dcdpr / jp / 25073170659

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fix(llm): Drop incomplete tool-call buffers on stream drain (#584)

When a stream ends abnormally (e.g. the provider closes the connection
before emitting a `ContentBlockStop`), the `EventBuilder::drain` method
was forwarding every buffered index through `handle_flush`. For
tool-call buffers, this produced an orphaned `tool_use` block in the
conversation — a block with no matching `tool_result`. Providers
(Anthropic included) reject the next request when they encounter this
inconsistency.

Tool-call buffers that reach `drain` are structurally incomplete by
definition: a normally-completed tool call always emits an explicit
`Flush` event before the stream ends. Reaching `drain` without one means
the stream was cut short. The safest recovery is to drop the buffer and
emit a warning, rather than persist a half-formed tool call that will
break the next conversation turn.

Text-producing buffers (`Reasoning`, `Message`, `Structured`) are
unaffected — partial output from those is still surfaced on drain so
that content isn't silently lost.

Signed-off-by: Jean Mertz <git@jeanmertz.com>

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