The abstract capability flag forces every backend to state whether it owns per-session raw artifacts, but TypeScript cannot express that a true flag requires replacing the concrete unsupported default. Without an implementer-facing obligation, a backend could advertise support and then fail with a contradictory unsupported diagnostic on first use.\n\nDocument the required pairing at the capability declaration. Keep readRaw concrete so backends that correctly report false inherit one fail-loud implementation instead of duplicating rejection code.
ApiProxyDefaults uses an exact optional property, so passing config.sessionExportCompressionLevel directly made the service object carry an explicit undefined that is not assignable to the resolved request shape. The full host build caught this distinction after the redundant fallback was removed.\n\nConditionally omit the property when Cordis has not supplied a value. Direct createApiProxy callers still receive the implementation-owned default, while configured plugin values pass through without introducing another defaulting site.
Master advanced again after the first merge-forward checkpoint, adding the web human-transcript command-input change. Preserve the earlier checkpoint and merge the new exact e03b51d7 base as a separate commit instead of rebasing or rewriting this merge-heavy stack.\n\nThe incremental merge is conflict-free and keeps the session-export review fixes based on the repository's current integration state.
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.
The response stream uses a fixed 64 KiB byte high-water mark; no deployment setting controls it. Calling that queue configured incorrectly suggested another tuning surface and obscured the concrete memory bound.\n\nName the fixed capacity directly while preserving the separate bound of one synchronous fflate push beyond the queued bytes.
The pre-stream error boundary covers both the live-session flush barrier and the persistence read, but its response attributed every failure to reading storage. A flush failure therefore produced a misleading diagnostic even though the response correctly withheld private backend details.\n\nUse preparation as the shared operation name and cover the flush-failure path explicitly. Both preparation stages now retain one stable, path-safe HTTP 500 without pretending to identify the failing stage.
The Cordis schema supplies the normal plugin default, while createApiProxy also owns the fallback required by direct programmatic callers. Repeating the same nullish fallback in ApiProxyService created a third defaulting site without adding a distinct invariant.\n\nPass the validated config value through unchanged and leave createApiProxy as the single implementation boundary that turns an optional request value into the required compression specification.
The fixture comment still said the Trajectory action used window.fetch after the implementation moved to a temporary download anchor. That wording implied client-side response handling and buffering which the browser-download design deliberately avoids.\n\nDescribe the actual native download-manager handoff while retaining the important contract: the fixture download stub only satisfies the host type and is unreachable through fixture dispatch.
Refresh PR #2258 onto master at 5427cbcc19 so the session-log export fixes are evaluated and mergeable against the current repository.\n\nPreserve master's SDK-toolchain removal, client theme bootstrap, and Python finish-reason changes intact. The only textual overlap is the generated config-catalog pairing record: both English and Chinese catalogs merge cleanly with the PR's compression setting and master's package moves, so regenerate that sidecar from the merged owners instead of choosing either stale hash.
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.
A present zero-byte .jsonl.zstd file was treated as though no artifact existed because readRaw returned undefined when frame scanning found nothing. That contradicted both the plaintext path and the logical zstd reader, and it made the export endpoint answer 404 for on-disk corruption.
Treat a present artifact without a complete header frame as corruption and reuse the zstd reader's existing diagnostic. The regression test now distinguishes an existing empty file from an absent path, and the bilingual JSONL storage contract records that zero-frame artifacts reject alongside other header and frame failures.
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.
