layer-shell: recompute the exclusive-zone reservation on unmap, not just on commit

ensure_layer_initial_configure (state.rs) already recomputes the usable
monitor rect when a layer surface's exclusive zone changes, but only from
the commit pre-hook - a surface that goes away without a final commit
(zwlr_layer_surface_v1's destroy path, layer_destroyed here) never ran that
check. unmap_layer's own zone change went unnoticed.

Found live by the AGS peer session: unmapping the bar for fullscreen logged
visible=false immediately, but `srd monitors` kept reporting the bar's old
reserved_top for as long as fullscreen lasted. Harmless there only because
toggle_fullscreen targets full_geometry, which ignores the reservation
outright - but wrong for anything that reads the reserved/usable rect while
a bar is unmapped without a clean exit (a crash, not just AGS's cooperative
fullscreen hide). Same zone_before/zone_after diff ensure_layer_initial_
configure already uses, run around unmap_layer instead of arrange().

Verified: cargo build --workspace, cargo clippy -p srdwm-wayland (0 new
warnings), cargo test -p srdwm-core (111/111).

1 files changed, 18 insertions, 0 deletions

diff --git a/crates/wayland/src/protocols.rs b/crates/wayland/src/protocols.rs
index a0aed3f..9f23c69 100644
--- a/crates/wayland/src/protocols.rs
+++ b/crates/wayland/src/protocols.rs
@@ -636,7 +636,25 @@ impl WlrLayerShellHandler for CompState {
             let mut map = layer_map_for_output(&output);
             let found = map.layers().find(|l| l.layer_surface() == &surface).cloned();
             if let Some(layer) = found {
+                // Same zone-change recompute `ensure_layer_initial_configure`
+                // already does on every commit that changes a layer's
+                // exclusive zone (state.rs) - but this is the *only* place
+                // that ever runs for a surface that goes away without one
+                // last commit. `unmap_layer` alone doesn't trigger it:
+                // reported live (by the AGS peer session) as a bar unmapping
+                // for fullscreen yet `srd monitors` still reporting the
+                // bar's old reserved_top for as long as fullscreen lasted --
+                // harmless there only because fullscreen targets
+                // `full_geometry`, which ignores the reservation anyway, but
+                // wrong for anything that reads `usable`/`geometry` while a
+                // bar is unmapped without exiting cleanly (a crash, not just
+                // AGS's cooperative fullscreen hide).
+                let zone_before = map.non_exclusive_zone();
                 map.unmap_layer(&layer);
+                let zone_after = map.non_exclusive_zone();
+                if zone_after != zone_before {
+                    self.pending.borrow_mut().push(srdwm_core::Event::MonitorAdded(srdwm_core::Monitor::new(0, "", srdwm_core::Rect::new(0, 0, 0, 0))));
+                }
                 break;
             }
         }