Relax legacy ContractClock receipt constraint

db/migrations/003_relax_legacy_receipt_skill.sql

@@ -0,0 +1,18 @@
+-- Migration 002 may already have run on a legacy database before its
+-- skill_name constraint reconciliation was added. Relax that obsolete column
+-- in a separately versioned migration so current installations are repaired.
+DO $$
+BEGIN
+    IF EXISTS (
+        SELECT 1
+        FROM information_schema.columns
+        WHERE table_schema = current_schema()
+          AND table_name = 'execution_receipts'
+          AND column_name = 'skill_name'
+          AND is_nullable = 'NO'
+    ) THEN
+        EXECUTE 'ALTER TABLE execution_receipts
+                 ALTER COLUMN skill_name DROP NOT NULL';
+    END IF;
+END
+$$;