fix(forwarder): handle Cursor summarize actions

Map Cursor's protocol-level SummarizeAction to manual context compaction while keeping the legacy /compact directive disabled.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/backend/forwarder/service.go

@@ -672,6 +672,7 @@ func (service *Service) decodeInboundIntent(requestID string, message *agentv1.A
 	default:
 		return InboundIntent{}, fmt.Errorf("unsupported client message kind: %s", clientKind)
 	}
+	intent.ManualCompaction = resolveInboundManualCompaction(message, intent.UserMessage)
 	return intent, nil
 }
 
@@ -751,6 +752,7 @@ func (service *Service) handleRunIntent(intent InboundIntent) error {
 	stream.mu.Lock()
 	stream.ThinkingEffort = strings.TrimSpace(intent.ThinkingEffort)
 	stream.SubagentModelOverrides = cloneSubagentModelOverrides(intent.SubagentModelOverrides)
+	stream.ManualCompaction = intent.ManualCompaction
 	stream.PendingProviderAction = providerActionNone
 	stream.PendingCompaction = nil
 	stream.PendingExecs = make(map[string]runtimecore.PendingExec)
@@ -788,6 +790,7 @@ func (service *Service) handleRunIntent(intent InboundIntent) error {
 		"subagent_model_override_count": len(intent.SubagentModelOverrides),
 		"subagent_model_overrides":      subagentModelOverrideSummaries(intent.SubagentModelOverrides),
 		"latest_user_text":              userMessageText(intent.UserMessage),
+		"manual_compaction_requested":   intent.ManualCompaction.Requested,
 	})
 	if err := service.publishCheckpoint(intent.RequestID, intent.ConversationID); err != nil {
 		return err
@@ -2643,6 +2646,38 @@ func conversationActionIsResume(action *agentv1.ConversationAction) bool {
 	return ok
 }
 
+func inboundConversationAction(message *agentv1.AgentClientMessage) *agentv1.ConversationAction {
+	if message == nil {
+		return nil
+	}
+	if action := message.GetConversationAction(); action != nil {
+		return action
+	}
+	if runRequest := message.GetRunRequest(); runRequest != nil {
+		return runRequest.GetAction()
+	}
+	return nil
+}
+
+func conversationActionIsSummarize(action *agentv1.ConversationAction) bool {
+	if action == nil {
+		return false
+	}
+	_, ok := action.GetAction().(*agentv1.ConversationAction_SummarizeAction)
+	return ok
+}
+
+func resolveInboundManualCompaction(message *agentv1.AgentClientMessage, userMessage *agentv1.UserMessage) manualCompactionDirective {
+	instruction, requested := parseManualCompactionRequest(userMessage)
+	if conversationActionIsSummarize(inboundConversationAction(message)) {
+		requested = true
+	}
+	return manualCompactionDirective{
+		Requested:   requested,
+		Instruction: instruction,
+	}
+}
+
 func conversationActionStartsRun(action *agentv1.ConversationAction) bool {
 	if action == nil {
 		return false
@@ -2650,6 +2685,7 @@ func conversationActionStartsRun(action *agentv1.ConversationAction) bool {
 	switch action.GetAction().(type) {
 	case *agentv1.ConversationAction_UserMessageAction,
 		*agentv1.ConversationAction_ResumeAction,
+		*agentv1.ConversationAction_SummarizeAction,
 		*agentv1.ConversationAction_StartPlanAction,
 		*agentv1.ConversationAction_ExecutePlanAction:
 		return true