Environment: Linux; real T3 dev server; fresh synthetic T3 home; T3CODE_DEV_SEED=0
Commit: f9b769843a7fd522d7a66cfffde62959cb863b50
Command: T3CODE_DEV_SEED=0 vp run dev --home-dir <synthetic-home>
Shared config.toml is empty; shared cloud-config-bundle-cache.json contains synthetic shared-cache.
Provider instance codex_work: driver=codex, homePath=<shared>, shadowHomePath=<work>.
Initial startup file state:
{
  "side": "after",
  "phase": "initial",
  "cacheExists": false,
  "cacheIsSymlink": false,
  "configIsSymlink": true,
  "cacheContent": null
}
Action: write .cloud-config-bundle-cache.json.tmp then os.replace over cloud-config-bundle-cache.json.
Stop server, restart against same synthetic home.
Restart file state:
{
  "side": "after",
  "phase": "restart",
  "cacheExists": true,
  "cacheIsSymlink": false,
  "configIsSymlink": true,
  "cacheContent": "{\"synthetic\":\"account-cache\"}\n"
}
No "Failed to create provider instance" entry in restart log.
Web verification after restart: Settings > Providers > second Codex instance; Refresh provider status.
Observed: Codex CLI version detected; Not authenticated (no credentials seeded); no cache file conflict.

Post-refresh filesystem observation:
Shared cache: {"synthetic":"shared-cache"}
Account-local cache: {"synthetic":"account-cache"}
Account cache remains a regular file: True