fix(rate-limits): treat empty policies as unlimited

apps/api/internal/store/rate_limit_status_test.go

@@ -16,6 +16,7 @@ func TestEffectiveModelRateLimitPolicyTreatsModelRulesAsAuthoritative(t *testing
 			map[string]any{"metric": "tpm_total", "limit": 240000},
 			map[string]any{"metric": "concurrent", "limit": 6},
 		}},
+		"runtime-policy-1",
 		map[string]any{},
 		map[string]any{"rules": []any{
 			map[string]any{"metric": "rpm", "limit": 30},
@@ -34,6 +35,48 @@ func TestEffectiveModelRateLimitPolicyTreatsModelRulesAsAuthoritative(t *testing
 	}
 }
 
+func TestEffectiveModelRateLimitPolicyTreatsEmptyRuntimePolicyAsUnlimited(t *testing.T) {
+	policy := effectiveModelRateLimitPolicy(
+		map[string]any{"rules": []any{
+			map[string]any{"metric": "rpm", "limit": 500},
+			map[string]any{"metric": "tpm_total", "limit": 100000},
+		}},
+		map[string]any{"rules": []any{}},
+		"runtime-policy-1",
+		map[string]any{},
+		map[string]any{},
+	)
+
+	if got := rateLimitForMetric(policy, "rpm"); got != 0 {
+		t.Fatalf("expected empty runtime policy rpm to mean unlimited, got %v", got)
+	}
+	if got := rateLimitForMetric(policy, "tpm_total"); got != 0 {
+		t.Fatalf("expected empty runtime policy tpm to mean unlimited, got %v", got)
+	}
+}
+
+func TestEffectiveModelRateLimitPolicyTreatsNegativeLimitAsUnlimited(t *testing.T) {
+	policy := effectiveModelRateLimitPolicy(
+		map[string]any{"rules": []any{
+			map[string]any{"metric": "rpm", "limit": 500},
+		}},
+		map[string]any{"rules": []any{
+			map[string]any{"metric": "rpm", "limit": -1},
+		}},
+		"runtime-policy-1",
+		map[string]any{},
+		map[string]any{},
+	)
+
+	if got := rateLimitForMetric(policy, "rpm"); got != -1 {
+		t.Fatalf("expected negative runtime rpm marker to be preserved, got %v", got)
+	}
+	status := metricStatus(10, 10, 0, rateLimitForMetric(policy, "rpm"), "")
+	if status.Limited {
+		t.Fatalf("expected negative runtime rpm marker to be reported as unlimited, got %+v", status)
+	}
+}
+
 func TestPriorityDemotionRecordFromEventPayloadKeepsReason(t *testing.T) {
 	createdAt := time.Date(2026, 5, 12, 9, 30, 0, 0, time.UTC)
 	record := priorityDemotionRecordFromEventPayload("event-1", "task-1", "fallback message", map[string]any{