fix(file-ops): preserve CWD across terminal environment re-creation (#26211)

Root cause: when the terminal environment (`_active_environments` entry) is
cleaned up and re-created during a long conversation, the new environment
always starts with the default config CWD (typically `~/.hermes/hermes-agent`)
instead of preserving the user's last-known working directory. Subsequent
relative-path writes (`write_file`, `execute_code`, shell commands) silently
land in the default CWD, making files appear to be "created but absent."

Fix: add `_last_known_cwd` dict that preserves the old environment's CWD
before the stale cache entry is invalidated. When a new environment is
created for the same task_id, we check `_last_known_cwd` first and use the
preserved CWD instead of the config default.

Changes:
- tools/file_tools.py: add `_last_known_cwd` dict, save CWD before stale
  cache invalidation, restore CWD on env recreation
- tests/tools/test_file_tools.py: add `TestLastKnownCwd` with 2 tests
  verifying CWD preservation and fallback behavior

Fixes #26211

tests/tools/test_file_tools.py

@@ -513,3 +513,105 @@ class TestPatchSchemaShape:
         params = PATCH_SCHEMA["parameters"]
         assert params["required"] == ["mode"]
         assert "anyOf" not in params and "oneOf" not in params
+
+
+# ---------------------------------------------------------------------------
+# _last_known_cwd tests (#26211: silent file creation failure in long conversations)
+# ---------------------------------------------------------------------------
+
+class TestLastKnownCwd:
+    """
+    When the terminal environment is cleaned up and re-created during a long
+    conversation, _last_known_cwd preserves the old environment's CWD so
+    subsequent file writes with relative paths land in the right directory.
+
+    Regression guard for issue #26211.
+    """
+
+    @patch("tools.terminal_tool._active_environments", new_callable=dict)
+    @patch("tools.file_tools._file_ops_cache", new_callable=dict)
+    @patch("tools.terminal_tool._get_env_config")
+    @patch("tools.terminal_tool._create_environment")
+    def test_last_known_cwd_preserved_across_env_recreation(
+        self, mock_create_env, mock_config, mock_cache, mock_active
+    ):
+        from tools.file_tools import _get_file_ops, _last_known_cwd
+
+        # Setup: create a mock env with a known CWD
+        mock_env = MagicMock()
+        mock_env.cwd = "/Users/user/project"
+        mock_create_env.return_value = mock_env
+        mock_config.return_value = {
+            "env_type": "local",
+            "cwd": "/default/path",
+            "timeout": 30,
+        }
+
+        task_id = "default"
+
+        # Preset _last_known_cwd to simulate a previous env's CWD
+        _last_known_cwd[task_id] = "/Users/user/project"
+
+        # Call _get_file_ops - should use _last_known_cwd for the new env
+        result = _get_file_ops(task_id)
+
+        # Verify the env was created with the saved CWD, not the default
+        create_call = mock_create_env.call_args
+        assert create_call is not None, "_create_environment was not called"
+        
+        # Find cwd in the kwargs
+        kwargs = create_call.kwargs if create_call.kwargs else {}
+        # cwd is passed as positional or keyword
+        cwd_passed = kwargs.get("cwd", None)
+        if cwd_passed is None:
+            # Try positional args
+            args = create_call.args if create_call.args else []
+            # Position: (env_type, image, cwd, timeout, ...)
+            if len(args) >= 3:
+                cwd_passed = args[2]
+        
+        assert cwd_passed == "/Users/user/project", \
+            f"Expected cwd='/Users/user/project', got {cwd_passed!r}"
+        
+        # Cleanup
+        _last_known_cwd.pop(task_id, None)
+        
+    @patch("tools.terminal_tool._active_environments", new_callable=dict)
+    @patch("tools.file_tools._file_ops_cache", new_callable=dict)
+    @patch("tools.terminal_tool._get_env_config")
+    @patch("tools.terminal_tool._create_environment")
+    def test_last_known_cwd_falls_back_to_config_default_when_not_set(
+        self, mock_create_env, mock_config, mock_cache, mock_active
+    ):
+        from tools.file_tools import _get_file_ops, _last_known_cwd
+
+        mock_env = MagicMock()
+        mock_env.cwd = "/default/path"
+        mock_create_env.return_value = mock_env
+        mock_config.return_value = {
+            "env_type": "local",
+            "cwd": "/config/default/path",
+            "timeout": 30,
+        }
+
+        # _get_file_ops resolves to "default"
+        task_id = "default"
+        
+        # Ensure _last_known_cwd is empty for this task
+        _last_known_cwd.pop(task_id, None)
+
+        result = _get_file_ops(task_id)
+        
+        create_call = mock_create_env.call_args
+        assert create_call is not None, "_create_environment was not called"
+        
+        kwargs = create_call.kwargs if create_call.kwargs else {}
+        cwd_passed = kwargs.get("cwd", None)
+        if cwd_passed is None:
+            args = create_call.args if create_call.args else []
+            if len(args) >= 3:
+                cwd_passed = args[2]
+        
+        # Should fall back to config default
+        assert cwd_passed == "/config/default/path", \
+            f"Expected cwd='/config/default/path', got {cwd_passed!r}"

tools/file_tools.py

@@ -555,6 +555,10 @@ def _is_expected_write_exception(exc: Exception) -> bool:
 
 _file_ops_lock = threading.Lock()
 _file_ops_cache: dict = {}
+# Per-task last-known CWD — preserved across env re-creation so
+# relative-path file writes land in the right directory after the
+# terminal environment is cleaned up and rebuilt (root cause of #26211).
+_last_known_cwd: dict = {}
 
 # Track files read per task to detect re-read loops and deduplicate reads.
 # Per task_id we store:
@@ -789,7 +793,13 @@ def _get_file_ops(task_id: str = "default") -> ShellFileOperations:
                 _last_activity[task_id] = time.time()
                 return cached
             else:
-                # Environment was cleaned up -- invalidate stale cache entry
+                # Environment was cleaned up -- preserve the old cwd before
+                # invalidating the stale cache entry (fixes #26211: silent
+                # file-creation failures in long-running conversations).
+                old_cwd = getattr(cached, "cwd", None)
+                if old_cwd:
+                    with _file_ops_lock:
+                        _last_known_cwd[task_id] = old_cwd
                 with _file_ops_lock:
                     _file_ops_cache.pop(task_id, None)
 
@@ -827,7 +837,7 @@ def _get_file_ops(task_id: str = "default") -> ShellFileOperations:
             else:
                 image = ""
 
-            cwd = overrides.get("cwd") or config["cwd"]
+            cwd = overrides.get("cwd") or _last_known_cwd.get(task_id) or config["cwd"]
             logger.info("Creating new %s environment for task %s...", env_type, task_id[:8])
 
             container_config = None