[Bug] 0.21.0 hangs for 10 minutes on cancel in the Chat view

Reproduce the Chat view cancellation flow with the stated Eclipse and plugin versions, then start with ChatView.onCancel and the cancellation path in LanguageServerWrapper. Inspect the lock contention at StreamMessageConsumer.consume using the supplied thread dump and related log output. Done means cancelling the request no longer blocks the Eclipse UI for minutes and the allowlist error is handled without leaving the model page empty.

Environment

• OS: RHEL 9.6
• Eclipse Version: 4.38
• Plugin Version: 0.21.0

Describe the bug
Open Chat
Open Java file
Ask /explain with the Claude Opus 4.8 medium model
Nothing happens for some time, so try to "cancel".
UI hangs for ~10 minutes (no CPU load).

After the hang three log entries are logged,

org.eclipse.lsp4e
Info
Fri Aug 07 11:31:30 CEST 2026
[LS:GitHub Copilot Language Server][Info]	[AuthManager] resolveSession: persisted store resolved a session

followed by an error

com.microsoft.copilot.eclipse
Error
Fri Aug 07 11:31:31 CEST 2026
[Error] org.eclipse.lsp4j.jsonrpc.ResponseErrorException: Invalid allowlist format: registry entries missing required fields

java.util.concurrent.CompletionException: org.eclipse.lsp4j.jsonrpc.ResponseErrorException: Invalid allowlist format: registry entries missing required fields
	at java.base/java.util.concurrent.CompletableFuture.wrapInCompletionException(CompletableFuture.java:323)
	at java.base/java.util.concurrent.CompletableFuture.encodeRelay(CompletableFuture.java:412)
	at java.base/java.util.concurrent.CompletableFuture.completeRelay(CompletableFuture.java:421)
	at java.base/java.util.concurrent.CompletableFuture$UniRelay.tryFire(CompletableFuture.java:1118)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:531)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2221)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.handleResponse(RemoteEndpoint.java:214)
	at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.consume(RemoteEndpoint.java:198)
	at org.eclipse.lsp4e.LanguageServerWrapper.lambda$3(LanguageServerWrapper.java:458)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.handleMessage(StreamMessageProducer.java:189)
	at org.eclipse.lsp4j.jsonrpc.json.StreamMessageProducer.listen(StreamMessageProducer.java:97)
	at org.eclipse.lsp4j.jsonrpc.json.ConcurrentMessageProcessor.run(ConcurrentMessageProcessor.java:97)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:545)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:328)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
	at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: org.eclipse.lsp4j.jsonrpc.ResponseErrorException: Invalid allowlist format: registry entries missing required fields
	... 11 more

Note: the model management page is empty (not sure it is related):

and it poplates only after the hang is resolved.

The UI itself hangs in this stack:

"main" #3 [161792] prio=6 os_prio=0 cpu=18177.04ms elapsed=211.23s tid=0x00007f5b2802ebf0 nid=161792 waiting for monitor entry  [0x00007f5b2e9fc000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at org.eclipse.lsp4j.jsonrpc.json.StreamMessageConsumer.consume(StreamMessageConsumer.java:67)
        - waiting to lock <0x000000040cf71510> (a java.lang.Object)
        at org.eclipse.lsp4e.LanguageServerWrapper.lambda$3(LanguageServerWrapper.java:458)
        at org.eclipse.lsp4e.LanguageServerWrapper$$Lambda/0x00000000680ccc00.consume(Unknown Source)
        at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.notify(RemoteEndpoint.java:135)
        at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.sendCancelNotification(RemoteEndpoint.java:185)
        at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint.lambda$request$1(RemoteEndpoint.java:157)
        at org.eclipse.lsp4j.jsonrpc.RemoteEndpoint$$Lambda/0x0000000068105000.run(Unknown Source)
        at org.eclipse.lsp4j.jsonrpc.JsonRpcRequestFuture.cancelRequest(JsonRpcRequestFuture.java:126)
        at org.eclipse.lsp4j.jsonrpc.JsonRpcRequestFuture.cancel(JsonRpcRequestFuture.java:99)
        at org.eclipse.lsp4e.LanguageServerWrapper.lambda$24(LanguageServerWrapper.java:1077)
        at org.eclipse.lsp4e.LanguageServerWrapper$$Lambda/0x00000000680cc400.apply(Unknown Source)
        at java.util.concurrent.CompletableFuture.uniExceptionally(java.base@25/CompletableFuture.java:1011)
        at java.util.concurrent.CompletableFuture$UniExceptionally.tryFire(java.base@25/CompletableFuture.java:995)
        at java.util.concurrent.CompletableFuture.postComplete(java.base@25/CompletableFuture.java:531)
        at java.util.concurrent.CompletableFuture.cancel(java.base@25/CompletableFuture.java:2554)
        at org.eclipse.lsp4e.LanguageServerWrapper.lambda$22(LanguageServerWrapper.java:1034)
        at org.eclipse.lsp4e.LanguageServerWrapper$$Lambda/0x00000000680cc800.apply(Unknown Source)
        at java.util.concurrent.CompletableFuture.uniExceptionally(java.base@25/CompletableFuture.java:1011)
        at java.util.concurrent.CompletableFuture$UniExceptionally.tryFire(java.base@25/CompletableFuture.java:995)
        at java.util.concurrent.CompletableFuture.postComplete(java.base@25/CompletableFuture.java:531)
        at java.util.concurrent.CompletableFuture.cancel(java.base@25/CompletableFuture.java:2554)
        at com.microsoft.copilot.eclipse.ui.chat.ChatView.lambda$35(ChatView.java:1413)
        at com.microsoft.copilot.eclipse.ui.chat.ChatView$$Lambda/0x0000000068dbf000.accept(Unknown Source)
        at java.lang.Iterable.forEach(java.base@25/Iterable.java:75)
        at com.microsoft.copilot.eclipse.ui.chat.ChatView.onCancel(ChatView.java:1412)
        at com.microsoft.copilot.eclipse.ui.chat.ActionBar.notifyCancel(ActionBar.java:825)
        at com.microsoft.copilot.eclipse.ui.chat.ActionBar.handleCancelMessage(ActionBar.java:818)
        at com.microsoft.copilot.eclipse.ui.chat.ActionBar$4.widgetSelected(ActionBar.java:473)
        at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:290)
        at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:91)
        at org.eclipse.swt.widgets.Display.sendEvent(Display.java:5894)
        at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1656)
        at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:5109)
        at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4546)

Full jstack:

thread_dump.txt