From dc5721243e2158b030fa4ce9a19ebb6cd029619c Mon Sep 17 00:00:00 2001
From: Drew Newberry <anewberry@nvidia.com>
Date: Tue, 1 Sep 2026 17:54:31 -0700
Subject: [PATCH 1/2] feat(gateway): support selective compute driver builds

Signed-off-by: Drew Newberry <anewberry@nvidia.com>
---
 .github/workflows/branch-checks.yml        |   9 ++
 README.md                                  |  12 +++
 architecture/compute-runtimes.md           |  17 ++--
 crates/openshell-gateway/Cargo.toml        |  14 ++-
 crates/openshell-gateway/src/lib.rs        | 102 ++++++++++++++++++---
 docs/reference/sandbox-compute-drivers.mdx |  19 ++++
 skills/debug-openshell-cluster/SKILL.md    |  16 +++-
 7 files changed, 159 insertions(+), 30 deletions(-)

diff --git a/.github/workflows/branch-checks.yml b/.github/workflows/branch-checks.yml
index 6739434bf0..6f941c89cb 100644
--- a/.github/workflows/branch-checks.yml
+++ b/.github/workflows/branch-checks.yml
@@ -182,6 +182,15 @@ jobs:
           cargo build -p openshell-sandbox --bin openshell-sandbox --no-default-features --features defaults-without-telemetry
           tasks/scripts/verify-telemetry-compiled-out.sh absent target/debug/openshell-sandbox
 
+      - name: Verify selective gateway compute-driver builds
+        run: |
+          cargo test -p openshell-gateway --all-targets --no-default-features
+          cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-docker
+          cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-kubernetes
+          cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-podman
+          cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-vm
+          cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-docker,compute-driver-vm
+
       - name: Verify the defaults-without-telemetry feature alias tracks the default feature set
         run: tasks/scripts/verify-defaults-without-telemetry.sh
 
diff --git a/README.md b/README.md
index 35faf5c1bc..0e512589b0 100644
--- a/README.md
+++ b/README.md
@@ -274,6 +274,18 @@ cargo build --release -p openshell-driver-vm --no-default-features --features de
 
 The resulting binaries contain no telemetry endpoint, no telemetry HTTP client, and no emission code. With telemetry compiled out, the gateway emits nothing and reports telemetry disabled to the sandboxes it launches. Cargo has no way to subtract a single default feature, so `defaults-without-telemetry` must be paired with `--no-default-features`; passing it on its own leaves the defaults in place and fails the build rather than producing a binary that still emits.
 
+The gateway also exposes separate Cargo features for its built-in compute drivers: `compute-driver-kubernetes`, `compute-driver-docker`, `compute-driver-podman`, and `compute-driver-vm`. Disable the default feature set, then enable only the drivers and telemetry mode required by the target binary. For example:
+
+```shell
+# Docker only, with telemetry support.
+cargo build --release -p openshell-gateway --no-default-features --features telemetry,compute-driver-docker
+
+# Docker and VM only, with telemetry compiled out.
+cargo build --release -p openshell-gateway --no-default-features --features compute-driver-docker,compute-driver-vm
+```
+
+Regular builds still include all four drivers through the default `in-tree-compute-drivers` compatibility feature.
+
 Telemetry events are limited to anonymous operational categories and counts, such as sandbox lifecycle outcomes, provider profile buckets, policy decision counts, and aggregate network activity denial categories. OpenShell telemetry does not collect sandbox names or IDs, hostnames, file paths, binary paths, prompts, credentials, provider names, model names, or user content.
 
 Opting out applies only to telemetry emitted by OpenShell. Third-party services, model providers, inference endpoints, agents, or tools that you configure and use with OpenShell may have their own terms and privacy practices.
diff --git a/architecture/compute-runtimes.md b/architecture/compute-runtimes.md
index e1e731a0ce..69ebfe7071 100644
--- a/architecture/compute-runtimes.md
+++ b/architecture/compute-runtimes.md
@@ -133,13 +133,16 @@ server constructs the common runtime adapter and snapshots `GetCapabilities`
 for either result. A configured UDS endpoint still takes precedence over a
 compiled registration with the same name.
 
-The `openshell-gateway` composition crate groups first-party registrations
-behind the `in-tree-compute-drivers` feature. `openshell-server` has no compute
-driver dependencies or backend-name dispatch. Protocol-only gateway builds
-disable the composition feature and link no compute-driver crates. E2E lanes
-compose that gateway with Docker, Podman, Kubernetes, and VM driver executables
-over the public UDS gRPC contract so an in-tree driver cannot silently depend
-on a server-only API.
+The `openshell-gateway` composition crate exposes one feature per first-party
+registration: `compute-driver-kubernetes`, `compute-driver-docker`,
+`compute-driver-podman`, and `compute-driver-vm`. Builds can enable any subset.
+The default `in-tree-compute-drivers` feature remains an alias for all four
+and retains the Windows MXC registration and unsupported-driver stubs.
+`openshell-server` has no compute driver dependencies or backend-name dispatch.
+Protocol-only gateway builds disable the default features and link no
+compute-driver crates. E2E lanes compose that gateway with Docker, Podman,
+Kubernetes, and VM driver executables over the public UDS gRPC contract so an
+in-tree driver cannot silently depend on a server-only API.
 
 ## Stop and Start Lifecycle
 
diff --git a/crates/openshell-gateway/Cargo.toml b/crates/openshell-gateway/Cargo.toml
index f9d02027e0..57742475df 100644
--- a/crates/openshell-gateway/Cargo.toml
+++ b/crates/openshell-gateway/Cargo.toml
@@ -40,9 +40,16 @@ openshell-driver-mxc = { path = "../openshell-driver-mxc", optional = true }
 [features]
 default = ["telemetry", "in-tree-compute-drivers"]
 in-tree-compute-drivers = [
-    "dep:openshell-driver-docker",
-    "dep:openshell-driver-kubernetes",
-    "dep:openshell-driver-podman",
+    "compute-driver-docker",
+    "compute-driver-kubernetes",
+    "compute-driver-podman",
+    "compute-driver-vm",
+    "dep:openshell-driver-mxc",
+]
+compute-driver-docker = ["dep:openshell-driver-docker", "dep:openshell-otel"]
+compute-driver-kubernetes = ["dep:openshell-driver-kubernetes", "dep:openshell-otel"]
+compute-driver-podman = ["dep:openshell-driver-podman", "dep:openshell-otel"]
+compute-driver-vm = [
     "dep:openshell-otel",
     "dep:hyper-util",
     "dep:nix",
@@ -51,7 +58,6 @@ in-tree-compute-drivers = [
     "dep:tonic",
     "dep:tower",
     "dep:tracing",
-    "dep:openshell-driver-mxc",
 ]
 telemetry = ["openshell-core/telemetry", "openshell-server/telemetry"]
 ## Convenience alias: every default feature except `telemetry`. Build a
diff --git a/crates/openshell-gateway/src/lib.rs b/crates/openshell-gateway/src/lib.rs
index 54ae5e5de3..fed1b844be 100644
--- a/crates/openshell-gateway/src/lib.rs
+++ b/crates/openshell-gateway/src/lib.rs
@@ -16,12 +16,34 @@ compile_error!(
      build a telemetry-free gateway with `--no-default-features --features defaults-without-telemetry`"
 );
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-vm"))]
 mod vm;
 
-#[cfg(feature = "in-tree-compute-drivers")]
+#[cfg(any(
+    all(target_os = "windows", feature = "in-tree-compute-drivers"),
+    all(
+        not(target_os = "windows"),
+        any(
+            feature = "compute-driver-docker",
+            feature = "compute-driver-kubernetes",
+            feature = "compute-driver-podman",
+            feature = "compute-driver-vm"
+        )
+    )
+))]
 use openshell_core::telemetry::TelemetryComputeDriver;
-#[cfg(feature = "in-tree-compute-drivers")]
+#[cfg(any(
+    all(target_os = "windows", feature = "in-tree-compute-drivers"),
+    all(
+        not(target_os = "windows"),
+        any(
+            feature = "compute-driver-docker",
+            feature = "compute-driver-kubernetes",
+            feature = "compute-driver-podman",
+            feature = "compute-driver-vm"
+        )
+    )
+))]
 use openshell_server::ComputeDriverRegistration;
 use openshell_server::ComputeDriverRegistry;
 
@@ -30,7 +52,15 @@ use openshell_server::ComputeDriverRegistry;
 pub fn install_default_compute_drivers() -> ComputeDriverRegistry {
     #[allow(unused_mut)]
     let mut registry = ComputeDriverRegistry::new();
-    #[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+    #[cfg(all(
+        not(target_os = "windows"),
+        any(
+            feature = "compute-driver-docker",
+            feature = "compute-driver-kubernetes",
+            feature = "compute-driver-podman",
+            feature = "compute-driver-vm"
+        )
+    ))]
     install_in_tree_compute_drivers(&mut registry);
     #[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
     install_mxc_compute_driver(&mut registry);
@@ -103,9 +133,18 @@ impl openshell_server::ComputeDriverFactory for MxcFactory {
     }
 }
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(
+    not(target_os = "windows"),
+    any(
+        feature = "compute-driver-docker",
+        feature = "compute-driver-kubernetes",
+        feature = "compute-driver-podman",
+        feature = "compute-driver-vm"
+    )
+))]
 fn install_in_tree_compute_drivers(registry: &mut ComputeDriverRegistry) {
     for registration in [
+        #[cfg(feature = "compute-driver-kubernetes")]
         ComputeDriverRegistration::new(
             "kubernetes",
             100,
@@ -128,6 +167,7 @@ fn install_in_tree_compute_drivers(registry: &mut ComputeDriverRegistry) {
                     "sa_token_ttl_secs",
                 ])
         }),
+        #[cfg(feature = "compute-driver-podman")]
         ComputeDriverRegistration::new(
             "podman",
             200,
@@ -148,6 +188,7 @@ fn install_in_tree_compute_drivers(registry: &mut ComputeDriverRegistry) {
                     "guest_tls_key",
                 ])
         }),
+        #[cfg(feature = "compute-driver-docker")]
         ComputeDriverRegistration::new(
             "docker",
             300,
@@ -169,6 +210,7 @@ fn install_in_tree_compute_drivers(registry: &mut ComputeDriverRegistry) {
                     "guest_tls_key",
                 ])
         }),
+        #[cfg(feature = "compute-driver-vm")]
         ComputeDriverRegistration::new("vm", u16::MAX, None, VmFactory).map(|registration| {
             registration
                 .with_telemetry_category(TelemetryComputeDriver::anonymous_category("vm"))
@@ -187,11 +229,11 @@ fn install_in_tree_compute_drivers(registry: &mut ComputeDriverRegistry) {
     }
 }
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-kubernetes"))]
 #[derive(Clone, Copy)]
 struct KubernetesFactory;
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-kubernetes"))]
 #[async_trait::async_trait]
 impl openshell_server::ComputeDriverFactory for KubernetesFactory {
     async fn build(
@@ -219,11 +261,11 @@ impl openshell_server::ComputeDriverFactory for KubernetesFactory {
     }
 }
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-docker"))]
 #[derive(Clone, Copy)]
 struct DockerFactory;
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-docker"))]
 #[async_trait::async_trait]
 impl openshell_server::ComputeDriverFactory for DockerFactory {
     async fn build(
@@ -251,11 +293,11 @@ impl openshell_server::ComputeDriverFactory for DockerFactory {
     }
 }
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-podman"))]
 #[derive(Clone, Copy)]
 struct PodmanFactory;
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-podman"))]
 #[async_trait::async_trait]
 impl openshell_server::ComputeDriverFactory for PodmanFactory {
     async fn build(
@@ -289,11 +331,11 @@ impl openshell_server::ComputeDriverFactory for PodmanFactory {
     }
 }
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-vm"))]
 #[derive(Clone, Copy)]
 struct VmFactory;
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(not(target_os = "windows"), feature = "compute-driver-vm"))]
 #[async_trait::async_trait]
 impl openshell_server::ComputeDriverFactory for VmFactory {
     async fn build(
@@ -333,7 +375,14 @@ impl openshell_server::ComputeDriverFactory for VmFactory {
     }
 }
 
-#[cfg(all(not(target_os = "windows"), feature = "in-tree-compute-drivers"))]
+#[cfg(all(
+    not(target_os = "windows"),
+    any(
+        feature = "compute-driver-docker",
+        feature = "compute-driver-podman",
+        feature = "compute-driver-vm"
+    )
+))]
 fn apply_guest_tls(
     ca: &mut Option<std::path::PathBuf>,
     cert: &mut Option<std::path::PathBuf>,
@@ -372,3 +421,28 @@ mod windows_tests {
         }
     }
 }
+
+#[cfg(all(test, not(target_os = "windows")))]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_registry_contains_exactly_the_enabled_compute_drivers() {
+        let expected: Vec<&str> = vec![
+            #[cfg(feature = "compute-driver-docker")]
+            "docker",
+            #[cfg(feature = "compute-driver-kubernetes")]
+            "kubernetes",
+            #[cfg(feature = "compute-driver-podman")]
+            "podman",
+            #[cfg(feature = "compute-driver-vm")]
+            "vm",
+        ];
+        assert_eq!(
+            install_default_compute_drivers()
+                .installed_driver_names()
+                .collect::<Vec<_>>(),
+            expected
+        );
+    }
+}
diff --git a/docs/reference/sandbox-compute-drivers.mdx b/docs/reference/sandbox-compute-drivers.mdx
index e46ebf8a23..98bcabab9a 100644
--- a/docs/reference/sandbox-compute-drivers.mdx
+++ b/docs/reference/sandbox-compute-drivers.mdx
@@ -40,6 +40,25 @@ an exited canonical process remains a terminal sandbox result. Exit code zero
 produces `Completed`; a nonzero or signal-normalized exit produces `Error`
 with the exact exit code. Driver and supervisor failures remain `Error`.
 
+## Build with Selected Compute Drivers
+
+Source builds of `openshell-gateway` can include any subset of the Docker,
+Podman, Kubernetes, and VM drivers. Enable the corresponding
+`compute-driver-docker`, `compute-driver-podman`, `compute-driver-kubernetes`,
+or `compute-driver-vm` Cargo features. For example, build a Docker-only gateway
+with telemetry support:
+
+```shell
+cargo build --release -p openshell-gateway --no-default-features --features telemetry,compute-driver-docker
+```
+
+The default `in-tree-compute-drivers` feature retains the full platform driver
+set, including MXC on Windows. The four selective features apply to non-Windows
+builds. A build with no default features and no driver features connects to
+external drivers only. Auto-detection probes only compiled registrations.
+To select a driver omitted from a custom build, configure its external
+`socket_path` as described below.
+
 ## Configure a Compute Driver
 
 Configure the compute driver on the gateway. Current releases accept one driver per gateway. Set `compute_drivers` in the gateway TOML file:
diff --git a/skills/debug-openshell-cluster/SKILL.md b/skills/debug-openshell-cluster/SKILL.md
index 7d47b18065..effa670ba6 100644
--- a/skills/debug-openshell-cluster/SKILL.md
+++ b/skills/debug-openshell-cluster/SKILL.md
@@ -21,11 +21,17 @@ The target deployment flow is:
 
 The `openshell-gateway` composition crate explicitly installs its compiled
 Docker, Podman, Kubernetes, and VM registrations at startup; `openshell-server`
-does not link compute-driver crates. With no configured driver, the
-gateway probes only installed registrations in priority order (Kubernetes,
-Podman, then Docker); VM has no probe and remains opt-in. A custom gateway
-binary may install a different set, so confirm the binary's registered drivers
-when auto-detection reports that no suitable driver is available.
+does not link compute-driver crates. Custom gateway binaries may include a
+subset of those registrations. With no configured driver, the gateway probes only
+installed registrations in priority order (Kubernetes, Podman, then Docker);
+VM has no probe and remains opt-in. Confirm the binary's registered drivers
+when auto-detection reports that no suitable driver is available. If
+configuration selects a driver that was not compiled in, the gateway treats
+the name as an external driver and reports a missing `socket_path` unless an
+endpoint is configured.
+
+See the [compute driver reference](https://docs.nvidia.com/openshell/latest/reference/sandbox-compute-drivers.md)
+for selective-build options and external-driver configuration.
 
 For local evaluation only, TLS may be disabled and the gateway can be reached through `http://127.0.0.1:<port>`.
 

From 2d375294014042c4efeffd68026961299ffbb739 Mon Sep 17 00:00:00 2001
From: Drew Newberry <anewberry@nvidia.com>
Date: Thu, 10 Sep 2026 16:56:18 -0700
Subject: [PATCH 2/2] feat(gateway): support selective Windows MXC builds

Signed-off-by: Drew Newberry <anewberry@nvidia.com>
---
 .../build-openshell-mxc-windows/SKILL.md      | 18 +++++-
 .github/workflows/branch-checks.yml           |  1 +
 Cargo.lock                                    |  2 +
 README.md                                     |  7 +-
 architecture/compute-runtimes.md              |  8 ++-
 architecture/windows-msvc-build.md            |  8 +++
 crates/openshell-driver-mxc/Cargo.toml        |  2 +-
 crates/openshell-gateway/Cargo.toml           |  3 +-
 crates/openshell-gateway/src/lib.rs           | 64 +++++++++++--------
 docs/reference/sandbox-compute-drivers.mdx    | 20 ++++--
 skills/debug-openshell-cluster/SKILL.md       |  4 ++
 tasks/scripts/windows-msvc.ps1                | 12 +++-
 12 files changed, 105 insertions(+), 44 deletions(-)

diff --git a/.agents/skills/build-openshell-mxc-windows/SKILL.md b/.agents/skills/build-openshell-mxc-windows/SKILL.md
index 8ce602ce9d..17d62a64f5 100644
--- a/.agents/skills/build-openshell-mxc-windows/SKILL.md
+++ b/.agents/skills/build-openshell-mxc-windows/SKILL.md
@@ -252,6 +252,13 @@ in the gateway build graph, but their Unix-socket standalone binaries do not.
 
 Windows must continue to reject unsupported compute drivers clearly.
 
+The gateway's `compute-driver-mxc` feature independently links and registers
+MXC on Windows. Each other `compute-driver-*` feature installs its own Windows
+rejection stub without linking that driver crate. The default
+`in-tree-compute-drivers` alias enables all five features. An MXC-only build
+uses `--no-default-features --features compute-driver-mxc` (add `telemetry`
+and `bundled-z3` as needed).
+
 | Driver | Windows build behavior | Runtime behavior |
 |---|---|---|
 | Docker | Driver crate excluded; gateway registration stub retained. | Gateway construction returns unsupported. |
@@ -263,11 +270,16 @@ The focused contract tasks for either native architecture run:
 
 ```text
 windows_builtin_compute_drivers_report_unsupported
+default_registry_contains_exactly_the_enabled_compute_drivers
 ```
 
-These tests are also included in the full x64 workspace test run. The focused
-task is available for local diagnosis; GitHub Actions does not re-run it after
-the full suite.
+The same tasks also run gateway library tests for protocol-only, MXC-only,
+Docker-stub-only, and MXC plus Docker-stub builds. Their logs use
+`test-<target>-selective-<variant>.log`.
+
+The default-feature tests are also included in the full workspace test run.
+The focused task is available for local diagnosis and selective-build
+validation; GitHub Actions does not re-run it after the full suite.
 
 ## Test Accounting Guidance
 
diff --git a/.github/workflows/branch-checks.yml b/.github/workflows/branch-checks.yml
index 6f941c89cb..15d49b82b3 100644
--- a/.github/workflows/branch-checks.yml
+++ b/.github/workflows/branch-checks.yml
@@ -189,6 +189,7 @@ jobs:
           cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-kubernetes
           cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-podman
           cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-vm
+          cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-mxc
           cargo test -p openshell-gateway --all-targets --no-default-features --features compute-driver-docker,compute-driver-vm
 
       - name: Verify the defaults-without-telemetry feature alias tracks the default feature set
diff --git a/Cargo.lock b/Cargo.lock
index c4ee4d0699..670f3bf053 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5811,6 +5811,7 @@ dependencies = [
  "log",
  "percent-encoding",
  "pin-project-lite",
+ "quinn",
  "rustls",
  "rustls-native-certs",
  "rustls-pki-types",
@@ -6123,6 +6124,7 @@ dependencies = [
  "aws-lc-rs",
  "log",
  "once_cell",
+ "ring",
  "rustls-pki-types",
  "rustls-webpki",
  "subtle",
diff --git a/README.md b/README.md
index 0e512589b0..70e6e5c09f 100644
--- a/README.md
+++ b/README.md
@@ -274,7 +274,7 @@ cargo build --release -p openshell-driver-vm --no-default-features --features de
 
 The resulting binaries contain no telemetry endpoint, no telemetry HTTP client, and no emission code. With telemetry compiled out, the gateway emits nothing and reports telemetry disabled to the sandboxes it launches. Cargo has no way to subtract a single default feature, so `defaults-without-telemetry` must be paired with `--no-default-features`; passing it on its own leaves the defaults in place and fails the build rather than producing a binary that still emits.
 
-The gateway also exposes separate Cargo features for its built-in compute drivers: `compute-driver-kubernetes`, `compute-driver-docker`, `compute-driver-podman`, and `compute-driver-vm`. Disable the default feature set, then enable only the drivers and telemetry mode required by the target binary. For example:
+The gateway also exposes separate Cargo features for its built-in compute drivers: `compute-driver-kubernetes`, `compute-driver-docker`, `compute-driver-podman`, `compute-driver-vm`, and `compute-driver-mxc`. Disable the default feature set, then enable only the drivers and telemetry mode required by the target binary. For example:
 
 ```shell
 # Docker only, with telemetry support.
@@ -282,9 +282,12 @@ cargo build --release -p openshell-gateway --no-default-features --features tele
 
 # Docker and VM only, with telemetry compiled out.
 cargo build --release -p openshell-gateway --no-default-features --features compute-driver-docker,compute-driver-vm
+
+# Windows MXC only, with telemetry support and bundled Z3.
+cargo build --release -p openshell-gateway --no-default-features --features telemetry,compute-driver-mxc,bundled-z3
 ```
 
-Regular builds still include all four drivers through the default `in-tree-compute-drivers` compatibility feature.
+Regular builds retain their platform driver set through the default `in-tree-compute-drivers` compatibility feature. On Windows, `compute-driver-mxc` selects MXC; the other four features install unsupported-driver stubs. On other platforms, MXC is excluded.
 
 Telemetry events are limited to anonymous operational categories and counts, such as sandbox lifecycle outcomes, provider profile buckets, policy decision counts, and aggregate network activity denial categories. OpenShell telemetry does not collect sandbox names or IDs, hostnames, file paths, binary paths, prompts, credentials, provider names, model names, or user content.
 
diff --git a/architecture/compute-runtimes.md b/architecture/compute-runtimes.md
index 69ebfe7071..2210a7d28f 100644
--- a/architecture/compute-runtimes.md
+++ b/architecture/compute-runtimes.md
@@ -135,9 +135,11 @@ compiled registration with the same name.
 
 The `openshell-gateway` composition crate exposes one feature per first-party
 registration: `compute-driver-kubernetes`, `compute-driver-docker`,
-`compute-driver-podman`, and `compute-driver-vm`. Builds can enable any subset.
-The default `in-tree-compute-drivers` feature remains an alias for all four
-and retains the Windows MXC registration and unsupported-driver stubs.
+`compute-driver-podman`, `compute-driver-vm`, and `compute-driver-mxc`. Builds
+can enable any subset. MXC links only on Windows; the other four features
+install rejection stubs on Windows and link their drivers on other platforms.
+The default `in-tree-compute-drivers` feature remains an alias for all five,
+preserving each platform's default registrations.
 `openshell-server` has no compute driver dependencies or backend-name dispatch.
 Protocol-only gateway builds disable the default features and link no
 compute-driver crates. E2E lanes compose that gateway with Docker, Podman,
diff --git a/architecture/windows-msvc-build.md b/architecture/windows-msvc-build.md
index cdea4a3fdc..dfcdbe6dd5 100644
--- a/architecture/windows-msvc-build.md
+++ b/architecture/windows-msvc-build.md
@@ -31,6 +31,14 @@ Windows. These registrations preserve config-file selection and reject
 unsupported drivers with a clear error without depending on their runtime
 crates.
 
+Each stub follows its corresponding `compute-driver-*` Cargo feature.
+`compute-driver-mxc` independently links and registers MXC, so a gateway built
+with only that feature has only the MXC registration. The default
+`in-tree-compute-drivers` alias enables all five features and preserves the
+existing MXC plus unsupported-driver registrations. The focused Windows
+contract tasks cover default, protocol-only, MXC-only, Docker-stub-only, and
+MXC plus Docker-stub compositions.
+
 The Windows lane does not build, release, package, or smoke-test standalone
 driver binaries for Docker, Kubernetes, Podman, or VM. Those binaries are Linux
 or macOS deliverables only.
diff --git a/crates/openshell-driver-mxc/Cargo.toml b/crates/openshell-driver-mxc/Cargo.toml
index 2f82e50e3b..1785c78133 100644
--- a/crates/openshell-driver-mxc/Cargo.toml
+++ b/crates/openshell-driver-mxc/Cargo.toml
@@ -14,7 +14,7 @@ repository.workspace = true
 name = "openshell_driver_mxc"
 
 [dependencies]
-openshell-core = { path = "../openshell-core" }
+openshell-core = { path = "../openshell-core", default-features = false }
 tokio = { workspace = true }
 tonic = { workspace = true }
 futures = { workspace = true }
diff --git a/crates/openshell-gateway/Cargo.toml b/crates/openshell-gateway/Cargo.toml
index 57742475df..ce3bf3b499 100644
--- a/crates/openshell-gateway/Cargo.toml
+++ b/crates/openshell-gateway/Cargo.toml
@@ -44,8 +44,9 @@ in-tree-compute-drivers = [
     "compute-driver-kubernetes",
     "compute-driver-podman",
     "compute-driver-vm",
-    "dep:openshell-driver-mxc",
+    "compute-driver-mxc",
 ]
+compute-driver-mxc = ["dep:openshell-driver-mxc"]
 compute-driver-docker = ["dep:openshell-driver-docker", "dep:openshell-otel"]
 compute-driver-kubernetes = ["dep:openshell-driver-kubernetes", "dep:openshell-otel"]
 compute-driver-podman = ["dep:openshell-driver-podman", "dep:openshell-otel"]
diff --git a/crates/openshell-gateway/src/lib.rs b/crates/openshell-gateway/src/lib.rs
index fed1b844be..bd05a27dac 100644
--- a/crates/openshell-gateway/src/lib.rs
+++ b/crates/openshell-gateway/src/lib.rs
@@ -20,7 +20,7 @@ compile_error!(
 mod vm;
 
 #[cfg(any(
-    all(target_os = "windows", feature = "in-tree-compute-drivers"),
+    all(target_os = "windows", feature = "compute-driver-mxc"),
     all(
         not(target_os = "windows"),
         any(
@@ -33,16 +33,11 @@ mod vm;
 ))]
 use openshell_core::telemetry::TelemetryComputeDriver;
 #[cfg(any(
-    all(target_os = "windows", feature = "in-tree-compute-drivers"),
-    all(
-        not(target_os = "windows"),
-        any(
-            feature = "compute-driver-docker",
-            feature = "compute-driver-kubernetes",
-            feature = "compute-driver-podman",
-            feature = "compute-driver-vm"
-        )
-    )
+    target_os = "windows",
+    feature = "compute-driver-docker",
+    feature = "compute-driver-kubernetes",
+    feature = "compute-driver-podman",
+    feature = "compute-driver-vm"
 ))]
 use openshell_server::ComputeDriverRegistration;
 use openshell_server::ComputeDriverRegistry;
@@ -62,12 +57,14 @@ pub fn install_default_compute_drivers() -> ComputeDriverRegistry {
         )
     ))]
     install_in_tree_compute_drivers(&mut registry);
-    #[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
+    #[cfg(all(target_os = "windows", feature = "compute-driver-mxc"))]
     install_mxc_compute_driver(&mut registry);
+    #[cfg(target_os = "windows")]
+    install_unsupported_windows_compute_drivers(&mut registry);
     registry
 }
 
-#[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
+#[cfg(all(target_os = "windows", feature = "compute-driver-mxc"))]
 fn install_mxc_compute_driver(registry: &mut ComputeDriverRegistry) {
     let registration = ComputeDriverRegistration::new("mxc", u16::MAX, None, MxcFactory)
         .expect("first-party driver name is valid")
@@ -76,8 +73,21 @@ fn install_mxc_compute_driver(registry: &mut ComputeDriverRegistry) {
     registry
         .install(registration)
         .expect("first-party driver names are unique");
+}
 
-    for name in ["docker", "kubernetes", "podman", "vm"] {
+#[cfg(target_os = "windows")]
+fn install_unsupported_windows_compute_drivers(registry: &mut ComputeDriverRegistry) {
+    let names: &[&str] = &[
+        #[cfg(feature = "compute-driver-docker")]
+        "docker",
+        #[cfg(feature = "compute-driver-kubernetes")]
+        "kubernetes",
+        #[cfg(feature = "compute-driver-podman")]
+        "podman",
+        #[cfg(feature = "compute-driver-vm")]
+        "vm",
+    ];
+    for &name in names {
         let registration = ComputeDriverRegistration::new(
             name,
             u16::MAX,
@@ -91,13 +101,13 @@ fn install_mxc_compute_driver(registry: &mut ComputeDriverRegistry) {
     }
 }
 
-#[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
+#[cfg(target_os = "windows")]
 #[derive(Clone, Copy)]
 struct UnsupportedWindowsFactory {
     name: &'static str,
 }
 
-#[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
+#[cfg(target_os = "windows")]
 #[async_trait::async_trait]
 impl openshell_server::ComputeDriverFactory for UnsupportedWindowsFactory {
     async fn build(
@@ -108,16 +118,16 @@ impl openshell_server::ComputeDriverFactory for UnsupportedWindowsFactory {
     }
 }
 
-#[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
+#[cfg(target_os = "windows")]
 fn unsupported_windows_compute_driver(name: &str) -> openshell_core::Error {
     openshell_core::Error::config(format!("compute driver '{name}' is unsupported on Windows"))
 }
 
-#[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
+#[cfg(all(target_os = "windows", feature = "compute-driver-mxc"))]
 #[derive(Clone, Copy)]
 struct MxcFactory;
 
-#[cfg(all(target_os = "windows", feature = "in-tree-compute-drivers"))]
+#[cfg(all(target_os = "windows", feature = "compute-driver-mxc"))]
 #[async_trait::async_trait]
 impl openshell_server::ComputeDriverFactory for MxcFactory {
     async fn build(
@@ -400,19 +410,17 @@ fn apply_guest_tls(
     }
 }
 
-#[cfg(all(test, target_os = "windows", feature = "in-tree-compute-drivers"))]
+#[cfg(all(test, target_os = "windows"))]
 mod windows_tests {
     use super::*;
 
     #[test]
     fn windows_builtin_compute_drivers_report_unsupported() {
         let registry = install_default_compute_drivers();
-        assert_eq!(
-            registry.installed_driver_names().collect::<Vec<_>>(),
-            ["docker", "kubernetes", "mxc", "podman", "vm"]
-        );
-
-        for name in ["docker", "kubernetes", "podman", "vm"] {
+        for name in registry
+            .installed_driver_names()
+            .filter(|name| *name != "mxc")
+        {
             let message = unsupported_windows_compute_driver(name).to_string();
             assert!(
                 message.contains("unsupported on Windows"),
@@ -422,7 +430,7 @@ mod windows_tests {
     }
 }
 
-#[cfg(all(test, not(target_os = "windows")))]
+#[cfg(test)]
 mod tests {
     use super::*;
 
@@ -433,6 +441,8 @@ mod tests {
             "docker",
             #[cfg(feature = "compute-driver-kubernetes")]
             "kubernetes",
+            #[cfg(all(target_os = "windows", feature = "compute-driver-mxc"))]
+            "mxc",
             #[cfg(feature = "compute-driver-podman")]
             "podman",
             #[cfg(feature = "compute-driver-vm")]
diff --git a/docs/reference/sandbox-compute-drivers.mdx b/docs/reference/sandbox-compute-drivers.mdx
index 98bcabab9a..885d897e4d 100644
--- a/docs/reference/sandbox-compute-drivers.mdx
+++ b/docs/reference/sandbox-compute-drivers.mdx
@@ -43,19 +43,27 @@ with the exact exit code. Driver and supervisor failures remain `Error`.
 ## Build with Selected Compute Drivers
 
 Source builds of `openshell-gateway` can include any subset of the Docker,
-Podman, Kubernetes, and VM drivers. Enable the corresponding
+Podman, Kubernetes, VM, and MXC drivers. Enable the corresponding
 `compute-driver-docker`, `compute-driver-podman`, `compute-driver-kubernetes`,
-or `compute-driver-vm` Cargo features. For example, build a Docker-only gateway
-with telemetry support:
+`compute-driver-vm`, or `compute-driver-mxc` Cargo features. For example, build
+a Docker-only gateway with telemetry support:
 
 ```shell
 cargo build --release -p openshell-gateway --no-default-features --features telemetry,compute-driver-docker
 ```
 
+On Windows, select only MXC with:
+
+```shell
+cargo build --release -p openshell-gateway --no-default-features --features telemetry,compute-driver-mxc,bundled-z3
+```
+
 The default `in-tree-compute-drivers` feature retains the full platform driver
-set, including MXC on Windows. The four selective features apply to non-Windows
-builds. A build with no default features and no driver features connects to
-external drivers only. Auto-detection probes only compiled registrations.
+set, including MXC on Windows. MXC links only on Windows. The other four
+features link drivers on non-Windows platforms; on Windows they install
+registrations that report the driver as unsupported. A build with no default
+features and no driver features connects to external drivers only.
+Auto-detection probes only compiled registrations.
 To select a driver omitted from a custom build, configure its external
 `socket_path` as described below.
 
diff --git a/skills/debug-openshell-cluster/SKILL.md b/skills/debug-openshell-cluster/SKILL.md
index effa670ba6..5b460ce7f6 100644
--- a/skills/debug-openshell-cluster/SKILL.md
+++ b/skills/debug-openshell-cluster/SKILL.md
@@ -30,6 +30,10 @@ configuration selects a driver that was not compiled in, the gateway treats
 the name as an external driver and reports a missing `socket_path` unless an
 endpoint is configured.
 
+On Windows, custom binaries can include MXC independently. Registrations for
+Docker, Podman, Kubernetes, and VM are rejection stubs when included; they do
+not enable those runtimes on Windows.
+
 See the [compute driver reference](https://docs.nvidia.com/openshell/latest/reference/sandbox-compute-drivers.md)
 for selective-build options and external-driver configuration.
 
diff --git a/tasks/scripts/windows-msvc.ps1 b/tasks/scripts/windows-msvc.ps1
index cab42fb719..63384e5cf7 100644
--- a/tasks/scripts/windows-msvc.ps1
+++ b/tasks/scripts/windows-msvc.ps1
@@ -536,7 +536,8 @@ function Invoke-UnsupportedContractTests([string] $RustTarget) {
     Assert-NativeTestTarget $RustTarget
 
     $tests = @(
-        "windows_builtin_compute_drivers_report_unsupported"
+        "windows_builtin_compute_drivers_report_unsupported",
+        "default_registry_contains_exactly_the_enabled_compute_drivers"
     )
     foreach ($test in $tests) {
         Invoke-VsCargo `
@@ -544,6 +545,15 @@ function Invoke-UnsupportedContractTests([string] $RustTarget) {
             -CargoArgs "cargo test -p openshell-gateway --target $RustTarget $test $Z3ServerFeatures" `
             -LogName "test-$RustTarget-unsupported-$test.log"
     }
+
+    foreach ($features in @("", "compute-driver-mxc", "compute-driver-docker", "compute-driver-mxc,compute-driver-docker")) {
+        $featureArgs = if ($features) { "--features $features" } else { "" }
+        $variant = if ($features) { $features.Replace(",", "-") } else { "protocol-only" }
+        Invoke-VsCargo `
+            -RustTarget $RustTarget `
+            -CargoArgs "cargo test -p openshell-gateway --lib --target $RustTarget --no-default-features $featureArgs $Z3ServerFeatures" `
+            -LogName "test-$RustTarget-selective-$variant.log"
+    }
 }
 
 function Get-Sha256([string] $Path) {