app-server: accept permission profile overrides (#18279)

## Why

`PermissionProfile` is becoming the canonical permissions shape shared
by core and app-server. After app-server responses expose the active
profile, clients need to be able to send that same shape back when
starting, resuming, forking, or overriding a turn instead of translating
through the legacy `sandbox`/`sandboxPolicy` shorthands.

This still needs to preserve the existing requirements/platform
enforcement model. A profile-shaped request can be downgraded or
rejected by constraints, but the server should keep the user's
elevated-access intent for project trust decisions. Turn-level profile
overrides also need to retain existing read protections, including
deny-read entries and bounded glob-scan metadata, so a permission
override cannot accidentally drop configured protections such as
`**/*.env = deny`.

## What changed

- Adds optional `permissionProfile` request fields to `thread/start`,
`thread/resume`, `thread/fork`, and `turn/start`.
- Rejects ambiguous requests that specify both `permissionProfile` and
the legacy `sandbox`/`sandboxPolicy` fields, including running-thread
resume requests.
- Converts profile-shaped overrides into core runtime filesystem/network
permissions while continuing to derive the constrained legacy sandbox
projection used by existing execution paths.
- Preserves project-trust intent for profile overrides that are
equivalent to workspace-write or full-access sandbox requests.
- Preserves existing deny-read entries and `globScanMaxDepth` when
applying turn-level `permissionProfile` overrides.
- Updates app-server docs plus generated JSON/TypeScript schema fixtures
and regression coverage.

## Verification

- `cargo test -p codex-app-server-protocol schema_fixtures`
- `cargo test -p codex-core
session_configuration_apply_permission_profile_preserves_existing_deny_read_entries`







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[//]: # (BEGIN SAPLING FOOTER)
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with [ReviewStack](https://reviewstack.dev/openai/codex/pull/18279).
* #18288
* #18287
* #18286
* #18285
* #18284
* #18283
* #18282
* #18281
* #18280
* __->__ #18279

codex-rs/core/src/session/mod.rs

@@ -189,7 +189,7 @@ use self::review::spawn_review_thread;
 use self::session::AppServerClientMetadata;
 use self::session::Session;
 use self::session::SessionConfiguration;
-use self::session::SessionSettingsUpdate;
+pub(crate) use self::session::SessionSettingsUpdate;
 #[cfg(test)]
 use self::turn::AssistantMessageStreamParsers;
 #[cfg(test)]
@@ -1308,6 +1308,14 @@ impl Session {
         Ok(())
     }
 
+    pub(crate) async fn validate_settings(
+        &self,
+        updates: &SessionSettingsUpdate,
+    ) -> ConstraintResult<()> {
+        let state = self.state.lock().await;
+        state.session_configuration.apply(updates).map(|_| ())
+    }
+
     pub(crate) async fn set_session_startup_prewarm(
         &self,
         startup_prewarm: SessionStartupPrewarmHandle,