Environment: Linux; real T3 dev server; fresh synthetic T3 home; T3CODE_DEV_SEED=0
Commit: 6ba3de70aff98460e573ffc57773e45e148026ba
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": "before",
  "phase": "initial",
  "cacheExists": true,
  "cacheIsSymlink": true,
  "configIsSymlink": true,
  "cacheContent": "{\"synthetic\":\"shared-cache\"}\n"
}
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": "before",
  "phase": "restart",
  "cacheExists": true,
  "cacheIsSymlink": false,
  "configIsSymlink": true,
  "cacheContent": "{\"synthetic\":\"account-cache\"}\n"
}
Actual server startup error:
ERROR (#28): Failed to create provider instance
  {
    instanceId: 'codex_work',
    driver: 'codex',
    detail: "Cannot create Codex shadow home entry 'cloud-config-bundle-cache.json' because '<shadow-home>/cloud-config-bundle-cache.json' already exists and is not a symlink."
  }
Web verification after restart: Settings > Providers > second Codex instance; Refresh provider status.
Observed: Disabled; cache file conflict reported.

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