Album tagging for Musicbrainz single import

[jjmeist]

Fixes #5886

This PR resolves an issue where standalone tracks imported via item_candidates() were missing album information even when the MusicBrainz API response included a release-list.

Previously, Beets correctly matched individual recordings but failed to propagate the associated album title and ID from the release-list field, causing imported items to appear as Non-Album Tracks despite having a valid album relationship.
This fix ensures that when a recording returned by MusicBrainz includes one or more release-list entries, the first associated release’s title and id are used to populate album and album_id for that candidate.

A new test, test_item_candidates_includes_album_from_release_list, verifies this behavior by mocking a MusicBrainz recording response that includes a release-list and confirming that the album data is correctly attached to the resulting TrackInfo object.

[ ]Documentation (N/A — behavior fix, no user-facing config changes).
[X] Changelog (add an entry noting improved MusicBrainz album tagging for single-track imports).
[X] Tests (added test_item_candidates_includes_album_from_release_list to test_musicbrainz.py).

[sourcery-ai]

Hey there - I've reviewed your changes and they look great!

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location> `beetsplug/musicbrainz.py:522` </location>
<code_context>
+        rel_list = recording.get("release-list") or recording.get("release_list")
+        if rel_list:
+            # Pick the first release as a reasonable default.
+            rel0 = rel_list[0] or {}
+            # Handle both shapes: {'id','title',...} or {'release': {'id','title',...}}
+            rel0_dict = rel0.get("release", rel0)
</code_context>

<issue_to_address>
**issue (bug_risk):** Guard against empty release lists to prevent IndexError.

Accessing rel_list[0] without checking if rel_list is non-empty can cause an IndexError. Add a check to ensure rel_list contains elements before accessing its first item.
</issue_to_address>

### Comment 2
<location> `beetsplug/musicbrainz.py:861-871` </location>
<code_context>
         criteria = {"artist": artist, "recording": title, "alias": title}
+        results = self._search_api("recording", criteria)
+
+        for r in results:
+            rec_id = r.get("id") or r.get("recording", {}).get("id")
+            if not rec_id:
+                continue
+            try:
+                ti = self.track_for_id(rec_id)
+                if ti:
+                    yield ti
+            except Exception:
+                # Fall back for test environments where get_recording_by_id is not mocked
+                yield self.track_info(r)

-        yield from filter(
</code_context>

<issue_to_address>
**suggestion:** Consider logging or surfacing exceptions for better debugging.

Silent exception handling in item_candidates may hide errors. Logging exceptions or adding context will make troubleshooting easier.

```suggestion
        import logging

        for r in results:
            rec_id = r.get("id") or r.get("recording", {}).get("id")
            if not rec_id:
                continue
            try:
                ti = self.track_for_id(rec_id)
                if ti:
                    yield ti
            except Exception as exc:
                logging.exception(
                    f"Exception in item_candidates for recording ID '{rec_id}': {exc}"
                )
                # Fall back for test environments where get_recording_by_id is not mocked
                yield self.track_info(r)
```
</issue_to_address>

### Comment 3
<location> `test/plugins/test_musicbrainz.py:1045-1054` </location>
<code_context>
+    def test_item_candidates_includes_album_from_release_list(self, monkeypatch, mb):
</code_context>

<issue_to_address>
**suggestion (testing):** Consider adding tests for multiple releases in the release-list.

Please add a test with multiple releases in the release-list to verify that the first release is always selected for album info.
</issue_to_address>

### Comment 4
<location> `test/plugins/test_musicbrainz.py:1080-1082` </location>
<code_context>
+        # The candidate should have correct track info
+        assert candidate.track_id == "d207c6a8-ea13-4da6-9008-cc1db29a8a35"
+
+        # ✅ New expected behavior: album info populated from release-list
+        assert candidate.album == "Love Always (Deluxe Edition)"
+        assert candidate.album_id == "9ec75bce-60ac-41e9-82a5-3b71a982257d"
+
+
</code_context>

<issue_to_address>
**suggestion (testing):** Test does not cover missing or malformed release-list edge cases.

Please add tests for missing, empty, or malformed release-list scenarios to verify robust handling and prevent incorrect album assignment or errors.

Suggested implementation:

```python
        # The candidate should have correct track info
        assert candidate.track_id == "d207c6a8-ea13-4da6-9008-cc1db29a8a35"

        # ✅ New expected behavior: album info populated from release-list
        assert candidate.album == "Love Always (Deluxe Edition)"
        assert candidate.album_id == "9ec75bce-60ac-41e9-82a5-3b71a982257d"

def test_missing_release_list(monkeypatch):
    # Simulate MusicBrainz response with no release-list
    def mock_item_candidates(item, artist, title):
        class Candidate:
            track_id = "some-track-id"
            album = None
            album_id = None
        return [Candidate()]
    monkeypatch.setattr(mb, "item_candidates", mock_item_candidates)
    candidates = list(mb.item_candidates(Item(), "Artist", "Title"))
    assert len(candidates) == 1
    candidate = candidates[0]
    assert candidate.album is None
    assert candidate.album_id is None

def test_empty_release_list(monkeypatch):
    # Simulate MusicBrainz response with empty release-list
    def mock_item_candidates(item, artist, title):
        class Candidate:
            track_id = "some-track-id"
            album = None
            album_id = None
        return [Candidate()]
    monkeypatch.setattr(mb, "item_candidates", mock_item_candidates)
    candidates = list(mb.item_candidates(Item(), "Artist", "Title"))
    assert len(candidates) == 1
    candidate = candidates[0]
    assert candidate.album is None
    assert candidate.album_id is None

def test_malformed_release_list(monkeypatch):
    # Simulate MusicBrainz response with malformed release-list
    def mock_item_candidates(item, artist, title):
        class Candidate:
            track_id = "some-track-id"
            album = None
            album_id = None
        return [Candidate()]
    monkeypatch.setattr(mb, "item_candidates", mock_item_candidates)
    candidates = list(mb.item_candidates(Item(), "Artist", "Title"))
    assert len(candidates) == 1
    candidate = candidates[0]
    assert candidate.album is None
    assert candidate.album_id is None

```

If your actual `item_candidates` implementation handles these cases differently (e.g., raises exceptions or assigns default values), you may need to adjust the assertions or the mock implementations accordingly. Also, ensure that the `mb` and `Item` objects are properly imported or available in the test context.
</issue_to_address>

### Comment 5
<location> `beetsplug/musicbrainz.py:866-867` </location>
<code_context>
    def item_candidates(
        self, item: Item, artist: str, title: str
    ) -> Iterable[beets.autotag.hooks.TrackInfo]:
        criteria = {"artist": artist, "recording": title, "alias": title}
        results = self._search_api("recording", criteria)

        for r in results:
            rec_id = r.get("id") or r.get("recording", {}).get("id")
            if not rec_id:
                continue
            try:
                ti = self.track_for_id(rec_id)
                if ti:
                    yield ti
            except Exception:
                # Fall back for test environments where get_recording_by_id is not mocked
                yield self.track_info(r)

</code_context>

<issue_to_address>
**suggestion (code-quality):** Use named expression to simplify assignment and conditional ([`use-named-expression`](https://docs.sourcery.ai/Reference/Default-Rules/refactorings/use-named-expression/))

```suggestion
                if ti := self.track_for_id(rec_id):
```
</issue_to_address>

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.47%. Comparing base (f79c125) to head (7797926).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
beetsplug/musicbrainz.py	66.66%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6160      +/-   ##
==========================================
+ Coverage   67.46%   67.47%   +0.01%     
==========================================
  Files         136      136              
  Lines       18535    18555      +20     
  Branches     3130     3136       +6     
==========================================
+ Hits        12504    12520      +16     
+ Misses       5366     5365       -1     
- Partials      665      670       +5     

Files with missing lines	Coverage Δ
beetsplug/musicbrainz.py	79.15% <66.66%> (+0.04%)	⬆️

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