A provider error (e.g. read ECONNRESET) routed the turn through the
streamText onError callback, which persisted an EMPTY assistant record
(buildErrorAssistantRecord -> text:'', parts:[]). The answer text already
streamed to and shown by the client was therefore lost from the persisted
row, the chat export, and reopened history — leaving only the error line.
The AI SDK v6 onError callback receives only { error } (no steps/text),
and the visible final answer streams in the last, not-yet-finished step,
so it is absent from every finished step.text. Accumulate it ourselves:
onChunk folds each 'text-delta' into inProgressText; onStepFinish moves a
finished step into capturedSteps and resets inProgressText. onError and
onAbort now persist the partial answer (finished steps' text + tool parts
via assistantParts, then the in-progress text appended last) through a new
shared pure helper buildPartialAssistantRecord, recording the cause in
metadata.error on the error path. Replaces buildErrorAssistantRecord; its
empty-turn shape is preserved when nothing streamed.
Complementary to the resilient-fetch reconnect: that reduces how often a
turn dies; this preserves what was produced when it dies anyway.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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