[codex] Move config loading into codex-config (#19487)

## Why

Config loading had become split across crates: `codex-config` owned the
config types and merge logic, while `codex-core` still owned the loader
that assembled the layer stack. This change consolidates that
responsibility in `codex-config`, so the crate that defines config
behavior also owns how configs are discovered and loaded.

To make that move possible without reintroducing the old dependency
cycle, the shell-environment policy types and helpers that
`codex-exec-server` needs now live in `codex-protocol` instead of
flowing through `codex-config`.

This also makes the migrated loader tests more deterministic on machines
that already have managed or system Codex config installed by letting
tests override the system config and requirements paths instead of
reading the host's `/etc/codex`.

## What Changed

- moved the config loader implementation from `codex-core` into
`codex-config::loader` and deleted the old `core::config_loader` module
instead of leaving a compatibility shim
- moved shell-environment policy types and helpers into
`codex-protocol`, then updated `codex-exec-server` and other downstream
crates to import them from their new home
- updated downstream callers to use loader/config APIs from
`codex-config`
- added test-only loader overrides for system config and requirements
paths so loader-focused tests do not depend on host-managed config state
- cleaned up now-unused dependency entries and platform-specific cfgs
that were surfaced by post-push CI

## Testing

- `cargo test -p codex-config`
- `cargo test -p codex-core config_loader_tests::`
- `cargo test -p codex-protocol -p codex-exec-server -p
codex-cloud-requirements -p codex-rmcp-client --lib`
- `cargo test --lib -p codex-app-server-client -p codex-exec`
- `cargo test --no-run --lib -p codex-app-server`
- `cargo test -p codex-linux-sandbox --lib`
- `cargo shear`
- `just bazel-lock-check`

## Notes

- I did not chase unrelated full-suite failures outside the migrated
loader surface.
- `cargo test -p codex-core --lib` still hits unrelated proxy-sensitive
failures on this machine, and Windows CI still shows unrelated
long-running/timeouting test noise outside the loader migration itself.

codex-rs/config/src/loader/macos.rs

@@ -0,0 +1,179 @@
+use super::merge_requirements_with_remote_sandbox_config;
+use crate::config_requirements::ConfigRequirementsToml;
+use crate::config_requirements::ConfigRequirementsWithSources;
+use crate::config_requirements::RequirementSource;
+use base64::Engine;
+use base64::prelude::BASE64_STANDARD;
+use core_foundation::base::TCFType;
+use core_foundation::string::CFString;
+use core_foundation::string::CFStringRef;
+use std::ffi::c_void;
+use std::io;
+use tokio::task;
+use toml::Value as TomlValue;
+
+const MANAGED_PREFERENCES_APPLICATION_ID: &str = "com.openai.codex";
+const MANAGED_PREFERENCES_CONFIG_KEY: &str = "config_toml_base64";
+const MANAGED_PREFERENCES_REQUIREMENTS_KEY: &str = "requirements_toml_base64";
+
+#[derive(Debug, Clone)]
+pub(super) struct ManagedAdminConfigLayer {
+    pub config: TomlValue,
+    pub raw_toml: String,
+}
+
+pub(super) fn managed_preferences_requirements_source() -> RequirementSource {
+    RequirementSource::MdmManagedPreferences {
+        domain: MANAGED_PREFERENCES_APPLICATION_ID.to_string(),
+        key: MANAGED_PREFERENCES_REQUIREMENTS_KEY.to_string(),
+    }
+}
+
+pub(crate) async fn load_managed_admin_config_layer(
+    override_base64: Option<&str>,
+) -> io::Result<Option<ManagedAdminConfigLayer>> {
+    if let Some(encoded) = override_base64 {
+        let trimmed = encoded.trim();
+        return if trimmed.is_empty() {
+            Ok(None)
+        } else {
+            parse_managed_config_base64(trimmed).map(Some)
+        };
+    }
+
+    match task::spawn_blocking(load_managed_admin_config).await {
+        Ok(result) => result,
+        Err(join_err) => {
+            if join_err.is_cancelled() {
+                tracing::error!("Managed config load task was cancelled");
+            } else {
+                tracing::error!("Managed config load task failed: {join_err}");
+            }
+            Err(io::Error::other("Failed to load managed config"))
+        }
+    }
+}
+
+fn load_managed_admin_config() -> io::Result<Option<ManagedAdminConfigLayer>> {
+    load_managed_preference(MANAGED_PREFERENCES_CONFIG_KEY)?
+        .as_deref()
+        .map(str::trim)
+        .map(parse_managed_config_base64)
+        .transpose()
+}
+
+pub(crate) async fn load_managed_admin_requirements_toml(
+    target: &mut ConfigRequirementsWithSources,
+    override_base64: Option<&str>,
+    host_name: Option<&str>,
+) -> io::Result<()> {
+    if let Some(encoded) = override_base64 {
+        let trimmed = encoded.trim();
+        if trimmed.is_empty() {
+            return Ok(());
+        }
+
+        merge_requirements_with_remote_sandbox_config(
+            target,
+            managed_preferences_requirements_source(),
+            parse_managed_requirements_base64(trimmed)?,
+            host_name,
+        );
+        return Ok(());
+    }
+
+    match task::spawn_blocking(load_managed_admin_requirements).await {
+        Ok(result) => {
+            if let Some(requirements) = result? {
+                merge_requirements_with_remote_sandbox_config(
+                    target,
+                    managed_preferences_requirements_source(),
+                    requirements,
+                    host_name,
+                );
+            }
+            Ok(())
+        }
+        Err(join_err) => {
+            if join_err.is_cancelled() {
+                tracing::error!("Managed requirements load task was cancelled");
+            } else {
+                tracing::error!("Managed requirements load task failed: {join_err}");
+            }
+            Err(io::Error::other("Failed to load managed requirements"))
+        }
+    }
+}
+
+fn load_managed_admin_requirements() -> io::Result<Option<ConfigRequirementsToml>> {
+    load_managed_preference(MANAGED_PREFERENCES_REQUIREMENTS_KEY)?
+        .as_deref()
+        .map(str::trim)
+        .map(parse_managed_requirements_base64)
+        .transpose()
+}
+
+fn load_managed_preference(key_name: &str) -> io::Result<Option<String>> {
+    #[link(name = "CoreFoundation", kind = "framework")]
+    unsafe extern "C" {
+        fn CFPreferencesCopyAppValue(key: CFStringRef, application_id: CFStringRef) -> *mut c_void;
+    }
+
+    let value_ref = unsafe {
+        CFPreferencesCopyAppValue(
+            CFString::new(key_name).as_concrete_TypeRef(),
+            CFString::new(MANAGED_PREFERENCES_APPLICATION_ID).as_concrete_TypeRef(),
+        )
+    };
+
+    if value_ref.is_null() {
+        tracing::debug!(
+            "Managed preferences for {MANAGED_PREFERENCES_APPLICATION_ID} key {key_name} not found",
+        );
+        return Ok(None);
+    }
+
+    let value = unsafe { CFString::wrap_under_create_rule(value_ref as _) }.to_string();
+    Ok(Some(value))
+}
+
+fn parse_managed_config_base64(encoded: &str) -> io::Result<ManagedAdminConfigLayer> {
+    let raw_toml = decode_managed_preferences_base64(encoded)?;
+    match toml::from_str::<TomlValue>(&raw_toml) {
+        Ok(TomlValue::Table(parsed)) => Ok(ManagedAdminConfigLayer {
+            config: TomlValue::Table(parsed),
+            raw_toml,
+        }),
+        Ok(other) => {
+            tracing::error!("Managed config TOML must have a table at the root, found {other:?}",);
+            Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "managed config root must be a table",
+            ))
+        }
+        Err(err) => {
+            tracing::error!("Failed to parse managed config TOML: {err}");
+            Err(io::Error::new(io::ErrorKind::InvalidData, err))
+        }
+    }
+}
+
+fn parse_managed_requirements_base64(encoded: &str) -> io::Result<ConfigRequirementsToml> {
+    toml::from_str::<ConfigRequirementsToml>(&decode_managed_preferences_base64(encoded)?).map_err(
+        |err| {
+            tracing::error!("Failed to parse managed requirements TOML: {err}");
+            io::Error::new(io::ErrorKind::InvalidData, err)
+        },
+    )
+}
+
+fn decode_managed_preferences_base64(encoded: &str) -> io::Result<String> {
+    String::from_utf8(BASE64_STANDARD.decode(encoded.as_bytes()).map_err(|err| {
+        tracing::error!("Failed to decode managed value as base64: {err}",);
+        io::Error::new(io::ErrorKind::InvalidData, err)
+    })?)
+    .map_err(|err| {
+        tracing::error!("Managed value base64 contents were not valid UTF-8: {err}",);
+        io::Error::new(io::ErrorKind::InvalidData, err)
+    })
+}