gui: fix deadlock — demand-driven chat streaming

The chat stream (ollie-9p read .../chat) blocks forever waiting for
data. Starting it on agent switch meant stopStreams() would block the
main thread trying to kill a hung process.

Fix: stream chat only while the agent is active.
- submit() starts the chat stream (agent is about to become active)
- Event handler stops chat on idle transition, starts on non-idle
- switchAgent() only starts chat if agent is already non-idle
- NativeStreamer::stop() uses SIGTERM+200ms then SIGKILL+100ms
  instead of immediate SIGKILL+1000ms

gui/nativestreamer.cpp

@@ -63,8 +63,11 @@ void NativeStreamer::stop()
     if (m_process) {
         disconnect(m_process, nullptr, this, nullptr);
         if (m_process->state() != QProcess::NotRunning) {
-            m_process->kill();
+            m_process->terminate();  // SIGTERM first
-            m_process->waitForFinished(1000);
+            if (!m_process->waitForFinished(200)) {
+                m_process->kill();   // SIGKILL if still alive
+                m_process->waitForFinished(100);
+            }
         }
         m_process->deleteLater();
         m_process = nullptr;

gui/ollie9pclient.cpp

@@ -223,6 +223,13 @@ void Ollie9pClient::handleEvent(const QString &eventLine)
                 m_agentStateValues[key] = payloadStr;
                 emit agentStateChanged(sidStr, aidStr, payloadStr);
                 emit activeStateChanged();
+                
+                // Demand-driven chat: stop on idle, start on activity.
+                if (payloadStr == QLatin1String("idle")) {
+                    m_chat->stop();
+                } else if (!m_chat->isRunning()) {
+                    m_chat->start(agentPath() + "/chat");
+                }
             } else {
                 // Non-active agent: need to check cache
                 const QString sidStr = sessionId.toString();
@@ -378,6 +385,12 @@ bool Ollie9pClient::submit(const QString &prompt)
 {
     if (m_activeSessionId.isEmpty() || m_agentId.isEmpty() || prompt.trimmed().isEmpty()) return false;
     if (!m_9p || !m_9p->isConnected()) return false;
+    
+    // Start chat stream before submitting — agent will become active.
+    if (!m_chat->isRunning()) {
+        m_chat->start(agentPath() + "/chat");
+    }
+    
     return m_9p->write(agentPath() + "/prompt", prompt.toUtf8());
 }
 
@@ -673,7 +686,11 @@ void Ollie9pClient::startActiveAgentStreams()
     if (!m_daemonConnected) return;
     if (m_activeSessionId.isEmpty() || m_agentId.isEmpty()) return;
 
-    m_chat->start(agentPath() + "/chat");
+    // Chat stream is demand-driven: started on submit(), stopped on idle.
+    // If the agent is already active (e.g. switching to a busy agent), start chat now.
+    if (m_activeState != "idle") {
+        m_chat->start(agentPath() + "/chat");
+    }
     m_state->start(agentPath() + "/statewait");
 }