fix(shell): review cleanup for the resizable sidebar

Restore the Fixed-mode main column class exactly as before (min-w-0 is
now applied only in Resizable mode, so the desktop default DOM stays
byte-identical), drop the unused committed drag flag, remove a stray
blank line and the redundant width-commit wrapper, and align the
separator keyboard step on the 8 px used by the file explorer pane.

frontend/src/components/EditorLayout.tsx

@@ -465,7 +465,6 @@ export default function EditorLayout() {
   // `activeView`, so 'dashboard' still maps to HomeDashboard everywhere.
   const isMobile = useIsMobile();
   const { sidebarMode, sidebarWidth, setSidebarWidth } = useSidebarLayout();
-  const commitSidebarWidth = useCallback((width: number) => setSidebarWidth(width), [setSidebarWidth]);
   const [mobileView, setMobileView] = useState<MobileView>('list');
   const [mobileSettingsSection, setMobileSettingsSection] = useState<SectionId | null>(null);
   // Optimistically flip to the detail surface the instant a row is tapped,
@@ -1052,7 +1051,7 @@ export default function EditorLayout() {
       const sidebarSlotEl = !isMobile && sidebarMode === 'resizable' ? (
         <SidebarResizePane
           sidebarWidth={sidebarWidth}
-          onCommitWidth={commitSidebarWidth}
+          onCommitWidth={setSidebarWidth}
         >
           {sidebarEl}
         </SidebarResizePane>
@@ -1400,7 +1399,7 @@ export default function EditorLayout() {
           {/* Left Sidebar (Stacks) */}
           {sidebarSlotEl}
           {/* Main Content Area */}
-          <div className="flex-1 min-w-0 flex flex-col overflow-hidden">
+          <div className={`${sidebarMode === 'resizable' ? 'min-w-0 ' : ''}flex-1 flex flex-col overflow-hidden`}>
             {topBarEl}
             {/* Main Workspace */}
             {workspaceEl}

frontend/src/components/sidebar/SidebarResizePane.tsx

@@ -18,7 +18,7 @@ const MIN_WORKSPACE = 560;
 /** Separator hit area in px between sidebar and workspace. */
 const HANDLE_FOOTPRINT = 12;
 /** Keyboard step per arrow press, in px. */
-const KEY_STEP = 16;
+const KEY_STEP = 8;
 
 interface SidebarResizePaneProps {
   sidebarWidth: number;
@@ -36,7 +36,6 @@ export function SidebarResizePane({ sidebarWidth, onCommitWidth, children }: Sid
     startX: number;
     startWidth: number;
     lastWidth: number;
-    committed: boolean;
   } | null>(null);
 
   // The pane's flex row (its parent: sidebar pane + separator + workspace)
@@ -104,7 +103,6 @@ export function SidebarResizePane({ sidebarWidth, onCommitWidth, children }: Sid
       startX: event.clientX,
       startWidth: effectiveWidth,
       lastWidth: effectiveWidth,
-      committed: false,
     };
     setDragging(true);
     event.currentTarget.setPointerCapture(event.pointerId);
@@ -124,9 +122,8 @@ export function SidebarResizePane({ sidebarWidth, onCommitWidth, children }: Sid
   const onSeparatorPointerUp = useCallback((event: React.PointerEvent<HTMLDivElement>) => {
     const drag = dragRef.current;
     if (drag === null || drag.pointerId !== event.pointerId) return;
-    // Snapshot and mark committed BEFORE releasing capture so the trailing
-    // lostpointercapture finds no drag and cleans up without a second commit.
-    drag.committed = true;
+    // The trailing lostpointercapture is a no-op: endDrag clears dragRef
+    // before capture releases, so nothing can commit a second time.
     try {
       onCommitWidth(Math.round(drag.lastWidth));
     } finally {

frontend/src/components/sidebar/__tests__/SidebarResizePane.test.tsx

@@ -247,14 +247,14 @@ describe('SidebarResizePane', () => {
     setup((w) => commits.push(w));
     separator().focus();
     await user.keyboard('{ArrowRight}');
-    expect(commits).toEqual([316]);
-    expect(separator()).toHaveAttribute('aria-valuenow', '316');
+    expect(commits).toEqual([308]);
+    expect(separator()).toHaveAttribute('aria-valuenow', '308');
     await user.keyboard('{Home}');
     expect(pane().style.width).toBe(`${SIDEBAR_WIDTH.min}px`);
     await user.keyboard('{End}');
     expect(pane().style.width).toBe(`${SIDEBAR_WIDTH.max}px`);
     expect(separator()).toHaveAttribute('aria-valuemax', String(SIDEBAR_WIDTH.max));
-    expect(commits).toEqual([316, SIDEBAR_WIDTH.min, SIDEBAR_WIDTH.max]);
+    expect(commits).toEqual([308, SIDEBAR_WIDTH.min, SIDEBAR_WIDTH.max]);
   });
 
   it('keyboard End clamps to the viewport-limited max in a narrow shell', async () => {