Treat bare desktop canvas as ready

Allow the Linux Desktop state collector to report a healthy canvas when XFCE has no active application window, as long as the display, visible windows, and screenshots are available.

Document the readiness rule in the linux-desktop skill and add regression coverage for the bare-desktop active_window=null case.

plugins/_desktop/helpers/desktop_state.py

@@ -372,7 +372,6 @@ def collect_active_window(env: dict[str, str], capabilities: dict[str, str], err
         return None
     result = run([capabilities["xdotool"], "getactivewindow"], env=env, timeout=3)
     if result.returncode != 0:
-        errors.append(command_output(result) or "xdotool could not read the active window.")
         return None
     window_id = result.stdout.strip().splitlines()[0] if result.stdout.strip() else ""
     if not window_id:

plugins/_desktop/skills/linux-desktop/SKILL.md

@@ -60,6 +60,8 @@ $DESKTOP key ctrl+s
 
 The script targets the persistent `agent-zero-desktop` X display, sets `DISPLAY`, `XAUTHORITY`, and `HOME` to the XFCE profile, then uses `xdotool` for input. Startup normally prepares this session. If `check` fails during explicit Desktop work, report that the Desktop runtime is not ready instead of installing packages ad hoc.
 
+If `observe --json --screenshot` shows a reachable display, visible Desktop/window entries, and a fresh screenshot, the Desktop is usable even when `active_window` is `null`; a bare XFCE desktop can have no active application window. Treat missing screenshots, missing display, or unavailable `xdotool`/`xwd` as blockers and stop with the specific readiness message instead of repeating clicks or inventing a fallback.
+
 For direct app launches without coordinates:
 
 ```bash

tests/test_office_desktop_state.py

@@ -92,6 +92,61 @@ def test_desktop_state_collects_x11_state_from_mocked_tools(tmp_path, monkeypatc
     assert [window["title"] for window in state["windows"]] == ["LibreOffice Calc", "Terminal"]
 
 
+def test_desktop_state_allows_missing_active_window_when_display_is_reachable(tmp_path, monkeypatch):
+    session_dir = tmp_path / "sessions"
+    profile_dir = tmp_path / "profiles" / desktop_state.SESSION_ID
+    session_dir.mkdir(parents=True)
+    profile_dir.mkdir(parents=True)
+    (session_dir / f"{desktop_state.SESSION_ID}.json").write_text(
+        '{"display": 120, "profile_dir": "%s"}' % profile_dir,
+        encoding="utf-8",
+    )
+
+    monkeypatch.setattr(desktop_state, "SESSION_DIR", session_dir)
+    monkeypatch.setattr(desktop_state, "PROFILE_DIR", tmp_path / "profiles")
+    monkeypatch.setattr(desktop_state.shutil, "which", lambda name: f"/usr/bin/{name}")
+
+    def fake_run(command, **kwargs):
+        del kwargs
+        name = Path(command[0]).name
+        if name == "xrandr":
+            return _completed(command, stdout="Screen 0: current 543 x 792, maximum 1920 x 1080\n")
+        if name == "xdotool" and command[1:3] == ["getmouselocation", "--shell"]:
+            return _completed(command, stdout="X=43\nY=244\nSCREEN=0\nWINDOW=18874412\n")
+        if name == "xdotool" and command[1] == "getactivewindow":
+            return _completed(
+                command,
+                returncode=1,
+                stderr="XGetWindowProperty[_NET_ACTIVE_WINDOW] failed (code=1)\n",
+            )
+        if name == "xdotool" and command[1] == "search":
+            return _completed(command, stdout="18874412\n")
+        if name == "xdotool" and command[1] == "getwindowname":
+            return _completed(command, stdout="Desktop\n")
+        if name == "xwininfo":
+            return _completed(
+                command,
+                stdout=(
+                    "  Absolute upper-left X:  0\n"
+                    "  Absolute upper-left Y:  0\n"
+                    "  Width: 543\n"
+                    "  Height: 792\n"
+                ),
+            )
+        if name == "xprop":
+            return _completed(command, stdout='WM_CLASS(STRING) = "xfdesktop", "Xfdesktop"\n')
+        raise AssertionError(f"unexpected command: {command}")
+
+    monkeypatch.setattr(desktop_state.subprocess, "run", fake_run)
+
+    state = desktop_state.collect_state()
+
+    assert state["ok"] is True
+    assert state["active_window"] is None
+    assert state["errors"] == []
+    assert [window["title"] for window in state["windows"]] == ["Desktop"]
+
+
 def test_desktop_state_screenshot_capture_uses_xwd_and_pillow_when_available(tmp_path, monkeypatch):
     monkeypatch.setattr(desktop_state, "SCREENSHOT_DIR", tmp_path)
     capabilities = {"xwd": "/usr/bin/xwd"}