## Why
Environment skill discovery needs two independent pieces of information:
- plugin namespaces from `plugin.json` files; and
- skill metadata from each `SKILL.md` file.
Today these happen in sequence. Codex waits for every plugin namespace
lookup to finish before it starts reading any skill files. On a remote
executor, that creates an avoidable network-latency barrier.
```text
before: walk -> namespace lookups -> skill reads -> build catalog
after: walk -> namespace lookups ─┐
-> skill reads ───────┴-> build catalog
```
## What changes
- Read and parse skill files without waiting for plugin namespace
discovery.
- Resolve root and nested plugin namespaces concurrently.
- Join both results only when constructing the final qualified skill
names.
- Keep the existing 64-skill concurrency bound, output ordering,
warnings, metadata behavior, and namespace rules.
## Testing
The regression test makes plugin manifest lookup wait until a `SKILL.md`
read has started. The old serialized pipeline would time out; the new
pipeline completes and still returns the correctly namespaced skill.
`just test -p codex-core-skills` passes all 111 tests.
## Out of scope
This does not add an exec-server endpoint, batch filesystem calls, or
reduce the number of files transferred. A frontmatter-only read or
server-side skill catalog can remain a separate follow-up if benchmarks
show that transferred bytes are the next bottleneck.
jif
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