chat: "Disconnect session" — end the whole session from the UI (first stab)

Adds a per-session teardown, distinct from the existing turn-only "stop":
- New WS 'disconnect' message → handleDisconnect → sessionManager.deleteSession,
  which fires _claudeKill (kills any in-flight Claude/OpenCode turn) + _sidecarUnsub,
  clears the idle timer, and drops the in-memory session. WS stays open so a new
  prompt starts fresh. Server acks with 'disconnected'.
- useChat: disconnectSession() + a 'disconnected' handler (commit partial stream,
  settle to idle).
- UI: an Unplug button in the chat DetailBar (shown while connected).

Scope note: targets the CURRENTLY-OPEN session (correct in-memory sessionKey).
Disconnecting an arbitrary *listed* session isn't wired yet — session-list rows are
keyed by the on-disk transcript uuid, which isn't the live sessionKey, so that needs
a reverse lookup + a REST endpoint. NOT yet deployed (needs a server restart).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/workspaces/officerdev/src/apps/Chat/types.ts

@@ -49,7 +49,8 @@ export type ServerMessage =
   | { type: 'result'; sessionId: string; cost: MessageCost }
   | { type: 'sync:messages'; sessionId: string; messages: Message[]; isGenerating: boolean; streamingText: string }
   | { type: 'error'; message: string; errorCode?: string }
-  | { type: 'stopped' };
+  | { type: 'stopped' }
+  | { type: 'disconnected' };
 
 export type Message = {
   id: string;

src/workspaces/officerdev/src/apps/ChatHistory/ChatDetailPanel.tsx

@@ -1,5 +1,6 @@
 import { useCallback } from 'react';
 import { useLocation } from 'react-router';
+import { Unplug } from 'lucide-react';
 import { usePanelChannel } from 'hooks/usePanelChannel';
 import { useAuth } from 'hooks/useAuth';
 import { useClaudeSessions } from 'state/useClaudeSessions';
@@ -29,9 +30,10 @@ type DetailBarProps = {
   sessionTitle: string | undefined;
   isConnected: boolean;
   isGenerating: boolean;
+  onDisconnect?: () => void;
 };
 
-function DetailBar({ sessionTitle, isConnected, isGenerating }: DetailBarProps) {
+function DetailBar({ sessionTitle, isConnected, isGenerating, onDisconnect }: DetailBarProps) {
   return (
     <div className="shrink-0 flex items-center px-4 py-2 border-b border-duck-dark/10 dark:border-foreground/10 bg-background/60">
       <div className="flex-1 min-w-0 text-center text-sm font-medium text-duck-dark/70 dark:text-foreground/70 truncate px-3">
@@ -46,6 +48,16 @@ function DetailBar({ sessionTitle, isConnected, isGenerating }: DetailBarProps)
           <span className="inline-block h-2 w-2 rounded-full bg-green-500" />
         )}
         <span>{!isConnected ? 'Disconnected' : isGenerating ? 'Working...' : ''}</span>
+        {isConnected && onDisconnect && (
+          <button
+            type="button"
+            onClick={onDisconnect}
+            title="End session — kills any running turn and releases it so it can be resumed elsewhere"
+            className="ml-1 p-1 rounded hover:bg-duck-dark/10 dark:hover:bg-foreground/10 hover:text-red-500 transition-colors cursor-pointer"
+          >
+            <Unplug className="h-3.5 w-3.5" />
+          </button>
+        )}
       </div>
     </div>
   );
@@ -92,7 +104,7 @@ function NewChat({ resumeSummary, resumeSessionId, initialMessages }: NewChatPro
 
   return (
     <div className="flex flex-col h-full">
-      <DetailBar sessionTitle={undefined} isConnected={chat.isConnected} isGenerating={chat.isGenerating} />
+      <DetailBar sessionTitle={undefined} isConnected={chat.isConnected} isGenerating={chat.isGenerating} onDisconnect={chat.disconnectSession} />
       <EmbeddableChat
         chat={chat}
         sessionId={undefined}

src/workspaces/officerdev/src/hooks/useChat.ts

@@ -202,6 +202,13 @@ export function useChat(initialSessionId?: string, initialModel?: string | null,
         commitStreaming();
         setIsGenerating(false);
         break;
+
+      case 'disconnected':
+        // Session torn down server-side (turn killed, in-memory session dropped). Commit any partial
+        // stream and settle to idle; the WS stays open so a new prompt starts a fresh session.
+        commitStreaming();
+        setIsGenerating(false);
+        break;
     }
   }
 
@@ -273,6 +280,12 @@ export function useChat(initialSessionId?: string, initialModel?: string | null,
     send({ type: 'stop' });
   }
 
+  // Tear down the whole session server-side (kill any in-flight turn + drop the in-memory session),
+  // freeing it so its transcript can be resumed elsewhere. Stronger than stopGeneration (turn only).
+  function disconnectSession() {
+    send({ type: 'disconnect' });
+  }
+
   return {
     messages,
     streamingText,
@@ -288,6 +301,7 @@ export function useChat(initialSessionId?: string, initialModel?: string | null,
     setThinkingLevel,
     sendPrompt,
     stopGeneration,
+    disconnectSession,
   };
 }