feat(tool-server): add start-metro tool

[hubgan]

Add start-metro tool for React Native Metro bundler startup

Summary

Adds a start-metro tool that starts a Metro bundler for a React Native project, or reuses an instance already running on the target port — complementing the existing stop-metro. Until now agents had to instruct users to run Metro manually (npx react-native start), which made fully automated RN app startup impossible. With this tool the start→run→debug loop can run end-to-end without a human in the loop.

What it does

start-metro returns { port, pid, status } where status is "started" or "reused":

• Reuse by default — probes the port's /status endpoint for the packager-status:running marker; if Metro is already up, returns status: "reused" without spawning a second server.
• reuseExisting: false — forces a fresh instance; errors instead of reusing a running Metro.
• Port conflict detection — if the port is held by a non-Metro process, fails fast with the offending PID(s) and tells the caller to free it with stop-metro, rather than spawning a Metro that would just fail to bind.
• Default & custom commands — runs npx react-native start --port <port> detached by default; pass command/args (e.g. "npm" + ["run", "start:local"]) to run a project's own start script verbatim (no flag injection — the caller owns its flags). Supports cache-reset via custom args.
• projectRoot — sets the working directory (and --projectRoot for the default command) for monorepos where the tool-server cwd isn't the app root.
• Readiness wait — polls /status until Metro is ready (60s timeout) before returning, folding boot-time error/exit listeners into the readiness race so a later natural exit can't crash the tool-server.

Implementation notes

• The detached + unref'd child outlives the tool-server (same pattern as simulator-server); stop-metro terminates it by port later.
• Accurate PID reporting: findListeningPids uses lsof -ti tcp:<port> -sTCP:LISTEN. The -sTCP:LISTEN filter is essential — a bare query also matches established client sockets (including the tool-server's own keep-alive to Metro), which would return the wrong PID. For wrapper commands (npx/npm run) the reported PID is the descendant that actually bound the port, not the wrapper.
• All process spawning uses spawn/execFileSync with no shell, so port and other inputs can never be shell-interpreted.

Files

• packages/tool-server/src/tools/simulator/start-metro.ts — the tool
• packages/tool-server/src/utils/setup-registry.ts — registration
• packages/tool-server/test/start-metro.test.ts — unit tests covering reuse, fresh start, custom command verbatim, LISTEN-only PID lookup, non-Metro port conflict, and reuseExisting: false
• Skill/docs updates (argent.md rule, argent-react-native-app-workflow SKILL, argent-metro-debugger failure-scenarios) to route agents to start-metro instead of shelling out to npx react-native start

Scope note

The optional --public-base-url flag for remote-agent workflows from the original scope is not included in this change. The reuse/fresh-start parameter is implemented as a boolean reuseExisting (default true) rather than a --no-reuse-existing flag.

[filip131311]

expo will not work after this PR