fix(growth): make active source canary idempotent

tests/test_external_market_offer_service.py

@@ -797,6 +797,27 @@ def test_targeted_marketplace_canary_activates_and_rollback_quarantines(monkeypa
     assert yahoo["has_runtime_data"] is True
     assert yahoo["write_enabled"] is True
 
+    one_candidate_readback = readback_external_offer_candidates(
+        engine,
+        candidates[:1],
+        source_code="yahoo_shopping",
+        ingestion_method="public_product_jsonld",
+    )
+    idempotent_activation = (
+        canary_service.activate_external_market_source_after_canary(
+            engine,
+            source_code="yahoo_shopping",
+            candidates=candidates[:1],
+            independent_readback=one_candidate_readback,
+            identity=identity,
+            minimum_verified_count=2,
+        )
+    )
+    assert idempotent_activation["status"] == "already_active_verified"
+    assert idempotent_activation["applied"] is True
+    assert idempotent_activation["state_changed"] is False
+    assert idempotent_activation["writes_database_count"] == 0
+
     rollback = canary_service.rollback_external_market_source_canary(
         engine,
         source_code="yahoo_shopping",