fix(acp): use background context for sink lifetime

Amolith created 

The request context passed to NewSession may be short-lived. The sink
needs to outlive the request to stream updates for the session.

Assisted-by: Claude Opus 4.5 via Crush

Change summary

internal/acp/agent.go | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

Detailed changes

internal/acp/agent.go 🔗 

@@ -71,7 +71,9 @@ func (a *Agent) NewSession(ctx context.Context, params acp.NewSessionRequest) (a
 	}
 
 	// Create and start the event sink to stream updates to this session.
-	sink := NewSink(ctx, a.conn, sess.ID)
+	// Use a background context since the sink needs to outlive the NewSession
+	// request.
+	sink := NewSink(context.Background(), a.conn, sess.ID)
 	sink.Start(a.app.Messages, a.app.Permissions)
 	a.sinks.Set(sess.ID, sink)