DL-427

Capture and wire mechanism for DL-426: the agent reads each blob:sha256:<hex> ref out of the committed lines the session tee already sees (the SDK wrote the file before the line) and uploads it on a dedicated best-effort unary (AgentGateway.PutSessionBlob → RunnerService.RelaySessionBlob), never the durable conversation lane; a hash is done only on success, FailedPrecondition, or oversize (15 MiB raw cap); bounded drop-oldest queue, no retry loop, no SDK patch

Status: Active (Matt, 2026-10-06)

Record: ../../agent/compass-agent-session-blobs/design.md#d1-capture-from-the-tee