A tool call truncated by max_tokens is discarded without a record

• Status: Todo
• Kind: Bug
• Authors: jp
• Date: 2026-09-07
• Label: domain=llm
• Label: package=jp_llm
• Label: type=bug

When a response runs out of output tokens while the model is still assembling a tool call, the partial call is dropped and nothing durable records that it existed.

TurnCoordinator::handle_streaming_event (crates/jp_cli/src/cmd/query/turn/coordinator.rs:322-324) collects the names via event_builder.incomplete_tool_calls(), with the comment "Capture tool-call buffers about to be discarded", purely so finish_notice can name them in a chrome line. The call is never executed and never persisted.

The reason itself is dropped too: transition_from_streaming takes it as _reason (coordinator.rs:364-367) and ignores it, and FinishReason does not appear anywhere in jp_conversation.

So the surviving record is the prose the model got through, which reads as if the assistant considered the action and chose not to take it. Replaying the conversation later shows the same thing, because there is nothing else to show.

What it costs

A caller asked for an edit, got an answer, and exited 0. The edit never happened and no artifact says so. jp conversation print cannot show it, and neither can the macOS app, since both read the stream.

Proposal

Record the finish reason on the turn, and the discarded tool call names with it. That gives the fact a second home, which is what a rare-but-consequential event wants: the user is not watching for it, so a durable record they can find afterwards serves them better than a line that scrolls past.

It also removes the reason finish_notice is currently the only witness to anything, which keeps --quiet free of exemptions.

Note on frequency

Rarer than it looks on Anthropic, where chain_on_max_tokens defaults to true and should_chain (crates/jp_llm/src/provider/anthropic.rs:447-451) swallows a MaxTokens finish to issue a continuation request. Chaining is Anthropic-only, so openai, google, cerebras, llamacpp, and openrouter reach this path normally, as does Anthropic once max_tokens is set explicitly.

Severity

Hidden. The dropped action is invisible in stdout, in the exit status, and in the conversation.