## Why
`experimentalFeature/list` reports effective feature enablement, but
currently does not resolve it against a working directory where
project-local config.toml files can exist and toggle on/off features
when merged into the effective config after resolving the various config
layers. That means we effectively (and incorrectly) ignore features set
in project-local config.
To address that, this PR exposes an optional `thread_id` param which
allows us to load the thread's `cwd.
## Testing
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server experimental_feature_list`
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