fix: kanban dispatcher prefers module argv over PATH hermes

Review finding: hermes_cli/kanban_db_dispatch.py::_resolve_hermes_argv still resolved which('hermes') before sys.executable -m hermes_cli.main while claiming to mirror gateway.run._resolve_hermes_bin, which this PR made module-first (#111569). Keep the explicit HERMES_BIN override first, then the module argv whenever hermes_cli is importable, PATH only as fallback; docstring updated.

hermes_cli/kanban_db_dispatch.py

@@ -2158,12 +2158,16 @@ def _hermes_path_argv(path: str) -> list[str]:
 def _resolve_hermes_argv() -> list[str]:
     """Resolve the ``hermes`` invocation as argv for ``Popen``: ``$HERMES_BIN``
     (path-like -> absolute; bare names keep PATH semantics, never a
-    same-directory file), then ``which("hermes")`` (Windows: safe PATH search,
-    batch shims fall back to the module form), then ``sys.executable -m
-    hermes_cli.main`` for shim-less environments (cron, systemd ``User=``,
-    launchd). Mirrors ``gateway.run._resolve_hermes_bin``; local because
-    ``hermes_cli`` sits below ``gateway`` in the dependency order.
+    same-directory file), then the running interpreter's ``sys.executable -m
+    hermes_cli.main`` (exactly this install; also covers shim-less cron,
+    systemd ``User=``, launchd), then ``which("hermes")`` (Windows: safe PATH
+    search, batch shims fall back to the module form) only when ``hermes_cli``
+    is not importable. The module argv must win over PATH: a PATH-first lookup
+    lets an attacker-planted ``hermes`` shadow the running install (#111569).
+    Mirrors ``gateway.run._resolve_hermes_bin``; local because ``hermes_cli``
+    sits below ``gateway`` in the dependency order.
     """
+    import importlib.util
     import shutil
 
     env_bin = os.environ.get("HERMES_BIN", "").strip()
@@ -2175,6 +2179,12 @@ def _resolve_hermes_argv() -> list[str]:
             return _hermes_path_argv(resolved_env_bin)
         return _module_hermes_argv()
 
+    try:
+        if importlib.util.find_spec("hermes_cli") is not None:
+            return _module_hermes_argv()
+    except Exception:
+        pass
+
     hermes_bin = _safe_which_no_cwd("hermes") if _kb._IS_WINDOWS else shutil.which("hermes")
     if hermes_bin:
         return _hermes_path_argv(hermes_bin)

tests/hermes_cli/test_kanban_db.py

@@ -1360,11 +1360,29 @@ def test_migrate_add_optional_columns_tolerates_concurrent_migration(kanban_home
 # launchd jobs, and other detached processes routinely run with a stripped
 # $PATH that doesn't include the venv's bin/, so a bare `["hermes", ...]`
 # spawn fails with FileNotFoundError and the task gets stuck. The resolver
-# prefers the PATH shim (familiar `ps` output) but falls back to the module
-# form so the spawn keeps working when PATH is missing the shim.
+# prefers the interpreter-bound module form (exactly this install; a PATH
+# shim could be attacker-planted or belong to another install, #111569) and
+# only falls back to the PATH shim when ``hermes_cli`` is not importable.
 # ---------------------------------------------------------------------------
 
 
+def test_resolve_hermes_argv_prefers_module_form_over_path_shim(monkeypatch):
+    """A `hermes` on PATH must not shadow the running install (#111569):
+    the module argv wins whenever ``hermes_cli`` is importable; only an
+    explicit ``$HERMES_BIN`` overrides it."""
+    import shutil
+    import sys
+    from hermes_cli import kanban_db_dispatch as kbd
+
+    monkeypatch.delenv("HERMES_BIN", raising=False)
+    monkeypatch.setattr(shutil, "which", lambda name: "/tmp/planted/hermes")
+    monkeypatch.setattr(kbd, "_safe_which_no_cwd", lambda name: "/tmp/planted/hermes")
+    assert kbd._resolve_hermes_argv() == [sys.executable, "-m", "hermes_cli.main"]
+
+    monkeypatch.setenv("HERMES_BIN", "/opt/hermes/bin/hermes")
+    assert kbd._resolve_hermes_argv() == ["/opt/hermes/bin/hermes"]
+
+
 def test_resolve_hermes_argv_falls_back_to_module_form_when_no_path_shim(monkeypatch):
     """When the shim is not on PATH, fall back to `python -m hermes_cli.main`.