fix(kanban): skip redundant WAL pragma on already-WAL connections

apply_wal_with_fallback() issued PRAGMA journal_mode=WAL on every call,
including connections to DBs already in WAL mode. This triggered the WAL
init code path, causing SQLite to acquire EXCLUSIVE, checkpoint, and unlink
kanban.db-{wal,shm}. Other open connections received (deleted) FDs and
raised sqlite3.OperationalError: disk I/O error.

Add a cheap read probe (PRAGMA journal_mode, no flock/checkpoint/unlink)
before the set-pragma path. If already wal, return early. The set-pragma
and DELETE fallback paths are unchanged.

Closes #31158. Addresses root cause that PRs #32226 and #32322 attempted
via connection-sharing/caching approaches.

hermes_state.py

@@ -170,6 +170,15 @@ def apply_wal_with_fallback(
 
     Never downgrades to DELETE if the on-disk DB header reports WAL — see _on_disk_journal_mode.
     """
+    # Read-only probe — no flock, no checkpoint, no WAL/SHM unlink.
+    # Skipping the set-pragma prevents WAL-init from unlinking files other connections hold open.
+    try:
+        current_mode = conn.execute("PRAGMA journal_mode").fetchone()
+        if current_mode and current_mode[0] == "wal":
+            return "wal"
+    except sqlite3.OperationalError:
+        pass
+
     try:
         conn.execute("PRAGMA journal_mode=WAL")
         return "wal"