docs: the band carves never grouped, contrary to the comment

The comment said the chooser action bar's band carves were "emitted right after
the plate so they CSG-group into its draw". CCE_PLATE_DEBUG says otherwise: 0 of
11 carves group in chooser mode, and that band is rejected by name — a band
flush with the plate's edge suppresses three of its four walls, and an
edge-suppressed carve is never eligible, whatever its emission order.

No behaviour change. The overlay path it actually takes is the correct one here;
only the comment was wrong, and it was wrong in the direction that would have
sent someone hunting for a bug in the grouping heuristic.

Co-Authored-By: Claude <[email protected]>

 src/main.rs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 4c8781e..992964e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1336,8 +1336,13 @@ impl Application for FilesystemApp {
             cce_ui::layout::bevel_width(),
         );
 
-        // Band carves, emitted right after the plate so they CSG-group into its
-        // draw: in chooser mode the action bar is a band carved into the bottom.
+        // Band carves, emitted right after the plate: in chooser mode the action
+        // bar is a band carved into the bottom. These do NOT CSG-group into the
+        // plate's draw, despite sitting immediately behind it — a band flush with
+        // the plate's edge suppresses three of its four walls, and an
+        // edge-suppressed carve is never eligible (its extended walls would smear
+        // across the whole host). The standalone overlay path shades it, which is
+        // correct here. `CCE_PLATE_DEBUG=1` names the rule.
         // (The header strip's menubar-style band was removed — the top of the
         // plate is flush; the breadcrumb row sits directly on the surface.)
         if cce_ui::layout::control_relief() {