## What changed
Move full/delta transcript selection into the shared `TranscriptMode::select` API and use it when building guardian prompts. Export `TranscriptCursor`, `TranscriptMode`, and `TranscriptSelection` from `codex-guardian-context`.
Preserve full-transcript fallback when the history version changes or the saved cursor exceeds the collected entry count. Select entries before profile retention, preserving their numbering and returning a proposed cursor that counts all collected entries. Hosts remain responsible for committing and invalidating cursors.
## Testing
Add a regression test verifying that sliding-window retention preserves the collected-entry cursor and that an appended entry is selected and numbered correctly in the next delta.
GitOrigin-RevId: a2192c08e23c18302b0105ba47aeb2780eb4a015
b3e0c49dfb