Don't let an unreadable profile dir abort CDP discovery

src/browser_harness/daemon.py

@@ -199,7 +199,10 @@ def _ws_from_devtools_active_port(http_url: str) -> str | None:
     for base in PROFILES:
         try:
             active = (base / "DevToolsActivePort").read_text(encoding="utf-8", errors="replace").splitlines()
-        except (FileNotFoundError, NotADirectoryError):
+        # PermissionError: macOS TCC guards ~/Library/Application Support/Google/Chrome,
+        # so a terminal without Full Disk Access gets EPERM here. Skip the profile and
+        # keep looking rather than killing discovery outright.
+        except (FileNotFoundError, NotADirectoryError, PermissionError):
             continue
         port = active[0].strip() if active else ""
         ws_path = active[1].strip() if len(active) > 1 else ""
@@ -241,7 +244,9 @@ def get_ws_url():
         for base in PROFILES:
             try:
                 active = (base / "DevToolsActivePort").read_text(encoding="utf-8", errors="replace").splitlines()
-            except (FileNotFoundError, NotADirectoryError):
+            # PermissionError: see _ws_from_devtools_active_port — an FDA-less terminal
+            # gets EPERM from TCC. Skipping lets the 9222/9223 probe below still run.
+            except (FileNotFoundError, NotADirectoryError, PermissionError):
                 continue
             port = active[0].strip() if active else ""
             ws_path = active[1].strip() if len(active) > 1 else ""

tests/unit/test_daemon.py

@@ -1,5 +1,7 @@
 import asyncio
 
+import pytest
+
 from browser_harness import daemon
 
 
@@ -293,3 +295,44 @@ def test_current_tab_meta_returns_not_attached_when_no_target_id():
     assert result == {"error": "not_attached"}
     # No CDP call should have been issued.
     assert d.cdp.calls == []
+
+
+class _DeniedProfile:
+    """A profile dir whose DevToolsActivePort read is refused by the OS.
+
+    macOS TCC guards ~/Library/Application Support/Google/Chrome, so a terminal
+    without Full Disk Access gets EPERM -- not ENOENT -- when reading the file.
+    """
+
+    def __truediv__(self, _name):
+        return self
+
+    def read_text(self, *_args, **_kwargs):
+        raise PermissionError(1, "Operation not permitted")
+
+    def __str__(self):
+        return "<denied-profile>"
+
+
+def test_ws_from_devtools_active_port_skips_profiles_it_cannot_read(monkeypatch):
+    monkeypatch.setattr(daemon, "PROFILES", [_DeniedProfile()])
+
+    # Must return None (no match) rather than propagating PermissionError.
+    assert daemon._ws_from_devtools_active_port("http://127.0.0.1:9222") is None
+
+
+def test_get_ws_url_reports_chrome_not_running_when_profiles_are_unreadable(monkeypatch):
+    """An unreadable profile must not abort discovery.
+
+    Before this was handled, a PermissionError escaped get_ws_url() as a fatal
+    traceback, so the daemon never reached its own fallbacks or the actionable
+    "start Chrome" error below.
+    """
+    # An explicit endpoint short-circuits discovery, so clear both overrides.
+    monkeypatch.delenv("BU_CDP_WS", raising=False)
+    monkeypatch.delenv("BU_CDP_URL", raising=False)
+    monkeypatch.setattr(daemon, "PROFILES", [_DeniedProfile()])
+    monkeypatch.setattr(daemon, "supported_browser_running", lambda: False)
+
+    with pytest.raises(RuntimeError, match="chrome-not-running"):
+        daemon.get_ws_url()