A user turn heals tool calls that were never answered
A crashed or interrupted loop leaves an assistant turn declaring a call with no result. Most providers reject that history outright, so the buffer closes the pair before the conversation moves on.
The rule
- Before a
user-role message is appended, every tool call declared in the buffer that has no matching tool result anywhere in the buffer is answered by a synthetictool-role message stating that the call was interrupted and returned no result. - The synthetic message is marked as healed, carries the id it answers, and is inserted directly after the turn that declared the call, not at the end of the buffer, because a result must be adjacent to its call.
- Healing runs only at this boundary: appending a
toolorassistantmessage never triggers it.
What it means
A crashed or interrupted loop can leave a buffer with an assistant turn that
declared a call and no result answering it. Healing does not wait for the
buffer to end before closing that pair: the synthetic result is inserted
directly after the turn that declared the call, wherever that is, because a
result has to sit next to its call for the history to be sendable at all. A
conversation that carried on past the crash — more turns appended after the
dangling call, before anyone appends a user message — still gets its
synthetic result inserted mid-buffer, not tacked onto the end.
The other clause worth noting: healing runs only at a user-turn boundary.
Appending a tool or assistant message never triggers it, even when the
buffer already holds an unanswered call.
Example
A call goes unanswered, and two more turns are appended before anyone
appends a user message:
[
{ "role": "assistant", "content": "", "metadata": { "tool_calls": [{ "tool_call_id": "c1", "name": "search" }] } },
{ "role": "user", "content": "anything?", "metadata": {} },
{ "role": "assistant", "content": "sorry, lost it", "metadata": {} }
][
{ "role": "assistant", "content": "", "metadata": { "tool_calls": [{ "tool_call_id": "c1", "name": "search" }] } },
{ "role": "tool", "content": "Tool call was interrupted; no result.", "metadata": { "tool_call_id": "c1", "healed": true } },
{ "role": "user", "content": "anything?", "metadata": {} },
{ "role": "assistant", "content": "sorry, lost it", "metadata": {} },
{ "role": "user", "content": "try again", "metadata": {} }
]The synthetic result lands at index 1, next to the call it answers, not at
the end where the new user turn was appended. Appending a tool message
against the same dangling call, instead of a user message, leaves the call
unanswered — healing never runs.