verification on linux / google chrome / repository playwright
main: 6575ce32508bd7908444241f3719aa33aaf77f90
pr: 4215470d07c5f950a76ad4365fd01042be3de225

real app setup on each revision:
add project /home/user/t3code in web ui; select codex gpt-6.1-sol; submit prompt; observe completed provider reply.
snooze one minute; wait for Woke; settle without opening; un-settle; mark unread.
this creates a genuine local visit through the app. no mock, fixture, synthetic timestamps or database writes.

main cold startup with actual browser localStorage copied into a clean browser context:
unread server visit before: 2026-10-30T14:30:18.351Z
real local visit: 2026-10-30T14:36:49.427Z
websocket emitted thread.visit visitedAt=2026-10-30T14:36:49.427Z without opened=true
server visit after: 2026-10-30T14:36:49.427Z
Done badge disappeared without opening the thread: BUG REPRODUCED

pr cold startup:
real local visit: 2026-10-30T14:55:28.309Z
unread server visit: 2026-10-30T14:48:34.297Z
local > server: true
startup emitted zero thread.visit commands; server watermark unchanged; Done remained.
reload emitted zero thread.visit commands; Done remained.
opening thread emitted thread.visit visitedAt=2026-10-30T14:56:40.278Z opened=true; Done cleared.
neighboring follow-up Codex gpt-6.1-sol turn completed with reply: neighboring follow-up verified.
its completion showed Done while away; opening cleared Done.

blacksmith checks:
cd apps/web && vp test run --project unit src/hooks/useThreadVisitedMigration.test.ts: 5/5 pass
vp run check:changed 9910c0e87469a44a18ce5c381533fc0a06c81ef1: format, lint, knip 1/2, knip 2/2, typecheck (2 packages), tests (1 file): pass
worker fetched shallow base history first so check:changed had a merge base.

limitation: warm-cache startup on main tried migration before connection and failed silently; a clean shell cache with the actual existing localStorage was necessary to expose the original overwrite.
unverified in real app: null-watermark initial migration and older-server compatibility (unit cases passed), native mobile, Electron shell, non-Codex providers, remote/relay.