v0.2.3

Smith v0.2.3

Smith 0.2.3 makes a failed sub-agent say why it failed.

Fixed: a failed child reports its actual cause

A child turn that failed reached the parent as a fixed internal error,
child turn failed, with the real cause discarded. The runtime emits that
cause immediately before completing the turn, but delegation ignored it and
substituted a constant string. Nothing else recovered it: a child's events are
not mirrored onto the parent stream, and a child session keeps no journal or
log file of its own. A provider rejection, a preflight budget failure, and an
internal fault were indistinguishable from each other and from a child that
never started.

Delegation now names the cause the child reported, keeping its kind,
retryability, and metadata, so a sub-agent that dies on a rejected request
reads as

sub-agent child-1 failed: child turn failed: Gemini provider rejected the request

A failure that never named a cause keeps the previous wording, and a parent
that branches on retryability now sees the child's answer rather than
delegation's.

Upgrading

Existing configuration, sessions, and protected checkpoints remain compatible.
The pinned Agent Runtime revision advances to 18dc8ec for this fix; nothing
else in the runtime contract changes.

Full Changelog: v0.2.2...v0.2.3