test(panel): Q5 names the successor frame it orders against

`!messages.is_empty()` could be satisfied by any unrelated semantic
message, so the row asserted an ordering against a frame it never
confirmed was there. It now requires the unwritten messages to contain
InstanceMessage::PanelFrame(PanelFramePayload::Absent) --- the successor
frame whose own transition raised the release.

The assertion bites: suppressing that payload while keeping the
cancellation fails the row, where the emptiness check would not have
noticed.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bqGA6s9tTUFzYpbeW3tai

src/daemon.rs

@@ -8813,9 +8813,16 @@ mod tests {
              merely both arriving"
         );
         assert!(
-            !messages.is_empty(),
-            "fixture: projection really did produce the successor frame \
-             whose own transition required that release"
+            messages.iter().any(|message| matches!(
+                message,
+                InstanceMessage::PanelFrame(pmacs_protocol::panel::PanelFramePayload::Absent)
+            )),
+            "fixture: the unwritten messages must contain THE SUCCESSOR \
+             FRAME --- the `Absent` payload whose own transition raised \
+             the release. A non-empty vec proves nothing: any unrelated \
+             semantic message would satisfy it, and the row would then \
+             assert an ordering against a frame that was never there. \
+             Got {messages:?}"
         );
         assert!(
             !states[&fid].has_pending_release(),