fix ui deadlock and infinite retry loop on 402 quota error

Author: xinyi-gong

com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/chat/ChatContentViewer.java

@@ -217,11 +217,17 @@ public void processTurnEvent(ChatProgressValue value) {
         errMsg = Messages.chat_model_unsupported_message;
       }
       if (StringUtils.isNotEmpty(errMsg)) {
-        // TODO: remove this error message replacement if statement when the CLS side warn message is aligned.
-        if (value.getCode() == 402) {
+        // Check once whether we're already on the fallback model
+        CopilotModel fallback = this.serviceManager.getModelService().getFallbackModel();
+        CopilotModel current = this.serviceManager.getModelService().getActiveModel();
+        boolean alreadyOnFallback = fallback != null && current != null
+            && fallback.getModelName().equals(current.getModelName());
+
+        // Only replace the error message with "switched to fallback" when we're NOT already
+        // on the fallback model. When already on fallback, show the original CLS message.
+        if (value.getCode() == 402 && !alreadyOnFallback) {
           CopilotPlan userPlan = this.serviceManager.getAuthStatusManager().getQuotaStatus().copilotPlan();
-          CopilotModel fallbackModel = this.serviceManager.getModelService().getFallbackModel();
-          String fallbackModelName = fallbackModel != null ? fallbackModel.getModelName()
+          String fallbackModelName = fallback != null ? fallback.getModelName()
               : Messages.chat_noQuotaView_fallbackModel;
 
           if (MenuUtils.isCfiPlan(userPlan)) {
@@ -235,15 +241,19 @@ public void processTurnEvent(ChatProgressValue value) {
 
         renderWarnMessageWithUpgradePlanButton(errMsg, value.getCode());
 
-        if (value.getCode() == 402
+        // Switch to fallback model and auto-retry, but only if not already on the fallback model
+        // to avoid an infinite loop of 402 → switch → resend → 402 → ...
+        if (value.getCode() == 402 && !alreadyOnFallback
             && this.serviceManager.getAuthStatusManager().getQuotaStatus().copilotPlan() != CopilotPlan.free) {
           this.serviceManager.getModelService().setFallBackModelAsActiveModel();
           this.serviceManager.getAuthStatusManager().checkQuota();
 
-          String previousInput = this.serviceManager.getUserPreferenceService().getPreviousInput(StringUtils.EMPTY);
+          String previousInput =
+              this.serviceManager.getUserPreferenceService().getPreviousInput(StringUtils.EMPTY);
           if (StringUtils.isNotEmpty(previousInput)) {
             IEventBroker eventBroker = PlatformUI.getWorkbench().getService(IEventBroker.class);
-            Map<String, Object> properties = Map.of("previousInput", previousInput, "needCreateUserTurn", false);
+            Map<String, Object> properties =
+                Map.of("previousInput", previousInput, "needCreateUserTurn", false);
             eventBroker.post(CopilotEventConstants.TOPIC_CHAT_ON_SEND, properties);
           }
         }

com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/chat/CopilotTurnWidget.java

@@ -25,6 +25,9 @@
  * A custom widget that displays a turn for the copilot.
  */
 public class CopilotTurnWidget extends BaseTurnWidget {
+
+  private Label modelInfoLabel;
+
   /**
    * Create the widget.
    */
@@ -71,8 +74,11 @@ public void renderModelInfo(String modelName, double billingMultiplier) {
         if (footer == null || footer.isDisposed()) {
           createFooter();
         }
+        if (modelInfoLabel != null && !modelInfoLabel.isDisposed()) {
+          modelInfoLabel.dispose();
+        }
         if (StringUtils.isNotBlank(modelName)) {
-          Label modelInfoLabel = new Label(footer, SWT.NONE);
+          modelInfoLabel = new Label(footer, SWT.NONE);
           // When token-based billing is enabled on the language server, the per-turn billing
           // multiplier is no longer a meaningful price signal, so render the model name on its
           // own. Fall back to the legacy "{model} - {multiplier}" format otherwise.
@@ -91,6 +97,9 @@ public void renderModelInfo(String modelName, double billingMultiplier) {
           modelInfoLabel.setLayoutData(labelGridData);
           modelInfoLabel.setData(CssConstants.CSS_CLASS_NAME_KEY, "model-info-label");
 
+          // Ensure footer stays at the bottom of the turn widget, even when
+          // warn widgets are appended after it (e.g. quota fallback retry).
+          footer.moveBelow(null);
           footer.requestLayout();
         }
       }, this);

com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/chat/services/ModelService.java

@@ -7,6 +7,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 
 import org.apache.commons.lang3.StringUtils;
@@ -348,7 +349,11 @@ public void setActiveModel(String modelName) {
       // Persist using the composite key for proper identification
       UserPreference preference = getUserPreference();
       preference.setChatModel(compositeKey);
-      persistUserPreference();
+      // Persist asynchronously to avoid deadlock: persistUserPreference() calls
+      // persistence().get() which blocks waiting for the LSP listener thread.
+      // If called on the UI thread while the listener is in syncExec, both threads
+      // deadlock.
+      CompletableFuture.runAsync(this::persistUserPreference);
 
       // Update observable
       ensureRealm(() -> activeModelObservable.setValue(model));