feat(web): new task opens straight into chat, context rail waits for content, frosted windows

New Task now opens directly as an empty ChatThread (NewTaskChat) instead of
a separate compose screen, sized like a real task window. The Scope/Activity
context rail in a task window no longer renders until there's actually
something to show (touched entities, activity, or an open question),
avoiding an empty-placeholder sidebar on every new task. Also fixes the
chat input defaulting to several lines tall on window open, centers the
empty-chat greeting vertically, and gives floating windows the same
frosted-glass look as the desktop's task launcher card.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/components/desktop-shell/NewTaskChat.svelte

@@ -0,0 +1,29 @@
+<script lang="ts">
+  // Content for the "new-task" window slot (windows.ts openNewTaskWindow) —
+  // a real ChatThread in its empty state rather than a separate compose
+  // screen, so starting a task looks and feels exactly like the task chat
+  // it becomes. Submitting the first message starts the task via
+  // startTask() and hands off to the real session window (see windows.ts's
+  // openTaskWindow) the moment the backend assigns an id.
+  import { startTask } from '$lib/stores/chat'
+  import { openTaskWindow, wm, NEW_TASK_WINDOW_ID } from '$lib/stores/windows'
+  import { truncateMiddle } from '$lib/utils'
+  import ChatThread from '$lib/components/ChatThread.svelte'
+
+  function onSend(text: string) {
+    startTask(text, (sessionId) => {
+      openTaskWindow(sessionId, truncateMiddle(text, 60))
+      wm.close(NEW_TASK_WINDOW_ID)
+    })
+  }
+</script>
+
+<ChatThread
+  messages={[]}
+  streaming={false}
+  connectionState="connected"
+  onSend={onSend}
+  onCancel={() => {}}
+  onReconnect={() => {}}
+  onDismissError={() => {}}
+/>

web/src/lib/components/desktop-shell/WindowLayer.svelte

@@ -7,13 +7,13 @@
   // wmPersist in windows.ts) need no extra bookkeeping to know what to render:
   //   app:<id>      -> registry component (windows.ts openAppWindow)
   //   session:<id>  -> SessionChatWindow (windows.ts openTaskWindow)
-  //   new-task      -> TaskLauncher (windows.ts openNewTaskWindow)
+  //   new-task      -> NewTaskChat (windows.ts openNewTaskWindow)
   //   anything else -> entity slug -> EntityDetailContent
   import { wm, dk, wmState, openEntityWindow, NEW_TASK_WINDOW_ID } from '$lib/stores/windows'
   import { appById, appIdFromWindowId } from '$lib/apps'
   import EntityDetailContent from '../EntityDetailContent.svelte'
   import SessionChatWindow from '../SessionChatWindow.svelte'
-  import TaskLauncher from './TaskLauncher.svelte'
+  import NewTaskChat from './NewTaskChat.svelte'
   import XIcon from '@lucide/svelte/icons/x'
   import MinusIcon from '@lucide/svelte/icons/minus'
   import Maximize2Icon from '@lucide/svelte/icons/maximize-2'
@@ -73,9 +73,7 @@
             {#if id.startsWith(SESSION_PREFIX)}
               <SessionChatWindow sessionId={id.slice(SESSION_PREFIX.length)} />
             {:else if id === NEW_TASK_WINDOW_ID}
-              <div class="flex h-full items-center justify-center p-6">
-                <TaskLauncher onStarted={() => wm.close(NEW_TASK_WINDOW_ID)} />
-              </div>
+              <NewTaskChat />
             {:else if app}
               <app.component />
             {:else}