docs(agents): record map pin rendering perf fix (signature guard + batched addLayers)

AGENTS.md

@@ -522,6 +522,21 @@ session with **no other memory of this project**. So:
   hand. Publishing with no photo is allowed; the spot stays **Unverified**
   (`SpotDetailPage` badge), the success toast says so, and the review queue's
   'no photo' flag lets a human look later. The pre-submit checklist still nudges.
+- **Map pin rendering (perf, 2026-09-29):** the spot/tour/event/crew marker
+  effect in `SpotMap.tsx` used to `clearLayers()` + rebuild **every** marker
+  whenever the parent handed it fresh arrays, and added each marker with a
+  per-marker `clusterGroup.addLayer()` (each call re-clusters the whole set) —
+  several synchronous full rebuilds per load on a few-hundred-pin map. Now:
+  (1) a **marker signature** (group geohash + spot/listing event ids + weather
+  colour/icon + layer toggles) short-circuits the effect when nothing that
+  affects the rendered pins changed — ids are enough because spot/listing/tour/
+  event/crew are all **addressable** (a new id on every edit), so unrelated array
+  churn (trust scores, comment/zap totals, re-sorts) no longer rebuilds the map;
+  (2) markers are collected and added with the plugin's bulk **`addLayers()` in
+  `requestAnimationFrame` batches of 150**, cancelled on effect re-run. One
+  cluster refresh per batch, pins paint progressively, main thread stays free.
+  **If you change what a marker renders, add it to the signature** or the update
+  will be skipped. `showSpots/showShops/showGear` are now effect deps.
 - **Empty-map nudge (2026-09-28):** `MapPage` distinguishes the two empties — the
   existing "No spots match" card is for *filters* (`filteredSpots.length === 0 &&
   allLocations.length > 0`) and a new "No spots mapped yet — be the first" card