feat(engineering): enforce V1-0 write invariants

docs/architecture/engineering-ontology-v1.md

@@ -159,6 +159,17 @@ Every major object should support fields equivalent to:
 - `created_at`
 - `updated_at`
 - `notes` (optional)
+- `extractor_version` (V1-0)
+- `canonical_home` (V1-0)
+
+**Naming note (V1-0, 2026-04-22).** The AtoCore `entities` table and
+`Entity` dataclass name the project-identifier field `project`, not
+`project_id`. This doc's "fields equivalent to" wording allows that
+naming flexibility — the `project` field on entity rows IS the
+`project_id` per spec. No storage rename is planned; downstream readers
+should treat `entity.project` as the project identifier. This was
+resolved in Codex's third-round audit of the V1 Completion Plan (see
+`docs/plans/engineering-v1-completion-plan.md`).
 
 ## Suggested Status Lifecycle