fix: inline label only for single reasoning segment

Author: ammar-agent

src/browser/components/Messages/MarkdownRenderer.tsx

@@ -8,7 +8,11 @@ interface MarkdownRendererProps {
   style?: React.CSSProperties;
 }
 
-export const MarkdownRenderer: React.FC<MarkdownRendererProps> = ({ content, className, style }) => {
+export const MarkdownRenderer: React.FC<MarkdownRendererProps> = ({
+  content,
+  className,
+  style,
+}) => {
   return (
     <div className={cn("markdown-content", className)} style={style}>
       <MarkdownCore content={content} />

src/browser/components/Messages/ReasoningMessage.tsx

@@ -18,8 +18,10 @@ export const ReasoningMessage: React.FC<ReasoningMessageProps> = ({ message, cla
   const isStreaming = message.isStreaming;
   const trimmedContent = content?.trim() ?? "";
   const hasContent = trimmedContent.length > 0;
+  const reasoningSegments = message.reasoningSegmentCount ?? 1;
   // OpenAI models often emit terse, single-line traces; surface them inline instead of hiding behind the label.
-  const isSingleLineTrace = !isStreaming && hasContent && !/[\r\n]/.test(trimmedContent);
+  const isSingleLineTrace =
+    !isStreaming && hasContent && reasoningSegments === 1 && !/[\r\n]/.test(trimmedContent);
   const isCollapsible = !isStreaming && hasContent && !isSingleLineTrace;
 
   // Auto-collapse when streaming ends

src/browser/utils/messages/StreamingMessageAggregator.ts

@@ -613,6 +613,7 @@ export class StreamingMessageAggregator {
       type: "reasoning",
       text: data.delta,
       timestamp: data.timestamp,
+      segmentCount: 1,
     });
 
     // Track delta for token counting and TPS calculation
@@ -798,15 +799,20 @@ export class StreamingMessageAggregator {
                 timestamp: lastMerged.timestamp ?? part.timestamp,
               };
             } else if (lastMerged?.type === "reasoning" && part.type === "reasoning") {
-              // Merge reasoning parts, preserving the first timestamp
+              // Merge reasoning parts, preserving the first timestamp and accumulating segment count
               mergedParts[mergedParts.length - 1] = {
                 type: "reasoning",
                 text: lastMerged.text + part.text,
                 timestamp: lastMerged.timestamp ?? part.timestamp,
+                segmentCount: (lastMerged.segmentCount ?? 1) + (part.segmentCount ?? 1),
               };
             } else {
               // Different type or tool part - add new part
-              mergedParts.push(part);
+              if (part.type === "reasoning") {
+                mergedParts.push({ ...part, segmentCount: part.segmentCount ?? 1 });
+              } else {
+                mergedParts.push(part);
+              }
             }
           }
 
@@ -843,6 +849,7 @@ export class StreamingMessageAggregator {
                 isPartial: message.metadata?.partial ?? false,
                 isLastPartOfMessage: isLastPart,
                 timestamp: part.timestamp ?? baseTimestamp,
+                reasoningSegmentCount: part.segmentCount ?? 1,
               });
             } else if (part.type === "text" && part.text) {
               // Skip empty text parts

src/common/types/message.ts

@@ -72,6 +72,7 @@ export interface MuxReasoningPart {
   type: "reasoning";
   text: string;
   timestamp?: number;
+  segmentCount?: number; // Number of merged reasoning deltas represented by this part
 }
 
 // File/Image part type for multimodal messages (matches AI SDK FileUIPart)
@@ -151,6 +152,7 @@ export type DisplayedMessage =
       isLastPartOfMessage?: boolean; // True if this is the last part of a multi-part message
       timestamp?: number;
       tokens?: number; // Reasoning tokens if available
+      reasoningSegmentCount?: number; // Number of merged reasoning deltas represented by this block
     }
   | {
       type: "stream-error";