Response-consumer cancellation already stopped lineage reads, persistence reads, and ZIP production, but the final attachment phase called readImage without the producer signal. A slow or stalled attachment backend could therefore keep working after the browser abandoned the download and prevent the producer from settling.\n\nExtend the attachment read seam with optional cancellation, forward it through the local backend into Node's filesystem read, and preserve the abort reason rather than wrapping it as a storage failure. The exporter now passes its combined request/consumer signal to every attachment read.\n\nCover both ownership boundaries: the local-store test proves filesystem forwarding and cancellation identity, while the assembled export test cancels a reader during a pending attachment provider call. Regenerate the Cordis API catalog and paired documentation so implementers can rely on the new contract.
Session-log ZIP entries always used DEFLATE level 6 even though compression level is a deployment tradeoff: CPU-constrained hosts may prefer low latency while bandwidth-constrained hosts may prefer smaller archives. A hardcoded level also violated the repository rule that deployment-varying plugin choices live in validated Config.
Add sessionExportCompressionLevel to ApiProxyService.Config as an integer 0-9 with default 6, resolve the same default once for direct createApiProxy callers, and pass the required level into the streaming module. Tests prove schema defaulting and rejection as well as a level-0 versus level-9 archive-size difference with identical extracted content. The generated config catalog, bilingual gateway README, and feature note document the knob and its tradeoff.
The ZIP loop checked desiredSize only after a push and responded to an overfull queue with setTimeout(0). A timer turn does not mean the consumer drained anything, so a slow or disconnected client still allowed the producer to enqueue the complete compressed archive while later artifact and attachment reads ran eagerly.
Give the ReadableStream a 64 KiB byte queuing strategy and block the single producer on a pull-released capacity gate whenever desiredSize is non-positive. Cancellation wakes that gate through the existing producer signal; synchronous fflate output is therefore bounded to the queue high-water mark plus one input push. A regression test exhausts timer turns without consuming and proves the next media entry remains unread until response pulling begins, and the bilingual contracts now describe the real bound.
Only the root raw-artifact read received the request signal. Lineage discovery and descendant reads could continue after disconnect, response-body cancellation did not stop the producer, and the root error boundary converted an abort rejection into an ordinary HTTP 500.
Combine request and response-consumer cancellation into the ZIP producer signal, forward it through every cancellable read, check it around the attachment seam, and terminate fflate exactly once when production stops. The pre-stream boundary now rethrows the original abort instead of translating it. Regression tests cover signal propagation, exact cancellation identity at the HTTP boundary, and a reader cancellation interrupting an in-flight descendant read; the bilingual host contract records these lifecycle semantics.
The exporter read persistence artifacts directly even when the requested root or a descendant was still live. Buffered session events could therefore be omitted from a successful download, so the advertised verbatim-artifact guarantee described storage accurately but captured an arbitrarily stale durability boundary.
Resolve each id against SessionStore and cross its authoritative flush barrier immediately before readRaw. Cold sessions remain a no-op, while live roots and descendants are made durable independently; this intentionally yields a per-session read-boundary snapshot rather than claiming an atomic lineage snapshot. A host-path regression test proves both artifacts change from stale to durable only through flush, and the bilingual host contract and Agent Note document the boundary.
SessionPersistence.readRaw previously used undefined for two unrelated states: a supported backend could not find the requested session, or the backend had no per-session artifact concept at all. The export endpoint consequently reported an existing SQLite-backed session as HTTP 404, which falsely diagnosed storage capability as session absence.
Make raw-artifact support an explicit backend capability. Unsupported backends now fail their inherited readRaw path loudly and the host answers 501 before reading, while undefined retains the single meaning of an absent artifact on a supporting backend. First-party backends, test providers, generated API catalogs, bilingual persistence docs, and export error contracts now state that distinction; focused tests cover both the 501 and the inherited rejection.
The export endpoint already streams a ZIP response, but the web client immediately converted that response into a Blob. That forced the complete archive through JavaScript memory before a download could start and coupled transport, buffering, object-URL lifetime, and filename handling to the trajectory view.
Navigate a temporary download anchor directly to the export endpoint instead. The browser now owns streaming and HTTP failure presentation, while a standalone delivery module owns URL construction and filename sanitization. Focused tests cover the handoff, rejection behavior, and the assembled session view; the package README and feature note record the new ownership boundary.
The persistence subsystem page gains the SessionRawArtifact section (with a
type-equiv manifest entry and zh counterpart), and the README and Agent Note
describe the drain-based backpressure instead of claiming the archive never
accumulates.
Tianyi Cui