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>

backend/app/services/discord_client.py

@@ -32,6 +32,13 @@ Two deliberate departures, both about the walk order, neither about content:
     the walk. gallery-dl skips only nested channels; one private thread the
     token cannot read would otherwise stop every channel after it.
 
+And one about content: a message is taken only if it has an image or video
+ATTACHMENT (`has_visual_attachment`). Discord is where creators chat as well
+as post, and the operator wants the art, not the conversation (2026-09-28): a
+text line, a lone archive or PSD, a pasted link's preview or a Tenor GIF is
+chat. A message that passes keeps every file gallery-dl would take, numbered
+as gallery-dl numbers them, so the on-disk names still match.
+
 FC runs on a plain-HTTP homelab; nothing here uses a secure-context Web API.
 """
 
@@ -79,6 +86,13 @@ _FORUM = frozenset({15, 16})            # forum, media: threads only
 _CATEGORY = 4
 _SERVER_WALK = _TEXT | _FORUM
 _EMBED_TYPES = frozenset({"image", "gifv", "video"})
+# What makes a message art rather than chat: an attached file FC imports as an
+# image or video. Mirrors importer.ALL_EXTS (not imported: that module is the
+# import pipeline, and this one is a network client).
+_VISUAL_EXTS = frozenset({
+    "png", "jpg", "jpeg", "gif", "webp", "bmp", "tif", "tiff",
+    "mp4", "mov", "avi", "mkv", "webm", "m4v", "wmv", "flv",
+})
 
 _URL_RE = re.compile(
     r"^(?:https?://)?(?:www\.|ptb\.|canary\.)?discord(?:app)?\.com/channels/"
@@ -163,6 +177,33 @@ def message_text(message: dict) -> str:
     return "\n".join(p for p in parts if p)
 
 
+def _message_and_snapshots(message: dict) -> list[dict]:
+    """The message itself, then each forwarded message it carries."""
+    return [message] + [
+        (s or {}).get("message") or {}
+        for s in message.get("message_snapshots") or []
+        if ((s or {}).get("message") or {}).get("type", 0) in MESSAGE_TYPES
+    ]
+
+
+def _is_visual(attachment: dict) -> bool:
+    ctype = (attachment.get("content_type") or "").lower()
+    if ctype.startswith(("image/", "video/")):
+        return True
+    name = attachment.get("filename") or attachment.get("url") or ""
+    return nameext_from_url(name)[1] in _VISUAL_EXTS
+
+
+def has_visual_attachment(message: dict) -> bool:
+    """Does this message, or a message it forwards, have an image or video
+    attached? The one test for "art, not chat" — see the module docstring."""
+    return any(
+        att.get("url") and _is_visual(att)
+        for snap in _message_and_snapshots(message)
+        for att in snap.get("attachments") or []
+    )
+
+
 @dataclass
 class MediaItem:
     """One file of a Discord message. `filename`/`extension` are gallery-dl's
@@ -212,6 +253,8 @@ class DiscordClient:
         self._server: dict = {}
         self._channels: dict[str, dict] = {}
         self._skip_feed = False
+        # Whose messages the walk takes (`only_from`); empty takes everyone's.
+        self._authors: frozenset[str] = frozenset()
 
     # -- request -----------------------------------------------------------
 
@@ -373,6 +416,43 @@ class DiscordClient:
             if meta["channel_type"] in _SERVER_WALK:
                 yield from self._feeds(meta["channel_id"], safe=True)
 
+    def only_from(self, authors) -> None:
+        """Take only messages posted by these people: user ids, usernames or
+        display names, any case. A creator's server is full of other members
+        posting their own pictures; the source is subscribed to the creator.
+        Empty or None takes everyone's, as before."""
+        self._authors = frozenset(
+            str(a).strip().lower() for a in authors or () if str(a).strip()
+        )
+
+    def _author_wanted(self, message: dict) -> bool:
+        if not self._authors:
+            return True
+        author = message.get("author") or {}
+        names = (author.get("id"), author.get("username"), author.get("global_name"))
+        return any(str(n).lower() in self._authors for n in names if n)
+
+    def source_label(self, url: str) -> str | None:
+        """What the source is called in Discord — `Server · #channel`, a
+        thread as `#parent › thread`, a whole server by its name — from the
+        metadata the walk loaded. None when the walk never got that far."""
+        try:
+            _, channel_id = parse_source_url(url)
+        except DiscordAPIError:
+            return None
+        server = self._server.get("server") or None
+        if channel_id is None:
+            return server
+        meta = self._channels.get(channel_id) or {}
+        name = meta.get("channel")
+        if not name:
+            return None
+        if name != "DMs":
+            name = f"#{name}"
+            if meta.get("is_thread") and meta.get("parent"):
+                name = f"#{meta['parent']} › {meta['channel']}"
+        return f"{server} · {name}" if server else name
+
     def skip_feed(self) -> None:
         """Optional core seam (#4413): end the current channel and go on to the
         next one. A tick's early-out means THIS channel has nothing new, not
@@ -440,6 +520,8 @@ class DiscordClient:
             for message in messages:
                 if message.get("type") not in MESSAGE_TYPES:
                     continue
+                if not self._author_wanted(message):
+                    continue
                 message["_meta"] = meta
                 yield message, meta, page_cursor
                 if self._skip_feed:
@@ -454,13 +536,14 @@ class DiscordClient:
     def extract_media(post: dict, included: dict | None = None) -> list[MediaItem]:
         """gallery-dl's file list for one message: attachments, then the first
         of video/image/thumbnail `proxy_url` of each file-bearing embed, then
-        the same for every forwarded snapshot; numbered from 1 across them."""
+        the same for every forwarded snapshot; numbered from 1 across them.
+
+        Empty for a message with no image or video attached: that is chat,
+        whatever else it carries (`has_visual_attachment`)."""
+        if not has_visual_attachment(post):
+            return []
         mid = str(post.get("id") or "")
-        snapshots = [post] + [
-            (s or {}).get("message") or {}
-            for s in post.get("message_snapshots") or []
-            if ((s or {}).get("message") or {}).get("type", 0) in MESSAGE_TYPES
-        ]
+        snapshots = _message_and_snapshots(post)
         found: list[tuple[str, str, str | None]] = []
         for snap in snapshots:
             for att in snap.get("attachments") or []:
@@ -498,10 +581,10 @@ class DiscordClient:
         """`(message:<id>, <id>)` — gates the message record through the seen
         ledger, like `post:<id>` on the other platforms.
 
-        None for a message with no files. gallery-dl wrote a sidecar only
-        beside a file, so a text-only chat line never became a post, and the
-        drop grouping (discord_grouping) is built on that: a channel's chatter
-        recorded as posts would bury the drops it exists to surface."""
+        None for a message `extract_media` takes nothing from, i.e. one with
+        no image or video attached. The drop grouping (discord_grouping) is
+        built on that: a channel's chatter recorded as posts would bury the
+        drops it exists to surface."""
         mid = post.get("id")
         mid = str(mid) if mid is not None else ""
         if not mid or not cls.extract_media(post):