RUN_ACCEPTED_EVENT

const RUN_ACCEPTED_EVENT: "run.accepted" = 'run.accepted';

Defined in: packages/ai/src/stream-to-response.ts:650

Name of the synthetic CUSTOM chunk a fresh durable producer appends to its log before pulling the first real chunk.

Flushing RUN_STARTED (above) makes a run joinable from the instant the stream EMITS something — but a chat() whose middleware boots a sandbox (create a container, install a CLI) legitimately emits nothing for minutes, and during that window the log is empty. Every joiner's empty-log fail-fast (memoryStream's first-chunk deadline, the client's rejoin connect deadline) then reads the run as gone — and the client clears its resume pointer, so a reload during the boot window permanently orphans a run that is still going.

This marker closes the window: it is appended (and flushed) before the producer stream is first pulled, so a join always finds a first chunk within milliseconds of the run being accepted. Takeover alignment is unaffected — a journal replay cannot reproduce the marker, and alignment already skips stored CUSTOM chunks as out-of-band for exactly that reason (see isBridgeCustomChunk in @tanstack/ai-sandbox).