diff --git a/extension/sidepanel.css b/extension/sidepanel.css
index 2f82719f..5b99b7bf 100644
--- a/extension/sidepanel.css
+++ b/extension/sidepanel.css
@@ -290,6 +290,32 @@ body::after {
   line-height: 1.5;
   word-break: break-word;
 }
+/* Collapsed reasoning disclosure */
+.agent-reasoning {
+  margin: 4px 0;
+}
+.agent-reasoning summary {
+  cursor: pointer;
+  font-size: 11px;
+  font-family: var(--font-mono);
+  color: var(--text-meta);
+  padding: 3px 0;
+  user-select: none;
+  list-style: none;
+}
+.agent-reasoning summary::before {
+  content: '▶ ';
+  font-size: 9px;
+}
+.agent-reasoning[open] summary::before {
+  content: '▼ ';
+}
+.agent-reasoning summary:hover {
+  color: var(--text-label);
+}
+.agent-reasoning .agent-tool {
+  margin-left: 4px;
+}
 /* Legacy classes kept for compat */
 .tool-name {
   color: var(--amber-500);
diff --git a/extension/sidepanel.js b/extension/sidepanel.js
index f3dfca42..16cd917f 100644
--- a/extension/sidepanel.js
+++ b/extension/sidepanel.js
@@ -196,8 +196,27 @@ function handleAgentEvent(entry) {
     if (thinking) thinking.remove();
     updateStopButton(false);
     stopFastPoll();
-    // Add timestamp
+    // Collapse tool calls into a "See reasoning" disclosure
     if (agentContainer) {
+      const tools = agentContainer.querySelectorAll('.agent-tool');
+      if (tools.length > 0) {
+        const details = document.createElement('details');
+        details.className = 'agent-reasoning';
+        const summary = document.createElement('summary');
+        summary.textContent = `See reasoning (${tools.length} step${tools.length > 1 ? 's' : ''})`;
+        details.appendChild(summary);
+        for (const tool of tools) {
+          details.appendChild(tool);
+        }
+        // Insert the disclosure before the text response (if any)
+        const textEl = agentContainer.querySelector('.agent-text');
+        if (textEl) {
+          agentContainer.insertBefore(details, textEl);
+        } else {
+          agentContainer.appendChild(details);
+        }
+      }
+      // Add timestamp
       const ts = document.createElement('span');
       ts.className = 'chat-time';
       ts.textContent = formatChatTime(entry.ts);