fix(#4313): guard EventSource.close() calls to suppress ERR_ABORTED noise

Add readyState !== CLOSED (2) guards to all EventSource.close() calls across
messages.js, sessions.js, panels.js, and terminal.js. Chromium reports
net::ERR_ABORTED when close() is called on an already-closed EventSource,
polluting the console during normal lifecycle transitions (session switch,
panel close, stream teardown).

Key hotspots:
- closeLiveStream() double-close via onerror → _closeSource chain
- _closeSessionEventsSSE, _gatewaySSE.onerror missing try/catch
- _kanbanStopPolling, terminal close handlers

20 close() calls guarded across 4 files, no structural changes to stream
lifecycle.

static/messages.js

@@ -1418,7 +1418,7 @@ function closeLiveStream(sessionId, streamId, source){
   // reattach path will rebuild it from INFLIGHT/server state if the user returns.
   if(typeof _clearLiveRunStatusTimer==='function') _clearLiveRunStatusTimer(sessionId);
   if(typeof hideLiveRunStatus==='function') hideLiveRunStatus(sessionId);
-  try{live.source.close();}catch(_){ }
+  try{if(live.source&&live.source.readyState!==2)live.source.close();}catch(_){ }
   delete LIVE_STREAMS[sessionId];
   // closeLiveStream() is called during session-switch teardown for any session
   // the user is no longer viewing. The stream is still active on the server,
@@ -2924,7 +2924,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
   function _wireSSE(source){
     const existingLive=LIVE_STREAMS[activeSid];
     if(existingLive&&existingLive.source&&existingLive.source!==source){
-      try{existingLive.source.close();}catch(_){ }
+      try{if(existingLive.source.readyState!==2)existingLive.source.close();}catch(_){ }
     }
     LIVE_STREAMS[activeSid]={streamId,source};
 
@@ -3672,7 +3672,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
       if(typeof finalizeThinkingCard==='function') finalizeThinkingCard();
       // Application-level error sent explicitly by the server (rate limit, crash, etc.)
       // This is distinct from the SSE network 'error' event below.
-      source.close();
+      try{if(source&&source.readyState!==2)source.close();}catch(_){ }
       _clearOwnerInflightState();
       _clearApprovalForOwner();
       _clearClarifyForOwner('terminal');
@@ -3782,7 +3782,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
         return;
       }
       if(typeof recordClientSSEError==='function') recordClientSSEError('chat-response',{ready_state:source?source.readyState:null,session_id:activeSid,stream_id:streamId,reason:'chat EventSource.onerror'});
-      source.close();
+      try{if(source&&source.readyState!==2)source.close();}catch(_){ }
       if(_deferStreamErrorIfOffline()) return;
       if(_deferStreamErrorIfPageHidden(source)) return;
       _closeSource(source);
@@ -3840,7 +3840,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
       _streamFadeCleanupReduceMotionListener();
       _smdEndParser();
       if(typeof finalizeThinkingCard==='function') finalizeThinkingCard();
-      source.close();
+      try{if(source&&source.readyState!==2)source.close();}catch(_){ }
       _clearOwnerInflightState();
       _clearApprovalForOwner();
       _clearClarifyForOwner('cancelled');
@@ -4445,7 +4445,7 @@ function stopApprovalPollingForSession(sid) {
 
 function stopApprovalPolling() {
   if (_approvalPollTimer) { clearInterval(_approvalPollTimer); _approvalPollTimer = null; }
-  if (_approvalEventSource) { try { _approvalEventSource.close(); } catch(_){} _approvalEventSource = null; }
+  if (_approvalEventSource) { try { if(_approvalEventSource.readyState!==2)_approvalEventSource.close(); } catch(_){} _approvalEventSource = null; }
   if (_approvalSSEHealthTimer) { clearInterval(_approvalSSEHealthTimer); _approvalSSEHealthTimer = null; }
   _approvalFallbackPollInFlight = false;
   _approvalPollingSessionId = null;
@@ -4581,7 +4581,7 @@ function startSessionStream(sid) {
         // it in the interim (stale onerror from a superseded stream), in
         // which case we must not stomp the live one.
         if (_sessionEventSource === es) {
-          try { es.close(); } catch (_) {}
+          try { if(es.readyState!==2)es.close(); } catch (_) {}
           _sessionEventSource = null;
         }
         _sessionStreamReconnectTimer = setTimeout(() => {
@@ -4600,7 +4600,7 @@ function startSessionStream(sid) {
 function stopSessionStream() {
   if (_sessionStreamReconnectTimer) { clearTimeout(_sessionStreamReconnectTimer); _sessionStreamReconnectTimer = null; }
   if (_sessionEventSource) {
-    try { _sessionEventSource.close(); } catch(_){}
+    try { if(_sessionEventSource.readyState!==2)_sessionEventSource.close(); } catch(_){}
     _sessionEventSource = null;
   }
   _sessionStreamSessionId = null;
@@ -5212,7 +5212,7 @@ function stopClarifyPollingForSession(sid) {
 }
 
 function stopClarifyPolling() {
-  if (_clarifyEventSource) { try { _clarifyEventSource.close(); } catch(_){} _clarifyEventSource = null; }
+  if (_clarifyEventSource) { try { if(_clarifyEventSource.readyState!==2)_clarifyEventSource.close(); } catch(_){} _clarifyEventSource = null; }
   if (_clarifyFallbackTimer) { clearInterval(_clarifyFallbackTimer); _clarifyFallbackTimer = null; }
   if (_clarifyHealthTimer) { clearInterval(_clarifyHealthTimer); _clarifyHealthTimer = null; }
   _clarifyFallbackPollInFlight = false;

static/panels.js

@@ -2044,13 +2044,13 @@ function _kanbanStartPolling(){
 
 function _kanbanStopPolling(){
   if (_kanbanPollTimer) { clearInterval(_kanbanPollTimer); _kanbanPollTimer = null; }
-  if (_kanbanEventSource) { try { _kanbanEventSource.close(); } catch(_) {} _kanbanEventSource = null; }
+  if (_kanbanEventSource) { try { if(_kanbanEventSource.readyState!==2)_kanbanEventSource.close(); } catch(_) {} _kanbanEventSource = null; }
 }
 
 function _kanbanStartEventStream(){
   // Tear down any prior stream before opening a new one (board switch,
   // login change, etc.).
-  if (_kanbanEventSource) { try { _kanbanEventSource.close(); } catch(_) {} _kanbanEventSource = null; }
+  if (_kanbanEventSource) { try { if(_kanbanEventSource.readyState!==2)_kanbanEventSource.close(); } catch(_) {} _kanbanEventSource = null; }
   const since = Number(_kanbanLatestEventId || 0);
   let url = '/api/kanban/events/stream' + _kanbanBoardQuery({since: since});
   let es;

static/sessions.js

@@ -3932,7 +3932,7 @@ function _installSidebarSseFocusHook(){
 
 function _closeSessionEventsSSE(){
   if(_sessionEventsSSE){
-    _sessionEventsSSE.close();
+    try{if(_sessionEventsSSE.readyState!==2)_sessionEventsSSE.close();}catch(_){ }
     _sessionEventsSSE = null;
   }
 }
@@ -4143,7 +4143,7 @@ function startGatewaySSE(){
     _gatewaySSE.onerror = () => {
       if(typeof recordClientSSEError==='function') recordClientSSEError('gateway-sessions',{ready_state:_gatewaySSE?_gatewaySSE.readyState:null,reason:'gateway EventSource.onerror'});
       if(_gatewaySSE){
-        _gatewaySSE.close();
+        try{if(_gatewaySSE.readyState!==2)_gatewaySSE.close();}catch(_){ }
         _gatewaySSE = null;
       }
       void probeGatewaySSEStatus();
@@ -4155,7 +4155,7 @@ function startGatewaySSE(){
 
 function stopGatewaySSE(){
   if(_gatewaySSE){
-    _gatewaySSE.close();
+    try{if(_gatewaySSE.readyState!==2)_gatewaySSE.close();}catch(_){ }
     _gatewaySSE = null;
   }
   stopGatewayPollFallback();

static/terminal.js

@@ -401,7 +401,7 @@ function _connectTerminalOutput(){
   const sid=_terminalSessionId();
   if(!sid)return;
   if(TERMINAL_UI.source){
-    try{TERMINAL_UI.source.close();}catch(_){}
+    try{if(TERMINAL_UI.source.readyState!==2)TERMINAL_UI.source.close();}catch(_){}
     TERMINAL_UI.source=null;
   }
   const url=new URL('api/terminal/output',document.baseURI||location.href);
@@ -419,7 +419,7 @@ function _connectTerminalOutput(){
   source.addEventListener('terminal_closed',()=>{
     if(TERMINAL_UI.source!==source)return;
     if(TERMINAL_UI.term)TERMINAL_UI.term.writeln('\r\n[terminal closed]\r\n');
-    try{source.close();}catch(_){}
+    try{if(source&&source.readyState!==2)source.close();}catch(_){}
     TERMINAL_UI.source=null;
     setTimeout(()=>closeComposerTerminal(null,{skipApi:true}),260);
   });
@@ -428,7 +428,7 @@ function _connectTerminalOutput(){
     let msg=t('terminal_error');
     try{msg=(JSON.parse(ev.data)||{}).error||msg;}catch(_){}
     if(TERMINAL_UI.term)TERMINAL_UI.term.writeln('\r\n[terminal error] '+msg+'\r\n');
-    try{source.close();}catch(_){}
+    try{if(source&&source.readyState!==2)source.close();}catch(_){}
     TERMINAL_UI.source=null;
   });
 }
@@ -557,7 +557,7 @@ async function closeComposerTerminal(sessionId,opts){
   opts=opts||{};
   const sid=sessionId||TERMINAL_UI.sessionId||_terminalSessionId();
   if(TERMINAL_UI.source){
-    try{TERMINAL_UI.source.close();}catch(_){}
+    try{if(TERMINAL_UI.source&&TERMINAL_UI.source.readyState!==2)TERMINAL_UI.source.close();}catch(_){}
     TERMINAL_UI.source=null;
   }
   if(sid&&!opts.skipApi){
@@ -588,7 +588,7 @@ async function closeComposerTerminal(sessionId,opts){
 async function restartComposerTerminal(){
   if(!TERMINAL_UI.open||TERMINAL_UI.collapsed)return;
   if(TERMINAL_UI.source){
-    try{TERMINAL_UI.source.close();}catch(_){}
+    try{if(TERMINAL_UI.source&&TERMINAL_UI.source.readyState!==2)TERMINAL_UI.source.close();}catch(_){}
     TERMINAL_UI.source=null;
   }
   if(TERMINAL_UI.term)TERMINAL_UI.term.reset();
@@ -646,7 +646,7 @@ async function _resizeComposerTerminal(){
 }
 
 window.addEventListener('beforeunload',()=>{
-  if(TERMINAL_UI.source)try{TERMINAL_UI.source.close();}catch(_){}
+  if(TERMINAL_UI.source)try{if(TERMINAL_UI.source&&TERMINAL_UI.source.readyState!==2)TERMINAL_UI.source.close();}catch(_){}
   if(TERMINAL_UI.sessionId){
     const url=new URL('api/terminal/close',document.baseURI||location.href).href;
     const body=JSON.stringify({session_id:TERMINAL_UI.sessionId});