perf: event-driven CDP readiness detection (−55s startup)

[lennney]

Summary

Replaces the 120×1s polling loop in ensure_injection with three-phase progressive CDP readiness detection. Typical startup drops from ~55s to 0-2s.

Design

Phase	Mechanism	Time
1	Monitor stderr for DevTools listening on ws:// → immediate injection	2-5s
2	Exponential backoff TCP probe (100ms→10s)	up to ~21s
3	1s polling (30 attempts) — original behaviour safety net	up to 30s

Phase 1 follows Playwright's Electron launcher pattern (92k★): pipe child stderr, match DevTools signal line. All Chromium-based apps print this when launched with --remote-debugging-port.

Key correctness detail

wait_for_cdp_ready returns Ok(()) only when the magic line is found; EOF returns Err. The spawn calls tx.send(()) only on success. This ensures Phase 1's fast path is genuinely reachable — distinct from EOF / I/O errors.

Also eliminates nested retry: self.inject() internally called retry_injection() (20×500ms), creating a hidden 10s delay. Phases 2 & 3 use try_inject() for a single TCP probe per attempt.

Performance

Metric	Before	After
Typical startup	~55s	~0-2s
Worst case	~446s	~66s

Test Coverage

4 mock tests for wait_for_cdp_ready:

• Magic line detection ✅
• Noise before magic line ✅
• EOF without magic line → Err ✅
• Empty stderr → Err ✅

All 64 launcher tests pass.

[BigPizzaV3]

当前 PR 的 Windows artifacts 检查仍然失败，暂时不能合并。最新 main 已包含 ChatGPT Desktop watcher 相关修复，请先 rebase/merge 最新 main，然后重新运行完整 CI；如果同步后仍失败，请根据失败日志修复并在 PR 中说明根因。合并前需要确保 Windows、macOS x64、macOS arm64 全部通过。