The webui stores display-only fields on messages (attachments, timestamp,
_ts) for UI rendering. These leaked into the conversation_history passed
to AIAgent.run_conversation(). Most providers ignore unknown fields, but
Z.AI/GLM tries to deserialize 'attachments' as its native ChatAttachments
type, causing HTTP 400 on every subsequent message after an image upload.
Fix: _sanitize_messages_for_api() creates a clean copy with only
API-standard keys (role, content, tool_calls, tool_call_id, name,
refusal) before passing to run_conversation(). Applied to both the
streaming path (streaming.py) and non-streaming path (routes.py).
Closes#66
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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