feat(perf): cover pipeline throughput (cpm) in performance probe (#945)

* feat(perf): cover pipeline throughput (cpm) in performance probe

Mirror the analysis pipeline's tpm for covers. A new coverPerfStore samples the
backfill `done` progress from cover:library-progress events and derives a rolling
one-minute covers-per-minute rate. Surfaced as a live diag in perfLiveStore, a
pinnable "Cover backfill" throughput card in the Monitor tab, and a cpm row in
the Cover pipeline overlay block.

* docs(changelog): note cover pipeline cpm metric (PR #945)

Add CHANGELOG entry and credits line for the cover-pipeline covers-per-minute
throughput metric in the Performance Probe.

src/hooks/useCoverPerfListener.ts

@@ -0,0 +1,39 @@
+import { useEffect } from 'react';
+import { listen } from '@tauri-apps/api/event';
+import { recordCoverProgress } from '../utils/perf/coverPerfStore';
+
+type CoverLibraryProgressPayload = {
+  serverIndexKey?: string;
+  done?: number;
+  total?: number;
+  pending?: number;
+};
+
+/** Wire Rust `cover:library-progress` events into the cover perf store. */
+export function useCoverPerfListener(active: boolean): void {
+  useEffect(() => {
+    if (!active) return;
+    let cancelled = false;
+    let unlisten: (() => void) | undefined;
+    void listen<CoverLibraryProgressPayload>('cover:library-progress', ({ payload }) => {
+      if (cancelled || typeof payload?.done !== 'number') return;
+      recordCoverProgress({
+        done: payload.done,
+        total: payload.total,
+        pending: payload.pending,
+      });
+    })
+      .then(fn => {
+        if (cancelled) {
+          fn();
+          return;
+        }
+        unlisten = fn;
+      })
+      .catch(() => {});
+    return () => {
+      cancelled = true;
+      unlisten?.();
+    };
+  }, [active]);
+}

src/hooks/useSidebarPerfProbe.ts

@@ -3,6 +3,7 @@ import { acquirePerfLivePoll, patchPerfLiveAnalysis } from '../utils/perf/perfLi
 import { setPerfProbeTelemetryActive } from '../utils/perf/perfTelemetry';
 import { useAnalysisPerfLast } from '../utils/perf/analysisPerfStore';
 import { useAnalysisPerfListener } from './useAnalysisPerfListener';
+import { useCoverPerfListener } from './useCoverPerfListener';
 import {
   getPerfProbeFlags,
   subscribePerfProbeFlags,
@@ -31,14 +32,28 @@ function useNeedAnalysisTelemetry(perfProbeOpen: boolean, livePins: ReadonlySet<
   );
 }
 
+function useNeedCoverTelemetry(perfProbeOpen: boolean, livePins: ReadonlySet<string>): boolean {
+  return useSyncExternalStore(
+    subscribePerfProbeFlags,
+    () => (
+      perfProbeOpen
+      || getPerfProbeFlags().showCoverPerfOverlay
+      || livePins.has('cover:cpm')
+    ),
+    () => perfProbeOpen,
+  );
+}
+
 /** Wires Ctrl+Shift+D probe modal and shared live metric polling. */
 export function useSidebarPerfProbe(): Result {
   const [perfProbeOpen, setPerfProbeOpen] = useState(false);
   const livePins = usePerfLiveOverlayPins();
   const analysisLast = useAnalysisPerfLast();
   const needAnalysis = useNeedAnalysisTelemetry(perfProbeOpen, livePins);
+  const needCover = useNeedCoverTelemetry(perfProbeOpen, livePins);
 
   useAnalysisPerfListener(needAnalysis);
+  useCoverPerfListener(needCover);
 
   useEffect(() => {
     setPerfProbeTelemetryActive(perfProbeOpen);