feat(search): Nominatim as the last-resort geocoder (#573)

Supersedes #350 by @sendmebits, ported onto the current component layout with fixes from review.

Verified before merge: format, package boundaries, unit suite, build, and the browser tracking suite; a browser harness for the change where one applies; adversarial review applied.

Co-authored-by: sendmebits <[email protected]>

src/search/defaults.js

@@ -8,8 +8,8 @@ import { createPresetGeocoder } from './presetGeocoder.js';
 
 /**
  * Coordinates and bundled names first — both answer offline and with no key —
- * then Google when configured, then keyless Photon. Transport stays local to
- * setup.
+ * then Google when configured, then keyless Photon, then the local Nominatim
+ * route as a last resort. Transport stays local to setup.
  *
  * `presets` is the caller's bundled place data. It is passed in rather than
  * imported so this package keeps reading no application state; with none
@@ -43,6 +43,21 @@ export function createDefaultPlaceSearch({
         },
       }),
       createPhotonGeocoder({ fetchImpl, endpoint: endpoints.photon }),
+      // Last resort: the local Nominatim route, which answers with no key when
+      // neither of the two above did. It speaks the same result shape, so it
+      // rides the existing Google adapter rather than needing its own.
+      createGoogleGeocoder({
+        request(query, { bias, signal }) {
+          const params = new URLSearchParams({ q: query });
+          if (bias) params.set('bounds', bias);
+          return fetchImpl(
+            `${endpoints.nominatim || '/api/geocode'}?${params}`,
+            {
+              signal,
+            },
+          );
+        },
+      }),
     ],
   });
   return {