fix(sqlite): fall back to journal_mode=DELETE on NFS/SMB/FUSE (#22043)

SQLite's WAL mode requires shared-memory (mmap) coordination and fcntl
byte-range locks that don't reliably work on network filesystems. Upstream
documents this explicitly:
  https://www.sqlite.org/wal.html#sometimes_queries_return_sqlite_busy_in_wal_mode

On NFS / SMB / some FUSE mounts / WSL1, 'PRAGMA journal_mode=WAL' raises
'sqlite3.OperationalError: locking protocol' (SQLITE_PROTOCOL). Before
this change, every feature backed by state.db or kanban.db broke silently:
  - /resume, /title, /history, /branch returned 'Session database not
    available.' with no cause
  - gateway logged the init failure at DEBUG (invisible in errors.log)
  - kanban dispatcher crashed every 60s, driving the known migration race
    (duplicate column name: consecutive_failures, #21708 / #21374)

Changes:
  - hermes_state.apply_wal_with_fallback(): shared helper that tries WAL
    and falls back to DELETE on SQLITE_PROTOCOL-style errors with one
    WARNING explaining why
  - hermes_state.get_last_init_error() + format_session_db_unavailable():
    capture the init failure cause and surface it in user-facing strings
    (with an NFS/SMB pointer for 'locking protocol')
  - hermes_cli/kanban_db.connect(): use the shared helper
  - gateway/run.py: bump SessionDB init failure log DEBUG -> WARNING
    (matches cli.py's existing correct behavior)
  - cli.py (4 sites) + gateway/run.py (5 sites): replace bare
    'Session database not available.' with format_session_db_unavailable()

Tests: 12 new tests in tests/test_hermes_state_wal_fallback.py + 1 new
test in tests/hermes_cli/test_kanban_db.py. Existing suites (state,
kanban, gateway, cli) remain green for all tests unrelated to pre-existing
failures on main.

Evidence: real-world user on NFSv3 mount (172.26.224.200:d2dfac12/home,
local_lock=none) reporting 'Session database not available.' on /resume;
'locking protocol' appears in 4 distinct log entries across backup,
kanban, TUI, and CLI paths in the same session.

closes #22032

tests/hermes_cli/test_kanban_db.py

@@ -914,3 +914,55 @@ def test_latest_summaries_batch_omits_tasks_without_summary(kanban_home):
         assert out == {t1: "alpha", t3: "charlie"}
         # Empty input → empty dict, no SQL syntax error from "IN ()".
         assert kb.latest_summaries(conn, []) == {}
+
+
+
+# ---------------------------------------------------------------------------
+# NFS / network-filesystem fallback (see hermes_state.apply_wal_with_fallback)
+# ---------------------------------------------------------------------------
+
+def test_connect_falls_back_to_delete_on_locking_protocol(kanban_home, caplog):
+    """kanban_db.connect() must handle ``locking protocol`` on NFS/SMB.
+
+    Without this fallback, the gateway's kanban dispatcher crashes every
+    60s and the kanban migration (``consecutive_failures`` ADD COLUMN) is
+    retried forever — which is what the real-world user report shows
+    (see hermes-agent issue #22032).
+    """
+    import sqlite3 as _sqlite3
+    from unittest.mock import patch as _patch
+
+    # Clear module cache so a fresh connect() is attempted
+    kb._INITIALIZED_PATHS.clear()
+
+    real_connect = _sqlite3.connect
+
+    class _WalBlockingConnection(_sqlite3.Connection):
+        def execute(self, sql, *args, **kwargs):  # type: ignore[override]
+            if "journal_mode=wal" in sql.lower().replace(" ", ""):
+                raise _sqlite3.OperationalError("locking protocol")
+            return super().execute(sql, *args, **kwargs)
+
+    def wal_blocking_connect(*args, **kwargs):
+        return real_connect(
+            *args, factory=_WalBlockingConnection, **kwargs
+        )
+
+    with _patch("hermes_cli.kanban_db.sqlite3.connect", side_effect=wal_blocking_connect):
+        with caplog.at_level("WARNING", logger="hermes_state"):
+            conn = kb.connect()
+
+    # One fallback warning, naming kanban.db
+    warnings = [
+        r for r in caplog.records
+        if r.levelname == "WARNING" and "kanban.db" in r.getMessage()
+    ]
+    assert len(warnings) >= 1, (
+        f"Expected a kanban.db WARNING, got: {[r.getMessage() for r in caplog.records]}"
+    )
+
+    # DB still usable end-to-end — create + list a task
+    t = kb.create_task(conn, title="post-fallback task")
+    tasks = kb.list_tasks(conn)
+    assert any(row.id == t for row in tasks)
+    conn.close()