fix(admin): spawn chrome.exe directly on Windows for chrome:// inspect URL (#290)

src/browser_harness/admin.py

@@ -517,7 +517,8 @@ def _open_chrome_inspect():
     """Open chrome://inspect/#remote-debugging so the user can tick the checkbox."""
     import platform, subprocess, webbrowser
     url = "chrome://inspect/#remote-debugging"
-    if platform.system() == "Darwin":
+    system = platform.system()
+    if system == "Darwin":
         try:
             subprocess.run([
                 "osascript",
@@ -527,6 +528,26 @@ def _open_chrome_inspect():
             return
         except Exception:
             pass
+    elif system == "Windows":
+        # webbrowser.open() routes chrome:// through ShellExecute, which has no
+        # registered handler for the scheme -> Windows shows a "Get an app to
+        # open this" dialog instead of opening Chrome. Hand the URL to chrome.exe
+        # directly. (#290)
+        for env_var, suffix in (
+            ("PROGRAMFILES", "Google/Chrome/Application/chrome.exe"),
+            ("PROGRAMFILES(X86)", "Google/Chrome/Application/chrome.exe"),
+            ("LOCALAPPDATA", "Google/Chrome/Application/chrome.exe"),
+        ):
+            base = os.environ.get(env_var)
+            if not base:
+                continue
+            candidate = Path(base) / suffix
+            if candidate.exists():
+                try:
+                    subprocess.Popen([str(candidate), url])
+                    return
+                except Exception:
+                    pass
     try:
         webbrowser.open(url, new=2)
     except Exception:

tests/unit/test_admin.py

@@ -1,3 +1,7 @@
+import platform
+import subprocess
+import webbrowser
+
 import pytest
 
 from browser_harness import admin
@@ -48,6 +52,46 @@ def test_stale_websocket_does_not_open_chrome_inspect():
     assert not admin._needs_chrome_remote_debugging_prompt(msg)
 
 
+def test_open_chrome_inspect_invokes_chrome_exe_directly_on_windows(tmp_path, monkeypatch):
+    """On Windows, webbrowser.open() can't handle chrome:// URLs (#290).
+
+    Without a registered protocol handler, ShellExecute pops a "Get an app to
+    open this" dialog instead of opening Chrome -- so the function must spawn
+    chrome.exe with the URL as a command-line argument instead.
+    """
+    chrome_exe = tmp_path / "Google" / "Chrome" / "Application" / "chrome.exe"
+    chrome_exe.parent.mkdir(parents=True)
+    chrome_exe.touch()
+
+    monkeypatch.setattr(platform, "system", lambda: "Windows")
+    monkeypatch.setenv("PROGRAMFILES", str(tmp_path))
+    monkeypatch.delenv("PROGRAMFILES(X86)", raising=False)
+    monkeypatch.delenv("LOCALAPPDATA", raising=False)
+
+    spawned, opened = [], []
+    monkeypatch.setattr(subprocess, "Popen", lambda argv, **kw: spawned.append(argv) or object())
+    monkeypatch.setattr(webbrowser, "open", lambda url, **kw: opened.append(url) or True)
+
+    admin._open_chrome_inspect()
+
+    assert spawned == [[str(chrome_exe), "chrome://inspect/#remote-debugging"]]
+    assert opened == [], "webbrowser.open fallback must not run when chrome.exe was spawned"
+
+
+def test_open_chrome_inspect_falls_back_to_webbrowser_when_no_chrome_exe_on_windows(monkeypatch):
+    monkeypatch.setattr(platform, "system", lambda: "Windows")
+    monkeypatch.delenv("PROGRAMFILES", raising=False)
+    monkeypatch.delenv("PROGRAMFILES(X86)", raising=False)
+    monkeypatch.delenv("LOCALAPPDATA", raising=False)
+
+    opened = []
+    monkeypatch.setattr(webbrowser, "open", lambda url, **kw: opened.append(url) or True)
+
+    admin._open_chrome_inspect()
+
+    assert opened == ["chrome://inspect/#remote-debugging"]
+
+
 def test_daemon_endpoint_names_discovers_valid_socket_names(tmp_path, monkeypatch):
     monkeypatch.setattr(admin.ipc, "IS_WINDOWS", False)
     monkeypatch.setattr(admin.ipc, "BH_TMP_DIR", None)  # shared-tmpdir mode