feat: improve model rate limit tracking

apps/api/internal/store/rate_limit_status_test.go

@@ -0,0 +1,32 @@
+package store
+
+import "testing"
+
+func TestEffectiveModelRateLimitPolicyTreatsModelRulesAsAuthoritative(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{
+			map[string]any{"metric": "rpm", "limit": 120},
+			map[string]any{"metric": "tpm_total", "limit": 240000},
+			map[string]any{"metric": "concurrent", "limit": 6},
+		}},
+		map[string]any{},
+		map[string]any{"rules": []any{
+			map[string]any{"metric": "rpm", "limit": 30},
+			map[string]any{"metric": "concurrent", "limit": 2},
+		}},
+	)
+
+	if got := rateLimitForMetric(policy, "rpm"); got != 30 {
+		t.Fatalf("expected model rpm limit to win, got %v", got)
+	}
+	if got := rateLimitForMetric(policy, "concurrent"); got != 2 {
+		t.Fatalf("expected model concurrent limit to win, got %v", got)
+	}
+	if got := rateLimitForMetric(policy, "tpm_total"); got != 0 {
+		t.Fatalf("expected missing model tpm limit to mean unlimited, got %v", got)
+	}
+}