Fix infinite update loop crashing the map (React error #185) (#34)

MediaMarkers.tsx was passing an inline arrow function as markerRef,
giving it a new identity on every render. useClusterer relies on ref
callback identity staying stable per marker (documented in its own
comment) - a fresh function each render makes React detach/reattach
every AdvancedMarker's ref on every render, which triggers the
setMarkers state update in a loop and blows past React's max update
depth, crashing the whole page with any geotagged media on the map.

Fixed by caching one stable ref-callback function per post id (same
pattern useClusterer itself uses internally), reading the post to tag
onto the marker from a ref instead of capturing it in a new closure.

Verified: npm run build, npm run lint.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: TomProkop

src/components/RouteMap/MediaMarkers.tsx

@@ -1,5 +1,6 @@
-import { useState } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import { useMap } from '@vis.gl/react-google-maps';
+import type { Marker } from '@googlemaps/markerclusterer';
 import { useMediaPosts, type MediaPost } from '../../hooks/useMediaPosts';
 import MediaMarker from './MediaMarker';
 import MediaLightbox from '../MediaLightbox';
@@ -14,21 +15,37 @@ export default function MediaMarkers() {
   const map = useMap();
   const setMediaMarkerRef = useClusterer(map, mediaClusterRenderer);
 
+  // Keeps the tagging ref callback below stable in identity (see caveat
+  // on useClusterer: a new function per render causes React to detach/
+  // reattach every AdvancedMarker's ref on every single render, which
+  // triggers an infinite setState loop in useClusterer). The post is
+  // read from this ref instead of being captured directly so the
+  // wrapper function itself never needs to change.
+  const postsById = useRef<Record<string, MediaPost>>({});
+  useEffect(() => {
+    const next: Record<string, MediaPost> = {};
+    for (const post of geotagged) next[post.id] = post;
+    postsById.current = next;
+  }, [geotagged]);
+
+  const taggingRefs = useRef<Record<string, (marker: Marker | null) => void>>({});
+  function getTaggingRef(id: string) {
+    if (!taggingRefs.current[id]) {
+      taggingRefs.current[id] = (marker: Marker | null) => {
+        // Tag the raw marker instance with its post so the cluster
+        // renderer (which only receives marker instances, not our
+        // React props) can pick a thumbnail to show on the bubble.
+        if (marker) Object.assign(marker, { __mediaPost: postsById.current[id] });
+        setMediaMarkerRef(id)(marker);
+      };
+    }
+    return taggingRefs.current[id];
+  }
+
   return (
     <>
       {geotagged.map((post) => (
-        <MediaMarker
-          key={post.id}
-          post={post}
-          onClick={() => setSelected(post)}
-          markerRef={(marker) => {
-            // Tag the raw marker instance with its post so the cluster
-            // renderer (which only receives marker instances, not our
-            // React props) can pick a thumbnail to show on the bubble.
-            if (marker) Object.assign(marker, { __mediaPost: post });
-            setMediaMarkerRef(post.id)(marker);
-          }}
-        />
+        <MediaMarker key={post.id} post={post} onClick={() => setSelected(post)} markerRef={getTaggingRef(post.id)} />
       ))}
       {selected && <MediaLightbox post={selected} onClose={() => setSelected(null)} />}
     </>