feat(library): lazy materialization foundation for remote tracks (§Phase1)

Adds nullable storage fields + availability column on tracks, remote
source/source_id identity on albums/artists, TrackRepository.materialize()
and get_or_create_remote() repos — groundwork for on-demand YTM library
(placeholders saved without audio, materialized in-place on first play).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/infrastructure/db/models/album.py

@@ -2,7 +2,7 @@
 
 import uuid
 
-from sqlalchemy import ForeignKey, Integer, String
+from sqlalchemy import ForeignKey, Integer, String, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.infrastructure.db.base import Base
@@ -11,6 +11,12 @@ from app.infrastructure.db.models.mixins import TimestampMixin, UUIDPrimaryKeyMi
 
 class AlbumModel(UUIDPrimaryKeyMixin, TimestampMixin, Base):
     __tablename__ = "albums"
+    __table_args__ = (
+        # Binds a remote (browsable) album to its local row for re-browse/save
+        # dedup. Multiple NULLs are allowed by Postgres, so locally-created
+        # albums (source/source_id both NULL) never collide on this.
+        UniqueConstraint("source", "source_id", name="uq_albums_source_source_id"),
+    )
 
     title: Mapped[str] = mapped_column(String(1024), index=True, nullable=False)
     artist_id: Mapped[uuid.UUID] = mapped_column(
@@ -21,3 +27,7 @@ class AlbumModel(UUIDPrimaryKeyMixin, TimestampMixin, Base):
     year: Mapped[int | None] = mapped_column(Integer, nullable=True)
     cover_path: Mapped[str | None] = mapped_column(String(1024), nullable=True)
     musicbrainz_id: Mapped[str | None] = mapped_column(String(36), index=True, nullable=True)
+
+    # -- remote identity (lazy materialization) --------------------------
+    source: Mapped[str | None] = mapped_column(String(32), nullable=True)
+    source_id: Mapped[str | None] = mapped_column(String(512), nullable=True)

app/infrastructure/db/models/artist.py

@@ -1,6 +1,6 @@
 """ORM model for artists."""
 
-from sqlalchemy import String
+from sqlalchemy import String, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.infrastructure.db.base import Base
@@ -9,6 +9,16 @@ from app.infrastructure.db.models.mixins import TimestampMixin, UUIDPrimaryKeyMi
 
 class ArtistModel(UUIDPrimaryKeyMixin, TimestampMixin, Base):
     __tablename__ = "artists"
+    __table_args__ = (
+        # Binds a remote (browsable) artist to its local row for re-browse/save
+        # dedup. Multiple NULLs are allowed by Postgres, so locally-created
+        # artists (source/source_id both NULL) never collide on this.
+        UniqueConstraint("source", "source_id", name="uq_artists_source_source_id"),
+    )
 
     name: Mapped[str] = mapped_column(String(512), index=True, nullable=False)
     musicbrainz_id: Mapped[str | None] = mapped_column(String(36), index=True, nullable=True)
+
+    # -- remote identity (lazy materialization) --------------------------
+    source: Mapped[str | None] = mapped_column(String(32), nullable=True)
+    source_id: Mapped[str | None] = mapped_column(String(512), nullable=True)

app/infrastructure/db/models/enums.py

@@ -64,3 +64,12 @@ class LyricsStatus(enum.StrEnum):
     FOUND = "found"
     NOT_FOUND = "not_found"
     PENDING = "pending"
+
+
+class TrackAvailability(enum.StrEnum):
+    """Whether a track's audio is on local storage or still a remote placeholder
+    (plan: lazy materialization). ``remote`` tracks have ``storage_uri = NULL``
+    until ``TrackRepository.materialize`` fills it in."""
+
+    LOCAL = "local"
+    REMOTE = "remote"

app/infrastructure/db/models/track.py

@@ -13,7 +13,7 @@ from sqlalchemy import DateTime, ForeignKey, Integer, String, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.infrastructure.db.base import Base
-from app.infrastructure.db.models.enums import MetadataStatus, StoragePolicy
+from app.infrastructure.db.models.enums import MetadataStatus, StoragePolicy, TrackAvailability
 from app.infrastructure.db.models.mixins import TimestampMixin, UUIDPrimaryKeyMixin
 
 
@@ -41,11 +41,20 @@ class TrackModel(UUIDPrimaryKeyMixin, TimestampMixin, Base):
     year: Mapped[int | None] = mapped_column(Integer, nullable=True)
 
     # -- file (original, stored as-is) -----------------------------------
-    storage_uri: Mapped[str] = mapped_column(String(2048), nullable=False)
-    file_format: Mapped[str] = mapped_column(String(32), nullable=False)
-    file_size: Mapped[int] = mapped_column(Integer, nullable=False)
+    # NULL on a remote placeholder (not yet materialized) — see ``availability``.
+    storage_uri: Mapped[str | None] = mapped_column(String(2048), nullable=True)
+    file_format: Mapped[str | None] = mapped_column(String(32), nullable=True)
+    file_size: Mapped[int | None] = mapped_column(Integer, nullable=True)
     bitrate: Mapped[int | None] = mapped_column(Integer, nullable=True)
 
+    # ``remote`` = placeholder with no local audio yet; materialize() flips this
+    # to ``local`` once the file is downloaded and ``storage_uri`` is filled in.
+    availability: Mapped[str] = mapped_column(
+        String(16),
+        nullable=False,
+        default=TrackAvailability.LOCAL.value,
+    )
+
     # -- dedup / external ids --------------------------------------------
     acoustid_fingerprint: Mapped[str | None] = mapped_column(String(64), index=True, nullable=True)
     musicbrainz_id: Mapped[str | None] = mapped_column(String(36), index=True, nullable=True)