feat: MCP server for Claude Desktop integration

[Supernova1744]

Summary

• Adds rtk mcp-serve — a synchronous stdio JSON-RPC 2.0 MCP server (no tokio, <10ms startup) that exposes RTK's full filter pipeline as a bash tool for Claude Desktop
• Adds rtk mcp-install — one-command installer that writes the MCP server entry into Claude Desktop's config on macOS, Windows, and Linux
• Adds source column (hook | mcp | direct) to the SQLite tracking database with a backward-compatible ALTER TABLE migration, so rtk gain --history distinguishes Claude Desktop usage from Claude Code hook usage

Architecture

Claude Desktop → tools/call bash {command: "git log -10"}
                      ↓
              rtk mcp-serve  (sync stdio JSON-RPC loop, no async)
                      ↓
              spawns: rtk git log -10  (existing filter pipeline)
                      ↓
              returns compact output (~80% fewer tokens)

New files

File	Purpose
src/mcp/protocol.rs	JSON-RPC 2.0 + MCP types (serde)
src/mcp/transport.rs	BufReader<Stdin> line reader + stdout writer
src/mcp/handler.rs	initialize, tools/list, tools/call, ping, shutdown
src/mcp/install.rs	Writes claude_desktop_config.json, cross-platform paths
tests/mcp_integration.rs	11 E2E tests — spawn binary, full JSON-RPC handshake over pipes
docs/MCP.md	Install, verify, troubleshoot guide

Test plan

• 41 unit tests (cargo test --bin rtk mcp) — all pass
• 11 integration tests (cargo test --test mcp_integration -- --ignored) — all pass on Linux and Windows
• Manual E2E: initialize → tools/list → tools/call git log -3 returns RTK-filtered output
• rtk mcp-install creates config at correct path, idempotent on second run
• Windows: shell builtins (echo, dir) fall back to cmd /C when RTK exits 127
• rtk gain --history shows source=mcp for Claude Desktop commands

How to test locally

cargo build --release
cargo test --test mcp_integration -- --ignored
rtk mcp-install   # then restart Claude Desktop

🤖 Generated with Claude Code

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[pszymkowiak]

[w] wshm · Automated triage by AI

📊 Automated PR Analysis

✨ Type	feature
🟡 Risk	medium

Summary

Adds an MCP server (rtk mcp-serve) and one-command installer (rtk mcp-install) so RTK can integrate with Claude Desktop via the Model Context Protocol, routing shell commands through RTK's existing filter pipeline. Also adds a source column to the SQLite tracking database to distinguish MCP usage from hook usage, with a backward-compatible migration.

Review Checklist

• Tests present
• Breaking change
• Docs updated

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Analyzed automatically by wshm · This is an automated analysis, not a human review.