feat(chat): show tool calls with expandable arguments in message history

Render tool-call-only assistant messages as compact cards with wrench
icon instead of empty bubbles. Click to expand and view tool arguments
as formatted JSON. Make thinking block full-width in chat thread.

ui/web/src/components/chat/message-bubble.tsx

@@ -1,6 +1,8 @@
-import { Bot, User } from "lucide-react";
+import { useState } from "react";
+import { Bot, User, Wrench, ChevronRight } from "lucide-react";
 import { MessageContent } from "./message-content";
 import type { ChatMessage } from "@/types/chat";
+import type { ToolCall } from "@/types/session";
 
 interface MessageBubbleProps {
   message: ChatMessage;
@@ -14,6 +16,25 @@ export function MessageBubble({ message }: MessageBubbleProps) {
     return null; // Tool messages are shown inline with assistant messages
   }
 
+  const hasContent = !!message.content?.trim();
+  const hasToolCalls = message.toolCalls && message.toolCalls.length > 0;
+
+  // Skip assistant messages with neither text nor tool calls
+  if (!isUser && !hasContent && !hasToolCalls) {
+    return null;
+  }
+
+  // Tool-call-only assistant message: render compact tool call list
+  if (!isUser && !hasContent && hasToolCalls) {
+    return (
+      <div className="space-y-1">
+        {message.toolCalls!.map((tc) => (
+          <ToolCallItem key={tc.id} toolCall={tc} />
+        ))}
+      </div>
+    );
+  }
+
   return (
     <div className={`flex gap-3 ${isUser ? "flex-row-reverse" : ""}`}>
       <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full border bg-background">
@@ -31,6 +52,13 @@ export function MessageBubble({ message }: MessageBubbleProps) {
             : "bg-card text-card-foreground border border-border shadow-sm"
         }`}
       >
+        {hasToolCalls && (
+          <div className="mb-2 space-y-1">
+            {message.toolCalls!.map((tc) => (
+              <ToolCallItem key={tc.id} toolCall={tc} compact />
+            ))}
+          </div>
+        )}
         <MessageContent content={message.content} role={message.role} />
         {message.timestamp && (
           <div className={`mt-1 text-[10px] ${isUser ? "text-primary-foreground/60" : "text-muted-foreground"}`}>
@@ -44,3 +72,39 @@ export function MessageBubble({ message }: MessageBubbleProps) {
     </div>
   );
 }
+
+function ToolCallItem({ toolCall, compact }: { toolCall: ToolCall; compact?: boolean }) {
+  const [expanded, setExpanded] = useState(false);
+  const hasArgs = toolCall.arguments && Object.keys(toolCall.arguments).length > 0;
+
+  return (
+    <div className={compact ? "" : "rounded-md border bg-muted/50 overflow-hidden"}>
+      <button
+        type="button"
+        onClick={() => hasArgs && setExpanded(!expanded)}
+        className={`flex items-center gap-1.5 w-full text-left ${
+          compact
+            ? "text-xs text-muted-foreground py-0.5"
+            : "px-3 py-1.5 text-sm hover:bg-muted/80 transition-colors"
+        } ${hasArgs ? "cursor-pointer" : "cursor-default"}`}
+      >
+        {compact ? (
+          <Wrench className="h-3 w-3 shrink-0" />
+        ) : (
+          <Wrench className="h-3.5 w-3.5 text-muted-foreground shrink-0" />
+        )}
+        <span className={`font-mono truncate ${compact ? "" : "text-xs"}`}>{toolCall.name}</span>
+        {hasArgs && (
+          <ChevronRight className={`h-3 w-3 shrink-0 ml-auto text-muted-foreground transition-transform ${expanded ? "rotate-90" : ""}`} />
+        )}
+      </button>
+      {expanded && hasArgs && (
+        <pre className={`text-[11px] text-muted-foreground overflow-x-auto ${
+          compact ? "pl-4.5 pb-1" : "px-3 pb-2 border-t bg-muted/30"
+        }`}>
+          {JSON.stringify(toolCall.arguments, null, 2)}
+        </pre>
+      )}
+    </div>
+  );
+}

ui/web/src/pages/chat/chat-thread.tsx

@@ -68,9 +68,7 @@ export function ChatThread({
 
         {/* Thinking block (extended thinking / reasoning) */}
         {isRunning && thinkingText && (
-          <div className="mx-auto max-w-[80%]">
-            <ThinkingBlock text={thinkingText} isStreaming={streamText === null} />
-          </div>
+          <ThinkingBlock text={thinkingText} isStreaming={streamText === null} />
         )}
 
         {/* Streaming text */}