Browser: Chromium, Linux, 1280x800 CSS viewport, light theme on both commits.
The web frontend was served by each commit's own Vite dev server. All backend processes used T3CODE_DEV_SEED=0 and explicit isolated --base-dir paths.
Run legacy-startup-driver.py against the two checkouts first. It creates each database with its own server's migrations, stops that server, inserts synthetic legacy projection rows, restarts, captures startup output, and reads imported conversations through the real CLI.
Case 1: legacy-archived has a valid created_at and malformed updated_at and archived_at; legacy-deleted has valid created_at and malformed updated_at and deleted_at. Message timestamps are valid.
Case 2: legacy-preview has valid thread timestamps and one preview message with malformed created_at and valid updated_at.
Malformed value in both cases: 2026-07-13T14:13:00.3NZ.
For each side, start its own dev:web frontend proxied to its backend port, then restart the server with the case's explicit isolated --base-dir. On base the server exits with Invalid date; on head it prints T3 Code server is ready.
In the shared preview browser, navigate to /settings/archived for case 1. Base shows fetch-session-state HTTP 502 after its server has exited. Head, paired using its synthetic server's startup credential, lists Archived legacy conversation. Deleted legacy conversation is absent; its non-null deletedAt is shown in the runtime transcript.
For case 2, pair with the head's isolated server and navigate to /<environment-id>/legacy-preview. The question appears. Repeat navigation on the base frontend, whose server exited with Invalid date; it shows fetch-session-state HTTP 502.
Record navigation to each destination on both sides. Capture stills after two screenshots at least 500ms apart are byte-identical. Inspect every still and recording before upload.
Public captures show the top 450 CSS pixels of the same 1280x800 viewport to omit operational model controls; the before archive recording is trimmed to begin after leaving the preceding case. No app content was altered.
AI-assisted; verified with the tests and tools listed above.