After story 871 the `agent` pin lives in the typed CRDT register
(`PipelineItemView.agent`), not the YAML front matter — the YAML
mutation was removed at the same time. Both spawn-resolution paths
(`auto_assign::story_checks::read_story_front_matter_agent` and
`start::validation::read_front_matter_agent`) still read only YAML
via parse_front_matter, which returns None for any story whose pin
was set via the post-871 typed setter. The spawn then falls back to
"first available coder," silently downgrading opus-pinned stories to
the first available sonnet — which is why 855/864/866 kept hitting the
80-turn watchdog limit despite the user's explicit opus pin.
Now: both paths consult `crdt_state::read_item()` first and use
`view.agent` if non-empty. YAML parsing remains as a fallback so older
stories whose CRDT entry doesn't yet have the field still resolve.
Adds a regression test that seeds an item with empty YAML, sets the
typed CRDT register via `set_agent`, and asserts
`read_story_front_matter_agent` returns the CRDT value.
dave
a8eac3c278