[pull] main from triggerdotdev:main - #736

Keep assistant steps and tool results replaced by inner compaction out
of subsequent `chat.agent()` model context. Turn completion now appends
only response steps generated after compaction, while preserving the
full visible conversation. Persistence hooks retain the complete
response, including same-ID replacements for approvals and handovers.

Track the completed-step boundary and trim the captured response before
model-message conversion. Same-ID handover continuations also skip their
original assistant prefix, avoiding a fallback that rebuilds uncompacted
model history.

Mono-RevId: 55a2d4354c501682b159c8853255b1f08a13d3cb