fix(#6105): close the drawer-over-picker stacking class via z-index, not per-site guards

Codex found the body-reparented picker (z-200, later body child) could be revealed
UNDER a full-screen drawer/panel via multiple paths (swipe, breakpoint resize,
profile-switch). Rather than guard each open-site (whack-a-mole + my resize guard
over-fired on keyboard reflows), fix the class once: .model-dropdown--floating gets
z-index:190 — above the composer-mobile-config-panel (z-180) it opens from, below
the mobile sidebar + workspace panel (both z-200) — so any drawer/panel that opens
covers the picker, matching master's stacking intent. Reverted the two boot.js
guards. Co-authored-by webtecnica.

static/boot.js

@@ -436,11 +436,6 @@ function _openMobileSidebarFromGesture(){
   if(_isDesktopWidth())return;
   const sidebar=document.querySelector('.sidebar');
   if(!sidebar)return;
-  // #6105/#6080: the phone model picker is reparented to <body> at z-index:200,
-  // the same level as the sidebar — as a later body child it would paint ON TOP
-  // of the drawer. Close it first (which also restores it into the footer) so a
-  // left-edge swipe reveals the session drawer cleanly, not an orphaned popover.
-  try{if(typeof closeModelDropdown==='function')closeModelDropdown();}catch(_){}
   try{if(typeof _syncMobileSidebarPanelFromMainView==='function')_syncMobileSidebarPanelFromMainView();}catch(_){}
   const layout=document.querySelector('.layout');
   if(layout)layout.classList.remove('sidebar-collapsed');
@@ -2482,23 +2477,6 @@ function applyEmptyStateSuggestionPref(){
 }
 
 window.addEventListener('resize',()=>{
-  // #6105/#6080: the floating phone model picker is a <body> child at z-index:200,
-  // the same level as the mobile sidebar drawer and the workspace panel. A direct
-  // landscape/tablet→phone resize can re-reveal an already-open drawer/panel
-  // *underneath* the picker (no click fires, so outside-click-close doesn't run).
-  // Close + restore the picker before we re-sync drawer state, but only when a
-  // phone-width layout will actually surface one of those z-200 siblings — so an
-  // ordinary keyboard/URL-bar reflow doesn't dismiss the picker mid-use.
-  try{
-    if(typeof closeModelDropdown==='function' && !_isDesktopWidth()){
-      const dd=document.getElementById('composerModelDropdown');
-      if(dd&&dd.classList.contains('open')){
-        const drawerOpen=!!document.querySelector('.sidebar.mobile-open');
-        const panelOpen=(typeof _workspacePanelMode!=='undefined'&&_workspacePanelMode&&_workspacePanelMode!=='closed');
-        if(drawerOpen||panelOpen) closeModelDropdown();
-      }
-    }
-  }catch(_){}
   _syncWorkspacePanelInlineWidth();
   syncWorkspacePanelState();
   if(!window.visualViewport) _forceMobileViewportReflow();

static/style.css

@@ -3253,8 +3253,15 @@
    Geist Contrast skin — both establish a fixed containing block that would
    otherwise resolve `fixed` against the FOOTER, dropping the menu below the
    fold). Same idiom as #profileDropdown. JS owns left/top/width/maxHeight; this
-   rule only flips positioning and relaxes the desktop width clamps. */
-.model-dropdown.model-dropdown--floating{position:fixed;left:0;bottom:auto;min-width:0;}
+   rule only flips positioning and relaxes the desktop width clamps.
+   z-index:190 is deliberate: ABOVE the .composer-mobile-config-panel (z-180) it
+   can be opened from, but BELOW the full-screen mobile sidebar drawer and
+   workspace panel (both z-200) — so whenever one of those surfaces opens (by
+   swipe, breakpoint resize, profile-switch, or any future path) it covers the
+   picker, exactly as it did on master when the picker lived inside the composer's
+   lower stacking context. This single stacking rule closes the whole "drawer
+   opened behind the floating picker" class without per-open-site guards. */
+.model-dropdown.model-dropdown--floating{position:fixed;left:0;bottom:auto;min-width:0;z-index:190;}
 .model-scope-note{position:sticky;top:0;z-index:2;padding:9px 14px;border-bottom:1px solid var(--border);color:var(--text);font-size:11px;font-weight:650;line-height:1.4;background:color-mix(in srgb,var(--surface) 82%,var(--accent-bg));box-shadow:0 1px 0 rgba(0,0,0,.12);}
 .model-group{padding:8px 14px 4px;font-size:10px;font-weight:700;letter-spacing:.04em;color:var(--muted);text-transform:uppercase;border-top:1px solid var(--border2);margin-top:2px;}.model-group.collapsible{cursor:pointer;user-select:none}.model-group.collapsible:before{content:'\25b6';display:inline-block;font-size:8px;margin-right:5px;transition:transform .15s ease}.model-group.collapsible.open:before{transform:rotate(90deg)}.model-group-body:empty{display:none}
 .model-group.sub{padding:4px 14px 2px 22px;font-size:9px;border-top:none;margin-top:0;letter-spacing:.03em;color:var(--muted);background:transparent;}.model-group.sub.collapsible:before{content:'\25b6';display:inline-block;font-size:7px;margin-right:4px;transition:transform .15s ease}.model-group.sub.collapsible.open:before{transform:rotate(90deg)}.model-group-body.sub{padding-left:8px;border-left:1px solid var(--border);}