Fix /frame/image 404: Immich v3 doesn't embed assets in album responses

GET /api/albums/{id} was assumed to return an "assets" array alongside
the album metadata (that's what the original plan/prior art expected),
but on Immich 3.0.3 AlbumResponseDto only has assetCount -- no assets
field at all. Confirmed against the OpenAPI spec served at
/api/spec.json and by testing directly against a real instance: the
assumption was simply wrong for this API version, not a permissions
issue (the album metadata call succeeds fine with a valid 200).

Assets for an album now come from POST /api/search/metadata with an
albumIds filter, which returns them under assets.items. Verified
end-to-end against the real Immich instance and album -- /frame/image
now returns a proper 200 with exactly 192,000 bytes, spread across all
six panel colors (not a degenerate all-white/black response).

Only fetches the first page of search results; fine for a photo frame
cycling through an album, but would need nextPage handling for anyone
pointing this at a very large album.

server/app/immich_client.py

@@ -15,10 +15,23 @@ class ImmichClient:
         resp.raise_for_status()
         return resp.json()
 
-    def get_album(self, album_id: str) -> dict:
-        resp = httpx.get(f"{self.base_url}/api/albums/{album_id}", headers=self._headers, timeout=10)
+    def list_album_assets(self, album_id: str) -> list[dict]:
+        """GET /api/albums/{id} doesn't embed assets in this Immich version
+        (AlbumResponseDto only has assetCount) -- assets live behind the
+        general search API instead, filtered by albumIds.
+
+        Only returns the first page. Fine for a photo frame cycling
+        through an album; worth adding nextPage pagination if someone
+        points this at an album large enough to need it.
+        """
+        resp = httpx.post(
+            f"{self.base_url}/api/search/metadata",
+            headers=self._headers,
+            json={"albumIds": [album_id]},
+            timeout=15,
+        )
         resp.raise_for_status()
-        return resp.json()
+        return resp.json().get("assets", {}).get("items", [])
 
     def download_asset_preview(self, asset_id: str) -> bytes:
         resp = httpx.get(

server/app/main.py

@@ -71,11 +71,10 @@ def frame_image():
 
     client = ImmichClient(cfg.immich_url, cfg.immich_api_key)
     try:
-        album = client.get_album(cfg.album_id)
+        assets = client.list_album_assets(cfg.album_id)
     except httpx.HTTPError as e:
         raise HTTPException(502, f"Could not reach Immich at {cfg.immich_url}: {e}") from e
 
-    assets = album.get("assets", [])
     if not assets:
         raise HTTPException(404, "Album has no photos")