fix(activity-log): no spinner flash on instant filtering

- re-query keeps current rows visible instead of clearing + showing the full 'Loading' spinner
- loading affordance is delayed ~180ms: instant responses show nothing; slow ones get a subtle dim (aria-busy)
- full spinner reserved for the genuine first load; append (load-more) shows no indicator

server/src/ledgrab/static/css/activity-log.css

@@ -577,6 +577,16 @@
     min-height: 0;
 }
 
+/* Subtle busy state while a slow re-query is in flight: the current rows stay
+   visible (no spinner flash) but dim slightly and stop accepting clicks until
+   the fresh results swap in. Only applied after a short delay, so instant
+   filtering shows nothing. */
+.al-list-container.al-busy {
+    opacity: 0.55;
+    pointer-events: none;
+    transition: opacity var(--duration-fast) var(--ease-out);
+}
+
 /* ── Tabular-nums utility ────────────────────────────────────────────────── */
 
 .tabular-nums { font-variant-numeric: tabular-nums; }

server/src/ledgrab/static/js/features/activity-log.ts

@@ -74,6 +74,13 @@ let _total = 0;
 let _expandedIds = new Set<string>();
 let _debounceTimer: ReturnType<typeof setTimeout> | null = null;
 let _liveEventListener: ((e: Event) => void) | null = null;
+// Loading UX: `_showSpinner` gates the full-panel spinner so it only appears
+// after a short delay (slow requests), never flashing on instant filtering.
+// `_hasLoadedOnce` distinguishes the genuine first load (spinner immediately)
+// from re-queries (keep current rows, subtle delayed busy hint).
+let _loadingDelayTimer: ReturnType<typeof setTimeout> | null = null;
+let _showSpinner = false;
+let _hasLoadedOnce = false;
 
 const _filters: ActiveFilters = {
     categories: [],
@@ -353,7 +360,7 @@ function _renderFilterToolbar(): string {
 // ─── List and state rendering ────────────────────────────────
 
 function _renderList(): string {
-    if (_loading && _entries.length === 0) {
+    if (_showSpinner && _entries.length === 0) {
         return `<div class="al-state al-loading" role="status" aria-live="polite">
     <div class="al-spinner"></div>
     <span>${escapeHtml(t('activity_log.loading'))}</span>
@@ -496,15 +503,58 @@ function _updateListContainer(): void {
 
 // ─── Data fetching ───────────────────────────────────────────
 
+/** Surface a loading affordance only when a request is slow enough to notice. */
+function _showDelayedBusy(): void {
+    if (!_loading) return;
+    if (_entries.length === 0) {
+        // Nothing to keep on screen — fall back to the full spinner.
+        _showSpinner = true;
+        _updateListContainer();
+    } else {
+        // Re-query of a populated list: keep the current rows, just dim them.
+        const c = document.getElementById('al-list-container');
+        c?.classList.add('al-busy');
+        c?.setAttribute('aria-busy', 'true');
+    }
+}
+
+/** Clear all loading affordances (timer, spinner flag, busy dim). Idempotent. */
+function _clearBusy(): void {
+    if (_loadingDelayTimer) {
+        clearTimeout(_loadingDelayTimer);
+        _loadingDelayTimer = null;
+    }
+    _showSpinner = false;
+    const c = document.getElementById('al-list-container');
+    c?.classList.remove('al-busy');
+    c?.removeAttribute('aria-busy');
+}
+
 async function _fetchPage(beforeSeq: number | null = null, append = false): Promise<void> {
     if (_loading) return;
     _loading = true;
     if (!append) {
-        _entries = [];
+        // Reset the cursor for a fresh query, but DON'T clear `_entries` — keep
+        // the current rows on screen so filtering an already-populated list
+        // never flashes the full "Loading" state (the new results replace them
+        // on arrival).
         _nextBeforeSeq = null;
         _hasMore = false;
     }
-    _updateListContainer();
+
+    if (!_hasLoadedOnce && !append) {
+        // Genuine first load — there's nothing to show yet, so the spinner is
+        // the correct (and expected) initial state. Show it immediately.
+        _showSpinner = true;
+        _updateListContainer();
+    } else if (!append) {
+        // Re-query (filter change / language change): defer any loading hint so
+        // near-instant responses show nothing at all; a slow request gets a
+        // subtle dim after the delay.
+        if (_loadingDelayTimer) clearTimeout(_loadingDelayTimer);
+        _loadingDelayTimer = setTimeout(_showDelayedBusy, 180);
+    }
+    // append (load-more): keep existing rows, no loading indicator.
 
     try {
         const qs = _buildQuery(beforeSeq);
@@ -524,15 +574,16 @@ async function _fetchPage(beforeSeq: number | null = null, append = false): Prom
         _nextBeforeSeq = page.next_before_seq;
         _hasMore = page.has_more;
         _total = page.total;
-        // Reset the loading flag BEFORE rendering: _renderList() shows the
-        // spinner whenever (_loading && _entries.length === 0), so a zero-result
-        // page (e.g. an unmatched entity-type filter, or a fresh install) would
-        // otherwise render the spinner here and spin forever — the finally below
-        // clears _loading but does not re-render.
+        _hasLoadedOnce = true;
+        // Clear loading affordances BEFORE rendering so a zero-result page
+        // renders the empty state (not the spinner) and a re-query swaps in the
+        // fresh, undimmed rows.
+        _clearBusy();
         _loading = false;
         _updateListContainer();
     } catch (e: unknown) {
         if (e && typeof e === 'object' && 'isAuth' in e) return;
+        _clearBusy();
         const container = document.getElementById('al-list-container');
         if (container) {
             container.innerHTML = `<div class="al-state al-error" role="alert">
@@ -542,6 +593,7 @@ async function _fetchPage(beforeSeq: number | null = null, append = false): Prom
         }
     } finally {
         _loading = false;
+        _clearBusy();
     }
 }