diff --git a/codex-rs/core/src/codex_delegate.rs b/codex-rs/core/src/codex_delegate.rs
index 2c57444dc5..aa3a6d932f 100644
--- a/codex-rs/core/src/codex_delegate.rs
+++ b/codex-rs/core/src/codex_delegate.rs
@@ -87,6 +87,7 @@ pub(crate) async fn run_codex_thread_interactive(
     subagent_source: SubAgentSource,
     initial_history: Option<InitialHistory>,
     git_enrichment_policy: GitEnrichmentPolicy,
+    windows_sandbox_proxy_settings_mode: codex_sandboxing::WindowsSandboxProxySettingsMode,
 ) -> Result<(Arc<Session>, SessionIo), CodexErr> {
     let (tx_sub, rx_sub) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
     let (tx_ops, rx_ops) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
@@ -139,6 +140,7 @@ pub(crate) async fn run_codex_thread_interactive(
         external_time_provider: Some(Arc::clone(&parent_session.services.time_provider)),
         inherited_multi_agent_version: Some(MultiAgentVersion::Disabled),
         git_enrichment_policy,
+        windows_sandbox_proxy_settings_mode,
     }))
     .or_cancel(&cancel_token)
     .await??;
@@ -224,6 +226,7 @@ pub(crate) async fn run_codex_thread_one_shot(
         subagent_source,
         initial_history,
         GitEnrichmentPolicy::Fresh,
+        codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
     ))
     .await?;
 
diff --git a/codex-rs/core/src/codex_delegate_tests.rs b/codex-rs/core/src/codex_delegate_tests.rs
index 4a4d061f46..d1bebf5620 100644
--- a/codex-rs/core/src/codex_delegate_tests.rs
+++ b/codex-rs/core/src/codex_delegate_tests.rs
@@ -212,6 +212,7 @@ async fn run_codex_thread_interactive_respects_pre_cancelled_spawn() {
             SubAgentSource::Review,
             /*initial_history*/ None,
             crate::session::GitEnrichmentPolicy::Fresh,
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
         ),
     )
     .await
diff --git a/codex-rs/core/src/guardian/review_session.rs b/codex-rs/core/src/guardian/review_session.rs
index 61955ac084..0340043660 100644
--- a/codex-rs/core/src/guardian/review_session.rs
+++ b/codex-rs/core/src/guardian/review_session.rs
@@ -680,6 +680,7 @@ async fn spawn_guardian_review_session(
         SubAgentSource::Other(GUARDIAN_REVIEWER_NAME.to_string()),
         initial_history,
         GitEnrichmentPolicy::Skip,
+        codex_sandboxing::WindowsSandboxProxySettingsMode::Preserve,
     ))
     .await?;
 
@@ -1254,6 +1255,31 @@ mod tests {
         }
     }
 
+    #[tokio::test]
+    async fn spawned_guardian_session_preserves_windows_sandbox_proxy_settings() {
+        let params = test_review_params().await;
+        let manager = GuardianReviewSessionManager::default();
+        manager
+            .initialize(params.parent_session, params.parent_turn)
+            .await
+            .expect("initialize Guardian session");
+        let mode = manager
+            .state
+            .lock()
+            .await
+            .trunk
+            .as_ref()
+            .expect("Guardian session")
+            .session
+            .windows_sandbox_proxy_settings_mode;
+
+        assert_eq!(
+            mode,
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Preserve
+        );
+        manager.shutdown().await;
+    }
+
     #[tokio::test]
     async fn guardian_review_session_config_change_invalidates_cached_session() {
         let parent_config = crate::config::test_config().await;
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index 7f8a6ca546..5af8a34a3d 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -455,6 +455,8 @@ pub(crate) struct SessionSpawnArgs {
     pub(crate) external_time_provider: Option<Arc<dyn TimeProvider>>,
     pub(crate) inherited_multi_agent_version: Option<MultiAgentVersion>,
     pub(crate) git_enrichment_policy: GitEnrichmentPolicy,
+    pub(crate) windows_sandbox_proxy_settings_mode:
+        codex_sandboxing::WindowsSandboxProxySettingsMode,
 }
 
 pub(crate) fn resolve_multi_agent_version(
@@ -544,6 +546,7 @@ impl Session {
             external_time_provider,
             inherited_multi_agent_version,
             git_enrichment_policy,
+            windows_sandbox_proxy_settings_mode,
         } = args;
         let (tx_sub, rx_sub) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
         let (tx_event, rx_event) = async_channel::unbounded();
@@ -732,6 +735,7 @@ impl Session {
             external_time_provider,
             multi_agent_version,
             git_enrichment_policy,
+            windows_sandbox_proxy_settings_mode,
         ))
         .await
         .map_err(|e| {
diff --git a/codex-rs/core/src/session/session.rs b/codex-rs/core/src/session/session.rs
index c7154ab122..41c24df898 100644
--- a/codex-rs/core/src/session/session.rs
+++ b/codex-rs/core/src/session/session.rs
@@ -37,6 +37,8 @@ pub(crate) struct Session {
     /// The set of enabled features should be invariant for the lifetime of the
     /// session.
     pub(super) features: ManagedFeatures,
+    pub(crate) windows_sandbox_proxy_settings_mode:
+        codex_sandboxing::WindowsSandboxProxySettingsMode,
     pub(super) multi_agent_version: OnceLock<MultiAgentVersion>,
     pub(super) mcp_refresh_pending: std::sync::atomic::AtomicBool,
     /// Serializes runtime refreshes without blocking calls that own a snapshot.
@@ -514,6 +516,7 @@ impl Session {
         external_time_provider: Option<Arc<dyn TimeProvider>>,
         multi_agent_version: Option<MultiAgentVersion>,
         git_enrichment_policy: GitEnrichmentPolicy,
+        windows_sandbox_proxy_settings_mode: codex_sandboxing::WindowsSandboxProxySettingsMode,
     ) -> anyhow::Result<Arc<Self>> {
         debug!(
             "Configuring session: model={}; provider={:?}",
@@ -1150,6 +1153,7 @@ impl Session {
                 state: Mutex::new(state),
                 managed_network_proxy_refresh_lock: Semaphore::new(/*permits*/ 1),
                 features: config.features.clone(),
+                windows_sandbox_proxy_settings_mode,
                 multi_agent_version,
                 mcp_refresh_pending: std::sync::atomic::AtomicBool::new(false),
                 mcp_refresh_lock: Semaphore::new(/*permits*/ 1),
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index 0cc73231e6..0b284dd5a7 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -5288,6 +5288,7 @@ async fn session_new_fails_when_zsh_fork_enabled_without_packaged_zsh() {
         /*external_time_provider*/ None,
         Some(config.multi_agent_version_from_features()),
         GitEnrichmentPolicy::Fresh,
+        codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
     )
     .await;
 
@@ -5539,6 +5540,8 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         state: Mutex::new(state),
         managed_network_proxy_refresh_lock: Semaphore::new(/*permits*/ 1),
         features: config.features.clone(),
+        windows_sandbox_proxy_settings_mode:
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
         multi_agent_version: OnceLock::from(config.multi_agent_version_from_features()),
         mcp_refresh_pending: std::sync::atomic::AtomicBool::new(true),
         mcp_refresh_lock: Semaphore::new(/*permits*/ 1),
@@ -5673,6 +5676,7 @@ async fn make_session_with_config_and_rx(
         /*external_time_provider*/ None,
         Some(config.multi_agent_version_from_features()),
         GitEnrichmentPolicy::Fresh,
+        codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
     )
     .await?;
 
@@ -5788,6 +5792,7 @@ async fn make_session_with_history_source_and_agent_control_and_rx(
         /*external_time_provider*/ None,
         Some(config.multi_agent_version_from_features()),
         GitEnrichmentPolicy::Fresh,
+        codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
     )
     .await?;
 
@@ -7702,6 +7707,8 @@ where
         state: Mutex::new(state),
         managed_network_proxy_refresh_lock: Semaphore::new(/*permits*/ 1),
         features: config.features.clone(),
+        windows_sandbox_proxy_settings_mode:
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
         multi_agent_version: OnceLock::from(config.multi_agent_version_from_features()),
         mcp_refresh_pending: std::sync::atomic::AtomicBool::new(true),
         mcp_refresh_lock: Semaphore::new(/*permits*/ 1),
diff --git a/codex-rs/core/src/session/tests/guardian_tests.rs b/codex-rs/core/src/session/tests/guardian_tests.rs
index c09b53b353..2ce44e0e9b 100644
--- a/codex-rs/core/src/session/tests/guardian_tests.rs
+++ b/codex-rs/core/src/session/tests/guardian_tests.rs
@@ -766,6 +766,8 @@ async fn guardian_subagent_does_not_inherit_parent_exec_policy_rules() {
         external_time_provider: None,
         inherited_multi_agent_version: None,
         git_enrichment_policy: GitEnrichmentPolicy::Skip,
+        windows_sandbox_proxy_settings_mode:
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Preserve,
     })
     .await
     .expect("spawn guardian subagent");
diff --git a/codex-rs/core/src/session/turn_context.rs b/codex-rs/core/src/session/turn_context.rs
index 8eb7e2a599..124842e8f5 100644
--- a/codex-rs/core/src/session/turn_context.rs
+++ b/codex-rs/core/src/session/turn_context.rs
@@ -360,6 +360,7 @@ impl TurnContext {
                 .config
                 .permissions
                 .windows_sandbox_private_desktop,
+            windows_sandbox_proxy_settings_mode: None,
             use_legacy_landlock: self.config.features.use_legacy_landlock(),
         }
     }
diff --git a/codex-rs/core/src/thread_manager.rs b/codex-rs/core/src/thread_manager.rs
index 3a4b876dc3..a4f5bebc7d 100644
--- a/codex-rs/core/src/thread_manager.rs
+++ b/codex-rs/core/src/thread_manager.rs
@@ -1676,6 +1676,8 @@ impl ThreadManagerState {
             external_time_provider: self.external_time_provider.clone(),
             inherited_multi_agent_version: multi_agent_version,
             git_enrichment_policy: GitEnrichmentPolicy::Fresh,
+            windows_sandbox_proxy_settings_mode:
+                codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
         }))
         .await?;
         let new_thread = self
diff --git a/codex-rs/core/src/tools/runtimes/apply_patch.rs b/codex-rs/core/src/tools/runtimes/apply_patch.rs
index 2573f4f821..2d59a4de0a 100644
--- a/codex-rs/core/src/tools/runtimes/apply_patch.rs
+++ b/codex-rs/core/src/tools/runtimes/apply_patch.rs
@@ -99,6 +99,7 @@ impl ApplyPatchRuntime {
             workspace_roots: attempt.workspace_roots.to_vec(),
             windows_sandbox_level: attempt.windows_sandbox_level,
             windows_sandbox_private_desktop: attempt.windows_sandbox_private_desktop,
+            windows_sandbox_proxy_settings_mode: None,
             use_legacy_landlock: attempt.use_legacy_landlock,
         })
     }
diff --git a/codex-rs/core/src/tools/runtimes/unified_exec.rs b/codex-rs/core/src/tools/runtimes/unified_exec.rs
index 9b0aeed52c..345a28a08d 100644
--- a/codex-rs/core/src/tools/runtimes/unified_exec.rs
+++ b/codex-rs/core/src/tools/runtimes/unified_exec.rs
@@ -302,6 +302,7 @@ impl<'a> ToolRuntime<UnifiedExecRequest, UnifiedExecProcess> for UnifiedExecRunt
         ctx: &ToolCtx,
     ) -> Result<UnifiedExecProcess, ToolError> {
         let base_command = &req.command;
+        let windows_sandbox_proxy_settings_mode = ctx.session.windows_sandbox_proxy_settings_mode;
         let session_shell = ctx.session.user_shell();
         let shell = req
             .turn_environment
@@ -464,6 +465,7 @@ impl<'a> ToolRuntime<UnifiedExecRequest, UnifiedExecProcess> for UnifiedExecRunt
                         .open_session_with_prepared_exec_env(
                             req.process_id,
                             &prepared.exec_request,
+                            windows_sandbox_proxy_settings_mode,
                             req.tty,
                             prepared.spawn_lifecycle,
                             req.turn_environment.environment.as_ref(),
@@ -510,6 +512,7 @@ impl<'a> ToolRuntime<UnifiedExecRequest, UnifiedExecProcess> for UnifiedExecRunt
                 network_proxy_launch,
                 /*environment_id*/ Some(&req.turn_environment.environment_id),
                 req.exec_server_env_config.clone(),
+                windows_sandbox_proxy_settings_mode,
                 req.tty,
                 Box::new(NoopSpawnLifecycle),
                 req.turn_environment.environment.as_ref(),
diff --git a/codex-rs/core/src/tools/sandboxing.rs b/codex-rs/core/src/tools/sandboxing.rs
index 56587a27d2..98332fd228 100644
--- a/codex-rs/core/src/tools/sandboxing.rs
+++ b/codex-rs/core/src/tools/sandboxing.rs
@@ -507,6 +507,7 @@ impl<'a> SandboxAttempt<'a> {
                 workspace_roots: self.workspace_roots.to_vec(),
                 windows_sandbox_level: self.windows_sandbox_level,
                 windows_sandbox_private_desktop: self.windows_sandbox_private_desktop,
+                windows_sandbox_proxy_settings_mode: None,
                 use_legacy_landlock: self.use_legacy_landlock,
             });
             exec_request.exec_server_enforce_managed_network = self.enforce_managed_network;
diff --git a/codex-rs/core/src/tools/sandboxing_tests.rs b/codex-rs/core/src/tools/sandboxing_tests.rs
index e1b261b7d6..d7fed8ba64 100644
--- a/codex-rs/core/src/tools/sandboxing_tests.rs
+++ b/codex-rs/core/src/tools/sandboxing_tests.rs
@@ -268,6 +268,7 @@ fn exec_server_env_keeps_command_native_and_carries_sandbox_context() {
             workspace_roots: vec![cwd_uri.clone()],
             windows_sandbox_level: codex_protocol::config_types::WindowsSandboxLevel::Disabled,
             windows_sandbox_private_desktop: false,
+            windows_sandbox_proxy_settings_mode: None,
             use_legacy_landlock: false,
         })
     );
diff --git a/codex-rs/core/src/unified_exec/mod_tests.rs b/codex-rs/core/src/unified_exec/mod_tests.rs
index 04cfa747ca..acf6d7d639 100644
--- a/codex-rs/core/src/unified_exec/mod_tests.rs
+++ b/codex-rs/core/src/unified_exec/mod_tests.rs
@@ -113,6 +113,7 @@ async fn exec_command_with_tty(
             .open_session_with_prepared_exec_env(
                 process_id,
                 &request,
+                codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
                 tty,
                 Box::new(NoopSpawnLifecycle),
                 turn.environments
@@ -753,6 +754,7 @@ async fn completed_pipe_commands_preserve_exit_code() -> anyhow::Result<()> {
         .open_session_with_prepared_exec_env(
             /*process_id*/ 1234,
             &request,
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
             /*tty*/ false,
             Box::new(NoopSpawnLifecycle),
             &environment,
@@ -793,6 +795,7 @@ async fn unified_exec_uses_remote_exec_server_when_configured() -> anyhow::Resul
         .open_session_with_prepared_exec_env(
             /*process_id*/ 1234,
             &request,
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
             /*tty*/ true,
             Box::new(NoopSpawnLifecycle),
             remote_test_env.environment(),
@@ -851,6 +854,7 @@ async fn remote_exec_server_rejects_inherited_fd_launches() -> anyhow::Result<()
         .open_session_with_prepared_exec_env(
             /*process_id*/ 1234,
             &request,
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
             /*tty*/ true,
             Box::new(TestSpawnLifecycle {
                 inherited_fds: vec![42],
diff --git a/codex-rs/core/src/unified_exec/process_manager.rs b/codex-rs/core/src/unified_exec/process_manager.rs
index dbd57378ea..098c70f026 100644
--- a/codex-rs/core/src/unified_exec/process_manager.rs
+++ b/codex-rs/core/src/unified_exec/process_manager.rs
@@ -177,9 +177,14 @@ fn exec_server_env_for_request(
 fn exec_server_params_for_request(
     process_id: i32,
     request: &ExecRequest,
+    windows_sandbox_proxy_settings_mode: codex_sandboxing::WindowsSandboxProxySettingsMode,
     tty: bool,
 ) -> codex_exec_server::ExecParams {
     let (env_policy, env) = exec_server_env_for_request(request);
+    let sandbox = request.exec_server_sandbox.clone().map(|mut sandbox| {
+        sandbox.windows_sandbox_proxy_settings_mode = Some(windows_sandbox_proxy_settings_mode);
+        sandbox
+    });
     // Sandbox retries reuse the unified-exec ID but start a distinct executor process.
     let exec_server_process_id = if request.exec_server_sandbox.is_some() {
         format!("{process_id}-{}", Uuid::new_v4())
@@ -195,7 +200,7 @@ fn exec_server_params_for_request(
         tty,
         pipe_stdin: false,
         arg0: request.arg0.clone(),
-        sandbox: request.exec_server_sandbox.clone(),
+        sandbox,
         enforce_managed_network: request.exec_server_enforce_managed_network,
         managed_network: request.exec_server_managed_network.clone(),
         network_proxy: request.exec_server_network_proxy.clone(),
@@ -1003,6 +1008,7 @@ impl UnifiedExecProcessManager {
         network_proxy_launch: Option<codex_network_proxy::RemoteNetworkProxyLaunchConfig>,
         environment_id: Option<&str>,
         exec_server_env_config: Option<ExecServerEnvConfig>,
+        windows_sandbox_proxy_settings_mode: codex_sandboxing::WindowsSandboxProxySettingsMode,
         tty: bool,
         spawn_lifecycle: SpawnLifecycleHandle,
         environment: &codex_exec_server::Environment,
@@ -1018,6 +1024,7 @@ impl UnifiedExecProcessManager {
         self.open_session_with_prepared_exec_env(
             process_id,
             &request,
+            windows_sandbox_proxy_settings_mode,
             tty,
             spawn_lifecycle,
             environment,
@@ -1038,6 +1045,7 @@ impl UnifiedExecProcessManager {
         &self,
         process_id: i32,
         request: &ExecRequest,
+        windows_sandbox_proxy_settings_mode: codex_sandboxing::WindowsSandboxProxySettingsMode,
         tty: bool,
         mut spawn_lifecycle: SpawnLifecycleHandle,
         environment: &codex_exec_server::Environment,
@@ -1053,7 +1061,12 @@ impl UnifiedExecProcessManager {
 
             let started = environment
                 .get_exec_backend()
-                .start(exec_server_params_for_request(process_id, request, tty))
+                .start(exec_server_params_for_request(
+                    process_id,
+                    request,
+                    windows_sandbox_proxy_settings_mode,
+                    tty,
+                ))
                 .await
                 .map_err(|err| UnifiedExecError::create_process(err.to_string()))?;
             spawn_lifecycle.after_spawn();
@@ -1100,22 +1113,21 @@ impl UnifiedExecProcessManager {
                 None::<String>
             }
         };
-        let windows_sandbox = if request.sandbox
-            == codex_sandboxing::SandboxType::WindowsRestrictedToken
-        {
-            Some(codex_sandboxing::WindowsSandboxSpawnRequest {
-                permission_profile: &request.permission_profile,
-                workspace_roots: &request.windows_sandbox_workspace_roots,
-                windows_sandbox_level: request.windows_sandbox_level,
-                proxy_enforced: request.network.is_some(),
-                network_proxy_restricting_sid: network_proxy_restricting_sid.as_deref(),
-                proxy_settings_mode: codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
-                filesystem_overrides: request.windows_sandbox_filesystem_overrides.as_ref(),
-                use_private_desktop: request.windows_sandbox_private_desktop,
-            })
-        } else {
-            None
-        };
+        let windows_sandbox =
+            if request.sandbox == codex_sandboxing::SandboxType::WindowsRestrictedToken {
+                Some(codex_sandboxing::WindowsSandboxSpawnRequest {
+                    permission_profile: &request.permission_profile,
+                    workspace_roots: &request.windows_sandbox_workspace_roots,
+                    windows_sandbox_level: request.windows_sandbox_level,
+                    proxy_enforced: request.network.is_some(),
+                    network_proxy_restricting_sid: network_proxy_restricting_sid.as_deref(),
+                    proxy_settings_mode: windows_sandbox_proxy_settings_mode,
+                    filesystem_overrides: request.windows_sandbox_filesystem_overrides.as_ref(),
+                    use_private_desktop: request.windows_sandbox_private_desktop,
+                })
+            } else {
+                None
+            };
         let spawn_result = codex_sandboxing::spawn_process(codex_sandboxing::SpawnRequest {
             command: &request.command,
             cwd: native_cwd.as_path(),
diff --git a/codex-rs/core/src/unified_exec/process_manager_tests.rs b/codex-rs/core/src/unified_exec/process_manager_tests.rs
index bd094ab3d7..ced51882a1 100644
--- a/codex-rs/core/src/unified_exec/process_manager_tests.rs
+++ b/codex-rs/core/src/unified_exec/process_manager_tests.rs
@@ -177,8 +177,16 @@ fn exec_server_params_use_path_uri_and_env_policy_overlay_contract() {
         exec_server_network_proxy: None,
     };
 
-    let params =
-        exec_server_params_for_request(/*process_id*/ 123, &request, /*tty*/ true);
+    let proxy_settings_mode = codex_sandboxing::WindowsSandboxProxySettingsMode::Preserve;
+    let params_for_request = |request: &ExecRequest| {
+        exec_server_params_for_request(
+            /*process_id*/ 123,
+            request,
+            proxy_settings_mode,
+            /*tty*/ true,
+        )
+    };
+    let params = params_for_request(&request);
 
     assert_eq!(params.process_id.as_str(), "123");
     assert_eq!(params.cwd, request.cwd);
@@ -200,10 +208,15 @@ fn exec_server_params_use_path_uri_and_env_policy_overlay_contract() {
     request.exec_server_sandbox = Some(
         codex_exec_server::FileSystemSandboxContext::from_permission_profile(permission_profile),
     );
-    let first =
-        exec_server_params_for_request(/*process_id*/ 123, &request, /*tty*/ true);
-    let second =
-        exec_server_params_for_request(/*process_id*/ 123, &request, /*tty*/ true);
+    let first = params_for_request(&request);
+    let second = params_for_request(&request);
+    assert_eq!(
+        first
+            .sandbox
+            .as_ref()
+            .and_then(|sandbox| sandbox.windows_sandbox_proxy_settings_mode),
+        Some(codex_sandboxing::WindowsSandboxProxySettingsMode::Preserve)
+    );
     assert!(first.process_id.as_str().starts_with("123-"));
     assert!(second.process_id.as_str().starts_with("123-"));
     assert_ne!(first.process_id, second.process_id);
diff --git a/codex-rs/exec-server-protocol/src/protocol.rs b/codex-rs/exec-server-protocol/src/protocol.rs
index 0468c413d5..b87b261d73 100644
--- a/codex-rs/exec-server-protocol/src/protocol.rs
+++ b/codex-rs/exec-server-protocol/src/protocol.rs
@@ -743,6 +743,7 @@ mod tests {
     use codex_network_proxy::NetworkProxyConfig;
     use codex_network_proxy::RemoteNetworkProxyConfig;
     use codex_network_proxy::RemoteNetworkProxyLaunchConfig;
+    use codex_protocol::config_types::WindowsSandboxProxySettingsMode;
     use codex_protocol::models::ManagedFileSystemPermissions;
     use codex_protocol::models::PermissionProfile;
     use codex_protocol::permissions::FileSystemAccessMode;
@@ -938,6 +939,17 @@ mod tests {
                 .expect("deserialize sandbox"),
             sandbox
         );
+        let preserve = FileSystemSandboxContext {
+            windows_sandbox_proxy_settings_mode: Some(WindowsSandboxProxySettingsMode::Preserve),
+            ..sandbox
+        };
+        let serialized = serde_json::to_value(&preserve).expect("serialize preserve mode");
+        assert_eq!(serialized["windowsSandboxProxySettingsMode"], "preserve");
+        assert_eq!(
+            serde_json::from_value::<FileSystemSandboxContext>(serialized)
+                .expect("deserialize preserve mode"),
+            preserve
+        );
     }
 
     #[test]
diff --git a/codex-rs/exec-server/src/process_sandbox.rs b/codex-rs/exec-server/src/process_sandbox.rs
index 864592c1a2..0c8327f585 100644
--- a/codex-rs/exec-server/src/process_sandbox.rs
+++ b/codex-rs/exec-server/src/process_sandbox.rs
@@ -52,6 +52,7 @@ struct PreparedWindowsSandboxRequest {
     windows_sandbox_level: codex_protocol::config_types::WindowsSandboxLevel,
     proxy_enforced: bool,
     network_proxy_restricting_sid: Option<String>,
+    proxy_settings_mode: WindowsSandboxProxySettingsMode,
     filesystem_overrides: Option<WindowsSandboxFilesystemOverrides>,
     use_private_desktop: bool,
 }
@@ -66,7 +67,7 @@ impl PreparedExecRequest {
                 windows_sandbox_level: request.windows_sandbox_level,
                 proxy_enforced: request.proxy_enforced,
                 network_proxy_restricting_sid: request.network_proxy_restricting_sid.as_deref(),
-                proxy_settings_mode: WindowsSandboxProxySettingsMode::Reconcile,
+                proxy_settings_mode: request.proxy_settings_mode,
                 filesystem_overrides: request.filesystem_overrides.as_ref(),
                 use_private_desktop: request.use_private_desktop,
             })
@@ -114,6 +115,9 @@ pub(crate) async fn prepare_exec_request(
             windows_sandbox: None,
         });
     };
+    let windows_sandbox_proxy_settings_mode = sandbox_context
+        .windows_sandbox_proxy_settings_mode
+        .unwrap_or_default();
     let runtime_paths = runtime_paths
         .ok_or_else(|| invalid_params("sandbox runtime paths are not configured".to_string()))?;
     // TODO(jif): Transport permissions before orchestrator-local paths are materialized,
@@ -212,8 +216,7 @@ pub(crate) async fn prepare_exec_request(
     let (program, args) = (program.into(), args.to_vec());
     let transform_request = SandboxDirectSpawnTransformRequest {
         workspace_roots,
-        windows_sandbox_proxy_settings_mode:
-            codex_sandboxing::WindowsSandboxProxySettingsMode::Reconcile,
+        windows_sandbox_proxy_settings_mode,
         transform: SandboxTransformRequest {
             command: SandboxCommand {
                 program,
@@ -271,6 +274,7 @@ pub(crate) async fn prepare_exec_request(
             windows_sandbox_level: sandbox_context.windows_sandbox_level,
             proxy_enforced,
             network_proxy_restricting_sid,
+            proxy_settings_mode: windows_sandbox_proxy_settings_mode,
             filesystem_overrides,
             use_private_desktop: sandbox_context.windows_sandbox_private_desktop,
         })
diff --git a/codex-rs/exec-server/src/process_sandbox_tests.rs b/codex-rs/exec-server/src/process_sandbox_tests.rs
index 23ce7871f2..3ea7e508d3 100644
--- a/codex-rs/exec-server/src/process_sandbox_tests.rs
+++ b/codex-rs/exec-server/src/process_sandbox_tests.rs
@@ -394,6 +394,8 @@ async fn managed_network_selects_elevated_windows_spawn() {
         cwd_uri.clone(),
     );
     sandbox.windows_sandbox_level = WindowsSandboxLevel::RestrictedToken;
+    sandbox.windows_sandbox_proxy_settings_mode =
+        Some(codex_sandboxing::WindowsSandboxProxySettingsMode::Preserve);
     let proxy_config = RemoteNetworkProxyConfig::from_effective_config(&NetworkProxyConfig {
         enabled: true,
         enable_socks5: false,
@@ -434,6 +436,10 @@ async fn managed_network_selects_elevated_windows_spawn() {
         );
         assert!(spawn.proxy_enforced);
         assert!(spawn.network_proxy_restricting_sid.is_some());
+        assert_eq!(
+            spawn.proxy_settings_mode,
+            codex_sandboxing::WindowsSandboxProxySettingsMode::Preserve
+        );
         assert_eq!(spawn.permission_profile, &permissions);
         assert_eq!(spawn.workspace_roots, std::slice::from_ref(&cwd));
     }
diff --git a/codex-rs/file-system/src/lib.rs b/codex-rs/file-system/src/lib.rs
index 21f1cc6e37..fa783074fc 100644
--- a/codex-rs/file-system/src/lib.rs
+++ b/codex-rs/file-system/src/lib.rs
@@ -2,6 +2,7 @@ mod find_up;
 
 use bytes::Bytes;
 use codex_protocol::config_types::WindowsSandboxLevel;
+use codex_protocol::config_types::WindowsSandboxProxySettingsMode;
 use codex_protocol::models::ManagedFileSystemPermissions;
 use codex_protocol::models::PermissionProfile;
 use codex_protocol::models::SandboxEnforcement;
@@ -291,6 +292,8 @@ pub struct FileSystemSandboxContext {
     pub windows_sandbox_level: WindowsSandboxLevel,
     #[serde(default)]
     pub windows_sandbox_private_desktop: bool,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub windows_sandbox_proxy_settings_mode: Option<WindowsSandboxProxySettingsMode>,
     #[serde(default)]
     pub use_legacy_landlock: bool,
 }
@@ -332,6 +335,7 @@ impl FileSystemSandboxContext {
             workspace_roots,
             windows_sandbox_level: WindowsSandboxLevel::Disabled,
             windows_sandbox_private_desktop: false,
+            windows_sandbox_proxy_settings_mode: None,
             use_legacy_landlock: false,
         }
     }
diff --git a/codex-rs/protocol/src/config_types.rs b/codex-rs/protocol/src/config_types.rs
index c00b69943e..c29ca9488a 100644
--- a/codex-rs/protocol/src/config_types.rs
+++ b/codex-rs/protocol/src/config_types.rs
@@ -283,6 +283,16 @@ pub enum WindowsSandboxLevel {
     Elevated,
 }
 
+/// Controls whether a Windows sandbox launch reconciles persistent proxy settings or preserves
+/// the settings established by another launch.
+#[derive(Deserialize, Debug, Clone, Copy, PartialEq, Eq, Default, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub enum WindowsSandboxProxySettingsMode {
+    #[default]
+    Reconcile,
+    Preserve,
+}
+
 #[derive(
     Debug,
     Serialize,
diff --git a/codex-rs/windows-sandbox-rs/src/identity.rs b/codex-rs/windows-sandbox-rs/src/identity.rs
index 9ac3402be1..860877dff2 100644
--- a/codex-rs/windows-sandbox-rs/src/identity.rs
+++ b/codex-rs/windows-sandbox-rs/src/identity.rs
@@ -371,4 +371,36 @@ mod tests {
             vec![8080]
         );
     }
+
+    #[test]
+    fn guardian_preserve_mode_does_not_churn_marker_with_empty_proxy_ports() {
+        let marker = SetupMarker {
+            version: crate::setup::SETUP_VERSION,
+            offline_username: "offline".to_string(),
+            online_username: "online".to_string(),
+            created_at: None,
+            proxy_ports: vec![3128, 8081],
+            allow_local_binding: true,
+        };
+        let env_map = HashMap::new();
+        let reconciled = desired_offline_proxy_settings(
+            Some(&marker),
+            WindowsSandboxProxySettingsMode::Reconcile,
+            &env_map,
+            SandboxNetworkIdentity::Offline,
+        );
+        assert_eq!(reconciled.proxy_ports, Vec::<u16>::new());
+
+        let desired = desired_offline_proxy_settings(
+            Some(&marker),
+            WindowsSandboxProxySettingsMode::Preserve,
+            &env_map,
+            SandboxNetworkIdentity::Offline,
+        );
+        assert_eq!(desired, marker.offline_proxy_settings());
+        assert_eq!(
+            marker.request_mismatch_reason(SandboxNetworkIdentity::Offline, &desired),
+            None
+        );
+    }
 }
diff --git a/codex-rs/windows-sandbox-rs/src/lib.rs b/codex-rs/windows-sandbox-rs/src/lib.rs
index d4db186b9c..f86f1741ce 100644
--- a/codex-rs/windows-sandbox-rs/src/lib.rs
+++ b/codex-rs/windows-sandbox-rs/src/lib.rs
@@ -35,14 +35,7 @@ impl fmt::Debug for WindowsSandboxCancellationToken {
     }
 }
 
-/// Controls whether a Windows sandbox launch reconciles persistent proxy
-/// firewall settings or preserves the settings established by another launch.
-#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
-pub enum WindowsSandboxProxySettingsMode {
-    #[default]
-    Reconcile,
-    Preserve,
-}
+pub use codex_protocol::config_types::WindowsSandboxProxySettingsMode;
 
 /// Network settings installed by an administrator during managed Windows sandbox setup.
 #[derive(Clone, Debug, Default, PartialEq, Eq)]