refactor(main): add_tag parses prefix at boundary; bare storage

Accepts 'character:Saber' user shortcut, parses via parse_kind_prefix,
stores tag.name bare. Character path accepts fandom_id (preferred) or
fandom_name for fandom association. Returns display_name in the
response so the client can render pills without a second round-trip.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/main.py

@@ -861,72 +861,86 @@ def reject_image_suggestion(image_id):
 @main.post("/image/<int:image_id>/tags/add")
 def add_tag(image_id):
     """
-    Minimal JSON endpoint to add a tag to an image.
+    JSON endpoint to add a tag to an image.
-    Accepts either 'artist:NAME' / 'archive:...' or a bare freeform tag ('mytag').
 
-    For character tags with a fandom suffix (e.g. 'character:Saber (Fate)'),
+    Accepts the user-facing 'kind:name' shortcut in the 'name' field
-    automatically creates/finds the fandom tag and adds it to the image.
+    (e.g. 'character:Saber'). Bare strings without a recognized prefix are
+    treated as user tags.
+
+    For character tags, optional 'fandom_id' (preferred) or 'fandom_name'
+    attaches the character to a fandom. Both omitted = null fandom (allowed).
     """
-    name = (request.form.get("name") or "").strip()
+    from app.utils.tag_prefix import parse_kind_prefix
-    if not name:
+    from app.utils.tag_names import underscores_to_spaces
+
+    raw = (request.form.get("name") or "").strip()
+    if not raw:
         abort(400)
 
-    # Normalize: keep explicit kind prefixes, otherwise treat as user tag
+    kind, name = parse_kind_prefix(raw)
-    if ":" in name:
+    if kind is None:
-        kind = name.split(":", 1)[0]
+        # No recognized prefix — treat as a user-typed general tag.
-        tag_name = name
-    else:
-        # No prefix — treat as a user-typed general tag. Strip underscores so
-        # WD14-style names pasted into the add box converge with our convention.
-        from app.utils.tag_names import underscores_to_spaces
         kind = "user"
-        tag_name = underscores_to_spaces(name)
+        name = underscores_to_spaces(name)
+    elif kind in ("character", "fandom"):
+        name = normalize_display_name(name)
 
     img = ImageRecord.query.get_or_404(image_id)
-    tag = Tag.query.filter_by(name=tag_name).first()
 
     fandom_tag = None
+    if kind == "character":
+        fandom_id = request.form.get("fandom_id", type=int)
+        fandom_name = (request.form.get("fandom_name") or "").strip() or None
 
-    if not tag:
+        if fandom_id:
-        # For new character tags, parse + normalize + link fandom
+            fandom_tag = Tag.query.filter_by(id=fandom_id, kind="fandom").first()
-        if kind == "character":
+            if fandom_tag is None:
-            char_part = tag_name.split(":", 1)[1]
+                return jsonify(ok=False, error="fandom_not_found"), 400
-            char_name, fandom_name = _parse_character_fandom(char_part)
+        elif fandom_name:
-            norm_char = normalize_display_name(char_name)
+            fandom_tag = _ensure_fandom_tag(fandom_name)
-            if fandom_name:
+
-                fandom_tag = _ensure_fandom_tag(fandom_name)
+        tag = Tag.query.filter_by(
-                tag_name = f"character:{norm_char} ({fandom_tag.name.split(':', 1)[1]})"
+            kind="character",
-            else:
+            name=name,
-                tag_name = f"character:{norm_char}"
+            fandom_id=fandom_tag.id if fandom_tag else None,
-        elif kind == "fandom":
+        ).first()
-            fandom_part = tag_name.split(":", 1)[1]
+        if tag is None:
-            tag_name = f"fandom:{normalize_display_name(fandom_part)}"
+            tag = Tag(
-        # Look up again under the normalized name — an existing row may match.
+                kind="character",
-        tag = Tag.query.filter_by(name=tag_name).first()
+                name=name,
-        if not tag:
+                fandom_id=fandom_tag.id if fandom_tag else None,
-            tag = Tag(name=tag_name, kind=kind)
+            )
-            if kind == "character" and fandom_name:
+            db.session.add(tag)
-                tag.fandom_id = fandom_tag.id
+            db.session.flush()
+    else:
+        tag = Tag.query.filter_by(kind=kind, name=name).first()
+        if tag is None:
+            tag = Tag(kind=kind, name=name)
             db.session.add(tag)
             db.session.flush()
-        elif kind == "character" and tag.fandom_id:
-            fandom_tag = Tag.query.get(tag.fandom_id)
-    elif tag.kind == "character" and tag.fandom_id:
-        # Existing character tag with a fandom — grab the fandom tag for auto-apply
-        fandom_tag = Tag.query.get(tag.fandom_id)
 
     if tag not in img.tags:
         img.tags.append(tag)
 
-    # Auto-apply fandom tag to the image
+    # Auto-apply fandom tag to the image (preserves today's UX feature).
     if fandom_tag and fandom_tag not in img.tags:
         img.tags.append(fandom_tag)
 
     db.session.commit()
 
-    result = {"name": tag.name, "kind": tag.kind}
+    result = {
+        "id": tag.id,
+        "name": tag.name,
+        "display_name": tag.display_name,
+        "kind": tag.kind,
+    }
     if fandom_tag:
-        result["fandom_tag"] = {"name": fandom_tag.name, "kind": fandom_tag.kind}
+        result["fandom_tag"] = {
+            "id": fandom_tag.id,
+            "name": fandom_tag.name,
+            "display_name": fandom_tag.display_name,
+            "kind": fandom_tag.kind,
+        }
     return jsonify(ok=True, tag=result)