fix(intent): fail closed INTENT_V2_DECISION_TIER unknown values to none

Align illegal-tier fallback with PlanTier's conservative policy so
unrecognized values never silently enable V2 query routing.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/intent/flags.go

@@ -59,7 +59,10 @@ func parseV2DecisionTier(raw string) V2DecisionTier {
 	case "all":
 		return V2TierAll
 	default:
-		return V2TierQuery
+		// E-7: fail closed to none, aligned with intentflow.parsePlanTier's
+		// conservative fallback. An unrecognized value must never silently
+		// enable V2 query routing.
+		return V2TierNone
 	}
 }
 

internal/intent/flags_test.go

@@ -23,6 +23,12 @@ func TestTierAllowsRisk(t *testing.T) {
 	}
 }
 
+func TestUnknownV2DecisionTierFailsClosedToNone(t *testing.T) {
+	if parseV2DecisionTier("definitely-not-a-tier") != V2TierNone {
+		t.Fatal("unknown INTENT_V2_DECISION_TIER must fail closed to none, not query")
+	}
+}
+
 func TestBuildV2ShadowReport_MismatchDetection(t *testing.T) {
 	SetFeatureFlagsForTest(FeatureFlags{IntentV2Shadow: true})
 	defer ResetFeatureFlagsForTest()