feat(quota-share): add usePoolsUsageAggregate hook for avg util + borrowing count (B/G5)

src/app/(dashboard)/dashboard/costs/quota-share/hooks/usePoolsUsageAggregate.ts

@@ -0,0 +1,75 @@
+"use client";
+
+import { useEffect, useState } from "react";
+import type { QuotaPool } from "@/lib/quota/dimensions";
+import type { PoolUsageSnapshot } from "@/lib/quota/types";
+
+export interface PoolsUsageAggregate {
+  avgUtilizationPercent: number; // 0-100
+  borrowingKeyCount: number;
+  loading: boolean;
+  error: string | null;
+}
+
+const POLL_MS = 15_000;
+
+export function usePoolsUsageAggregate(pools: QuotaPool[]): PoolsUsageAggregate {
+  const [state, setState] = useState<PoolsUsageAggregate>({
+    avgUtilizationPercent: 0,
+    borrowingKeyCount: 0,
+    loading: true,
+    error: null,
+  });
+
+  useEffect(() => {
+    let mounted = true;
+    const ids = pools.map((p) => p.id);
+    if (ids.length === 0) {
+      setState({ avgUtilizationPercent: 0, borrowingKeyCount: 0, loading: false, error: null });
+      return;
+    }
+
+    const fetchAll = async () => {
+      try {
+        const snapshots = await Promise.all(
+          ids.map((id) => fetch(`/api/quota/pools/${id}/usage`).then((r) => (r.ok ? r.json() : null)))
+        );
+        if (!mounted) return;
+        const valid = snapshots.filter((s): s is { usage: PoolUsageSnapshot } => s !== null && !!s.usage);
+        let totalUtil = 0;
+        let utilCount = 0;
+        let borrowing = 0;
+        for (const { usage } of valid) {
+          for (const dim of usage.dimensions) {
+            if (dim.limit > 0) {
+              totalUtil += (dim.consumedTotal / dim.limit) * 100;
+              utilCount += 1;
+            }
+            for (const key of dim.perKey) {
+              if (key.borrowing) borrowing += 1;
+            }
+          }
+        }
+        setState({
+          avgUtilizationPercent: utilCount > 0 ? totalUtil / utilCount : 0,
+          borrowingKeyCount: borrowing,
+          loading: false,
+          error: null,
+        });
+      } catch (err) {
+        if (mounted) {
+          setState((s) => ({ ...s, loading: false, error: err instanceof Error ? err.message : "fetch failed" }));
+        }
+      }
+    };
+
+    void fetchAll();
+    const interval = setInterval(fetchAll, POLL_MS);
+    return () => {
+      mounted = false;
+      clearInterval(interval);
+    };
+  }, [pools.map((p) => p.id).join(",")]); // eslint-disable-line react-hooks/exhaustive-deps
+
+  return state;
+}