loadThrough now assigns its low-water target only when it owns the loop
(retargeting stays inside the running-jump branch): a call refused while
a plain load-earlier pull holds the pager no longer leaves jumpTargetSeq
behind to drag a later jump all the way to the head. The loop also
carries the doOpen stale-pass guard so a mid-flight resync stops it
instead of paging the new stream generation toward the old target.
Session.loadThrough(seq) loops the existing prepend pager (200-message
pages) until the window covers the target seq, with a shared low-water
retarget for repeated calls, a no-progress guard against empty pages
still claiming history, and loadOlder's fail-soft error posture. Busy
state rides the existing loadingOlder snapshot bit.
Single RemoteError with a merge-extensible, domain-prefixed code map;
owners throw at the failure point; streams surface marked failures;
clients consume ctx.remote directly with isRemoteFailure as the only
discrimination point and construct no failure instances.
A steer or follow-up accepted while a turn is closing is now claimed by a
fresh turn at the driver's clean exit instead of stranding in the inbox;
cancellation and pre-step rejection still park accepted work. Continuable
subagent follow-ups accept image parts: the wire is upload-shaped, the Host
admits and persists each batch before inbox acceptance, and delivery is
refused when the child model declines image input. The queue dock renders
durable image thumbnails instead of an [image] text marker.
Fixes#3186
Tianyi Cui