fix(tools): reject directory targets in open_preview (#95853)

Existing directories were reported as success:true while the preview
pane opened nothing. Fail closed with an explicit error and do not
emit preview.open. HTTP(S) URLs and regular files are unchanged.

tests/tools/test_open_preview_tool.py

@@ -23,3 +23,60 @@ def test_emitter_failure_is_reported():
 
     desktop_ui.set_emitter(_boom)
     assert "no window" in json.loads(op.open_preview_tool("https://x.example"))["error"]
+
+
+def _capture_emits():
+    emitted: list = []
+
+    def _emit(_sid, event, payload):
+        emitted.append((event, payload))
+
+    desktop_ui.set_emitter(_emit)
+    return emitted
+
+
+def test_existing_directory_is_an_error_not_success(tmp_path):
+    """#95853: a directory must not report success while opening nothing."""
+    emitted = _capture_emits()
+    folder = tmp_path / "Active"
+    folder.mkdir()
+
+    result = json.loads(op.open_preview_tool(str(folder)))
+
+    assert "error" in result
+    assert "director" in result["error"].lower()
+    assert result.get("success") is not True
+    assert emitted == []
+
+
+def test_existing_file_still_opens(tmp_path):
+    emitted = _capture_emits()
+    path = tmp_path / "notes.md"
+    path.write_text("hi", encoding="utf-8")
+
+    result = json.loads(op.open_preview_tool(str(path)))
+
+    assert result["success"] is True
+    assert result["url"] == str(path)
+    assert emitted == [("preview.open", {"url": str(path), "label": ""})]
+
+
+def test_https_url_is_not_treated_as_a_directory():
+    emitted = _capture_emits()
+    result = json.loads(op.open_preview_tool("https://example.com/docs"))
+
+    assert result["success"] is True
+    assert emitted[0][0] == "preview.open"
+
+
+def test_file_uri_directory_is_an_error(tmp_path):
+    emitted = _capture_emits()
+    folder = tmp_path / "docs"
+    folder.mkdir()
+    uri = folder.resolve().as_uri()
+
+    result = json.loads(op.open_preview_tool(uri))
+
+    assert "error" in result
+    assert "director" in result["error"].lower()
+    assert emitted == []

tools/open_preview_tool.py

@@ -6,7 +6,10 @@ the normalizer + open action. Emits ``preview.open`` via ``desktop_ui``: the ren
 the pane for the window that asked and never steals focus for a background session.
 """
 
+import os
 import re
+from pathlib import Path
+from urllib.parse import unquote, urlparse
 
 from tools import desktop_ui
 from tools.registry import tool_error
@@ -28,6 +31,39 @@ def _normalize_target(raw: str) -> str:
     return v
 
 
+def _local_fs_path(target: str) -> Path | None:
+    """Return a filesystem path for local targets; None for http(s) URLs."""
+    raw = (target or "").strip()
+    if not raw:
+        return None
+    if "://" in raw:
+        parsed = urlparse(raw)
+        if parsed.scheme.lower() != "file":
+            return None
+        path = unquote(parsed.path or "")
+        if parsed.netloc and parsed.netloc not in {"", "localhost"}:
+            path = f"//{parsed.netloc}{path}"
+        elif (
+            os.name == "nt"
+            and len(path) >= 3
+            and path[0] == "/"
+            and path[2] == ":"
+        ):
+            path = path[1:]
+        return Path(path) if path else None
+    return Path(raw).expanduser()
+
+
+def _is_existing_directory(target: str) -> bool:
+    path = _local_fs_path(target)
+    if path is None:
+        return False
+    try:
+        return path.is_dir()
+    except OSError:
+        return False
+
+
 def open_preview_tool(url: str, label: str = "") -> str:
     """Ask the desktop GUI to show ``url`` in the preview pane beside the chat."""
     target = _normalize_target(url or "")
@@ -35,6 +71,12 @@ def open_preview_tool(url: str, label: str = "") -> str:
         return tool_error(
             "url is required — a web URL (https://…), a localhost dev server, or a "
             "file path to show in the preview pane.")
+    if _is_existing_directory(target):
+        return tool_error(
+            "directories are not previewable — pass a file path or a URL. "
+            f"{target} is a directory."
+        )
+
     label = (label or "").strip()
     return desktop_ui.emit_or_error(
         "preview.open",