What
When running in headless mode (--output-format stream-json) and the sandbox is required but unavailable, Claude Code now emits a proper JSON error result instead of only writing to stderr.
Details
- Error message includes:
"Sandbox required but unavailable: {reason}. Set sandbox.failIfUnavailable=false to allow unsandboxed execution." - The JSON result includes all standard fields (session_id, uuid, duration, etc.) for proper parsing by automation tools
Evidence
Headless sandbox error handling (search for "Sandbox required but unavailable:")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.