Enforce required environment skills before model inference (#51157)

## What changed

- Accept per-environment `skills.required` lists through `environment/add` and `environments.toml`.
- Before inference, require each named skill to be enabled and supplied by the selected environment. Missing skills fail the turn before a model request, including when environment setup fails.
- Stop applying an environment's requirements after it is deselected. Exempt isolated Guardian reviewers, which have no skill catalog.

## Testing

Add tests for available, missing, disabled, and wrong-environment skills, failed environment setup, recovery after deselection, and propagation of TOML requirements to the correct environment.

GitOrigin-RevId: 302ced4774697d2f414f745fe0535e71f747eda2

codex-rs/app-server-protocol/src/protocol/v2/environment.rs

@@ -47,6 +47,9 @@ pub struct EnvironmentAddParams {
     #[ts(type = "number | null")]
     #[ts(optional = nullable)]
     pub connect_timeout_ms: Option<u64>,
+    /// Required skills supplied by this environment, checked before model inference.
+    #[ts(optional = nullable)]
+    pub skills: Option<EnvironmentSkillsParams>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
@@ -54,6 +57,15 @@ pub struct EnvironmentAddParams {
 #[ts(export_to = "v2/")]
 pub struct EnvironmentAddResponse {}
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct EnvironmentSkillsParams {
+    /// Exact catalog names that must be available from this environment.
+    #[ts(optional = nullable)]
+    pub required: Option<Vec<String>>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(rename_all = "camelCase", export_to = "v2/")]