Fix a fake monitor's layer-shell surfaces misrouting onto the real primary

Live incident, root-caused jointly with the AGS peer session: creating a
fake monitor visibly shrank the real primary output's usable area
(full_y stayed 0 throughout - its true position never moved) each time,
tracking almost exactly one bar height per fake monitor created.

create_virtual_head registered its new Output in udev.virtual_heads but
never in CompState::outputs, the list output_for_wl searches to resolve
a client-named wl_output back to anything. new_layer_surface's own
fallback for an output it can't resolve is landing on the primary output
- so AGS's own per-monitor bar, aimed at the fake monitor it reasonably
believed was a new real one, silently landed on the real primary output
instead, stacking its own exclusive-zone reservation on top of the real
bar already there. Two fake monitors, two misrouted bars, two zone
increments, matching the observed climb exactly.

Fixed by registering (and, on removal, deregistering) a virtual head's
Output in CompState::outputs the same way bring_up_head already does for
a real one. Also adds Monitor::is_virtual / MonitorInfo's "virtual" JSON
field, requested directly by the AGS peer session as the real
discriminator their own temporary FAKE- name-pattern match was standing
in for.

The X-position half of this same incident was AGS's own remembered-
layout restore treating a fake monitor's wl_output as a real hotplug --
already fixed on their side (readArrangeable() now filters split/virtual
outputs).

2 files changed, 44 insertions, 0 deletions

diff --git a/crates/platform/src/ipc/tests.rs b/crates/platform/src/ipc/tests.rs
index aa86e95..591be56 100644
--- a/crates/platform/src/ipc/tests.rs
+++ b/crates/platform/src/ipc/tests.rs
@@ -497,6 +497,30 @@ fn set_monitor_split_with_neither_name_nor_a_resolvable_id_errors() {
 }
 
 #[test]
+fn monitors_query_marks_a_virtual_output_so_a_client_does_not_treat_it_as_a_real_hotplug() {
+    let dir = tempfile::tempdir().unwrap();
+    let mut server = IpcServer::bind_in(dir.path(), "test").unwrap();
+    let wm = Rc::new(RefCell::new(WindowManager::new()));
+    let real = srdwm_core::Monitor::new(0, "eDP-1", srdwm_core::Rect::new(0, 0, 1920, 1080));
+    let mut fake = srdwm_core::Monitor::new(1, "FAKE-1", srdwm_core::Rect::new(1920, 0, 1920, 1080));
+    fake.is_virtual = true;
+    wm.borrow_mut().set_monitors(vec![real, fake]);
+
+    let mut client = UnixStream::connect(&server.path).unwrap();
+    let mut reader = std::io::BufReader::new(client.try_clone().unwrap());
+    client.write_all(b"{\"cmd\":\"monitors\"}\n").unwrap();
+    server.poll(&wm);
+    let line = read_line(&mut reader);
+
+    let parsed: serde_json::Value = serde_json::from_str(&line).unwrap();
+    let monitors = parsed["monitors"].as_array().unwrap();
+    let real = monitors.iter().find(|m| m["name"] == "eDP-1").unwrap();
+    let fake = monitors.iter().find(|m| m["name"] == "FAKE-1").unwrap();
+    assert_eq!(real["virtual"], false, "a real output must not be marked virtual");
+    assert_eq!(fake["virtual"], true, "a fake monitor must be marked virtual so a client can tell it apart from a real hotplug");
+}
+
+#[test]
 fn monitors_query_lists_a_disabled_output_alongside_live_ones() {
     // What the AGS peer session asked for directly: a disabled output
     // must not just vanish from `srd monitors` - it needs a row
diff --git a/crates/platform/src/ipc/types.rs b/crates/platform/src/ipc/types.rs
index 1dc95f6..df11592 100644
--- a/crates/platform/src/ipc/types.rs
+++ b/crates/platform/src/ipc/types.rs
@@ -288,6 +288,21 @@ pub(crate) struct MonitorInfo {
     // actually displaying. See `WorkspaceInfo::monitor` for the same fact
     // indexed from the other direction.
     pub(crate) active_workspace: usize,
+    // `true` for a fully virtual/headless output (`srd dispatch create
+    // fake-monitor`) - a real `wl_output` global with no DRM connector
+    // behind it. Requested directly by the AGS peer session after a fake
+    // monitor's `wl_output` caused a real live incident: it looks like an
+    // ordinary new physical monitor to any client watching the core
+    // Wayland registry (unlike `wlr-output-management-v1`, which already
+    // excludes it), so AGS's own remembered-layout restore treated one
+    // appearing as a real hotplug and repositioned the *real* monitor to
+    // make room for it. Before this field existed, AGS's only option was
+    // matching the name against `^FAKE-` - this is the real
+    // discriminator that pattern was standing in for. `#[serde(rename)]`
+    // rather than a field literally named `virtual` because that word is
+    // a reserved identifier in Rust.
+    #[serde(rename = "virtual")]
+    pub(crate) is_virtual: bool,
 }
 
 /// Pushed to every subscriber (and used as `subscribe`'s own initial
@@ -446,6 +461,7 @@ pub(crate) fn monitor_snapshot(wm: &std::rc::Rc<std::cell::RefCell<WindowManager
         split: m.split,
         scale: m.scale,
         active_workspace: wm.workspace_for_monitor(m.id),
+        is_virtual: m.is_virtual,
     });
     // Disabled-but-still-connected outputs, appended rather than merged in
     // by name - see `MonitorInfo::enabled`'s own doc comment for why
@@ -482,6 +498,10 @@ pub(crate) fn monitor_snapshot(wm: &std::rc::Rc<std::cell::RefCell<WindowManager
         // "shows nothing, not tracked" the same way `id: u32::MAX` above
         // is a deliberate not-a-real-value sentinel for this same entry.
         active_workspace: 0,
+        // A fake monitor is never administratively disabled/re-enabled --
+        // see `virtual_heads.rs`'s own module doc comment - so this
+        // branch (disabled-but-still-connected outputs) can never be one.
+        is_virtual: false,
     });
     live.chain(disabled).collect()
 }