#880: retry 429 mid-walk when paginating Tidal Favorite Tracks (don't truncate)

The Favorites collection walker (_iter_collection_resource_ids) broke on ANY
non-200 — including a transient 429. So a rate-limit mid-pagination silently
truncated the collection: the log shows `status=429` then `Retrieved 98/100`,
and the mirror saved 98 of a 524-track favorites list. The auto-sync cycle only
"worked" because it dodged the 429. The regular-playlist paginator already
retries 429; the collection walker didn't.

Fix: retry the same cursor page with backoff (5/10/15/20s, 4 attempts) on 429,
mirroring the playlist paginator; 401/403 still bail (+ reconnect flag), other
non-200 still break. Regression tests: 429 mid-walk completes the full chain;
exhausted retries return partial without hanging; 429 doesn't set reconnect.

core/tidal_client.py

@@ -1655,6 +1655,8 @@ class TidalClient:
 
         ids: List[str] = []
         next_path: Optional[str] = None
+        consecutive_429 = 0
+        MAX_PAGE_RETRIES = 4
 
         while True:
             if next_path:
@@ -1687,6 +1689,28 @@ class TidalClient:
                 logger.warning(f"Tidal collection page request failed: {e}")
                 break
 
+            # Rate limited mid-walk → retry the SAME cursor page with backoff
+            # rather than silently truncating the collection. Without this a 429
+            # on page ~5 capped a 513-track favorites list at ~98 (issue #880);
+            # the regular-playlist paginator already retries 429 the same way.
+            if resp.status_code == 429:
+                consecutive_429 += 1
+                if consecutive_429 <= MAX_PAGE_RETRIES:
+                    backoff = 5.0 * consecutive_429  # 5s, 10s, 15s, 20s
+                    logger.warning(
+                        f"Tidal collection {expected_type} rate limited (429) — "
+                        f"retry {consecutive_429}/{MAX_PAGE_RETRIES} in {backoff}s "
+                        f"({len(ids)} fetched so far)"
+                    )
+                    time.sleep(backoff)
+                    continue  # next_path/cursor unchanged → re-request same page
+                logger.error(
+                    f"Tidal collection {expected_type} still rate limited after "
+                    f"{MAX_PAGE_RETRIES} retries — returning {len(ids)} IDs "
+                    f"(PARTIAL: the collection may be larger)"
+                )
+                break
+
             if resp.status_code != 200:
                 # 401/403 = scope/permission issue. Token predates the
                 # `collection.read` scope expansion or the user revoked
@@ -1704,6 +1728,8 @@ class TidalClient:
                     )
                 break
 
+            consecutive_429 = 0  # a good page → reset the retry budget
+
             try:
                 data = resp.json()
             except ValueError as e:

tests/test_tidal_collection_tracks.py

@@ -252,6 +252,55 @@ class TestIterCollectionTrackIds:
 
         assert ids == []
 
+    def test_429_mid_walk_retries_and_completes(self):
+        """Regression for #880: a 429 mid-pagination must RETRY the same
+        cursor page (with backoff), not truncate the collection. Before the
+        fix a transient 429 on page ~5 capped a 513-track favorites list at
+        ~98 (the log showed `status=429` then `Retrieved 98/100`)."""
+        client = _make_authed_client()
+        # page1 (200) → 429 (transient) → page2 (200, end of chain)
+        responses = iter([
+            _FakeResp(200, _PAGE_ONE),
+            _FakeResp(429, text=""),       # rate limited — retry, don't truncate
+            _FakeResp(200, _PAGE_TWO),
+        ])
+        with patch.object(client, '_ensure_valid_token', return_value=True), \
+             patch('core.tidal_client.requests.get', side_effect=lambda *a, **kw: next(responses)), \
+             patch('core.tidal_client.time.sleep'):
+            ids = client._iter_collection_track_ids()
+
+        assert ids == ['1001', '1002', '1003', '1004', '1005']  # full chain, nothing dropped
+
+    def test_429_does_not_set_reconnect_flag(self):
+        """A rate-limit is transient, NOT a scope problem — must not tell the
+        user to reconnect."""
+        client = _make_authed_client()
+        responses = iter([_FakeResp(200, _PAGE_ONE), _FakeResp(429, text=""), _FakeResp(200, _PAGE_TWO)])
+        with patch.object(client, '_ensure_valid_token', return_value=True), \
+             patch('core.tidal_client.requests.get', side_effect=lambda *a, **kw: next(responses)), \
+             patch('core.tidal_client.time.sleep'):
+            client._iter_collection_track_ids()
+
+        assert client.collection_needs_reconnect() is False
+
+    def test_429_exhausts_retries_returns_partial(self):
+        """If the 429s never clear, give up after the retry budget and return
+        what we have (PARTIAL) rather than looping forever."""
+        client = _make_authed_client()
+
+        def gen():
+            yield _FakeResp(200, _PAGE_ONE)
+            while True:
+                yield _FakeResp(429, text="")
+
+        responses = gen()
+        with patch.object(client, '_ensure_valid_token', return_value=True), \
+             patch('core.tidal_client.requests.get', side_effect=lambda *a, **kw: next(responses)), \
+             patch('core.tidal_client.time.sleep'):
+            ids = client._iter_collection_track_ids()
+
+        assert ids == ['1001', '1002', '1003']  # page 1 survives; no hang
+
 
 # ---------------------------------------------------------------------------
 # get_collection_tracks_count