## 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.
## Disclaimer
This is only here for iteration purpose! Do not make any code rely on
this
## Why
Skills still live behind `codex-core` discovery and injection paths, but
the extension system needs an authority-aware home before that logic can
move. This adds that boundary without changing current skills behavior,
and keeps host, executor, and remote skills distinct so future
list/read/search flows do not collapse back to ambient local paths.
## What changed
- Add the `codex-skills-extension` workspace/Bazel crate under
`ext/skills`.
- Define the initial catalog, authority, provider, and turn-state types
for authority-bound skill packages and resources.
- Register placeholder thread/config/prompt/turn lifecycle contributors
plus host, executor, and remote provider aggregation points.
- Capture the remaining extraction work as TODOs, including the missing
extension API hooks needed for per-turn catalog construction and typed
skill injection.
- Keep plugins outside the runtime skills model: plugin-installed skills
are treated as materialized host-owned skill sources once available.
## Verification
- Not run locally.
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