diff --git a/CHANGELOG.md b/CHANGELOG.md
index 463cd24..782ba8d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+- Distinguish an unreadable gamescope panel list from a confirmed empty list in
+  Desktop Capture and Control (issue #73). Failed discovery now asks users to
+  check SteamVR and report the exact message and SteamOS version, rather than
+  claiming no panel is open. This does not establish a new capture fix.
+
 - Treat headset aliases and other CSV metadata as plain text in power and heat
   exports, so spreadsheet formula prefixes cannot run when a report is opened.
 
diff --git a/docs/evidence/panel-discovery-2026-10-24.md b/docs/evidence/panel-discovery-2026-10-24.md
new file mode 100644
index 0000000..6d7d43c
--- /dev/null
+++ b/docs/evidence/panel-discovery-2026-10-24.md
@@ -0,0 +1,50 @@
+# Panel discovery investigation, 2026-10-24
+
+Base: v0.4.16 (`040581a`). Scope: issue #73, Desktop Capture and Control.
+
+## Evidence and change
+
+Issue #73 reports SteamOS 0.4.5 with its desktop visibly running, without a
+Frame Control version or steps. The maintainer's 2026-10-12 comment identifies
+the duplicate `loadPanels` UI function fixed in 0.4.3 and requests the exact
+remaining message and SteamOS build if it persists. There is no reporter
+follow-up. At this base, the functions are distinct and the existing Node
+regression checks their uniqueness and the Desktop GET request.
+
+Read-only source inspection found a remaining diagnostic ambiguity:
+`read_props()` returns `{}` for failed/timed-out X queries and missing root
+properties. `panels()` treated that like a confirmed empty focusable-window
+list. With no detected Plasma process it claimed no panel was open; with Plasma
+it claimed SteamOS was not listing the desktop. Neither claim follows from an
+unreadable list.
+
+The change checks for the presence of `GAMESCOPE_FOCUSABLE_WINDOWS` before
+those claims. An absent list now reports unknown panel state, suggests checking
+SteamVR and retrying/Headset view, and asks for the exact message and SteamOS
+version if persistent. Missing-tool and whole-run deadline explanations retain
+precedence. No new probes, retries, timeouts, input or capture routes are added.
+
+## Real-device boundary
+
+A preliminary read-only SSH inspection returned SteamOS 0.5.6, BUILD_ID
+`20261015.6141207`, battery 99%, discharging, and X0/X1 socket names. It made
+no headset changes. The shared lock was absent at that moment.
+
+The subsequent atomic `mkdir /tmp/frame-test.lock` failed with `File exists`.
+The guarded command exited with status 3 before the session, X-property or
+panel-helper probes ran. The other task's lock was left alone. No application
+was installed, started, stopped or focused; no headset settings changed.
+
+Blocker: the shared device was occupied, and its current build differs from
+the reported 0.4.5 build. There is no safe reproduction establishing a further
+capture/discovery fix for the original report. This PR improves a demonstrated
+diagnostic error; it must not close #73 as a verified new capture fix.
+
+## Offline verification
+
+Focused Python regressions distinguish absent, focus-only, failed/timed-out X
+queries, confirmed empty and desktop-running lists. Existing tests cover
+missing tools, alternate displays, successful discovery and the 12-second
+deadline. The production page's Node behavior test verifies that both Capture
+and Control preserve the unreadable-list advice. These use fake X/HTTP/DOM
+boundaries and do not prove real SteamOS 0.4.5 capture or physical input.
diff --git a/docs/streaming.md b/docs/streaming.md
index 7f96a75..e0f1e18 100644
--- a/docs/streaming.md
+++ b/docs/streaming.md
@@ -285,6 +285,13 @@ How (**verified 2026-09-29**, SteamOS 0.4.1, build 20260925.6191901):
   [#73](https://github.com/saphid/frame-control/issues/73) (SteamOS 0.4.5, desktop
   open but not found). The likely cause there was the page itself: a second
   `loadPanels` (the panel switcher's) replaced the Desktop view's, fixed in #84.
+  If the `GAMESCOPE_FOCUSABLE_WINDOWS` property cannot be read, discovery now
+  reports that the panel list is unreadable and whether a panel is open is
+  unknown. A failed X connection or missing property is not evidence that the
+  desktop is closed. Check that SteamVR is running, retry or use Headset view;
+  if it persists, report the exact message and SteamOS version. The confirmed
+  empty-list advice is retained when the property is present but empty.
+  [2026-10-24 investigation and verification limits](evidence/panel-discovery-2026-10-24.md).
 - Tested from the iPhone app (Simulator): a tap on the Desktop view focused a
   text box in the panel and the text field typed into it; a trackpad move went
   exactly (+40, +25).
diff --git a/tests/page/desk_panels.mjs b/tests/page/desk_panels.mjs
index 5ddf353..dcf4910 100644
--- a/tests/page/desk_panels.mjs
+++ b/tests/page/desk_panels.mjs
@@ -40,6 +40,15 @@ function page(answer) {
   if (!p.noPanelWhy().startsWith("The headset's desktop is running")) fail("why for capture: " + p.noPanelWhy());
   if (!p.ctrlTarget().why.startsWith("The headset's desktop is running")) fail("why for control: " + p.ctrlTarget().why);
 }
+// An unreadable list is unknown: both Capture and Control retain that distinction.
+{
+  const why = "Frame Control couldn't read gamescope's panel list, so it can't tell whether an app panel is open. " +
+    "Check that SteamVR is running in the headset, then try again or use the Headset view. " +
+    "If this persists, report your SteamOS version and this exact message.";
+  const p = page(() => ({ panels: [], focus: null, why }));
+  await p.loadPanels();
+  if (p.noPanelWhy() !== why || p.ctrlTarget().why !== why) fail("unreadable list reason lost");
+}
 // An older headset script without "why": the generic advice.
 {
   const p = page(() => ({ panels: [], focus: null }));
diff --git a/tests/test_touch.py b/tests/test_touch.py
index 5d0c7c6..b501e91 100644
--- a/tests/test_touch.py
+++ b/tests/test_touch.py
@@ -355,6 +355,8 @@ class FindingPanels(unittest.TestCase):
         t.subprocess.run = lambda *a, **k: subprocess.CompletedProcess(a, 0, out, "")
         self.assertEqual(self.real_read_props(":0"), {"GAMESCOPE_FOCUSABLE_WINDOWS": [1, 0, 2, 3, 769, 4],
                                                       "GAMESCOPE_FOCUSED_WINDOW": [0]})
+        t.subprocess.run = lambda *a, **k: subprocess.CompletedProcess(a, 0, "GAMESCOPE_FOCUSABLE_WINDOWS(CARDINAL) = \n", "")
+        self.assertEqual(self.real_read_props(":0"), {"GAMESCOPE_FOCUSABLE_WINDOWS": []})
         t.subprocess.run = lambda *a, **k: subprocess.CompletedProcess(a, 0, "GAMESCOPE_FOCUSED_WINDOW:  not found.\n", "")
         self.assertEqual(self.real_read_props(":0"), {})
 
@@ -392,17 +394,52 @@ class FindingPanels(unittest.TestCase):
         self.assertIn("Headset view", out["why"])
 
     def test_desktop_running_but_not_listed(self):
+        self.props[(":0", "GAMESCOPE_FOCUSABLE_WINDOWS")] = []
         self.t.desktop_running = lambda: True
         out = self.t.panels()
         self.assertEqual(out["panels"], [])
         self.assertIn("desktop is running", out["why"])
 
     def test_nothing_open(self):
+        self.props[(":0", "GAMESCOPE_FOCUSABLE_WINDOWS")] = []
         out = self.t.panels()
         self.assertEqual(out, {"focus": None, "focus_display": None, "panels": [],
                                "why": "No app panel is open in the headset. Open the desktop or an app in "
                                       "the headset, then try again."})
 
+    def test_absent_list_is_unknown_even_when_desktop_is_running(self):
+        for desktop in (False, True):
+            with self.subTest(desktop=desktop):
+                self.t.desktop_running = lambda: desktop
+                self.t._ROOT.clear()
+                out = self.t.panels()
+                self.assertEqual(out["panels"], [])
+                self.assertIn("couldn't read gamescope's panel list", out["why"])
+                self.assertIn("can't tell whether", out["why"])
+                self.assertIn("Headset view", out["why"])
+                self.assertNotIn("No app panel is open", out["why"])
+
+    def test_focus_property_without_panel_list_is_unknown(self):
+        self.props[(":0", "GAMESCOPE_FOCUSED_WINDOW")] = [0]
+        self.assertIn("couldn't read gamescope's panel list", self.t.panels()["why"])
+
+    def test_failed_xprop_does_not_claim_no_panels_are_open(self):
+        t = self.t
+        t.read_props = self.real_read_props
+        saved = t.subprocess.run
+        self.addCleanup(setattr, t.subprocess, "run", saved)
+        for failure in ("refused", "timeout"):
+            with self.subTest(failure=failure):
+                def run(*args, **kwargs):
+                    if failure == "timeout":
+                        raise subprocess.TimeoutExpired(args[0], kwargs["timeout"])
+                    return subprocess.CompletedProcess(args[0], 1, "", "Can't open display")
+                t.subprocess.run = run
+                t._ROOT.clear()
+                out = t.panels()
+                self.assertIn("couldn't read gamescope's panel list", out["why"])
+                self.assertNotIn("No app panel is open", out["why"])
+
     def test_missing_x_tools_are_named(self):
         self.plasma_on(":0")
         self.t.shutil.which = lambda tool: None if tool == "xwininfo" else "/usr/bin/" + tool
diff --git a/ui/frame_touch.py b/ui/frame_touch.py
index 8f1be7d..427314c 100644
--- a/ui/frame_touch.py
+++ b/ui/frame_touch.py
@@ -271,7 +271,7 @@ def panels(limit=None):
         out["why"] = ("The headset took too long to list its panels (its X tools didn't answer in time). "
                       + ("Some may be missing. " if found else "") + "Try again, or use the Headset view.")
     elif not found:
-        out["why"] = why_none(unfound)
+        out["why"] = why_none(unfound, props)
     return out
 
 
@@ -295,13 +295,18 @@ def desktop_running():
     return False
 
 
-def why_none(listed):
+def why_none(listed, props):
     """Why panels() found nothing, in words the person at the computer can act on.
-    listed: how many of the windows gamescope lists aren't X11 windows on any display."""
+    listed: how many of the windows gamescope lists aren't X11 windows on any display.
+    props: the root properties actually read; an absent list is not an empty list."""
     missing = [tool for tool in ("xprop", "xwininfo") if not shutil.which(tool)]
     if missing:
         return (f"This SteamOS build has no {' or '.join(missing)}, which Frame Control uses to find the "
                 "headset's panels. Use the Headset view instead, and please report your SteamOS version.")
+    if "GAMESCOPE_FOCUSABLE_WINDOWS" not in props:
+        return ("Frame Control couldn't read gamescope's panel list, so it can't tell whether an app panel is open. "
+                "Check that SteamVR is running in the headset, then try again or use the Headset view. "
+                "If this persists, report your SteamOS version and this exact message.")
     if listed:
         # gamescope lists windows, but none is an X11 window on any display: a Wayland
         # window (a desktop drawn straight to gamescope, say) can't be found or captured this way.