ai-chat: forward or document body behavior during tool continuation path

[ask-bonk]

Context

In #886, we added forwarding of custom body fields to onChatMessage via options.body. However, this only applies to the initial CF_AGENT_USE_CHAT_REQUEST path. The tool continuation path (CF_AGENT_TOOL_RESULT) does not forward body, so options.body will be undefined during auto-continue after client tool results.

Problem

Users who rely on body data (e.g., model selection, temperature) for every onChatMessage invocation will find it missing on tool continuation calls. They would need to manually store it on the first call (e.g., in Durable Object state) and retrieve it on subsequent calls.

Possible approaches

1. Persist and re-forward body — Store the custom body fields from the initial request and automatically pass them through on tool continuations so options.body is always available.
2. Document the current behavior — Make it clear in docs/JSDoc that options.body is only populated on the initial chat request and is undefined during tool continuations, with guidance on how users can persist it themselves.

References

• PR: feat(ai-chat): forward custom body fields to onChatMessage options #886
• Review nit: feat(ai-chat): forward custom body fields to onChatMessage options #886 (comment)

[whoiskatrin]

/bonk implement this carefully with tests included

[ask-bonk]

Created PR #895

github run