## Why
The skills extension needs the resolved turn environments to build a
real per-turn `SkillListQuery`. The previous `TurnLifecycleContributor`
hook only had a turn id, so it could only seed a placeholder query and
never carry the executor authorities that executor-scoped skill routing
will need.
Moving catalog resolution onto `TurnInputContributor` puts the skills
extension on the same turn-preparation path that already has the
environment ids and working directories for the submitted turn, while
keeping the actual prompt injection work for follow-up changes.
## What changed
- switch `ext/skills` from `TurnLifecycleContributor` to
`TurnInputContributor`
- build `executor_authorities` from `TurnInputContext.environments` and
pass them through `SkillListQuery`
- keep storing the resolved catalog in `SkillsTurnState`, but drop the
placeholder query helper that no longer matches the real data flow
- update the extension TODOs to reflect that per-turn catalog resolution
now happens in the turn-input contributor, and that prompt/context
injection still needs to move later
## Testing
- Not run locally.
## Why
`ContextualUserFragment` needs to be usable behind `dyn` for render-only
paths, but associated constants made the trait non-object-safe.
## What changed
- Replaced associated constants with trait methods so `dyn
ContextualUserFragment` can render fragments.
- Preserved the existing typed `T::matches_text(text)` registration
pattern via `type_markers()`.
- Kept default `render()` on the main trait so implementations only
provide role, markers, and body.
- Added unit coverage for rendering a `Box<dyn ContextualUserFragment>`.
## Verification
- `cargo test -p codex-core contextual_user_fragment_is_dyn_compatible`
- `just fix -p codex-core`
jif