Start Core Hub FastAPI replacement foundation

docs/specs/contract-governance.md

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+# Contract Governance
+
+Core Hub contracts change through workplans, not incidental implementation edits.
+
+## Change Rule
+
+Any change to a route, schema, event type, manifest field, fixture, or catalog entry must record:
+
+- affected contract artifact;
+- compatibility impact;
+- known consumers;
+- migration or cancellation path;
+- test or smoke evidence.
+
+## Compatibility Notes
+
+Compatibility notes belong beside the relevant spec or fixture. A compatibility note must say whether behavior is preserved, replaced, deprecated, or intentionally cancelled.
+
+## Review Rhythm
+
+Regular self-optimization reviews should look for recurring error states, workarounds that should become product behavior, redundant information passing, overly complex handoffs, and slow validation loops. Findings become workplans when they need code, contract, or operational changes.