Honor per-environment shell variable policies (#38902)

## What changed

- Carry `ShellEnvironmentPolicy` in each resolved `EnvironmentConfig` and use
  the selected turn environment's policy for shell commands, user shell tasks,
  and unified exec.
- Infer the policy from the thread configuration when an environment does not
  provide its own resolved configuration.
- Redact the policy from `EnvironmentConfig` debug output because it can contain
  explicit environment variable values.

## Testing

- Verify shell handlers and unified exec filter inherited variables according
  to the selected environment while preserving its explicit overrides.

GitOrigin-RevId: 9f6a52aa4af60e5f17251a0e1b11e1926b779055

codex-rs/protocol/src/environment.rs

@@ -1,8 +1,10 @@
 use crate::capabilities::SelectedCapabilityRoot;
+use crate::config_types::ShellEnvironmentPolicy;
 use crate::models::PermissionProfileSnapshot;
 
 /// Configuration supplied for a thread's selected environment.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[allow(clippy::large_enum_variant)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum EnvironmentConfigState {
     /// Preserve the existing thread-derived environment configuration.
     FromThread,
@@ -15,12 +17,26 @@ pub enum EnvironmentConfigState {
 }
 
 /// Resolved configuration for a thread/environment attachment.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, PartialEq)]
 pub struct EnvironmentConfig {
     /// Whether shell tools may start login shells in this environment.
     pub allow_login_shell: bool,
     /// Resolved permissions for this thread's environment attachment.
     pub permission_profile: PermissionProfileSnapshot,
+    /// Controls which environment variables shell commands may inherit.
+    pub shell_environment_policy: ShellEnvironmentPolicy,
     /// Capability roots selected for this thread's environment attachment.
     pub selected_capability_roots: Vec<SelectedCapabilityRoot>,
 }
+
+impl std::fmt::Debug for EnvironmentConfig {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        formatter
+            .debug_struct("EnvironmentConfig")
+            .field("allow_login_shell", &self.allow_login_shell)
+            .field("permission_profile", &self.permission_profile)
+            .field("shell_environment_policy", &"<redacted>")
+            .field("selected_capability_roots", &self.selected_capability_roots)
+            .finish()
+    }
+}