Fix Windows: registry write crash, process liveness probes, and drive-relative /tmp paths

[neelsvan]

Summary

Three fixes that make the CLI usable on Windows. All changes are behind sys.platform == "win32" except the os.rename -> os.replace swap, which is equivalent-or-better on POSIX. No POSIX behavior changes.

1. os.replace for registry writes (registry.py)

os.rename raises FileExistsError (WinError 183) when the destination exists -- which is every save after the first. launch crashed on a clean Windows machine right after creating the initial registry file.

2. Windows-safe process liveness probes (utils.py)

os.kill(pid, 0) is a POSIX idiom. On Windows, signal 0 maps to CTRL_C_EVENT and the call raises OSError (WinError 87, "The parameter is incorrect") for ordinary processes, so every registry liveness check crashed -- status, stop, attach, and cleanup were all unusable. The fix probes with OpenProcess(PROCESS_QUERY_LIMITED_INFORMATION) (ERROR_ACCESS_DENIED still proves existence) and adds a GetProcessTimes-based start-time token so the PID-reuse identity check works on Windows too, instead of silently returning None via the ps -o lstart= fallback.

3. Absolute temp paths on Windows (registry.py, launcher.py)

"/tmp/chrome-agent" is drive-relative on Windows -- it resolves against the current drive. Instances registered while working on one drive are invisible from another, and every command reports "No instances registered". The registry and session root now resolve via tempfile.gettempdir() on Windows.

Testing

• Windows 11, Python 3.14.3, Chrome 151 -- full lifecycle verified manually (launch / status / navigate / Runtime.evaluate / screenshot / attach with +Network.requestWillBeSent / stop, from two different drives):
  • main: 29 failed, 49 errors, 86 passed
  • this branch: 9 failed, 8 errors, 147 passed
  • remaining failures are POSIX-semantics tests (SIGTERM-based attach exits, /proc-based sweep identity) and fingerprint/viewport assertions that do not hold in this environment
• Linux (python:3.12-slim container, no Chrome installed) -- identical results on main and this branch (44 passed / 6 failed / 9 errors; every failure is BrowserNotFoundError from the missing browser), confirming no POSIX regressions in the touched modules (test_registry and test_pid_identity pass fully).

Not addressed (out of scope): os.kill(pid, 15) in registry.py maps to TerminateProcess on Windows rather than a graceful SIGTERM -- functional, but stop is a hard kill there.