feat(ui): redesign workspace shell with context panel, tabbed sidebars, and faster diff UX (#433)

* feat: tabbed right sidebar, context panel, floating diff comments

* fix: auto-close left sidebar when context panel opens

- Increase default context panel width from 520 to 600 pixels
- Increase sidebar minimum width from 200 to 300 pixels
- Replace collapsible component with custom button in diff view

* refactoring: rework sidebars, tabs, and file tree layout

- Rewrite AnimatedTabs as segment-style with sliding indicator
- Upgrade SidebarFilesTree to match FilesView features (context menus,
  git status, file icons, CRUD dialogs, fuzzy search ranking)
- Restructure FilesView header: tabs row + actions row, remove breadcrumbs
- Show relative path in context panel header, track active tab
- Allow left sidebar to stay open alongside context panel
- Hide diff/files tabs from header on desktop (mobile-only)
- Move chevron after group name in session sidebar
- Compact tab heights in right sidebar and git view
- Size PreviewToggleButton to match other action buttons
- Remove directory loading spinner from folder icons

* feat: add project icon and color customization

- Enable users to assign custom icons to projects
- Allow users to choose accent colors for projects
- Stabilize repo status UI during project switching

* feat: add scroll fade indicators to editor tabs

* style: reduce spacing and icon sizes in header

* style: adjust tab component padding from uniform to vertical-horizontal

* feat: Add session state indicators to project tabs

* feat: Enhance session status handling and improve UI responsiveness

* fix: preserve upstream tracking on branch rename

* fix: improve initial remote selection for pull requests

- Uses saved remote name from previous session when available
- Selects remote based on tracking branch when possible
- Falls back to origin or first available remote

* perf(diff): faster highlight, stable stacked scroll

- split/unified Pierre worker pools; prefer shiki-wasm
- align diff CSS line-height; disable scroll anchoring; drop WebKit compositing hacks
- harden stacked pin/align (cancel on user scroll/input); prevent overscroll
- make overlay scrollbar MutationObserver optional; disable for diff container

* feat: handle binary files in diff view

* fix: adjust project tabs layout and drag regions

* style: update drag overlay visual styling

* feat: enable number keys to switch projects in the sidebar

* fix: recognize octet-stream as text-based MIME type

* feat: add keyboard navigation to context panel

* feat: add session pinning to sidebar

- Pin important sessions to keep them at the top
- Pinned sessions persist across browser sessions

* refactor: move context usage display from chat input to header

packages/ui/src/lib/opencode/client.ts

@@ -464,6 +464,7 @@ class OpencodeService {
       'application/toml',
       'application/x-sh',
       'application/x-shellscript',
+      'application/octet-stream',
     ];
     
     return textBasedTypes.includes(lowerMime);
@@ -683,21 +684,43 @@ class OpencodeService {
       throw new Error('Message must have at least one part (text or file)');
     }
 
-    // Use SDK session.prompt() method
-    // DON'T send messageID - let server generate it (fixes Claude empty response issue)
-    await this.client.session.prompt({
-      sessionID: params.id,
-      ...(this.currentDirectory ? { directory: this.currentDirectory } : {}),
-      // messageID intentionally omitted - server will generate
-      model: {
-        providerID: params.providerID,
-        modelID: params.modelID
+    // Use async prompt endpoint so the client doesn't block waiting
+    // for model work (SSE will deliver output/status).
+    // This avoids 504s from proxy timeouts on long-running turns.
+    const base = this.baseUrl.replace(/\/+$/, '');
+    const url = new URL(`${base}/session/${encodeURIComponent(params.id)}/prompt_async`);
+    if (this.currentDirectory) {
+      url.searchParams.set('directory', this.currentDirectory);
+    }
+
+    const response = await fetch(url.toString(), {
+      method: 'POST',
+      headers: {
+        'content-type': 'application/json',
+        accept: 'application/json',
       },
-      agent: params.agent,
-      variant: params.variant,
-      parts
+      body: JSON.stringify({
+        model: {
+          providerID: params.providerID,
+          modelID: params.modelID,
+        },
+        agent: params.agent,
+        variant: params.variant,
+        parts,
+      }),
     });
 
+    if (!response.ok) {
+      let detail = '';
+      try {
+        detail = await response.text();
+      } catch {
+        // ignore
+      }
+      const suffix = detail && detail.trim().length > 0 ? `: ${detail.trim()}` : '';
+      throw new Error(`Failed to send message (${response.status})${suffix}`);
+    }
+
     // Return temporary ID for optimistic UI
     // Real messageID will come from server via SSE events
     return tempMessageId;