feat: a Discord source can remove the posts it took from people outside its poster list (#4486)

"Remove posts from other posters" on a Discord source with an "Only posts by"
list previews what goes, per poster, then deletes it behind a typed token:

- posts whose record names a poster not on the list (by id, username or
  display name); posts that record no poster are left alone and counted;
- images found only on those posts; one also on a kept post stays, and a
  synthetic drop's link never keeps one;
- their attachments, and every drop that absorbed one of them, so the grouping
  sweep regroups what remains.

Preview and apply share one predicate, and a parity test holds them to it.
The post record now also saves the poster's display name.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_discord_poster_cleanup.py

@@ -0,0 +1,131 @@
+"""Removing a Discord source's posts by people outside its poster list (#4486).
+
+Real Postgres (db_sync): the predicates read `raw_metadata->>'author'`, which
+only the database can evaluate. The test that matters runs preview and apply
+on one fixture and asserts they agree AND that the rows went (snippet #3087).
+"""
+
+import pytest
+from sqlalchemy import func, select
+
+from backend.app.models import (
+    Artist,
+    ImageProvenance,
+    ImageRecord,
+    Post,
+    PostAttachment,
+    Source,
+)
+from backend.app.services import discord_poster_cleanup as cleanup
+
+pytestmark = pytest.mark.integration
+
+
+def _image(db, artist, tmp_path, name, post):
+    f = tmp_path / f"{name}.png"
+    f.write_bytes(b"x")
+    img = ImageRecord(
+        artist_id=artist.id, path=str(f), sha256=name.ljust(64, "0"),
+        size_bytes=1, mime="image/png", origin="downloaded", primary_post_id=post.id,
+    )
+    db.add(img)
+    db.flush()
+    return img
+
+
+def _post(db, source, mid, raw, **extra):
+    p = Post(
+        source_id=source.id, artist_id=source.artist_id, external_post_id=mid,
+        raw_metadata=raw, **extra,
+    )
+    db.add(p)
+    db.flush()
+    return p
+
+
+def _fixture(db, tmp_path, authors=("Todding",)):
+    """Todding's post, two of Jake's (one sharing an image with Todding's), an
+    old post with no poster, and a drop that absorbed Todding's and Jake's."""
+    artist = Artist(name="Todding", slug="todding-cleanup")
+    db.add(artist)
+    db.flush()
+    src = Source(
+        artist_id=artist.id, platform="discord",
+        url="https://discord.com/channels/1/2",
+        config_overrides={"discord_authors": list(authors)} if authors else None,
+    )
+    db.add(src)
+    db.flush()
+    todd = _post(db, src, "10", {"author": "todding", "author_name": "Todding", "author_id": "1"})
+    jake1 = _post(db, src, "11", {"author": "jakeboii", "author_id": "8"})
+    jake2 = _post(db, src, "12", {"author": "jakeboii", "author_id": "8"})
+    old = _post(db, src, "13", {"category": "discord"})
+    drop = _post(db, src, "fc-drop:10", None, synthesized_by="discord_drop")
+    todd.absorbed_by_post_id = drop.id
+    jake1.absorbed_by_post_id = drop.id
+
+    art = _image(db, artist, tmp_path, "art", todd)
+    meme = _image(db, artist, tmp_path, "meme", jake1)
+    shared = _image(db, artist, tmp_path, "shared", jake2)
+    legacy = _image(db, artist, tmp_path, "legacy", old)
+    db.add_all([
+        ImageProvenance(image_record_id=shared.id, post_id=todd.id, source_id=src.id),
+        ImageProvenance(image_record_id=art.id, post_id=drop.id, source_id=src.id),
+        ImageProvenance(image_record_id=meme.id, post_id=drop.id, source_id=src.id),
+        PostAttachment(
+            post_id=jake2.id, artist_id=artist.id, sha256="z" * 64,
+            path="/store/z/f.zip", original_filename="f.zip", ext=".zip", size_bytes=1,
+        ),
+    ])
+    db.commit()
+    return src, {
+        "todd": todd.id, "jake1": jake1.id, "jake2": jake2.id, "old": old.id,
+        "drop": drop.id, "art": art.id, "meme": meme.id, "shared": shared.id,
+        "legacy": legacy.id,
+    }
+
+
+def test_preview_matches_apply_and_the_rows_go(db_sync, tmp_path):
+    src, ids = _fixture(db_sync, tmp_path)
+
+    projected = cleanup.preview(db_sync, source_id=src.id)
+    assert projected["authors"] == ["todding"]
+    assert projected["posters"] == [{"poster": "jakeboii", "posts": 2}]
+    assert projected["unknown_posts"] == 1
+
+    done = cleanup.apply(db_sync, source_id=src.id, images_root=tmp_path)
+    assert projected["posts"] == done["posts_deleted"] == 2
+    assert projected["images"] == done["images_deleted"] == 1  # the meme only
+    assert projected["attachments"] == done["attachments_deleted"] == 1
+    assert projected["drops"] == done["drops_deleted"] == 1
+
+    post_ids = set(db_sync.execute(select(Post.id).where(Post.source_id == src.id)).scalars())
+    assert post_ids == {ids["todd"], ids["old"]}
+    image_ids = set(db_sync.execute(
+        select(ImageRecord.id).where(ImageRecord.id.in_(
+            [ids["art"], ids["meme"], ids["shared"], ids["legacy"]]))
+    ).scalars())
+    # The meme was only Jake's. The shared piece is also on Todding's post, and
+    # the drop's link to the art was never what kept it.
+    assert image_ids == {ids["art"], ids["shared"], ids["legacy"]}
+    assert not (tmp_path / "meme.png").exists()
+    # Todding's message is back in the feed, for the sweep to regroup.
+    assert db_sync.get(Post, ids["todd"]).absorbed_by_post_id is None
+    assert db_sync.execute(select(func.count(PostAttachment.id)).where(
+        PostAttachment.sha256 == "z" * 64)).scalar_one() == 0
+
+
+def test_a_poster_matches_by_display_name_or_id_too(db_sync, tmp_path):
+    src, _ = _fixture(db_sync, tmp_path, authors=("8",))
+    projected = cleanup.preview(db_sync, source_id=src.id)
+    assert projected["posters"] == [{"poster": "Todding", "posts": 1}]
+
+
+def test_no_list_means_nothing_to_remove(db_sync, tmp_path):
+    src, _ = _fixture(db_sync, tmp_path, authors=())
+    with pytest.raises(cleanup.PosterCleanupError):
+        cleanup.preview(db_sync, source_id=src.id)
+
+
+def test_the_token_names_what_the_preview_showed():
+    assert cleanup.confirm_token({"posts": 2, "images": 1}) == "remove-2-posts-1-images"