fix(test): disables helper auto-detect must follow symlinks (#7654)

ep_disable_chat#75 ran with `disables: ["@feature:chat"]` declared in
ep.json but the helper printed "No 'disables' declared — running
standard test suite" and exec'd a vanilla `playwright test`, with
@feature:chat-tagged tests running anyway and timing out one by one.

Root cause: the auto-detect used `find -maxdepth 3 plugin_packages/
-name ep.json -not -path '*/.versions/*'`. Live-plugin-manager
installs plugins under `plugin_packages/.versions/<name>@<ver>/`
and exposes them as symlinks at `plugin_packages/ep_<name>`. find(1)
doesn't follow symlinks by default, so:
  - the .versions/ ep.json was excluded by -not -path
  - the symlink at plugin_packages/ep_<name> was visited but find
    didn't recurse into it because it's a symlink, not a real dir
=> 0 candidates found, helper falls through to standard mode.

Switch to a shell glob with `-f` membership tests, which resolve
symlinks correctly. Verified against a synthetic install: the helper
now finds the disables list and prints "Plugin disables: @feature:chat"
before running pass 1.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

bin/run-frontend-tests-with-disables.sh

@@ -71,12 +71,22 @@ elif [[ -n "$EP_JSON" ]]; then
   DISABLES="$(read_disables_from_json "$EP_JSON")"
 else
   # Auto-detect from plugin_packages/. Skip if 0 or >1 disabling plugins.
+  #
+  # Live-plugin-manager installs plugins under plugin_packages/.versions/
+  # and exposes them as symlinks at plugin_packages/ep_<name>. find(1)
+  # doesn't follow symlinks by default, so iterate via shell glob and
+  # `-f $dir/ep.json` (which DOES resolve symlinks) instead.
   declare -a CANDIDATES=()
   if [[ -d plugin_packages ]]; then
-    while IFS= read -r f; do
+    shopt -s nullglob
+    for dir in plugin_packages/ep_*; do
+      [[ -L "$dir" || -d "$dir" ]] || continue
+      f="$dir/ep.json"
+      [[ -f "$f" ]] || continue
       d="$(read_disables_from_json "$f")"
       [[ -n "$d" ]] && CANDIDATES+=("$d")
-    done < <(find plugin_packages -maxdepth 3 -name ep.json -not -path '*/.versions/*' 2>/dev/null)
+    done
+    shopt -u nullglob
   fi
   if [[ ${#CANDIDATES[@]} -eq 1 ]]; then
     DISABLES="${CANDIDATES[0]}"