#845 tests: lift history-path resolver to core/ + seam-test the delete-safety

resolve_history_audio_path drives a DESTRUCTIVE delete (os.remove), but lived
endpoint-bound in web_server with zero tests. Lifted to core/matching/history_paths
with injected effects (exists / resolve_library_path / lookup_titled_paths) so the
fallback chain — and the collision-safety that stops delete() from removing the
wrong same-title file — is a clean importable seam. web_server now wraps it (DB
lookup + os.path.exists + prefix resolver injected); behavior preserved.

9 tests lock it: recorded-path hit, prefix-resolve fallback, single tracks-table
candidate, and the safety rules — multiple same-title candidates with NO artist ->
None (refuse to guess), artist filter picks only the matching path, artist named
but unmatched -> None, no-title/empty-lookup -> None. Full suite green (5906).

core/matching/history_paths.py

@@ -0,0 +1,65 @@
+"""Resolve a ``library_history`` row to a playable on-disk file.
+
+Lifted out of ``web_server`` so the fallback chain — and its collision-safety —
+is an importable, unit-tested seam. This matters because a *destructive* delete
+(``/api/verification/<id>/delete`` → ``os.remove``) trusts the path this returns:
+if the tracks-table fallback guessed the wrong same-title file, delete would
+remove the wrong track. The rules below are exactly that guard, and the tests
+lock them.
+
+Side effects are injected so the decision logic is pure:
+  - ``exists(path) -> bool``                     (os.path.exists)
+  - ``resolve_library_path(raw) -> str | None``  (transfer/download/library prefix swap)
+  - ``lookup_titled_paths(title) -> list[str]``  (tracks.file_path WHERE LOWER(title)=LOWER(?))
+"""
+
+from __future__ import annotations
+
+from typing import Any, Callable, Dict, List, Optional
+
+
+def resolve_history_audio_path(
+    row: Dict[str, Any],
+    *,
+    exists: Callable[[str], bool],
+    resolve_library_path: Callable[[str], Optional[str]],
+    lookup_titled_paths: Callable[[str], List[str]],
+) -> Optional[str]:
+    """Return the on-disk path for a history row, or None. Fallback chain:
+    1. the recorded path as-is,
+    2. the prefix-swap resolver (Docker↔host / transfer→library),
+    3. the tracks-table mirror by title (knows the CURRENT path after a rename),
+       resolved the same way — but only when it can be picked UNAMBIGUOUSLY.
+    """
+    raw_path = (row.get("file_path") or "").strip()
+    if raw_path and exists(raw_path):
+        return raw_path
+
+    resolved = resolve_library_path(raw_path) if raw_path else None
+    if resolved and exists(resolved):
+        return resolved
+
+    title = (row.get("title") or "").strip()
+    if not title:
+        return None
+
+    artist = (row.get("artist_name") or "").strip()
+    candidates = [p for p in (lookup_titled_paths(title) or []) if p]
+
+    # Same-title collisions across artists exist, and delete() trusts this path,
+    # so be strict: when the row names an artist, only accept candidates whose
+    # path mentions it; with no artist, only an unambiguous single candidate.
+    artist_l = artist.lower()
+    if artist_l:
+        candidates = [p for p in candidates if artist_l in p.lower()]
+    elif len(candidates) != 1:
+        return None
+
+    for cand in candidates:
+        cand_resolved = resolve_library_path(cand)
+        if cand_resolved and exists(cand_resolved):
+            return cand_resolved
+    return None
+
+
+__all__ = ["resolve_history_audio_path"]

tests/matching/test_history_paths.py

@@ -0,0 +1,87 @@
+"""Seam tests for resolve_history_audio_path — the fallback chain a DESTRUCTIVE
+delete trusts. The collision-safety rules (artist filter / single-candidate) are
+what stop delete() from removing the wrong same-title file, so they're locked here."""
+
+from __future__ import annotations
+
+from core.matching.history_paths import resolve_history_audio_path
+
+
+def _resolver(existing=(), resolve_map=None, titled=None):
+    existing = set(existing)
+    resolve_map = resolve_map or {}
+    titled = titled or {}
+    return dict(
+        exists=lambda p: p in existing,
+        resolve_library_path=lambda raw: resolve_map.get(raw),
+        lookup_titled_paths=lambda title: list(titled.get(title.lower(), [])),
+    )
+
+
+def test_recorded_path_used_when_it_exists():
+    r = resolve_history_audio_path({'file_path': '/m/a.mp3'}, **_resolver(existing={'/m/a.mp3'}))
+    assert r == '/m/a.mp3'
+
+
+def test_falls_back_to_prefix_resolved_path():
+    r = resolve_history_audio_path(
+        {'file_path': '/transfer/a.mp3'},
+        **_resolver(existing={'/library/a.mp3'}, resolve_map={'/transfer/a.mp3': '/library/a.mp3'}))
+    assert r == '/library/a.mp3'
+
+
+def test_tracks_table_single_candidate_no_artist():
+    r = resolve_history_audio_path(
+        {'file_path': '/gone.mp3', 'title': 'Song'},
+        **_resolver(existing={'/library/song.mp3'},
+                    resolve_map={'/lib/song.mp3': '/library/song.mp3'},
+                    titled={'song': ['/lib/song.mp3']}))
+    assert r == '/library/song.mp3'
+
+
+def test_collision_no_artist_multiple_candidates_returns_none():
+    # THE safety rule: same title, no artist to disambiguate -> refuse to guess
+    # (delete() must not remove an arbitrary one of two same-title files).
+    r = resolve_history_audio_path(
+        {'file_path': '', 'title': 'Intro'},
+        **_resolver(existing={'/library/a/intro.mp3', '/library/b/intro.mp3'},
+                    resolve_map={'/a/intro.mp3': '/library/a/intro.mp3', '/b/intro.mp3': '/library/b/intro.mp3'},
+                    titled={'intro': ['/a/intro.mp3', '/b/intro.mp3']}))
+    assert r is None
+
+
+def test_artist_filter_picks_only_the_matching_path():
+    # Two same-title files by different artists -> only the one whose path
+    # mentions the row's artist is eligible (won't delete the other artist's file).
+    r = resolve_history_audio_path(
+        {'file_path': '', 'title': 'Intro', 'artist_name': 'Alpha'},
+        **_resolver(existing={'/music/Alpha/intro.mp3', '/music/Beta/intro.mp3'},
+                    resolve_map={'/Alpha/intro.mp3': '/music/Alpha/intro.mp3',
+                                 '/Beta/intro.mp3': '/music/Beta/intro.mp3'},
+                    titled={'intro': ['/Alpha/intro.mp3', '/Beta/intro.mp3']}))
+    assert r == '/music/Alpha/intro.mp3'
+
+
+def test_artist_named_but_no_path_mentions_it_returns_none():
+    r = resolve_history_audio_path(
+        {'file_path': '', 'title': 'Intro', 'artist_name': 'Gamma'},
+        **_resolver(existing={'/music/Alpha/intro.mp3'},
+                    resolve_map={'/Alpha/intro.mp3': '/music/Alpha/intro.mp3'},
+                    titled={'intro': ['/Alpha/intro.mp3']}))
+    assert r is None
+
+
+def test_no_title_returns_none():
+    assert resolve_history_audio_path({'file_path': '/gone.mp3'}, **_resolver()) is None
+
+
+def test_nothing_resolves_returns_none():
+    assert resolve_history_audio_path(
+        {'file_path': '/gone.mp3', 'title': 'X'},
+        **_resolver(titled={'x': ['/also/gone.mp3']})) is None
+
+
+def test_empty_lookup_returns_none():
+    # DB-error proxy: lookup yields [] -> None (never a stray delete target).
+    assert resolve_history_audio_path(
+        {'file_path': '', 'title': 'X'}, **_resolver(titled={})) is None

web_server.py

@@ -7598,40 +7598,27 @@ def _resolve_history_audio_path(row):
     3. the tracks table — the media-server mirror knows the CURRENT path for
        this title+artist even after a rename — resolved the same way.
     """
-    raw_path = (row.get('file_path') or '').strip()
-    if raw_path and os.path.exists(raw_path):
-        return raw_path
-    resolved = _resolve_library_file_path(raw_path) if raw_path else None
-    if resolved and os.path.exists(resolved):
-        return resolved
-    title = (row.get('title') or '').strip()
-    if not title:
-        return None
-    artist = (row.get('artist_name') or '').strip()
-    try:
-        conn = get_database()._get_connection()
-        cursor = conn.cursor()
-        cursor.execute(
-            "SELECT file_path FROM tracks WHERE file_path IS NOT NULL AND LOWER(title) = LOWER(?)",
-            (title,))
-        candidates = [r[0] for r in cursor.fetchall() if r[0]]
-    except Exception as e:
-        logger.debug(f"[Verification] tracks-table path fallback failed: {e}")
-        return None
-    # Same-title collisions across artists exist (and delete() trusts this
-    # path), so be strict: when the row names an artist, only accept
-    # candidates whose path mentions it; otherwise only an unambiguous
-    # single candidate.
-    artist_l = artist.lower()
-    if artist_l:
-        candidates = [p for p in candidates if artist_l in p.lower()]
-    elif len(candidates) != 1:
-        return None
-    for cand in candidates:
-        cand_resolved = _resolve_library_file_path(cand)
-        if cand_resolved and os.path.exists(cand_resolved):
-            return cand_resolved
-    return None
+    def _lookup_titled_paths(title):
+        # tracks-table mirror: paths for this title (knows the CURRENT path
+        # after a media-server rename). [] on any DB error → resolver returns None.
+        try:
+            conn = get_database()._get_connection()
+            cursor = conn.cursor()
+            cursor.execute(
+                "SELECT file_path FROM tracks WHERE file_path IS NOT NULL AND LOWER(title) = LOWER(?)",
+                (title,))
+            return [r[0] for r in cursor.fetchall() if r[0]]
+        except Exception as e:
+            logger.debug(f"[Verification] tracks-table path fallback failed: {e}")
+            return []
+
+    from core.matching.history_paths import resolve_history_audio_path
+    return resolve_history_audio_path(
+        row,
+        exists=os.path.exists,
+        resolve_library_path=_resolve_library_file_path,
+        lookup_titled_paths=_lookup_titled_paths,
+    )
 
 
 @app.route('/api/verification/<int:history_id>/stream', methods=['GET'])