docs-frontmatter-cleanup: the 11 invalid last_updated frontmatter scalars quoted — double-quote convention applied uniformly (one escaped quote in phase-0.md), annotation prose verbatim; PyYAML sweep over docs/**/*.md + tasks/*.md reports 0 failures, taskgraph validate green (79 tasks); task status -> completed with Notes (recorded sweep command, date-scalar caveat) + Summary

docs/architecture/core-contract.md

@@ -1,8 +1,8 @@
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 status: draft
-last_updated: 2026-10-10 (ADR-024 — the mem engine joins the family;
+last_updated: "2026-10-10 (ADR-024 — the mem engine joins the family;
 the Store concept prose admits the engine-native constructor
-exception)
+exception)"
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 # Core contract