## Stack
This is the foundation PR for the permission-profile inheritance stack.
- This PR adds config-level `extends` resolution and merge semantics.
- Follow-up: #23705 applies resolved profiles at runtime and updates the
active-profile protocol surfaces.
## Why
Permission profiles are starting to carry enough policy that
copy-pasting near-identical definitions becomes hard to review and easy
to drift. Before the runtime can consume inherited profiles, the config
layer needs one explicit resolver that can merge parent chains and
reject unsafe or invalid inheritance shapes.
## What changed
- Add `extends` to permission-profile TOML and resolve parent chains in
inheritance order.
- Merge inherited profile TOML with the existing config merge behavior
while preserving the permission-specific normalization needed for
network domain keys.
- Keep parent descriptions out of resolved child profiles and record
inherited profile names separately for downstream consumers.
- Reject undefined parents, unsupported built-in parents, and
inheritance cycles with targeted errors.
- Cover resolver behavior with TOML fixture tests and refresh the
generated config schema.
## Validation
- `cargo test -p codex-config`
- `cargo test -p codex-core permissions_profiles_`
## Why
App-server clients need a way to update a thread's next-turn settings
without starting a turn, adding transcript content, or waiting for turn
lifecycle events. This gives settings UI a direct path for durable
thread settings while clients observe the eventual effective state
through a notification.
This is a simplified rework of PR
https://github.com/openai/codex/pull/22509. In particular, it changes
the `thread/settings/update` api to return immediately rather than
waiting and returning the effective (updated) thread settings. This
makes the new api consistent with `turn/start` and greatly reduces the
complexity of the implementation relative to the earlier attempt.
## What Changed
- Adds experimental `thread/settings/update` with partial-update request
fields and an empty acknowledgment response.
- Adds experimental `thread/settings/updated`, carrying full effective
`ThreadSettings` and scoped by `threadId` to subscribed clients for the
affected thread.
- Shares durable settings validation with `turn/start`, including
`sandboxPolicy` plus `permissions` rejection and `serviceTier: null`
clearing.
- Emits the same settings notification when `turn/start` overrides
change the stored effective thread settings.
- Regenerates app-server protocol schema fixtures and updates
`app-server/README.md`.
