fix: a Discord source takes only messages with an image attached, from the posters it names, and knows its channel's name (#4481)

- A message with no image or video attachment is chat: extract_media returns
  nothing for it, so nothing downloads and no post record is written. A
  message that passes keeps every file, numbered as gallery-dl numbers them.
- `discord_authors` in a source's config limits the walk to those posters
  (id, username or display name); the edit dialog has a field for it and no
  longer drops config keys it has no field for.
- source.display_name (migration 0115), refreshed by every Discord walk, shows
  on Subscriptions in place of the two-id URL; a Discord post card names its
  channel from the record's `channel`.

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

tests/test_discord_client.py

@@ -153,9 +153,11 @@ def test_an_embeds_identity_ignores_its_signature():
     def embed(sig):
         return {"type": "image", "image": {"proxy_url": f"https://media/p/x.png?ex={sig}"}}
 
-    one = DiscordClient.extract_media(_msg(9, embeds=[embed("a")]))[0].media_id
-    two = DiscordClient.extract_media(_msg(9, embeds=[embed("b")]))[0].media_id
-    assert one == two and len(one) <= 33
+    art = [{"url": "https://cdn/a/1.png"}]
+    one = DiscordClient.extract_media(_msg(9, attachments=art, embeds=[embed("a")]))[1]
+    two = DiscordClient.extract_media(_msg(9, attachments=art, embeds=[embed("b")]))[1]
+    assert one.kind == two.kind == "embed"
+    assert one.media_id == two.media_id and len(one.media_id) <= 33
 
 
 def test_post_seams():
@@ -165,11 +167,52 @@ def test_post_seams():
 
 
 def test_a_text_only_message_is_not_a_post():
-    """gallery-dl never made one: chat lines would bury the drops."""
+    """Chat lines would bury the drops."""
     assert DiscordClient.post_record_key(_msg(6, content="brb")) is None
     assert DiscordClient.post_meta(_msg(1))["date"].startswith("2026-09-20")
 
 
+def test_a_message_without_an_attached_image_is_chat():
+    """Operator 2026-09-28: only content with an image attached. A lone
+    archive, a link preview or a Tenor GIF takes nothing and records nothing."""
+    chat = [
+        _msg(1, content="the stash", attachments=[
+            {"url": "https://cdn/a/Links_Stash.rar", "content_type": "application/x-rar"},
+        ]),
+        _msg(2, content="look", embeds=[
+            {"type": "image", "image": {"proxy_url": "https://media/p/x.png"}},
+        ]),
+        _msg(3, content="lol", embeds=[
+            {"type": "gifv", "video": {"proxy_url": "https://media/p/t.mp4"}},
+        ]),
+        _msg(4, content="wip", attachments=[{"url": "https://cdn/a/wip.psd"}]),
+    ]
+    for m in chat:
+        assert DiscordClient.extract_media(m) == []
+        assert DiscordClient.post_record_key(m) is None
+
+
+def test_an_attached_image_takes_every_file_numbered_as_gallery_dl_does():
+    """The gate decides WHETHER a message is taken, never which of its files:
+    the rar beside the image keeps its number, so on-disk names still match."""
+    m = _msg(7, attachments=[
+        {"url": "https://cdn/a/pack.rar"},
+        {"url": "https://cdn/a/noext", "content_type": "image/png"},
+    ])
+    items = DiscordClient.extract_media(m)
+    assert [(i.num, i.filename) for i in items] == [(1, "pack"), (2, "noext")]
+    assert DiscordClient.post_record_key(m) == ("message:7", "7")
+    video = _msg(8, attachments=[{"url": "https://cdn/a/clip.MP4?ex=1"}])
+    assert len(DiscordClient.extract_media(video)) == 1
+
+
+def test_a_forwarded_image_counts_as_attached():
+    m = _msg(9, message_snapshots=[
+        {"message": {"type": 0, "attachments": [{"url": "https://cdn/a/fwd.png"}]}},
+    ])
+    assert DiscordClient.post_record_key(m) == ("message:9", "9")
+
+
 # -- the walk --------------------------------------------------------------------
 
 def test_a_channel_pages_newest_first_and_skips_system_messages():
@@ -206,6 +249,50 @@ def test_messages_carry_server_and_channel_metadata():
     assert meta["parent"] == "Art"
 
 
+def _one_channel(messages):
+    return {
+        "/guilds/1": _ok({"id": "1", "name": "Todding's Server"}),
+        "/guilds/1/channels": _ok([
+            {"id": "4", "type": 4, "name": "Todding"},
+            {"id": "2", "type": 0, "name": "banana-land", "parent_id": "4"},
+        ]),
+        ("/channels/2/messages", None): _ok(messages),
+        ("/channels/2/threads/search", 0): _ok({"threads": []}),
+    }
+
+
+def test_only_from_takes_the_creators_messages_and_no_one_elses():
+    """Operator 2026-09-28: in the creator's server, another member posting a
+    meme is not the creator's art. Matched by id, username or display name."""
+    creator = {"id": "7", "username": "todding", "global_name": "Todding"}
+    other = {"id": "8", "username": "jakeboii", "global_name": "Jake Boii"}
+    msgs = [_msg(3, author=creator), _msg(2, author=other), _msg(1, author=creator)]
+    url = "https://discord.com/channels/1/2"
+
+    everyone = _client(_one_channel([dict(m) for m in msgs]))
+    assert [mid for mid, _ in _ids(everyone, url)] == ["3", "2", "1"]
+    for who in (["Todding"], ["TODDING "], ["7"]):
+        client = _client(_one_channel([dict(m) for m in msgs]))
+        client.only_from(who)
+        assert [mid for mid, _ in _ids(client, url)] == ["3", "1"]
+    client = _client(_one_channel([dict(m) for m in msgs]))
+    client.only_from([])
+    assert len(_ids(client, url)) == 3
+
+
+def test_the_source_label_names_the_server_and_channel_the_walk_read():
+    client = _client(_one_channel([]))
+    url = "https://discord.com/channels/1/2"
+    assert client.source_label(url) is None  # nothing walked yet
+    list(client.iter_posts(url))
+    assert client.source_label(url) == "Todding's Server · #banana-land"
+    assert client.source_label("https://discord.com/channels/1") == "Todding's Server"
+    client._channels["9"] = {"channel": "wip", "is_thread": True, "parent": "banana-land"}
+    assert client.source_label("https://discord.com/channels/1/9") == (
+        "Todding's Server · #banana-land › wip"
+    )
+
+
 def test_a_server_walks_text_then_threads_newest_created_first_and_skips_private():
     routes = {
         "/guilds/1": _ok({"id": "1", "name": "S"}),

tests/test_post_feed_service.py

@@ -283,6 +283,27 @@ async def test_scroll_item_shape_minimal(db):
     assert "description_full" not in item
 
 
+@pytest.mark.asyncio
+async def test_a_discord_post_names_its_channel(db):
+    """#4481: the card says which channel a message came from. Read from the
+    record's `channel`; never on another platform, even with the same key."""
+    artist = await _seed_artist(db, "todding-ch")
+    dsrc = await _seed_source(db, artist.id, "discord", "https://discord.com/channels/1/2")
+    psrc = await _seed_source(db, artist.id, "patreon", "https://p/todding-ch")
+    now = datetime.now(UTC)
+    d = await _seed_post(db, dsrc.id, external_id="D1", post_date=now)
+    d.raw_metadata = {"category": "discord", "channel": "banana-land"}
+    blank = await _seed_post(db, dsrc.id, external_id="D2", post_date=now)
+    blank.raw_metadata = {"category": "discord", "channel": "  "}
+    p = await _seed_post(db, psrc.id, external_id="P1", post_date=now)
+    p.raw_metadata = {"channel": "not-discord"}
+    await db.commit()
+
+    page = await PostFeedService(db).scroll(cursor=None, limit=10, artist_id=artist.id)
+    by_id = {it["external_post_id"]: it["channel"] for it in page["items"]}
+    assert by_id == {"D1": "banana-land", "D2": None, "P1": None}
+
+
 @pytest.mark.asyncio
 async def test_scroll_surfaces_translation_fields(db):
     # #143: a translated post exposes the translated title/description + source