After F3 of the sync field-meta overhaul, every read of "last modified"
goes through `deriveUpdatedAt(record)` over `__fieldMeta`. The legacy
`updatedAt` field on existing IndexedDB rows was deliberately left in
place by v53 (its comment explicitly defers the row-rewrite to a later
cleanup) so the cut-over could proceed without a full DB rewrite.
This v55 upgrade walks every sync-relevant table (`Object.keys(TABLE_TO_APP)`)
and `delete row.updatedAt`. Idempotent (rows without the field are a
no-op), best-effort (try/catch per table guards against a registry
entry that doesn't yet have a Dexie store row).
Local-only tables (_pendingChanges, _activity, _clientIdentity,
_aiDebugLog) never carried `updatedAt`, so they stay out of the sweep.
Plan: docs/plans/sync-field-meta-overhaul.md (F3-fu row in Shipping Log).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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