[BUG] Auto Mode sends unsupported "afk-mode-2026-01-31" beta header causing API 400 error

Bug Description

When Auto Mode is active in the VS Code extension, Claude Code sends the afk-mode-2026-01-31 value in the anthropic-beta header, which the API rejects with a 400 error.

Error Message

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"Unexpected value(s) afk-mode-2026-01-31 for the anthropic-beta header. Please consult our documentation at docs.claude.com or try again without the header."},"request_id":"req_011CYzK2HKC3cUKSrnQbCxX5"}

Root Cause

In cli.js, the afk-mode-2026-01-31 header is conditionally added when isAutoModeActive() returns true, but this value is not in the supported beta set and is rejected by the API.

Environment

• Claude Code version: 2.1.74 (both CLI and VS Code extension)
• OS: macOS (Darwin 24.4.0)
• Node.js: v22.14.0
• ANTHROPIC_BASE_URL: https://api.anthropic.com (direct, no proxy)

Steps to Reproduce

1. Open Claude Code in VS Code
2. Activate Auto Mode
3. Send a message
4. Observe API 400 error

Expected Behavior

Auto Mode should work without sending unsupported beta headers.