feat(model): nullable Post.source_id + denormalized Post.artist_id; retire sidecar synthetics

Operator-asked 2026-06-01 after the Dymkens orphan investigation
(Scribe plan #540). The pre-2030 sidecar-synthetic Source pattern
(`sidecar:<platform>:<slug>` enabled=false rows) existed solely to
satisfy `Post.source_id NOT NULL`, and leaked into the Subscriptions
UI as phantom subscriptions. Now the data model says what's true:
filesystem-imported content with no live subscription has NULL
source_id, full stop.

## Schema (alembic 0030)

- `post.artist_id` — NEW NOT NULL FK to artist (CASCADE). Backfilled
  from source.artist_id in the migration. Indexed for the artist-filter
  queries.
- `post.source_id` — NOT NULL → nullable; FK ondelete CASCADE → SET
  NULL. Deleting a Source detaches its Posts instead of destroying
  archived content (subscription ends, archive stays).
- `image_provenance.source_id` — same nullable + SET NULL.
- Partial unique index `uq_post_artist_external_id_null_source` on
  (artist_id, external_post_id) WHERE source_id IS NULL — guards
  filesystem-import dedup since the existing source-bound unique
  ignores NULLs (Postgres treats NULL != NULL).
- Sidecar synthetic Sources deleted: NULL out FKs in post,
  image_provenance first, then DELETE FROM source WHERE url LIKE
  'sidecar:%'. The Dymkens cleanup.

## Model + service changes

- `Post.source_id` → `Mapped[int | None]`; new `Post.artist_id`
  denormalized.
- `ImageProvenance.source_id` → `Mapped[int | None]`.
- Importer: `_source_for_sidecar` (synthetic-creating) →
  `_lookup_source_for_sidecar` (returns None when no subscription).
  `_find_or_create_post` takes required `artist_id`; matches on
  (source_id, external_post_id) for source-bound posts or
  (artist_id, external_post_id) for NULL-source posts.
- Service queries switched off the Source detour to use Post.artist_id
  directly: post_feed_service.scroll/around/get_post (LEFT JOIN to
  Source so NULL-source posts surface); artist_service date_row/
  activity/post_count; provenance_service.for_image/for_post (LEFT
  JOIN); gallery_service._provenance_exists_where_artist via
  Post.artist_id instead of ImageProvenance.source_id → Source.
- `_to_dict` and provenance dict-builders emit `"source": null` for
  NULL-source rows.

## Frontend

- `ProvenancePanel.vue` + `PostCard.vue`: render `e.source?.platform
  ?? 'filesystem import'` so NULL-source posts get a clear
  "filesystem import" affordance instead of a NaN crash.

## Tests

- `test_importer_upsert_helpers`: removed the four synthetic-anchor
  tests; added `_find_or_create_post_idempotent_with_null_source`
  (dedup via the partial unique index) and
  `_lookup_source_for_sidecar_returns_*` (existing-subscription +
  none cases). The existing `_find_or_create_post_idempotent` now
  also passes `artist_id` and asserts it.
- 8 other test files updated: every direct `Post(...)` construction
  gains `artist_id=<artist>.id`. The `_seed_post` helper in
  `test_post_feed_service` looks up artist_id from the source row so
  callsites stay one-arg.

## Verification on deploy

After alembic 0030 runs:
- `SELECT COUNT(*) FROM source WHERE url LIKE 'sidecar:%'` → 0.
- `SELECT COUNT(*) FROM post WHERE source_id IS NULL` → count of
  filesystem-imported posts (Dymkens + any other historical).
- Every `post.artist_id` non-null; consistent with source.artist_id
  for source-bound rows.
- Subscriptions tab: no Dymkens phantom row.
- Artist detail → Posts/Gallery: Dymkens's content still reachable
  via Post.artist_id.
- Provenance panel renders "filesystem import" chip for NULL-source
  posts; PostCard same.

## Out of scope

- UI to manage/delete orphan NULL-source Posts. Data model is right;
  UI follows if operator wants it.

alembic/versions/0030_nullable_post_source_id_denorm_artist_id.py

@@ -0,0 +1,141 @@
+"""nullable post.source_id + denormalized post.artist_id; retire sidecar synthetics
+
+Revision ID: 0030
+Revises: 0029
+Create Date: 2026-06-01
+
+Operator-asked 2026-06-01 after the Dymkens orphan investigation: the
+sidecar synthetic Source pattern (`sidecar:<platform>:<slug>` rows
+with enabled=false) was technically correct but misled the operator
+into thinking they had phantom subscriptions. The synthetics existed
+solely to satisfy `Post.source_id NOT NULL` for filesystem-imported
+content with no real subscription.
+
+This migration makes the data model honest:
+
+1. **Post gets a denormalized `artist_id` column** so artist filters
+   work without traversing `Post → Source.artist_id`. Backfilled from
+   the existing Source linkage, then NOT NULL'd.
+2. **`Post.source_id` becomes nullable**, FK ondelete `CASCADE` → `SET
+   NULL`. Deleting a Source detaches its Posts instead of destroying
+   imported content (semantically: subscription ends, archive stays).
+3. **`ImageProvenance.source_id` becomes nullable** with the same FK
+   semantic change.
+4. **Sidecar synthetic Sources are deleted** — first NULL out the
+   FKs from Post + ImageProvenance pointing at them (so the implicit
+   CASCADE doesn't fire), then delete. DownloadEvent FK is unchanged
+   (still CASCADE'd, NOT NULL'd) — synthetics have `enabled=false`
+   so no events exist for them.
+
+Uniqueness handling: the existing `uq_post_source_external_id`
+(source_id, external_post_id) keeps working for source-bound Posts
+(Postgres treats NULL != NULL so NULL-source rows aren't deduped by
+it). A second partial unique index covers the NULL-source case on
+(artist_id, external_post_id) so filesystem-imported posts still
+dedupe within an artist.
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy import text
+
+revision: str = "0030"
+down_revision: Union[str, None] = "0029"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+
+    # Step 1: add Post.artist_id, initially nullable for backfill.
+    op.add_column(
+        "post",
+        sa.Column("artist_id", sa.Integer, nullable=True),
+    )
+    op.create_foreign_key(
+        "post_artist_id_fkey", "post", "artist",
+        ["artist_id"], ["id"], ondelete="CASCADE",
+    )
+
+    # Step 2: backfill from Source.artist_id (every existing Post has a
+    # Source today, so every row gets populated).
+    conn.execute(text("""
+        UPDATE post p
+        SET artist_id = s.artist_id
+        FROM source s
+        WHERE p.source_id = s.id AND p.artist_id IS NULL
+    """))
+
+    # Sanity: count any remaining NULLs. Should be zero pre-this-migration.
+    remaining = conn.execute(text(
+        "SELECT COUNT(*) FROM post WHERE artist_id IS NULL"
+    )).scalar_one()
+    if remaining:
+        raise RuntimeError(
+            f"alembic 0030: {remaining} post rows have no resolvable "
+            f"artist_id after backfill. Investigate before continuing."
+        )
+
+    # Step 3: enforce NOT NULL + add index for artist-filter queries.
+    op.alter_column("post", "artist_id", nullable=False)
+    op.create_index("ix_post_artist_id", "post", ["artist_id"])
+
+    # Step 4: relax post.source_id + flip FK to SET NULL.
+    op.alter_column("post", "source_id", nullable=True)
+    op.drop_constraint("post_source_id_fkey", "post", type_="foreignkey")
+    op.create_foreign_key(
+        "post_source_id_fkey", "post", "source",
+        ["source_id"], ["id"], ondelete="SET NULL",
+    )
+
+    # Step 5: relax image_provenance.source_id + flip FK to SET NULL.
+    op.alter_column("image_provenance", "source_id", nullable=True)
+    op.drop_constraint(
+        "image_provenance_source_id_fkey", "image_provenance",
+        type_="foreignkey",
+    )
+    op.create_foreign_key(
+        "image_provenance_source_id_fkey", "image_provenance", "source",
+        ["source_id"], ["id"], ondelete="SET NULL",
+    )
+
+    # Step 6: partial unique index on (artist_id, external_post_id) for
+    # NULL-source Posts. The existing uq_post_source_external_id keeps
+    # guarding source-bound rows; NULL-source rows now dedupe within
+    # an artist.
+    op.execute(
+        "CREATE UNIQUE INDEX uq_post_artist_external_id_null_source "
+        "ON post (artist_id, external_post_id) "
+        "WHERE source_id IS NULL"
+    )
+
+    # Step 7: retire sidecar synthetic Sources. NULL out the references
+    # FIRST (the new FK is SET NULL so CASCADE wouldn't fire anyway, but
+    # being explicit makes the intent clear). Then delete the synthetic
+    # source rows. Any DownloadEvent rows under synthetics CASCADE-die
+    # with the source — synthetics have enabled=false so there shouldn't
+    # be any in practice.
+    conn.execute(text("""
+        UPDATE post
+        SET source_id = NULL
+        WHERE source_id IN (SELECT id FROM source WHERE url LIKE 'sidecar:%')
+    """))
+    conn.execute(text("""
+        UPDATE image_provenance
+        SET source_id = NULL
+        WHERE source_id IN (SELECT id FROM source WHERE url LIKE 'sidecar:%')
+    """))
+    deleted = conn.execute(text(
+        "DELETE FROM source WHERE url LIKE 'sidecar:%' RETURNING id"
+    )).rowcount
+    print(f"alembic 0030: deleted {deleted} sidecar synthetic source rows")
+
+
+def downgrade() -> None:
+    # Lossy migration — the deleted sidecar synthetics can't be
+    # restored from the orphan post.source_id / image_provenance.source_id
+    # values, and the partial unique index encodes a constraint that
+    # NULL-source Posts may now exist. No safe downgrade.
+    pass

backend/app/models/image_provenance.py

@@ -34,8 +34,12 @@ class ImageProvenance(Base):
     post_id: Mapped[int] = mapped_column(
         ForeignKey("post.id", ondelete="CASCADE"), nullable=False, index=True
     )
-    source_id: Mapped[int] = mapped_column(
-        ForeignKey("source.id", ondelete="CASCADE"), nullable=False, index=True
+    # Nullable since alembic 0030 — provenance rows for filesystem-imported
+    # content with no subscription have NULL source_id. FK ondelete SET
+    # NULL so deleting a Source detaches its provenance rows instead of
+    # destroying the linkage between image and post.
+    source_id: Mapped[int | None] = mapped_column(
+        ForeignKey("source.id", ondelete="SET NULL"), nullable=True, index=True
     )
     captured_metadata: Mapped[dict | None] = mapped_column(JSON, nullable=True)
     captured_at: Mapped[datetime] = mapped_column(

backend/app/models/post.py

@@ -1,6 +1,9 @@
-"""Post — provenance anchor for content downloaded from a Source.
+"""Post — provenance anchor for one creator post (may contain many images).
 
-A Post is one creator post; it may contain many images/videos.
+`source_id` is nullable since alembic 0030 — filesystem-imported posts
+with no live subscription have NULL source_id. `artist_id` is the
+denormalized always-present link to the creator (added in 0030 so
+artist-filter queries don't depend on the Source detour).
 """
 
 from datetime import datetime
@@ -14,12 +17,25 @@ from .base import Base
 class Post(Base):
     __tablename__ = "post"
     __table_args__ = (
+        # Source-bound dedup. Postgres treats NULL != NULL so rows
+        # with source_id IS NULL aren't deduped by this constraint;
+        # the partial unique index `uq_post_artist_external_id_null_source`
+        # (created in alembic 0030) covers that case via
+        # (artist_id, external_post_id).
         UniqueConstraint("source_id", "external_post_id", name="uq_post_source_external_id"),
     )
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True)
-    source_id: Mapped[int] = mapped_column(
-        ForeignKey("source.id", ondelete="CASCADE"), nullable=False, index=True
+    source_id: Mapped[int | None] = mapped_column(
+        ForeignKey("source.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    # Denormalized; always equals source.artist_id when source_id is set
+    # (the importer is responsible for keeping them consistent on insert).
+    # Filter queries (artist detail, artist-scoped posts feed) use this
+    # directly instead of joining through Source.
+    artist_id: Mapped[int] = mapped_column(
+        ForeignKey("artist.id", ondelete="CASCADE"),
+        nullable=False, index=True,
     )
     external_post_id: Mapped[str] = mapped_column(String(128), nullable=False)
     post_url: Mapped[str | None] = mapped_column(Text, nullable=True)

backend/app/services/artist_service.py

@@ -58,13 +58,17 @@ class ArtistService:
             )
         ).scalar_one()
 
+        # Posts under this artist that have at least one image attached.
+        # Use Post.artist_id (alembic 0030) for the artist filter; keep
+        # the ImageProvenance JOIN so date bounds reflect only image-
+        # bearing posts (matches the original semantic). NULL-source
+        # posts now surface too.
         date_row = (
             await self.session.execute(
                 select(func.min(Post.post_date), func.max(Post.post_date))
                 .select_from(Post)
                 .join(ImageProvenance, ImageProvenance.post_id == Post.id)
-                .join(Source, Source.id == ImageProvenance.source_id)
-                .where(Source.artist_id == aid)
+                .where(Post.artist_id == aid)
             )
         ).first()
         dmin, dmax = date_row if date_row else (None, None)
@@ -98,14 +102,14 @@ class ArtistService:
             )
         ).all()
 
+        # Same Post.artist_id direct filter — counts NULL-source posts too.
         month = func.date_trunc("month", Post.post_date).label("m")
         activity = (
             await self.session.execute(
                 select(month, func.count(func.distinct(ImageProvenance.image_record_id)))
                 .select_from(Post)
                 .join(ImageProvenance, ImageProvenance.post_id == Post.id)
-                .join(Source, Source.id == ImageProvenance.source_id)
-                .where(and_(Source.artist_id == aid, Post.post_date.isnot(None)))
+                .where(and_(Post.artist_id == aid, Post.post_date.isnot(None)))
                 .group_by(month)
                 .order_by(month)
             )
@@ -114,9 +118,7 @@ class ArtistService:
         post_count = (
             await self.session.execute(
                 select(func.count(func.distinct(Post.id)))
-                .select_from(Post)
-                .join(Source, Source.id == Post.source_id)
-                .where(Source.artist_id == aid)
+                .where(Post.artist_id == aid)
             )
         ).scalar_one()
 

backend/app/services/gallery_service.py

@@ -133,10 +133,16 @@ def _provenance_clause(post_id, artist_id):
             ImageProvenance.post_id == post_id,
         )
     if artist_id is not None:
+        # Use Post.artist_id (alembic 0030 denormalized column) instead
+        # of joining through ImageProvenance.source_id → Source.artist_id.
+        # The denormalization is the always-present linkage; the source
+        # path now drops NULL-source provenance rows (filesystem-imported
+        # content) which would otherwise vanish from artist-filtered
+        # gallery views.
         return exists().where(
             ImageProvenance.image_record_id == ImageRecord.id,
-            ImageProvenance.source_id == Source.id,
-            Source.artist_id == artist_id,
+            ImageProvenance.post_id == Post.id,
+            Post.artist_id == artist_id,
         )
     return None
 

backend/app/services/importer.py

@@ -212,10 +212,10 @@ class Importer:
         which would lose the surrounding scan's progress — and re-run `stmt`
         (scalar_one) to return the row the other worker created.
 
-        Centralizes the pattern shared by _find_or_create_source,
-        _source_for_sidecar, and _find_or_create_post. The plain
-        SELECT-then-INSERT version lost races under the 5-min recovery sweep
-        (operator-flagged 2026-05-26)."""
+        Centralizes the pattern shared by _find_or_create_source and
+        _find_or_create_post. The plain SELECT-then-INSERT version lost
+        races under the 5-min recovery sweep (operator-flagged
+        2026-05-26)."""
         existing = self.session.execute(stmt).scalar_one_or_none()
         if existing is not None:
             return existing
@@ -258,47 +258,25 @@ class Importer:
             lambda: Source(artist_id=artist_id, platform=platform, url=url),
         )
 
-    def _source_for_sidecar(
-        self, *, artist_id: int, platform: str, artist_slug: str,
-    ) -> Source:
-        """Sidecar-import Source resolver. Used by both filesystem imports
-        and gallery-dl downloads (both write sidecar JSON, both flow through
-        _apply_sidecar / _capture_attachment).
+    def _lookup_source_for_sidecar(
+        self, *, artist_id: int, platform: str,
+    ) -> Source | None:
+        """Find the real subscription Source for (artist, platform), or
+        None if no subscription exists.
 
-        Source represents a subscription feed (one per artist+platform — the
-        URL polled by the FC-3 downloader). The filesystem importer used to
-        call _find_or_create_source(url=sd.post_url), creating one Source
-        row per post URL — 100s of junk Sources per artist, all with
-        enabled=True, polluting the artist detail page and tricking the
-        subscription checker into trying to poll patreon post URLs as feeds.
-        Operator-flagged 2026-05-26; consolidated via alembic 0022.
-
-        Resolution order: prefer a real (non-sidecar) Source over a
-        synthetic anchor. When alembic 0022 ran, it may have rewritten
-        per-post Sources into `sidecar:<platform>:<slug>` synthetic
-        anchors. If the operator later added the real subscription, both
-        rows now coexist. A naive `ORDER BY id ASC LIMIT 1` lookup would
-        pick the older synthetic and silently attach every gallery-dl
-        download to the wrong Source — operator-flagged 2026-05-31 after
-        the Subscriptions UI surfaced the phantom anchors. Pick the real
-        one when one exists; fall back to the synthetic; only create a
-        new synthetic when nothing exists for (artist, platform).
+        Pre-alembic-0030 this method would CREATE a synthetic
+        `sidecar:<platform>:<slug>` Source when no real one existed —
+        because `Post.source_id` was NOT NULL and the importer needed
+        something to attach Posts to. Alembic 0030 relaxed both
+        `Post.source_id` and `ImageProvenance.source_id` to nullable, so
+        synthetic anchors are obsolete; the importer now leaves
+        source_id as None when no subscription exists for the (artist,
+        platform). Operator-asked 2026-06-01: synthetic Sources had
+        leaked into the Subscriptions UI as phantom subscriptions and
+        the operator wanted the data model to truthfully say "this
+        content has no live subscription."
         """
-        real_stmt = (
-            select(Source)
-            .where(
-                Source.artist_id == artist_id,
-                Source.platform == platform,
-                ~Source.url.like("sidecar:%"),
-            )
-            .order_by(Source.id.asc())
-            .limit(1)
-        )
-        real = self.session.execute(real_stmt).scalar_one_or_none()
-        if real is not None:
-            return real
-
-        any_stmt = (
+        stmt = (
             select(Source)
             .where(
                 Source.artist_id == artist_id,
@@ -307,29 +285,37 @@ class Importer:
             .order_by(Source.id.asc())
             .limit(1)
         )
-        return self._get_or_create(
-            any_stmt,
-            lambda: Source(
-                artist_id=artist_id,
-                platform=platform,
-                url=f"sidecar:{platform}:{artist_slug}",
-                enabled=False,
-            ),
-        )
+        return self.session.execute(stmt).scalar_one_or_none()
 
     def _find_or_create_post(
-        self, *, source_id: int, external_post_id: str,
+        self, *, source_id: int | None, external_post_id: str,
+        artist_id: int,
     ) -> Post:
-        """Race-safe find-or-create on `post` keyed by
-        (source_id, external_post_id). Mirrors `_find_or_create_source`
-        — same savepoint + IntegrityError-recovery pattern."""
+        """Race-safe find-or-create on `post`. Keyed by
+        (source_id, external_post_id) when source_id is set — the
+        `uq_post_source_external_id` constraint guards. For NULL-source
+        posts the existence check matches on (artist_id, external_post_id),
+        which the partial unique index `uq_post_artist_external_id_null_source`
+        (alembic 0030) guards. Same savepoint + IntegrityError-recovery
+        pattern as the rest of the helpers."""
+        if source_id is not None:
             stmt = select(Post).where(
                 Post.source_id == source_id,
                 Post.external_post_id == external_post_id,
             )
+        else:
+            stmt = select(Post).where(
+                Post.source_id.is_(None),
+                Post.artist_id == artist_id,
+                Post.external_post_id == external_post_id,
+            )
         return self._get_or_create(
             stmt,
-            lambda: Post(source_id=source_id, external_post_id=external_post_id),
+            lambda: Post(
+                source_id=source_id,
+                artist_id=artist_id,
+                external_post_id=external_post_id,
+            ),
         )
 
     def import_one(self, source: Path) -> ImportResult:
@@ -370,12 +356,14 @@ class Importer:
             return None
         sd = parse_sidecar(data)
         platform = sd.platform or "unknown"
-        src = self._source_for_sidecar(
-            artist_id=artist.id, platform=platform, artist_slug=artist.slug,
+        src = self._lookup_source_for_sidecar(
+            artist_id=artist.id, platform=platform,
         )
         epid = sd.external_post_id or sc.stem
         return self._find_or_create_post(
-            source_id=src.id, external_post_id=epid,
+            source_id=src.id if src else None,
+            external_post_id=epid,
+            artist_id=artist.id,
         )
 
     def _capture_attachment(
@@ -858,14 +846,15 @@ class Importer:
             src = explicit_source
         else:
             platform = sd.platform or "unknown"
-            src = self._source_for_sidecar(
+            src = self._lookup_source_for_sidecar(
                 artist_id=artist.id, platform=platform,
-                artist_slug=artist.slug,
             )
 
         epid = sd.external_post_id or sc.stem
         post = self._find_or_create_post(
-            source_id=src.id, external_post_id=epid,
+            source_id=src.id if src else None,
+            external_post_id=epid,
+            artist_id=artist.id,
         )
         if sd.post_url is not None:
             post.post_url = sd.post_url
@@ -901,7 +890,7 @@ class Importer:
                     ImageProvenance(
                         image_record_id=record.id,
                         post_id=post.id,
-                        source_id=src.id,
+                        source_id=src.id if src else None,
                         captured_metadata=sd.raw,
                     )
                 )

backend/app/services/post_feed_service.py

@@ -69,13 +69,19 @@ class PostFeedService:
             raise ValueError("direction must be 'older' or 'newer'")
 
         sort_key = _sort_key()
+        # Artist via the denormalized Post.artist_id (alembic 0030);
+        # Source via LEFT JOIN since post.source_id can now be NULL for
+        # filesystem-imported posts with no live subscription. A
+        # platform= filter implicitly excludes NULL-source posts (they
+        # have no platform); an artist_id= filter still surfaces them
+        # because Post.artist_id is always set.
         stmt = (
             select(Post, Artist, Source)
-            .join(Source, Post.source_id == Source.id)
-            .join(Artist, Source.artist_id == Artist.id)
+            .join(Artist, Post.artist_id == Artist.id)
+            .outerjoin(Source, Post.source_id == Source.id)
         )
         if artist_id is not None:
-            stmt = stmt.where(Source.artist_id == artist_id)
+            stmt = stmt.where(Post.artist_id == artist_id)
         if platform is not None:
             stmt = stmt.where(Source.platform == platform)
         if cursor:
@@ -135,8 +141,8 @@ class PostFeedService:
         cursor for each end. Returns None if the post doesn't exist."""
         anchor = (await self.session.execute(
             select(Post, Artist, Source)
-            .join(Source, Post.source_id == Source.id)
-            .join(Artist, Source.artist_id == Artist.id)
+            .join(Artist, Post.artist_id == Artist.id)
+            .outerjoin(Source, Post.source_id == Source.id)
             .where(Post.id == post_id)
         )).one_or_none()
         if anchor is None:
@@ -168,8 +174,8 @@ class PostFeedService:
     async def get_post(self, post_id: int) -> dict | None:
         row = (await self.session.execute(
             select(Post, Artist, Source)
-            .join(Source, Post.source_id == Source.id)
-            .join(Artist, Source.artist_id == Artist.id)
+            .join(Artist, Post.artist_id == Artist.id)
+            .outerjoin(Source, Post.source_id == Source.id)
             .where(Post.id == post_id)
         )).one_or_none()
         if row is None:
@@ -260,7 +266,7 @@ class PostFeedService:
         return out
 
     def _to_dict(
-        self, post: Post, artist: Artist, source: Source,
+        self, post: Post, artist: Artist, source: Source | None,
         thumbs_map: dict, atts_map: dict,
     ) -> dict:
         plain_full = html_to_plain(post.description) if post.description else None
@@ -269,6 +275,9 @@ class PostFeedService:
         else:
             description_plain, truncated = truncate_at_word(plain_full, DESCRIPTION_LIMIT)
         thumbs_entry = thumbs_map.get(post.id, {"thumbs": [], "more": 0})
+        # `source` is null for filesystem-imported posts with no live
+        # subscription (alembic 0030). Frontend renders that as a
+        # "filesystem import" affordance instead of a platform chip.
         return {
             "id": post.id,
             "external_post_id": post.external_post_id,
@@ -279,7 +288,10 @@ class PostFeedService:
             "description_plain": description_plain,
             "description_truncated": truncated,
             "artist": {"id": artist.id, "name": artist.name, "slug": artist.slug},
-            "source": {"id": source.id, "platform": source.platform},
+            "source": (
+                {"id": source.id, "platform": source.platform}
+                if source is not None else None
+            ),
             "thumbnails": thumbs_entry["thumbs"],
             "thumbnails_more": thumbs_entry["more"],
             "attachments": atts_map.get(post.id, []),

backend/app/services/provenance_service.py

@@ -70,11 +70,15 @@ class ProvenanceService:
         rec = await self.session.get(ImageRecord, image_id)
         if rec is None:
             return None
+        # Artist via Post.artist_id (alembic 0030); Source via LEFT JOIN
+        # since both Post.source_id and ImageProvenance.source_id can be
+        # NULL for filesystem-imported content. Frontend renders source=
+        # null as "filesystem import."
         stmt = (
             select(ImageProvenance, Post, Source, Artist)
             .join(Post, Post.id == ImageProvenance.post_id)
-            .join(Source, Source.id == ImageProvenance.source_id)
-            .join(Artist, Artist.id == Source.artist_id)
+            .join(Artist, Artist.id == Post.artist_id)
+            .outerjoin(Source, Source.id == ImageProvenance.source_id)
             .where(ImageProvenance.image_record_id == image_id)
             .order_by(ImageProvenance.captured_at.asc(),
                       ImageProvenance.id.asc())
@@ -90,7 +94,7 @@ class ProvenanceService:
                     "captured_at": ip.captured_at.isoformat()
                     if ip.captured_at else None,
                     "post": _post_dict(post),
-                    "source": _source_dict(src),
+                    "source": _source_dict(src) if src is not None else None,
                     "artist": _artist_dict(art),
                 }
                 for ip, post, src, art in rows
@@ -99,10 +103,12 @@ class ProvenanceService:
         }
 
     async def for_post(self, post_id: int) -> dict | None:
+        # Same LEFT JOIN to Source — get_post must succeed for a
+        # NULL-source post.
         stmt = (
             select(Post, Source, Artist)
-            .join(Source, Source.id == Post.source_id)
-            .join(Artist, Artist.id == Source.artist_id)
+            .join(Artist, Artist.id == Post.artist_id)
+            .outerjoin(Source, Source.id == Post.source_id)
             .where(Post.id == post_id)
         )
         row = (await self.session.execute(stmt)).first()
@@ -111,7 +117,7 @@ class ProvenanceService:
         post, src, art = row
         return {
             "post": _post_dict(post),
-            "source": _source_dict(src),
+            "source": _source_dict(src) if src is not None else None,
             "artist": _artist_dict(art),
             "attachments": await self._attachments_for_posts([post.id]),
         }

backend/app/services/source_service.py

@@ -157,7 +157,7 @@ class SourceService:
         if artist_id is not None:
             stmt = stmt.where(Source.artist_id == artist_id)
         if not include_synthetic:
-            # Filesystem-import sidecar anchors (importer._source_for_sidecar)
+            # Pre-alembic-0030 sidecar synthetic anchors
             # have url='sidecar:<platform>:<slug>' and exist only to give
             # imported Posts a NOT-NULL Source FK. They aren't pollable
             # feeds; the Subscriptions UI used to render them as phantom

frontend/src/components/modal/ProvenancePanel.vue

@@ -19,7 +19,12 @@
         v-for="e in state.entries" :key="e.provenance_id" class="fc-prov__card"
       >
         <div class="fc-prov__head">
-          <span class="fc-prov__platform">{{ e.source.platform }}</span>
+          <!-- Posts with no live subscription have source=null (alembic
+               0030); render an explicit "filesystem import" affordance
+               instead of a platform chip. -->
+          <span class="fc-prov__platform">
+            {{ e.source?.platform ?? 'filesystem import' }}
+          </span>
           <span v-if="postDate(e)" class="fc-prov__date">{{ postDate(e) }}</span>
         </div>
         <button

frontend/src/components/posts/PostCard.vue

@@ -7,7 +7,12 @@
     @keydown.enter="onCardClick"
   >
     <div class="fc-post-card__head">
-      <v-chip size="x-small" variant="tonal">{{ post.source.platform }}</v-chip>
+      <!-- Posts with no live subscription have source=null (alembic
+           0030); show a "filesystem import" affordance instead of a
+           platform chip. -->
+      <v-chip size="x-small" variant="tonal">
+        {{ post.source?.platform ?? 'filesystem import' }}
+      </v-chip>
       <RouterLink
         :to="{ name: 'artist', params: { slug: post.artist.slug } }"
         class="fc-post-card__artist"
@@ -25,7 +30,7 @@
         v-if="post.post_url"
         :href="post.post_url" target="_blank" rel="noopener"
         icon="mdi-open-in-new" size="x-small" variant="text"
-        :aria-label="`open original post on ${post.source.platform}`"
+        :aria-label="`open original post on ${post.source?.platform ?? 'web'}`"
         @click.stop
       />
       <v-btn

tests/test_api_artist.py

@@ -37,8 +37,8 @@ async def test_artist_overview_post_count(client, db):
     )
     db.add(s)
     await db.flush()
-    db.add(Post(source_id=s.id, external_post_id="p1"))
-    db.add(Post(source_id=s.id, external_post_id="p2"))
+    db.add(Post(source_id=s.id, artist_id=a.id, external_post_id="p1"))
+    db.add(Post(source_id=s.id, artist_id=a.id, external_post_id="p2"))
     await db.flush()
     await db.commit()
     resp = await client.get("/api/artist/lyra")

tests/test_api_posts.py

@@ -25,7 +25,7 @@ async def seeded_post(db):
     db.add(source)
     await db.flush()
     post = Post(
-        source_id=source.id, external_post_id="API1",
+        source_id=source.id, artist_id=artist.id, external_post_id="API1",
         post_title="Hello", post_url="https://p/alice-api/1",
         post_date=datetime.now(UTC),
         description="<p>hi</p>",
@@ -123,7 +123,8 @@ async def post_timeline(db):
     posts = []
     for i in range(5):
         p = Post(
-            source_id=source.id, external_post_id=f"TL{i}",
+            source_id=source.id, artist_id=artist.id,
+            external_post_id=f"TL{i}",
             post_title=f"post {i}", post_date=base + timedelta(days=i),
         )
         db.add(p)
@@ -189,7 +190,7 @@ async def test_detail_returns_uncapped_thumbnails(client, db):
     db.add(s)
     await db.flush()
     p = Post(
-        source_id=s.id, external_post_id="DETAIL10",
+        source_id=s.id, artist_id=a.id, external_post_id="DETAIL10",
         post_title="big post", description="<p>body</p>",
     )
     db.add(p)

tests/test_api_provenance.py

@@ -26,7 +26,8 @@ async def _seed_full(db):
                     url="https://patreon.test/alice")
     db.add(source)
     await db.flush()
-    post = Post(source_id=source.id, external_post_id="555",
+    post = Post(source_id=source.id, artist_id=artist.id,
+                external_post_id="555",
                 post_url="https://patreon.test/p/555", post_title="Set 1",
                 post_date=datetime(2023, 8, 1, tzinfo=UTC),
                 description="<p>hi</p>", attachment_count=2)

tests/test_artist_service.py

@@ -25,7 +25,7 @@ async def _fixture(db):
     db.add(src)
     await db.flush()
     post = Post(
-        source_id=src.id, external_post_id="p1",
+        source_id=src.id, artist_id=artist.id, external_post_id="p1",
         post_date=datetime(2026, 3, 1, tzinfo=UTC),
     )
     db.add(post)

tests/test_gallery_provenance_filter.py

@@ -35,7 +35,7 @@ async def _post(db, artist_name, slug, ext):
                url=f"https://patreon.test/{slug}")
     db.add(s)
     await db.flush()
-    p = Post(source_id=s.id, external_post_id=ext)
+    p = Post(source_id=s.id, artist_id=a.id, external_post_id=ext)
     db.add(p)
     await db.flush()
     return a, s, p

tests/test_gallery_service.py

@@ -152,7 +152,8 @@ async def _seed_image_with_post(
     db.add(source)
     await db.flush()
     post = Post(
-        source_id=source.id, external_post_id=external_post_id,
+        source_id=source.id, artist_id=artist.id,
+        external_post_id=external_post_id,
         post_title="A Post", post_date=post_date,
     )
     db.add(post)

tests/test_importer_upsert_helpers.py

@@ -88,11 +88,36 @@ def test_find_or_create_post_idempotent(importer, artist_row, db_sync):
     )
     p1 = importer._find_or_create_post(
         source_id=src.id, external_post_id="ext-001",
+        artist_id=artist_row.id,
     )
     p2 = importer._find_or_create_post(
         source_id=src.id, external_post_id="ext-001",
+        artist_id=artist_row.id,
     )
     assert p1.id == p2.id
+    assert p1.artist_id == artist_row.id
+
+
+def test_find_or_create_post_idempotent_with_null_source(
+    importer, artist_row, db_sync,
+):
+    """Post.source_id is nullable since alembic 0030 — filesystem-imported
+    posts with no live subscription have NULL source_id. The partial
+    unique index `uq_post_artist_external_id_null_source` on
+    (artist_id, external_post_id) WHERE source_id IS NULL guards the
+    dedup; the helper matches on the same (artist_id, external_post_id)
+    keys when source_id is None."""
+    p1 = importer._find_or_create_post(
+        source_id=None, external_post_id="fs-001",
+        artist_id=artist_row.id,
+    )
+    p2 = importer._find_or_create_post(
+        source_id=None, external_post_id="fs-001",
+        artist_id=artist_row.id,
+    )
+    assert p1.id == p2.id
+    assert p1.source_id is None
+    assert p1.artist_id == artist_row.id
 
 
 def test_find_or_create_source_recovers_from_integrity_error(
@@ -147,13 +172,13 @@ def test_find_or_create_source_recovers_from_integrity_error(
     assert recovered.id == pre_existing.id
 
 
-def test_source_for_sidecar_reuses_existing_subscription(
+def test_lookup_source_for_sidecar_returns_existing_subscription(
     importer, artist_row, db_sync,
 ):
-    """The filesystem-import sidecar resolver should attach to whatever
-    Source already exists for (artist, platform) — the canonical subscription
-    Source — regardless of its URL. Without this, every imported post
-    spawned its own Source row.
+    """The sidecar-import Source lookup returns the existing Source for
+    (artist, platform) when one exists — letting filesystem-imported
+    content attach to the artist's real subscription instead of being
+    orphaned.
     """
     canonical = Source(
         artist_id=artist_row.id, platform="patreon",
@@ -162,84 +187,30 @@ def test_source_for_sidecar_reuses_existing_subscription(
     db_sync.add(canonical)
     db_sync.flush()
 
-    resolved = importer._source_for_sidecar(
+    resolved = importer._lookup_source_for_sidecar(
         artist_id=artist_row.id, platform="patreon",
-        artist_slug=artist_row.slug,
     )
+    assert resolved is not None
     assert resolved.id == canonical.id
 
 
-def test_source_for_sidecar_creates_synthetic_anchor_when_none_exists(
+def test_lookup_source_for_sidecar_returns_none_when_no_subscription(
     importer, artist_row, db_sync,
 ):
-    """No subscription Source for this (artist, platform) yet. The helper
-    creates one synthetic anchor (enabled=False, url='sidecar:<plat>:<slug>')
-    so subsequent imports reuse it instead of spawning per-post Sources.
+    """Alembic 0030 made Post.source_id nullable; the importer no
+    longer creates synthetic `sidecar:<platform>:<slug>` anchor rows
+    when no real subscription exists. The lookup returns None and the
+    caller carries that through as a NULL source_id on the new Post.
     """
-    resolved = importer._source_for_sidecar(
+    resolved = importer._lookup_source_for_sidecar(
         artist_id=artist_row.id, platform="pixiv",
-        artist_slug=artist_row.slug,
     )
-    assert resolved.url == f"sidecar:pixiv:{artist_row.slug}"
-    assert resolved.enabled is False
-    assert resolved.artist_id == artist_row.id
-    assert resolved.platform == "pixiv"
+    assert resolved is None
 
-    # Second call returns the same row (no new Source spawned).
-    again = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="pixiv",
-        artist_slug=artist_row.slug,
+    # Verify no Source row was created as a side effect.
+    count = db_sync.execute(
+        select(Source).where(
+            Source.artist_id == artist_row.id, Source.platform == "pixiv",
         )
-    assert again.id == resolved.id
-
-
-def test_source_for_sidecar_distinct_platforms_distinct_anchors(
-    importer, artist_row, db_sync,
-):
-    """One synthetic anchor per (artist, platform). Different platforms get
-    different anchors even when no campaign Source exists for either.
-    """
-    p = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="patreon",
-        artist_slug=artist_row.slug,
-    )
-    x = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="pixiv",
-        artist_slug=artist_row.slug,
-    )
-    assert p.id != x.id
-    assert p.platform == "patreon"
-    assert x.platform == "pixiv"
-
-
-def test_source_for_sidecar_prefers_real_over_synthetic_when_both_exist(
-    importer, artist_row, db_sync,
-):
-    """When BOTH a synthetic anchor AND a real Source exist for the same
-    (artist, platform), the resolver must return the REAL one. This is the
-    fix for the 2026-05-31 phantom-subscription bug: alembic 0022 had
-    rewritten an older per-post Source row into a sidecar synthetic, and
-    the operator later added the real subscription. The old `ORDER BY
-    id ASC LIMIT 1` lookup picked the older synthetic (lower id),
-    silently attaching every gallery-dl download to the wrong Source.
-    """
-    synthetic = Source(
-        artist_id=artist_row.id, platform="patreon",
-        url=f"sidecar:patreon:{artist_row.slug}", enabled=False,
-    )
-    db_sync.add(synthetic)
-    db_sync.flush()
-    real = Source(
-        artist_id=artist_row.id, platform="patreon",
-        url="https://www.patreon.com/testartist", enabled=True,
-    )
-    db_sync.add(real)
-    db_sync.flush()
-    assert synthetic.id < real.id  # ordering precondition
-
-    resolved = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="patreon",
-        artist_slug=artist_row.slug,
-    )
-    assert resolved.id == real.id
-    assert resolved.url == "https://www.patreon.com/testartist"
+    ).all()
+    assert count == []

tests/test_migration_0007.py

@@ -17,7 +17,7 @@ async def _post(db, **post_kwargs):
     db.add(src)
     await db.flush()
     post = Post(
-        source_id=src.id, external_post_id="p1",
+        source_id=src.id, artist_id=artist.id, external_post_id="p1",
         post_date=datetime(2026, 3, 1, tzinfo=UTC),
         **post_kwargs,
     )

tests/test_migration_0008.py

@@ -62,7 +62,7 @@ async def _run_backfill(db):
 async def test_backfill_primary_post(db):
     rec = await _img(db, 1)
     a, s = await _artist_source(db, "Alice", "alice")
-    post = Post(source_id=s.id, external_post_id="1")
+    post = Post(source_id=s.id, artist_id=a.id, external_post_id="1")
     db.add(post)
     await db.flush()
     rec.primary_post_id = post.id
@@ -78,7 +78,7 @@ async def test_backfill_primary_post(db):
 async def test_backfill_provenance_fallback(db):
     rec = await _img(db, 1)
     a, s = await _artist_source(db, "Bob", "bob")
-    post = Post(source_id=s.id, external_post_id="2")
+    post = Post(source_id=s.id, artist_id=a.id, external_post_id="2")
     db.add(post)
     await db.flush()
     db.add(ImageProvenance(image_record_id=rec.id, post_id=post.id,

tests/test_post_feed_service.py

@@ -7,6 +7,7 @@ boundary, and the thumbnails/attachments composition.
 from datetime import UTC, datetime, timedelta
 
 import pytest
+from sqlalchemy import select
 
 from backend.app.models import (
     Artist,
@@ -59,8 +60,13 @@ async def _seed_post(
     db, source_id: int, *, external_id: str,
     post_date=None, downloaded_at=None, title=None, description=None,
 ):
+    # Post.artist_id is NOT NULL since alembic 0030; look it up from
+    # the source so callsites don't have to thread the artist through.
+    artist_id = (await db.execute(
+        select(Source.artist_id).where(Source.id == source_id)
+    )).scalar_one()
     p = Post(
-        source_id=source_id, external_post_id=external_id,
+        source_id=source_id, artist_id=artist_id, external_post_id=external_id,
         post_title=title, post_date=post_date,
         description=description,
     )

tests/test_provenance_service.py

@@ -37,7 +37,7 @@ async def _seed_post(db, *, artist_name, slug, platform, ext_id,
     db.add(source)
     await db.flush()
     post = Post(
-        source_id=source.id, external_post_id=ext_id,
+        source_id=source.id, artist_id=artist.id, external_post_id=ext_id,
         post_url=f"https://{platform}.test/p/{ext_id}",
         post_title=title, post_date=datetime(2023, 8, 1, tzinfo=UTC),
         description=desc, attachment_count=count,

tests/test_source_service.py

@@ -138,7 +138,7 @@ async def test_update_changes_fields(db):
 @pytest.mark.asyncio
 async def test_list_hides_sidecar_synthetic_anchors(db):
     """Filesystem-import synthetic Sources (url='sidecar:<platform>:<slug>',
-    enabled=False — see importer._source_for_sidecar) used to leak into the
+    enabled=False — historical pre-alembic-0030 artifact) used to leak into the
     Subscriptions UI as phantom subscriptions because list() didn't filter
     them. They aren't pollable feeds; hide by default."""
     artist = await _artist(db, "Alice")