resume/forkSession fails with 400 on sessions containing tool_use blocks

Description

When using the Agent SDK's resume option to resume a session that contains tool_use blocks, the API returns a 400 error:

cache_control cannot be set for empty text blocks

or

messages: text content blocks must be non-empty

Reproduction

1. Create a session via query() that uses tools (Read, Edit, Bash, etc.)
2. Let it complete
3. Resume with query({ prompt: 'follow up', options: { resume: sessionId } })
4. API rejects with 400

Simple text-only sessions resume fine. Only sessions with tool_use blocks are affected.

Root Cause

The JSONL session transcript contains empty text blocks ({"type": "text", "text": ""}) that appear between tool_use blocks. When the SDK replays the conversation with cache_control annotations, the API rejects these empty blocks.

Workaround

Sanitizing the JSONL file before resuming — removing content blocks where type === "text" and text is empty or whitespace — resolves the issue.

Environment

• @anthropic-ai/claude-agent-sdk v0.2.88
• Claude Code CLI (latest)
• macOS, Node.js v24.1.0

Related Issues

• #2203, #24662, #23440, #14132 (all same family)
• agent-sdk-typescript #89