fix(importer): Source = one per (artist, platform), not one per post — filesystem importer's sidecar paths now reuse the artist's existing subscription Source (or create one synthetic anchor with enabled=False) instead of fabricating a new Source per post URL. Alembic 0022 consolidates existing per-post Sources to canonical (prefers campaign URL; falls back to sidecar:<platform>:<slug>) and re-parents Posts + ImageProvenance, merging Post collisions.

Operator-flagged 2026-05-26: Atole artist detail page showed 406 Sources where 1 was right.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_importer_upsert_helpers.py

@@ -145,3 +145,68 @@ def test_find_or_create_source_recovers_from_integrity_error(
         artist_id=artist_row.id, platform="patreon", url=canonical_url,
     )
     assert recovered.id == pre_existing.id
+
+
+def test_source_for_sidecar_reuses_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.
+    """
+    canonical = Source(
+        artist_id=artist_row.id, platform="patreon",
+        url="https://www.patreon.com/cw/testartist", enabled=True,
+    )
+    db_sync.add(canonical)
+    db_sync.flush()
+
+    resolved = importer._source_for_sidecar(
+        artist_id=artist_row.id, platform="patreon",
+        artist_slug=artist_row.slug,
+    )
+    assert resolved.id == canonical.id
+
+
+def test_source_for_sidecar_creates_synthetic_anchor_when_none_exists(
+    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.
+    """
+    resolved = importer._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"
+
+    # 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,
+    )
+    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"