feat: enable headless spawn for Grok once relay confirms streaming-json support

[khaliqgant]

Summary

Grok supports a headless CLI mode via --output-format streaming-json (https://docs.x.ai/build/overview), producing NDJSON events similar to Claude's stream-json format. Once relay validates spawnCli({ transport: 'headless' }) against Grok's protocol, Pear can drop PTY for Grok too.

Current state

Claude, Codex, and OpenCode already route through spawnCli({ transport: 'headless' }) (relay 8.3.0). Grok is explicitly excluded pending relay confirmation:

// Grok supports --output-format streaming-json but relay compatibility
// with its specific protocol hasn't been confirmed — stays on PTY for now.
const useHeadless = !shellSession && ['claude', 'codex', 'opencode'].includes(spawnCliLabel(nextInput.cli))

See: src/main/broker.ts → spawnAgentOnce

What needs to happen

1. Confirm with relay that spawnCli({ transport: 'headless' }) works for grok --output-format streaming-json
2. Confirm whether a Grok-specific harness config is needed (analogous to HeadlessAppServerHarnessConfig for OpenCode) or if the generic headless transport handles it
3. Add 'grok' to the headless CLI list — one-line change

Related

• PR feat: add Grok as first-class harness #138: Grok harness UI wiring
• PR ⛔ DO NOT MERGE — feat: upgrade @agent-relay to 8.3.0, wire headless spawn routing and runtime tracking #139: relay 8.3.0 + claude/codex headless routing