ships /usr/bin/lownotes-mcp.

Tests

• Bridge relay: a test connects the bridge to a real server over a named pipe on Windows (a Unix socket on CI), then runs initialize and tools/call and checks the exit code when the client closes.
• Refusals: a wrong token comes back as a JSON-RPC error with the request's id. Both "LowNotes not open" and "MCP off" are answered on the first request, while notifications are skipped.
• Token lookup: the bridge finds the token reference the app saved, and only while MCP is enabled.
• Manual: with MCP off, echo '{"jsonrpc":"2.0","id":1,"method":"initialize"}' | lownotes-mcp prints the error and exits 1.

Full AGENTS.md verification on Windows: bun install --frozen-lockfile, version:check, check, check:e2e, bun test, the Python script tests, cargo fmt --check, cargo clippy --lib --bins --tests -D warnings, cargo test --locked --lib, bun run build and test:e2e all pass.

Not verified locally: the macOS universal release path and the Arch package. Both run only in the release workflow.

Closes #102