fix(modal): autocomplete picks resolve by tag_id, not just by name

Clicking an autocomplete row (or pressing Enter on a highlighted row)
now sends tag_id in the add-tag POST. Server attaches that exact tag,
skipping parse_kind_prefix. Same-name ambiguity — e.g. a character
tag 'Yidhari' and a user tag 'Yidhari' both matching the autocomplete
query 'yid' — now resolves by whichever row the user picked, instead
of silently routing to the user-kind fallback.

Bare free-text input (no click) still goes through parse_kind_prefix
with its kind: shortcut and kind='user' default. The fandom picker
path is untouched.

The click handler also stashes tag_id on the dataset so the keyboard
Enter path on a highlighted row picks up the same resolution.

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

app/main.py

@@ -932,61 +932,76 @@ def add_tag(image_id):
     """
     JSON endpoint to add a tag to an image.
 
-    Accepts the user-facing 'kind:name' shortcut in the 'name' field
-    (e.g. 'character:Saber'). Bare strings without a recognized prefix are
-    treated as user tags.
+    Resolution order:
+      - If 'tag_id' is provided, attach that exact tag (used when the
+        autocomplete picker resolves a specific row). Auto-applies the
+        character's fandom if set. Skips parse_kind_prefix entirely.
+      - Else parse the user-facing 'kind:name' shortcut in the 'name' field
+        (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).
+    For character tags created via the parse path, optional 'fandom_id'
+    (preferred) or 'fandom_name' attaches the character to a fandom. Both
+    omitted = null fandom (allowed).
     """
     from app.utils.tag_prefix import parse_kind_prefix
     from app.utils.tag_names import underscores_to_spaces
 
-    raw = (request.form.get("name") or "").strip()
-    if not raw:
-        abort(400)
-
-    kind, name = parse_kind_prefix(raw)
-    if kind is None:
-        # No recognized prefix — treat as a user-typed general tag.
-        kind = "user"
-        name = underscores_to_spaces(name)
-    elif kind in ("character", "fandom"):
-        name = normalize_display_name(name)
-
     img = ImageRecord.query.get_or_404(image_id)
 
+    explicit_tag_id = request.form.get("tag_id", type=int)
     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 fandom_id:
-            fandom_tag = Tag.query.filter_by(id=fandom_id, kind="fandom").first()
-            if fandom_tag is None:
-                return jsonify(ok=False, error="fandom_not_found"), 400
-        elif fandom_name:
-            fandom_tag = _ensure_fandom_tag(fandom_name)
-
-        tag = Tag.query.filter_by(
-            kind="character",
-            name=name,
-            fandom_id=fandom_tag.id if fandom_tag else None,
-        ).first()
+    if explicit_tag_id:
+        # Autocomplete-picker path: attach the exact clicked tag.
+        tag = Tag.query.get(explicit_tag_id)
         if tag is None:
-            tag = Tag(
+            return jsonify(ok=False, error="tag_not_found"), 404
+        if tag.kind == "character" and tag.fandom_id:
+            fandom_tag = Tag.query.get(tag.fandom_id)
+    else:
+        raw = (request.form.get("name") or "").strip()
+        if not raw:
+            abort(400)
+
+        kind, name = parse_kind_prefix(raw)
+        if kind is None:
+            # No recognized prefix — treat as a user-typed general tag.
+            kind = "user"
+            name = underscores_to_spaces(name)
+        elif kind in ("character", "fandom"):
+            name = normalize_display_name(name)
+
+        if kind == "character":
+            fandom_id = request.form.get("fandom_id", type=int)
+            fandom_name = (request.form.get("fandom_name") or "").strip() or None
+
+            if fandom_id:
+                fandom_tag = Tag.query.filter_by(id=fandom_id, kind="fandom").first()
+                if fandom_tag is None:
+                    return jsonify(ok=False, error="fandom_not_found"), 400
+            elif fandom_name:
+                fandom_tag = _ensure_fandom_tag(fandom_name)
+
+            tag = Tag.query.filter_by(
                 kind="character",
                 name=name,
                 fandom_id=fandom_tag.id if fandom_tag else None,
-            )
-            db.session.add(tag)
-            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()
+            ).first()
+            if tag is None:
+                tag = Tag(
+                    kind="character",
+                    name=name,
+                    fandom_id=fandom_tag.id if fandom_tag else None,
+                )
+                db.session.add(tag)
+                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()
 
     if tag not in img.tags:
         img.tags.append(tag)