[BUG] VS Code extension: first user message lost when IDE tools injected via deferred_tools_delta

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

API Error: 400 {"id":"1776394414315-tja4r6er1pssc","type":"error","error":{"type":"request_error","message":"{\ "type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"messages.2: user messages must
have non-empty content\"},\"request_id\":\"req_011Ca8b2u7MHTk5wh5mFKgc7\"}","raw_body":"{\"type\":\"error\",\"e
rror\":{\"type\":\"invalid_request_error\",\"message\":\"messages.2: user messages must have non-empty
content\"},\"request_id\":\"req_011Ca8b2u7MHTk5wh5mFKgc7\"}"}}

What Should Happen?

API Error: 400 {"id":"1776394414315-tja4r6er1pssc","type":"error","error":{"type":"request_error","message":"{\ "type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"messages.2: user messages must
have non-empty content\"},\"request_id\":\"req_011Ca8b2u7MHTk5wh5mFKgc7\"}","raw_body":"{\"type\":\"error\",\"e
rror\":{\"type\":\"invalid_request_error\",\"message\":\"messages.2: user messages must have non-empty
content\"},\"request_id\":\"req_011Ca8b2u7MHTk5wh5mFKgc7\"}"}}

Error Messages/Logs

Steps to Reproduce

API Error: 400 {"id":"1776394414315-tja4r6er1pssc","type":"error","error":{"type":"request_error","message":"{\ "type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"messages.2: user messages must
have non-empty content\"},\"request_id\":\"req_011Ca8b2u7MHTk5wh5mFKgc7\"}","raw_body":"{\"type\":\"error\",\"e
rror\":{\"type\":\"invalid_request_error\",\"message\":\"messages.2: user messages must have non-empty
content\"},\"request_id\":\"req_011Ca8b2u7MHTk5wh5mFKgc7\"}"}}

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.112

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_