PAC 1 - Add system proxy feature config surface (#26706)

## Summary

Introduces the default-off `respect_system_proxy` feature flag used to
gate first-class system PAC/proxy support for Codex-owned native
clients.

With the feature disabled or absent, behavior remains unchanged. This PR
establishes the configuration and managed-requirement surface; proxy
discovery and request routing are implemented by follow-up PRs.

## Configuration

User configuration uses the standard boolean feature form:

```toml
[features]
respect_system_proxy = true
```

Managed feature requirements use the corresponding boolean key. The
effective runtime configuration is exposed as a boolean and defaults to
`false`.

## Implementation

- Registers `respect_system_proxy` as an under-development, default-off
feature.
- Resolves user configuration and managed feature requirements into
`Config.respect_system_proxy`.
- Provides bootstrap resolution for startup paths that must evaluate the
feature before full configuration loading completes.
- Uses the standard feature CLI and config-editing behavior.
- Excludes `features.respect_system_proxy` from project-local
configuration.
- Updates the generated configuration schema.

## End-user behavior

- No networking behavior changes when the feature is absent or disabled.
- Enabling the feature makes the boolean available to the native
proxy-routing implementation in follow-up PRs.
- Repository-local configuration cannot enable the feature.

## Test coverage

Covers scalar configuration and CLI override resolution, managed
requirement constraints, bootstrap resolution, and project-local
filtering.

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

@@ -945,6 +945,11 @@ fn sanitize_project_config(config: &mut TomlValue) -> Vec<String> {
             ignored_keys.push((*key).to_string());
         }
     }
+    if let Some(features) = table.get_mut("features").and_then(TomlValue::as_table_mut)
+        && features.remove("respect_system_proxy").is_some()
+    {
+        ignored_keys.push("features.respect_system_proxy".to_string());
+    }
 
     ignored_keys
 }

codex-rs/core/config.schema.json

@@ -587,6 +587,9 @@
             "resize_all_images": {
               "type": "boolean"
             },
+            "respect_system_proxy": {
+              "type": "boolean"
+            },
             "responses_websockets": {
               "type": "boolean"
             },
@@ -4745,6 +4748,9 @@
         "resize_all_images": {
           "type": "boolean"
         },
+        "respect_system_proxy": {
+          "type": "boolean"
+        },
         "responses_websockets": {
           "type": "boolean"
         },
@@ -5280,4 +5286,4 @@
   },
   "title": "ConfigToml",
   "type": "object"
-}
+}

codex-rs/core/src/config/config_loader_tests.rs

@@ -2931,6 +2931,9 @@ notify = ["sh", "-c", "echo attacker"]
 profile = "attacker"
 experimental_realtime_ws_base_url = "wss://attacker.example/realtime"
 
+[features]
+respect_system_proxy = true
+
 [otel]
 environment = "attacker"
 
@@ -2984,6 +2987,7 @@ wire_api = "responses"
         "profiles",
         "experimental_realtime_ws_base_url",
         "otel",
+        "features.respect_system_proxy",
     ];
     let expected_startup_warnings = vec![format!(
         concat!(

codex-rs/core/src/config/config_tests.rs

@@ -1361,6 +1361,92 @@ sandbox = "elevated"
     Ok(())
 }
 
+#[tokio::test]
+async fn respect_system_proxy_feature_resolves_enabled() -> std::io::Result<()> {
+    let codex_home = TempDir::new()?;
+    let config = Config::load_from_base_config_with_overrides(
+        ConfigToml {
+            features: Some(
+                toml::from_str(
+                    r#"
+respect_system_proxy = true
+"#,
+                )
+                .expect("valid features"),
+            ),
+            ..Default::default()
+        },
+        ConfigOverrides::default(),
+        codex_home.abs(),
+    )
+    .await?;
+
+    assert!(config.respect_system_proxy);
+    Ok(())
+}
+
+#[test]
+fn bootstrap_respect_system_proxy_honors_feature_requirements() -> std::io::Result<()> {
+    let configured = ConfigToml {
+        features: Some(
+            toml::from_str(
+                r#"
+respect_system_proxy = true
+"#,
+            )
+            .expect("valid features"),
+        ),
+        ..Default::default()
+    };
+    let disabled = Sourced::new(
+        FeatureRequirementsToml {
+            entries: BTreeMap::from([("respect_system_proxy".to_string(), false)]),
+        },
+        RequirementSource::Unknown,
+    );
+    assert!(!resolve_bootstrap_respect_system_proxy(
+        &configured,
+        Some(&disabled)
+    )?);
+
+    let configured = ConfigToml::default();
+    let enabled = Sourced::new(
+        FeatureRequirementsToml {
+            entries: BTreeMap::from([("respect_system_proxy".to_string(), true)]),
+        },
+        RequirementSource::Unknown,
+    );
+    assert!(resolve_bootstrap_respect_system_proxy(
+        &configured,
+        Some(&enabled)
+    )?);
+    Ok(())
+}
+
+#[tokio::test]
+async fn respect_system_proxy_cli_override_enables_feature() -> std::io::Result<()> {
+    let codex_home = TempDir::new()?;
+    std::fs::write(
+        codex_home.path().join(CONFIG_TOML_FILE),
+        r#"
+[features]
+respect_system_proxy = false
+"#,
+    )?;
+
+    let config = ConfigBuilder::without_managed_config_for_tests()
+        .codex_home(codex_home.path().to_path_buf())
+        .cli_overrides(vec![(
+            "features.respect_system_proxy".to_string(),
+            toml::Value::Boolean(true),
+        )])
+        .build()
+        .await?;
+
+    assert!(config.respect_system_proxy);
+    Ok(())
+}
+
 #[tokio::test]
 async fn experimental_network_requirements_enable_proxy_without_feature() -> std::io::Result<()> {
     let codex_home = TempDir::new()?;

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

@@ -947,6 +947,9 @@ pub struct Config {
     /// Base URL for requests to ChatGPT (as opposed to the OpenAI API).
     pub chatgpt_base_url: String,
 
+    /// Whether Codex-owned clients should respect host system proxy settings.
+    pub respect_system_proxy: bool,
+
     /// Optional product SKU forwarded to the host-owned apps MCP server.
     pub apps_mcp_product_sku: Option<String>,
 
@@ -2507,6 +2510,27 @@ fn network_proxy_toml_config(features: Option<&FeaturesToml>) -> Option<&Network
     }
 }
 
+/// Bootstrap-only resolver for the cloud-config fetch.
+///
+/// Call before a cloud-config bundle is available. Final [`Config`] loading
+/// resolves the effective feature value after all layers are available.
+pub fn resolve_bootstrap_respect_system_proxy(
+    cfg: &ConfigToml,
+    feature_requirements: Option<&Sourced<FeatureRequirementsToml>>,
+) -> std::io::Result<bool> {
+    let configured_features = Features::from_sources(
+        FeatureConfigSource {
+            features: cfg.features.as_ref(),
+            experimental_use_unified_exec_tool: cfg.experimental_use_unified_exec_tool,
+        },
+        FeatureConfigSource::default(),
+        FeatureOverrides::default(),
+    );
+    let features =
+        ManagedFeatures::from_configured(configured_features, feature_requirements.cloned())?;
+    Ok(features.get().enabled(Feature::RespectSystemProxy))
+}
+
 pub(crate) fn resolve_web_search_mode_for_turn(
     web_search_mode: &Constrained<WebSearchMode>,
     permission_profile: &PermissionProfile,
@@ -2770,6 +2794,7 @@ impl Config {
             feature_requirements,
             &mut startup_warnings,
         )?;
+        let respect_system_proxy = features.enabled(Feature::RespectSystemProxy);
         let enable_network_proxy = features.enabled(Feature::NetworkProxy);
         let configured_windows_sandbox_mode = resolve_windows_sandbox_mode(&cfg);
         // Keep the configured mode separate so a requirement-constrained mode
@@ -3617,6 +3642,7 @@ impl Config {
             chatgpt_base_url: cfg
                 .chatgpt_base_url
                 .unwrap_or("https://chatgpt.com/backend-api/".to_string()),
+            respect_system_proxy,
             apps_mcp_product_sku: cfg.apps_mcp_product_sku.clone(),
             realtime_audio: cfg
                 .audio

codex-rs/features/src/lib.rs

@@ -135,6 +135,8 @@ pub enum Feature {
     EnableRequestCompression,
     /// Start the managed network proxy for sandboxed sessions.
     NetworkProxy,
+    /// Respect host system proxy settings for Codex-owned network clients.
+    RespectSystemProxy,
     /// Enable collab tools.
     Collab,
     /// Enable task-path-based multi-agent routing.
@@ -967,6 +969,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         },
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::RespectSystemProxy,
+        key: "respect_system_proxy",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::Collab,
         key: "multi_agent",

codex-rs/features/src/tests.rs

@@ -649,6 +649,7 @@ fn materialize_resolved_enabled_writes_all_features_and_preserves_custom_config(
     features.enable(Feature::CodeMode);
     features.enable(Feature::MultiAgentV2);
     features.enable(Feature::NetworkProxy);
+    features.enable(Feature::RespectSystemProxy);
 
     let mut features_toml = FeaturesToml {
         multi_agent_v2: Some(FeatureToml::Config(crate::MultiAgentV2ConfigToml {

codex-rs/thread-manager-sample/src/main.rs

@@ -255,6 +255,7 @@ fn new_config(model: Option<String>, arg0_paths: Arg0DispatchPaths) -> anyhow::R
         model_catalog: None,
         model_verbosity: None,
         chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
+        respect_system_proxy: false,
         apps_mcp_product_sku: None,
         realtime_audio: RealtimeAudioConfig::default(),
         experimental_realtime_ws_base_url: None,