gui: require explicit agent selection for statewait/chat

- setActiveSessionId now selects only the session; it clears m_agentId
  and never auto-selects a lone agent.
- startStateStream no longer re-resolves or falls back to another agent;
  it only runs when the explicit active agent still exists.
- QML now handles activeAgentId changes explicitly and keeps the right
  pane blank/disabled when no session or no agent is selected.

gui/main.qml

@@ -210,7 +210,19 @@ ApplicationWindow {
         target: ollie
         function onActiveSessionIdChanged() {
             chatModel.reset()
-            if (ollie.activeAgentId) {
+            if (ollie.activeSessionId && ollie.activeAgentId) {
+                var log = ollie.readLogForSession(ollie.activeSessionId, ollie.activeAgentId)
+                if (log) {
+                    chatModel.appendData(log)
+                    chatModel.trimFront(20)
+                }
+            }
+            scrollTimer.start()
+            buildSessionTree()
+        }
+        function onActiveAgentIdChanged() {
+            chatModel.reset()
+            if (ollie.activeSessionId && ollie.activeAgentId) {
                 var log = ollie.readLogForSession(ollie.activeSessionId, ollie.activeAgentId)
                 if (log) {
                     chatModel.appendData(log)
@@ -218,7 +230,6 @@ ApplicationWindow {
                 }
             }
             scrollTimer.start()
-            // Expand the active session in the tree
             buildSessionTree()
         }
         function onStreamingDone() {

gui/ollie9pclient.cpp

@@ -62,25 +62,9 @@ void Ollie9pClient::setActiveSessionId(const QString &id)
 		return;
 	}
 
-	// Discover agents. If exactly one, use it automatically (backward compat).
-	QStringList agents = getAgents(id);
-	if (agents.size() == 1) {
-		m_agentId = agents.first();
-
-		QByteArray stateOut = run9p({"read", agentPath() + "/state"});
-		QString stateStr = QString::fromUtf8(stateOut).trimmed();
-		if (!stateStr.isEmpty())
-			m_activeState = stateStr;
-	}
-
 	emit activeSessionIdChanged();
 	emit activeAgentIdChanged();
 	emit activeStateChanged();
-
-	if (!m_agentId.isEmpty()) {
-		startChatStream();
-		startStateStream();
-	}
 }
 
 void Ollie9pClient::refreshSessions()
@@ -453,17 +437,10 @@ void Ollie9pClient::startStateStream()
 	// Check if session still exists before starting
 	if (m_activeSessionId.isEmpty() || m_agentId.isEmpty()) return;
 
-	// Verify the current agent directory still exists
+	// The active agent must be explicitly selected. Do not re-resolve
+	// or auto-fallback here; just stop if the selection is no longer valid.
 	QStringList agents = getAgents(m_activeSessionId);
-	if (agents.isEmpty()) {
-		// Session or agent directory gone — don't start
-		return;
-	}
-	if (!agents.contains(m_agentId)) {
-		// Current agent no longer exists — fall back to first available
-		m_agentId = agents.first();
-		emit activeAgentIdChanged();
-	}
+	if (agents.isEmpty() || !agents.contains(m_agentId)) return;
 
     m_stateProc = new QProcess(this);
     connect(m_stateProc, &QProcess::readyReadStandardOutput, this, &Ollie9pClient::onStateReadyRead);