Add call logs latency improvement to June 29 What's New (#1096)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: bets-margulies-vapi

fern/changelog/2026-06-29.mdx

@@ -5,6 +5,7 @@
 2. **AI-Generated Tool Failure and Completion Messages**: You can now set `role: 'system'` on request-failed [tool messages](https://docs.vapi.ai/tools/custom-tools), and the dashboard has a new UI for configuring AI-generated messages when tools fail or complete. This gives assistants more natural responses when tools hit errors.
 
 3. **Call Logs Improvements**:
+    - Significant latency improvements across both the dashboard and the `/calls` API endpoints.
     - The call detail flyout now shows which assistant or squad handled the call, includes a link to the assistant or squad, and indicates which phone number was used.
     - In squad or handoff calls, transcript messages now show which assistant said what, making it easier to trace conversation flow.