refactor(tests): re-architect tests + fix CI failures (#5946)

* refactor: re-architect tests to mirror the codebase

* Update tests.yml

* fix: add missing tool_error imports after registry refactor

* fix(tests): replace patch.dict with monkeypatch to prevent env var leaks under xdist

patch.dict(os.environ) can leak TERMINAL_ENV across xdist workers,
causing test_code_execution tests to hit the Modal remote path.

* fix(tests): fix update_check and telegram xdist failures

- test_update_check: replace patch("hermes_cli.banner.os.getenv") with
  monkeypatch.setenv("HERMES_HOME") — banner.py no longer imports os
  directly, it uses get_hermes_home() from hermes_constants.

- test_telegram_conflict/approval_buttons: provide real exception classes
  for telegram.error mock (NetworkError, TimedOut, BadRequest) so the
  except clause in connect() doesn't fail with "catching classes that do
  not inherit from BaseException" when xdist pollutes sys.modules.

* fix(tests): accept unavailable_models kwarg in _prompt_model_selection mock

tests/hermes_cli/test_update_check.py

@@ -15,7 +15,7 @@ def test_version_string_no_v_prefix():
     assert not __version__.startswith("v"), f"__version__ should not start with 'v', got {__version__!r}"
 
 
-def test_check_for_updates_uses_cache(tmp_path):
+def test_check_for_updates_uses_cache(tmp_path, monkeypatch):
     """When cache is fresh, check_for_updates should return cached value without calling git."""
     from hermes_cli.banner import check_for_updates
 
@@ -27,15 +27,15 @@ def test_check_for_updates_uses_cache(tmp_path):
     cache_file = tmp_path / ".update_check"
     cache_file.write_text(json.dumps({"ts": time.time(), "behind": 3}))
 
-    with patch("hermes_cli.banner.os.getenv", return_value=str(tmp_path)):
-        with patch("hermes_cli.banner.subprocess.run") as mock_run:
-            result = check_for_updates()
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    with patch("hermes_cli.banner.subprocess.run") as mock_run:
+        result = check_for_updates()
 
     assert result == 3
     mock_run.assert_not_called()
 
 
-def test_check_for_updates_expired_cache(tmp_path):
+def test_check_for_updates_expired_cache(tmp_path, monkeypatch):
     """When cache is expired, check_for_updates should call git fetch."""
     from hermes_cli.banner import check_for_updates
 
@@ -49,15 +49,15 @@ def test_check_for_updates_expired_cache(tmp_path):
 
     mock_result = MagicMock(returncode=0, stdout="5\n")
 
-    with patch("hermes_cli.banner.os.getenv", return_value=str(tmp_path)):
-        with patch("hermes_cli.banner.subprocess.run", return_value=mock_result) as mock_run:
-            result = check_for_updates()
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    with patch("hermes_cli.banner.subprocess.run", return_value=mock_result) as mock_run:
+        result = check_for_updates()
 
     assert result == 5
     assert mock_run.call_count == 2  # git fetch + git rev-list
 
 
-def test_check_for_updates_no_git_dir(tmp_path):
+def test_check_for_updates_no_git_dir(tmp_path, monkeypatch):
     """Returns None when .git directory doesn't exist anywhere."""
     import hermes_cli.banner as banner
 
@@ -66,19 +66,15 @@ def test_check_for_updates_no_git_dir(tmp_path):
     fake_banner.parent.mkdir(parents=True, exist_ok=True)
     fake_banner.touch()
 
-    original = banner.__file__
-    try:
-        banner.__file__ = str(fake_banner)
-        with patch("hermes_cli.banner.os.getenv", return_value=str(tmp_path)):
-            with patch("hermes_cli.banner.subprocess.run") as mock_run:
-                result = banner.check_for_updates()
-        assert result is None
-        mock_run.assert_not_called()
-    finally:
-        banner.__file__ = original
+    monkeypatch.setattr(banner, "__file__", str(fake_banner))
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    with patch("hermes_cli.banner.subprocess.run") as mock_run:
+        result = banner.check_for_updates()
+    assert result is None
+    mock_run.assert_not_called()
 
 
-def test_check_for_updates_fallback_to_project_root():
+def test_check_for_updates_fallback_to_project_root(tmp_path, monkeypatch):
     """Dev install: falls back to Path(__file__).parent.parent when HERMES_HOME has no git repo."""
     import hermes_cli.banner as banner
 
@@ -87,14 +83,12 @@ def test_check_for_updates_fallback_to_project_root():
         pytest.skip("Not running from a git checkout")
 
     # Point HERMES_HOME at a temp dir with no hermes-agent/.git
-    import tempfile
-    with tempfile.TemporaryDirectory() as td:
-        with patch("hermes_cli.banner.os.getenv", return_value=td):
-            with patch("hermes_cli.banner.subprocess.run") as mock_run:
-                mock_run.return_value = MagicMock(returncode=0, stdout="0\n")
-                result = banner.check_for_updates()
-        # Should have fallen back to project root and run git commands
-        assert mock_run.call_count >= 1
+    monkeypatch.setenv("HERMES_HOME", str(tmp_path))
+    with patch("hermes_cli.banner.subprocess.run") as mock_run:
+        mock_run.return_value = MagicMock(returncode=0, stdout="0\n")
+        result = banner.check_for_updates()
+    # Should have fallen back to project root and run git commands
+    assert mock_run.call_count >= 1
 
 
 def test_prefetch_non_blocking():