Browser takes about 5 seconds to close and looks frozen #457

Part of #87.

What the user sees (Apple Silicon Mac, alpha.20): each Browser close takes about 4.2-4.3 s. Home only disables the close button, so the window looks frozen, then vanishes: #87 (comment)

Cause: a fixed 4.0 s wait in the guest profile flush (quitGuestProfileDiskWriters, scripts/browser-selkies-control-service.mjs, graceMs=4000) even after the writers have exited. The Home-side visible "Closing…" state is in the 0.8.0 final batch; this issue is the guest fix, which needs a new Browser VM image (with #383).

Done means

• The guest returns as soon as the profile writers have exited (test in browser-profile-disk-flush.test.mjs), and still waits up to the limit when they have not.
• Home shows a visible "Closing…" state until the window goes (0.8.0 batch; tick when it ships).
• Installed Mac check: close time recorded here, well under 4 s, profile still saved on reopen.

Acceptance record — 3 November 2026

The writer-grace repair is present in the integrated Jetson source from dfd613263, with the earlier focused regression proof in #90. Confirm its guest image binding and record actual Close latency and saved-profile reopen on the selected Mac release candidate. PR #526 separately fixes a false TURN relay-port occupancy result. Keep its lifecycle regression with #131. This issue retains the visible Close and timing checks above.