fix(tools): remove unnecessary crontab requirement from cronjob tool (#1638)

* fix(tools): remove unnecessary crontab requirement from cronjob tool

The hermes cron system is internal — it uses a JSON-based scheduler
ticked by the gateway (cron/scheduler.py), not system crontab.

The check for shutil.which('crontab') was preventing the cronjob tool
from being available in environments without crontab installed (e.g.
minimal Ubuntu containers).

Changes:
- Remove shutil.which('crontab') check from check_cronjob_requirements()
- Remove unused shutil import
- Update docstring to clarify internal scheduler is used
- Update tests to reflect new behavior and add coverage for all
  session modes (interactive, gateway, exec_ask)

Fixes #1589

* test: add HERMES_EXEC_ASK coverage for cronjob requirements

Adds missing test for the exec_ask session mode, complementing
the cherry-picked fix from PR #1633.

---------

Co-authored-by: Bartok9 <bartokmagic@proton.me>

tests/tools/test_cronjob_tools.py

@@ -62,22 +62,44 @@ class TestScanCronPrompt:
 
 
 class TestCronjobRequirements:
-    def test_requires_crontab_binary_even_in_interactive_mode(self, monkeypatch):
+    def test_requires_no_crontab_binary(self, monkeypatch):
+        """Cron is internal (JSON-based scheduler), no system crontab needed."""
         monkeypatch.setenv("HERMES_INTERACTIVE", "1")
         monkeypatch.delenv("HERMES_GATEWAY_SESSION", raising=False)
         monkeypatch.delenv("HERMES_EXEC_ASK", raising=False)
-        monkeypatch.setattr("shutil.which", lambda name: None)
+        # Even with no crontab in PATH, the cronjob tool should be available
+        # because hermes uses an internal scheduler, not system crontab.
+        assert check_cronjob_requirements() is True
 
-        assert check_cronjob_requirements() is False
-
-    def test_accepts_interactive_mode_when_crontab_exists(self, monkeypatch):
+    def test_accepts_interactive_mode(self, monkeypatch):
         monkeypatch.setenv("HERMES_INTERACTIVE", "1")
         monkeypatch.delenv("HERMES_GATEWAY_SESSION", raising=False)
         monkeypatch.delenv("HERMES_EXEC_ASK", raising=False)
-        monkeypatch.setattr("shutil.which", lambda name: "/usr/bin/crontab")
 
         assert check_cronjob_requirements() is True
 
+    def test_accepts_gateway_session(self, monkeypatch):
+        monkeypatch.delenv("HERMES_INTERACTIVE", raising=False)
+        monkeypatch.setenv("HERMES_GATEWAY_SESSION", "1")
+        monkeypatch.delenv("HERMES_EXEC_ASK", raising=False)
+
+        assert check_cronjob_requirements() is True
+
+    def test_accepts_exec_ask(self, monkeypatch):
+        monkeypatch.delenv("HERMES_INTERACTIVE", raising=False)
+        monkeypatch.delenv("HERMES_GATEWAY_SESSION", raising=False)
+        monkeypatch.setenv("HERMES_EXEC_ASK", "1")
+
+        assert check_cronjob_requirements() is True
+
+    def test_rejects_when_no_session_env(self, monkeypatch):
+        """Without any session env vars, cronjob tool should not be available."""
+        monkeypatch.delenv("HERMES_INTERACTIVE", raising=False)
+        monkeypatch.delenv("HERMES_GATEWAY_SESSION", raising=False)
+        monkeypatch.delenv("HERMES_EXEC_ASK", raising=False)
+
+        assert check_cronjob_requirements() is False
+
 
 # =========================================================================
 # schedule_cronjob