diff --git a/api/server/controllers/agents/client.js b/api/server/controllers/agents/client.js
index 75833796fa..725f504aec 100644
--- a/api/server/controllers/agents/client.js
+++ b/api/server/controllers/agents/client.js
@@ -358,16 +358,30 @@ class AgentClient extends BaseClient {
    * endpoint named by `activityEndpoint` (default: the agent's).
    */
   async resolveActivityLabelLLM() {
-    return resolveActivityLabelModel({
-      req: this.options.req,
-      agent: this.options.agent,
-      ids: {
-        messageId: this.responseMessageId,
-        conversationId: this.conversationId,
-        parentMessageId: this.parentMessageId,
-      },
-      db: { getUserKey: db.getUserKey, getUserKeyValues: db.getUserKeyValues },
-    });
+    /** Memoized per response: resolution reads provider config and can hit the
+     *  database for user keys, and nothing it depends on changes between
+     *  batches of the same run — so re-resolving on every batch (twice, with
+     *  usage accounting) is repeated credential work for an identical result.
+     *  The promise is cached rather than the value so concurrent batches share
+     *  one in-flight resolution. */
+    this.activityLabelLLMPromise =
+      this.activityLabelLLMPromise ??
+      resolveActivityLabelModel({
+        req: this.options.req,
+        agent: this.options.agent,
+        ids: {
+          messageId: this.responseMessageId,
+          conversationId: this.conversationId,
+          parentMessageId: this.parentMessageId,
+        },
+        db: { getUserKey: db.getUserKey, getUserKeyValues: db.getUserKeyValues },
+      }).catch((error) => {
+        /** Never cache a rejection: a transient credential read failure would
+         *  otherwise disable labels for the rest of the response. */
+        this.activityLabelLLMPromise = null;
+        throw error;
+      });
+    return this.activityLabelLLMPromise;
   }
 
   /**
diff --git a/client/src/components/Chat/Messages/Content/ContentParts.tsx b/client/src/components/Chat/Messages/Content/ContentParts.tsx
index ecc40256f6..cfdcc14798 100644
--- a/client/src/components/Chat/Messages/Content/ContentParts.tsx
+++ b/client/src/components/Chat/Messages/Content/ContentParts.tsx
@@ -30,9 +30,15 @@ const getToolGroupId = (parts: PartWithIndex[], fallbackScope: number): string =
   if (!firstPart) {
     return 'empty';
   }
-  const toolCallId = getToolCallId(firstPart.part);
-  if (toolCallId) {
-    return `tool:${toolCallId}`;
+  /** Keyed on the first TOOL CALL, not the first part. An activity label
+   *  absorbs the block's leading THINK part when its text lands, so keying on
+   *  `parts[0]` would flip the key mid-run — remounting the group and losing
+   *  whatever the user had expanded. The tool calls themselves do not move. */
+  for (const { part } of parts) {
+    const toolCallId = getToolCallId(part);
+    if (toolCallId) {
+      return `tool:${toolCallId}`;
+    }
   }
   return `fallback:${fallbackScope}:${firstPart.idx}`;
 };