[Bug] Haiku subagent fails after Skill use: 400 system.4.type must be 'text'
Status Open
Reported on v2.1.296
Maintainer reply None cached
Activity 0 comments · opened Oct 13, 2026
Bug Description
Follow-up to my earlier report (first request id req_011Cfv9F2fbyXhJZawwueKgU).
Still reproduces on Claude Code 2.1.296 (latest on npm, 2026-10-13).
Bug: after any Skill invocation in a session, the next subagent dispatched with model: haiku intermittently fails before its first tool call with:
API Error: 400 system.4.type: Input should be 'text'
Model sent to the API: claude-haiku-5-5.
Repro (same session):
- Invoke any skill (ours or third party, e.g. superpowers:writing-skills, figma:figma-implement-motion).
- Dispatch 3 general-purpose subagents with model: haiku, prompt "reply ok".
Result today: 1 of 3 failed.
- New failing request id: req_011CfyQadFmRJQjuRdvMLmBr
- Earlier failing ids (2026-10-11): req_011CfvAUvsMqdnfiQPm5mJyw, req_011CfvAm9N8h7iLepW6vZVsL, req_011CfvAYmccFfMxnM1zqrgG4, req_011CfvAiFLiiQpaePBM1kDkn, req_011CfvAe6iSxYK2N9nKg8akE
Without a prior skill invocation the haiku dispatch passes every time. Sonnet and opus subagents are never affected. Looks like a non-text block is injected at system index 4 for haiku requests after skill content is loaded.
Environment Info
- Platform: darwin
- Terminal: ghostty
- Version: 2.1.296
- Feedback ID: b13c7b63-648d-4519-8d75-df24c11ba463