Fix flaky extension SW boot: set XDG_RUNTIME_DIR before Chrome launch

Headless Chrome logged "XDG_RUNTIME_DIR is invalid or not set" and the three
MV3 extension service workers intermittently failed to spawn
(DidStartWorkerFail: 5), so /gpt /gemini /flow never connected. Create and
export a valid per-user runtime dir before launching Chrome. Purely additive.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

start_hf.sh

@@ -121,6 +121,14 @@ if [ -n "$DATABASE_URL" ]; then
     ( while sleep 300; do /opt/profilesync/profilesync backup >/dev/null 2>&1 || true; done ) &
 fi
 
+# 6c. Provide a valid per-user runtime dir. Chrome's mojo/IPC layer and each MV3
+#     extension service worker need this; without it Chrome logs
+#     "XDG_RUNTIME_DIR is invalid or not set" and the extension service workers
+#     intermittently fail to spawn (DidStartWorkerFail) → the gpt/gemini/flow
+#     extensions never connect. Purely additive: just creates a dir and exports it.
+export XDG_RUNTIME_DIR=/tmp/runtime-chrome
+mkdir -p "$XDG_RUNTIME_DIR" && chmod 700 "$XDG_RUNTIME_DIR"
+
 # 7. Launch Chrome Headless
 # NOTE: do NOT add --renderer-process-limit=1 / --process-per-site / --no-zygote here.
 # Each of the 3 extensions runs an MV3 service worker (its own renderer) and the chat