feat(sdk): expose Windows isolation tier

src/core/mxc-sdk/README.md

@@ -49,7 +49,9 @@ available to feed a policy: [`available_tools_policy`] (PATH + tool/SDK env
 dirs), [`user_profile_policy`], and [`temporary_files_policy`].
 
 [`platform_support`] is the Rust port of `getPlatformSupport` — reports host
-support and the available containment backends.
+support and the available containment backends. On Windows,
+`PlatformSupport::isolation_tier` reports the process-container tier selected
+for the default policy.
 
 ## Live stdio + kill (streaming)
 

src/core/mxc-sdk/src/lib.rs

@@ -70,8 +70,8 @@ mod sandbox;
 pub use mxc_engine::policy;
 pub use mxc_engine::{
     available_tools_policy, build_request, platform_support, temporary_files_policy,
-    user_profile_policy, Error, ErrorCode, FilesystemPolicyResult, PlatformSupport, SandboxPolicy,
-    SandboxRequest,
+    user_profile_policy, Error, ErrorCode, FilesystemPolicyResult, IsolationTier, PlatformSupport,
+    SandboxPolicy, SandboxRequest,
 };
 
 pub use sandbox::{Output, Sandbox, StreamCloser, WaitOutcome};

src/core/mxc-sdk/tests/sdk_helpers.rs

@@ -12,6 +12,9 @@ use mxc_sdk::{
 #[cfg(target_os = "macos")]
 use mxc_sdk::{spawn_sandbox, WaitOutcome};
 
+#[cfg(target_os = "windows")]
+use mxc_sdk::IsolationTier;
+
 fn env_pairs(pairs: &[(&str, &str)]) -> Vec<(String, String)> {
     pairs
         .iter()
@@ -25,6 +28,8 @@ fn platform_support_reports_host() {
     // Every platform this test runs on (macOS/Linux/Windows in CI) is supported.
     assert!(support.is_supported, "reason: {:?}", support.reason);
     assert!(!support.available_methods.is_empty());
+    #[cfg(not(target_os = "windows"))]
+    assert_eq!(support.isolation_tier, None);
 }
 
 #[cfg(target_os = "macos")]
@@ -215,6 +220,9 @@ fn platform_support_windows_is_processcontainer() {
         support.available_methods,
         vec!["processcontainer".to_string()]
     );
+    let _: IsolationTier = support
+        .isolation_tier
+        .expect("Windows probe should select an isolation tier");
 }
 
 #[test]

src/core/mxc_engine/src/lib.rs

@@ -22,7 +22,8 @@
 //! - [`run`] / [`resolve_runner`] (Windows) — run-to-completion backend
 //!   selection and execution.
 //! - [`run_state_aware`] — state-aware lifecycle backend resolution + dispatch.
-//! - [`platform_support`] / [`PlatformSupport`] — host support detection.
+//! - [`platform_support`] / [`PlatformSupport`] / [`IsolationTier`] — host
+//!   support detection.
 //! - [`Error`] / [`ErrorCode`] — the crate-owned error facade over
 //!   `wxc_common`'s internal error type.
 
@@ -35,7 +36,7 @@ mod run;
 mod state_aware;
 
 pub use error::{Error, ErrorCode};
-pub use platform::{platform_support, PlatformSupport};
+pub use platform::{platform_support, IsolationTier, PlatformSupport};
 pub use policy::{
     available_tools_policy, build_request, temporary_files_policy, user_profile_policy,
     FilesystemPolicyResult, SandboxPolicy, SandboxRequest,

src/core/mxc_engine/src/platform.rs

@@ -12,6 +12,11 @@
 //! `dispatch.rs`, so both the public SDK and the executor binaries can share a
 //! single implementation.
 
+#[cfg(target_os = "windows")]
+use appcontainer_common::fallback_detector::{self, IsolationTier as BackendIsolationTier};
+#[cfg(target_os = "windows")]
+use wxc_common::models::ContainerPolicy;
+
 /// Platform support information — the Rust analogue of the SDK
 /// `PlatformSupport` type.
 #[derive(Debug, Clone, Default)]
@@ -23,14 +28,28 @@ pub struct PlatformSupport {
     /// Containment backends available on this host, by wire name
     /// (e.g. `"seatbelt"`, `"bubblewrap"`, `"processcontainer"`).
     pub available_methods: Vec<String>,
+    /// Isolation tier selected for the default Windows process-container policy.
+    ///
+    /// `None` on non-Windows hosts or when the Windows capability probe fails.
+    pub isolation_tier: Option<IsolationTier>,
+}
+
+/// Windows process-container isolation tier selected by the runtime probe.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum IsolationTier {
+    /// BaseContainer via `Experimental_CreateProcessInSandbox`.
+    BaseContainer,
+    /// AppContainer with BFS filesystem isolation.
+    AppContainerBfs,
+    /// AppContainer with host DACL augmentation.
+    AppContainerDacl,
 }
 
 /// Detect MXC support on the current host.
 ///
-/// Mirrors the SDK's `getPlatformSupport`, restricted to the backends the
-/// `mxc-sdk` library can actually run. On Windows the isolation tier and UI
-/// capabilities come from the in-process fallback probe rather than a
-/// `wxc-exec --probe` subprocess.
+/// Mirrors the SDK's `getPlatformSupport`. Available methods are restricted to
+/// the backends this crate can run. On Windows the isolation tier comes from the
+/// in-process fallback probe rather than a `wxc-exec --probe` subprocess.
 pub fn platform_support() -> PlatformSupport {
     #[cfg(target_os = "macos")]
     {
@@ -68,9 +87,18 @@ pub fn platform_support() -> PlatformSupport {
 
     #[cfg(target_os = "windows")]
     {
+        let isolation_tier = fallback_detector::detect(&ContainerPolicy::default(), true)
+            .ok()
+            .map(|decision| match decision.tier {
+                BackendIsolationTier::BaseContainer => IsolationTier::BaseContainer,
+                BackendIsolationTier::AppContainerBfs => IsolationTier::AppContainerBfs,
+                BackendIsolationTier::AppContainerDacl => IsolationTier::AppContainerDacl,
+            });
+
         PlatformSupport {
             is_supported: true,
             available_methods: vec!["processcontainer".to_string()],
+            isolation_tier,
             ..Default::default()
         }
     }
@@ -98,3 +126,19 @@ fn command_succeeds(program: &str, args: &[&str]) -> bool {
         .map(|s| s.success())
         .unwrap_or(false)
 }
+
+#[cfg(all(test, target_os = "windows"))]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn base_container_tier_matches_probe() {
+        let isolation_tier = platform_support()
+            .isolation_tier
+            .expect("Windows probe should select an isolation tier");
+        assert_eq!(
+            isolation_tier == IsolationTier::BaseContainer,
+            appcontainer_common::fallback_detector::is_base_container_usable()
+        );
+    }
+}