Add flyout hover-to-expand for collapsed sidebar

When the sidebar is collapsed to a 56px icon rail, hovering expands it
as a translucent overlay (240px) on top of the page content for quick
sub-menu access. Left 56px stays solid, the overlapping portion uses
subtle backdrop-filter blur. Auto-closes on navigation or mouse leave.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/Web/StellaOps.Web/src/app/layout/app-sidebar/app-sidebar.component.ts

@@ -72,6 +72,9 @@ interface NavSectionGroup {
     <aside
       class="sidebar"
       [class.sidebar--collapsed]="collapsed"
+      [class.sidebar--flyout]="flyoutOpen()"
+      (mouseenter)="onSidebarMouseEnter()"
+      (mouseleave)="onSidebarMouseLeave()"
       role="navigation"
       aria-label="Main navigation"
     >
@@ -93,11 +96,11 @@ interface NavSectionGroup {
         @for (group of displaySectionGroups(); track group.id) {
           <div
             class="sb-group"
-            [class.sb-group--collapsed]="!collapsed && sidebarPrefs.collapsedGroups().has(group.id)"
+            [class.sb-group--collapsed]="!effectiveCollapsed && sidebarPrefs.collapsedGroups().has(group.id)"
             role="group"
             [attr.aria-label]="group.label"
           >
-            @if (!collapsed) {
+            @if (!effectiveCollapsed) {
               <button
                 type="button"
                 class="sb-group__header"
@@ -115,10 +118,10 @@ interface NavSectionGroup {
             <div class="sb-group__body" [id]="'nav-grp-' + group.id">
               <div class="sb-group__body-inner">
                 @for (section of group.sections; track section.id; let sectionFirst = $first) {
-                  @if (!collapsed && !sectionFirst) {
+                  @if (!effectiveCollapsed && !sectionFirst) {
                     <div class="sb-divider"></div>
                   }
-                  @if (!collapsed && section.displayChildren.length > 0) {
+                  @if (!effectiveCollapsed && section.displayChildren.length > 0) {
                     <!-- Section with foldable children: link + chevron toggle -->
                     <div class="sb-section" [class.sb-section--folded]="sidebarPrefs.collapsedSections().has(section.id)">
                       <div class="sb-section__head">
@@ -127,7 +130,7 @@ interface NavSectionGroup {
                           [icon]="section.icon"
                           [route]="section.route"
                           [badge]="section.sectionBadge"
-                          [collapsed]="collapsed"
+                          [collapsed]="effectiveCollapsed"
                         ></app-sidebar-nav-item>
                         <button
                           type="button"
@@ -151,7 +154,7 @@ interface NavSectionGroup {
                               [route]="child.route"
                               [badge]="child.badge ?? null"
                               [isChild]="true"
-                              [collapsed]="collapsed"
+                              [collapsed]="effectiveCollapsed"
                             ></app-sidebar-nav-item>
                           }
                         </div>
@@ -164,7 +167,7 @@ interface NavSectionGroup {
                       [icon]="section.icon"
                       [route]="section.route"
                       [badge]="section.sectionBadge"
-                      [collapsed]="collapsed"
+                      [collapsed]="effectiveCollapsed"
                     ></app-sidebar-nav-item>
                   }
                 }
@@ -215,13 +218,45 @@ interface NavSectionGroup {
       color: var(--color-sidebar-text);
       overflow: hidden;
       position: relative;
-      transition: width 0.3s cubic-bezier(0.22, 1, 0.36, 1);
+      transition: width 0.3s cubic-bezier(0.22, 1, 0.36, 1),
+                  box-shadow 0.3s ease;
     }
 
     .sidebar--collapsed {
       width: 56px;
     }
 
+    /* ---- Flyout overlay (collapsed + mouse hover) ---- */
+    .sidebar--collapsed.sidebar--flyout {
+      width: 240px;
+      /* Left 56px stays solid (the existing rail), right portion is subtly translucent */
+      background:
+        linear-gradient(
+          90deg,
+          var(--color-sidebar-bg) 0px,
+          var(--color-sidebar-bg) 56px,
+          color-mix(in srgb, var(--color-sidebar-bg) 96%, transparent) 57px,
+          color-mix(in srgb, var(--color-sidebar-bg) 94%, transparent) 100%
+        );
+      backdrop-filter: blur(16px);
+      -webkit-backdrop-filter: blur(16px);
+      box-shadow:
+        4px 0 24px rgba(0, 0, 0, 0.3),
+        1px 0 0 rgba(245, 166, 35, 0.08);
+    }
+
+    .sidebar--collapsed.sidebar--flyout .sb-group__header,
+    .sidebar--collapsed.sidebar--flyout .sb-divider,
+    .sidebar--collapsed.sidebar--flyout .sb-section__head,
+    .sidebar--collapsed.sidebar--flyout .sb-section__body {
+      animation: flyoutFadeIn 0.2s ease-out both;
+    }
+
+    @keyframes flyoutFadeIn {
+      from { opacity: 0; transform: translateX(-6px); }
+      to   { opacity: 1; transform: translateX(0); }
+    }
+
     .sidebar::after {
       content: '';
       position: absolute;
@@ -307,6 +342,10 @@ interface NavSectionGroup {
       padding: 0.5rem 0.25rem;
     }
 
+    .sidebar--collapsed.sidebar--flyout .sidebar__nav {
+      padding: 0.5rem 0.5rem;
+    }
+
     /* ================================================================
        Nav group (collapsible section cluster)
        ================================================================ */
@@ -604,11 +643,31 @@ interface NavSectionGroup {
       padding: 0.375rem 0.25rem 0.5rem;
     }
 
+    .sidebar--collapsed.sidebar--flyout .sidebar__footer {
+      padding: 0.5rem 0.625rem 0.625rem;
+    }
+
     .sidebar--collapsed .sidebar__version {
       font-size: 0;
       opacity: 0;
       overflow: hidden;
     }
+
+    .sidebar--collapsed.sidebar--flyout .sidebar__version {
+      font-size: 0.5625rem;
+      opacity: 1;
+      overflow: visible;
+    }
+
+    /* ---- Flyout: disable on mobile ---- */
+    @media (max-width: 991px) {
+      .sidebar.sidebar--collapsed.sidebar--flyout {
+        width: 280px;
+        backdrop-filter: none;
+        -webkit-backdrop-filter: none;
+        box-shadow: none;
+      }
+    }
   `],
   changeDetection: ChangeDetectionStrategy.OnPush,
 })
@@ -622,11 +681,29 @@ export class AppSidebarComponent implements AfterViewInit {
 
   readonly sidebarPrefs = inject(SidebarPreferenceService);
 
-  @Input() collapsed = false;
+  private _collapsed = false;
+  @Input()
+  get collapsed(): boolean { return this._collapsed; }
+  set collapsed(value: boolean) {
+    this._collapsed = value;
+    if (!value) this.closeFlyout();
+  }
+
+  /** Flyout open state (collapsed rail + mouse hovering) */
+  readonly flyoutOpen = signal(false);
+
+  /** Effective collapsed state: collapsed AND not in flyout mode */
+  get effectiveCollapsed(): boolean {
+    return this._collapsed && !this.flyoutOpen();
+  }
+
   @Output() mobileClose = new EventEmitter<void>();
   @Output() collapseToggle = new EventEmitter<void>();
   @ViewChild('sidebarNav', { static: false }) sidebarNavRef!: ElementRef<HTMLElement>;
 
+  private flyoutEnterTimer: ReturnType<typeof setTimeout> | null = null;
+  private flyoutLeaveTimer: ReturnType<typeof setTimeout> | null = null;
+
   private readonly pendingApprovalsCount = signal(0);
 
   /**
@@ -834,12 +911,14 @@ export class AppSidebarComponent implements AfterViewInit {
 
   constructor() {
     this.loadPendingApprovalsBadge();
+    this.destroyRef.onDestroy(() => this.clearFlyoutTimers());
     this.router.events
       .pipe(takeUntilDestroyed(this.destroyRef))
       .subscribe((event) => {
         if (event instanceof NavigationEnd) {
           this.loadPendingApprovalsBadge();
           this.doctorTrendService.refresh();
+          this.closeFlyout();
         }
       });
   }
@@ -921,6 +1000,34 @@ export class AppSidebarComponent implements AfterViewInit {
     return this.authService.hasAnyScope(scopes);
   }
 
+  /** Flyout: expand sidebar as translucent overlay when hovering the collapsed rail */
+  onSidebarMouseEnter(): void {
+    if (!this._collapsed || window.innerWidth <= 991) return;
+    this.clearFlyoutTimers();
+    this.flyoutEnterTimer = setTimeout(() => this.flyoutOpen.set(true), 150);
+  }
+
+  onSidebarMouseLeave(): void {
+    this.clearFlyoutTimers();
+    this.flyoutLeaveTimer = setTimeout(() => this.flyoutOpen.set(false), 300);
+  }
+
+  private closeFlyout(): void {
+    this.clearFlyoutTimers();
+    this.flyoutOpen.set(false);
+  }
+
+  private clearFlyoutTimers(): void {
+    if (this.flyoutEnterTimer) {
+      clearTimeout(this.flyoutEnterTimer);
+      this.flyoutEnterTimer = null;
+    }
+    if (this.flyoutLeaveTimer) {
+      clearTimeout(this.flyoutLeaveTimer);
+      this.flyoutLeaveTimer = null;
+    }
+  }
+
   private loadPendingApprovalsBadge(): void {
     if (!this.approvalApi) {
       return;