fix(quota): apply the equal-split fallback in the pool usage snapshot (#13159)

The equal-split fallback was applied when computing allocations but not when building the pool usage snapshot, so `sqliteQuotaStore.ts:201` still read `totalWeight > 0 ? alloc.weight : 0` — a zero-weight pool reported every member at 0 instead of its equal share. Probe on your head: 9/9 pass in `tests/unit/quota-pool-usage-equal-split.test.ts`, with the bug confirmed unfixed on the tip.

Thanks, @datrixlab — fixing the snapshot path and not just the allocation path is the part that makes the dashboard numbers agree with the enforcement.

**Batch validation** — boarded with the other 10 PRs of your batch into one worktree cut from `release/v3.8.51`; every PR verified as an ancestor of the combined HEAD before validating.

- Focused tests across all 11 PRs: **104/104 pass** on the combined tree.
- Gates on the combined tree: `check-changelog-integrity` PASS, `check-complexity` PASS, `check-cognitive-complexity` PASS, `typecheck:core` PASS, `check:open-sse-typecheck` PASS.
- `check-file-size` is red, but reproduces with byte-identical line counts on the pure `release/v3.8.51` tip (`open-sse/handlers/imageGeneration.ts` 3304, `open-sse/services/combo/roundRobinCombo.ts` 1221, `open-sse/utils/stream.ts` 3115). Inherited base-red, nothing added by this batch — it is also why this PR's "Fast Quality Gates" check was red.

src/lib/quota/redisQuotaStore.ts

@@ -271,7 +271,13 @@ export class RedisQuotaStore implements QuotaStore {
         const consumed = await this.peek(alloc.apiKeyId, dim);
         consumedTotal += consumed;
 
-        const effectiveWeight = totalWeight > 0 ? alloc.weight : 0;
+        // Equal-split fallback, matching enforce.ts: when every allocation in the
+        // pool has weight 0, each counts as an equal share, so the snapshot
+        // describes the budget enforcement actually grants. The old ternary could
+        // not do this -- totalWeight === 0 implies every alloc.weight is 0, so both
+        // arms returned 0 -- and every key rendered as borrowing all it consumed.
+        const effectiveWeight =
+          totalWeight > 0 ? alloc.weight : allocations.length > 0 ? 100 / allocations.length : 0;
         const fairShare = (effectiveWeight / 100) * planDim.limit;
         const deficit = consumed - fairShare;
         const borrowing = consumed > fairShare;

src/lib/quota/sqliteQuotaStore.ts

@@ -198,7 +198,13 @@ export class SqliteQuotaStore implements QuotaStore {
         const consumed = await this.peek(alloc.apiKeyId, dim);
         consumedTotal += consumed;
 
-        const effectiveWeight = totalWeight > 0 ? alloc.weight : 0;
+        // Equal-split fallback, matching enforce.ts: when every allocation in the
+        // pool has weight 0, each counts as an equal share, so the snapshot
+        // describes the budget enforcement actually grants. The old ternary could
+        // not do this -- totalWeight === 0 implies every alloc.weight is 0, so both
+        // arms returned 0 -- and every key rendered as borrowing all it consumed.
+        const effectiveWeight =
+          totalWeight > 0 ? alloc.weight : allocations.length > 0 ? 100 / allocations.length : 0;
         const fairShare = (effectiveWeight / 100) * planDim.limit;
         const deficit = consumed - fairShare;
         const borrowing = consumed > fairShare;

tests/unit/quota-pool-usage-equal-split.test.ts

@@ -0,0 +1,159 @@
+/**
+ * tests/unit/quota-pool-usage-equal-split.test.ts
+ *
+ * Regression: enforce.ts applies an equal-split fallback when every allocation
+ * in a pool has weight 0 (see quota-equal-split.test.ts), but neither quota
+ * store did the same in poolUsageWithDimensions. GET /api/quota/pools/[id]/usage
+ * therefore reported fairShare = 0 for every key in such a pool, so each one
+ * rendered as borrowing its entire consumption while enforcement was happily
+ * granting it 100/N of the budget. Same pool, two answers.
+ *
+ * The tell was that the store's ternary could not do anything: weights are
+ * non-negative, so `totalWeight === 0` implies every `alloc.weight` is already
+ * 0, and `totalWeight > 0 ? alloc.weight : 0` returned `alloc.weight` either
+ * way. The branch existed exactly where the fallback belonged.
+ *
+ * This is the same divergence class as quota-pool-usage-summed-budget.test.ts,
+ * which corrected the accountCount side of the enforce↔usage split.
+ *
+ * Levels:
+ *   A (structural): both stores compute effectiveWeight with the equal-split
+ *     fallback, in the same shape enforce.ts uses, and the no-op form is gone.
+ *   B (logic): replicate the store's per-key math to prove the fallback fixes
+ *     fairShare and clears the bogus borrowing flag, and that pools with real
+ *     weights are untouched.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const ROOT = join(fileURLToPath(import.meta.url), "..", "..", "..");
+const read = (rel: string) => readFileSync(join(ROOT, rel), "utf8");
+
+const STORES = [
+  "src/lib/quota/sqliteQuotaStore.ts",
+  "src/lib/quota/redisQuotaStore.ts",
+] as const;
+
+// ---------------------------------------------------------------------------
+// Level A — structural: both stores carry the enforce.ts fallback
+// ---------------------------------------------------------------------------
+
+for (const store of STORES) {
+  test(`${store} applies the equal-split fallback to effectiveWeight`, () => {
+    const src = read(store);
+    assert.ok(
+      /100 \/ allocations\.length/.test(src),
+      "store must fall back to an equal 100/N share when the pool has no weights"
+    );
+    assert.ok(
+      /allocations\.length > 0\s*\?\s*100 \/ allocations\.length\s*:\s*0/.test(src),
+      "the equal split must guard against an empty allocation list, like enforce.ts"
+    );
+  });
+
+  test(`${store} no longer zeroes effectiveWeight when the pool has no weights`, () => {
+    const src = read(store);
+    assert.ok(
+      !/const effectiveWeight = totalWeight > 0 \? alloc\.weight : 0;/.test(src),
+      "the old ternary was a no-op and must not come back"
+    );
+  });
+}
+
+test("enforce.ts is still the shape the stores are mirroring", () => {
+  const src = read("src/lib/quota/enforce.ts");
+  assert.ok(
+    /allocCount > 0\s*\?\s*100 \/ allocCount\s*:\s*0/.test(src),
+    "enforce.ts must keep the equal-split fallback the stores now mirror"
+  );
+});
+
+// ---------------------------------------------------------------------------
+// Level B — logic: the fallback corrects fairShare and the borrowing flag
+//
+// Replicates the per-key math from poolUsageWithDimensions:
+//   fairShare = (effectiveWeight / 100) × planDim.limit
+//   deficit   = consumed - fairShare
+//   borrowing = consumed > fairShare
+// ---------------------------------------------------------------------------
+
+/** The store's per-key snapshot, parameterised by the effectiveWeight rule. */
+function perKey(
+  allocations: Array<{ weight: number }>,
+  index: number,
+  limit: number,
+  consumed: number,
+  withFallback: boolean
+) {
+  const totalWeight = allocations.reduce((sum, a) => sum + a.weight, 0);
+  const alloc = allocations[index]!;
+  const effectiveWeight = withFallback
+    ? totalWeight > 0
+      ? alloc.weight
+      : allocations.length > 0
+        ? 100 / allocations.length
+        : 0
+    : totalWeight > 0
+      ? alloc.weight
+      : 0;
+  const fairShare = (effectiveWeight / 100) * limit;
+  return { fairShare, deficit: consumed - fairShare, borrowing: consumed > fairShare };
+}
+
+test("all-zero pool: the snapshot now grants the same share enforcement does", () => {
+  const allocations = [{ weight: 0 }, { weight: 0 }];
+  const LIMIT = 1000;
+  const CONSUMED = 100;
+
+  const before = perKey(allocations, 0, LIMIT, CONSUMED, false);
+  assert.equal(before.fairShare, 0, "sanity: the bug gave every key a zero share");
+  assert.equal(before.deficit, CONSUMED, "sanity: the whole consumption read as a deficit");
+  assert.equal(before.borrowing, true, "sanity: every key was flagged as borrowing");
+
+  const after = perKey(allocations, 0, LIMIT, CONSUMED, true);
+  assert.equal(after.fairShare, 500, "two unweighted keys split the limit evenly");
+  assert.equal(after.deficit, -400, "a key inside its share runs a negative deficit");
+  assert.equal(after.borrowing, false, "and must not be flagged as borrowing");
+});
+
+test("all-zero pool: the snapshot share matches what enforce.ts computes", () => {
+  const allocations = [{ weight: 0 }, { weight: 0 }, { weight: 0 }, { weight: 0 }];
+  const LIMIT = 1000;
+
+  // enforce.ts: effectiveWeight = 100 / allocCount when poolTotalWeight === 0
+  const enforced = (100 / allocations.length / 100) * LIMIT;
+  const snapshot = perKey(allocations, 2, LIMIT, 0, true).fairShare;
+
+  assert.equal(snapshot, enforced, "usage and enforcement must agree on the fair share");
+  assert.equal(snapshot, 250, "four unweighted keys get a quarter each");
+});
+
+test("weighted pools are untouched by the fallback", () => {
+  const allocations = [{ weight: 70 }, { weight: 30 }];
+  const LIMIT = 1000;
+
+  for (const index of [0, 1]) {
+    const before = perKey(allocations, index, LIMIT, 0, false);
+    const after = perKey(allocations, index, LIMIT, 0, true);
+    assert.equal(after.fairShare, before.fairShare, "a weighted pool keeps its shares");
+  }
+  assert.equal(perKey(allocations, 0, LIMIT, 0, true).fairShare, 700);
+  assert.equal(perKey(allocations, 1, LIMIT, 0, true).fairShare, 300);
+});
+
+test("a pool where one key carries all the weight still starves the rest", () => {
+  // totalWeight > 0, so the fallback must not engage: a 0-weight key next to a
+  // weighted one is a deliberate allocation, not an unconfigured pool.
+  const allocations = [{ weight: 100 }, { weight: 0 }];
+  const LIMIT = 1000;
+
+  assert.equal(perKey(allocations, 0, LIMIT, 0, true).fairShare, 1000);
+  assert.equal(
+    perKey(allocations, 1, LIMIT, 0, true).fairShare,
+    0,
+    "an explicitly unweighted key in a weighted pool keeps its zero share"
+  );
+});