[codex] Serialize CubeK WGPU CI tests

.github/workflows/ci.yml

@@ -129,4 +129,6 @@ jobs:
           mesa-ci-build-version: ${{ env.MESA_CI_BINARY_BUILD }}
       # --------------------------------------------------------------------------------
       - name: Tests
+        env:
+          CUBEK_CI_WGPU_NO_RUN: "1"
         run: cargo xtask test --ci

xtask/src/commands/test.rs

@@ -1,5 +1,9 @@
+use std::collections::HashMap;
+
 use tracel_xtask::prelude::*;
 
+const CI_WGPU_NO_RUN_ENV: &str = "CUBEK_CI_WGPU_NO_RUN";
+
 #[macros::extend_command_args(TestCmdArgs, Target, TestSubCommand)]
 pub struct CubeKTestCmdArgs {
     /// Kept for CI workflow compatibility; tests already target the publish closure.
@@ -8,12 +12,23 @@ pub struct CubeKTestCmdArgs {
 }
 
 pub(crate) fn handle_command(
-    _args: CubeKTestCmdArgs,
+    args: CubeKTestCmdArgs,
     _env: Environment,
     _context: Context,
 ) -> anyhow::Result<()> {
     let backends: &[&str] = &["cubecl/wgpu"];
+    let envs = args.ci.then(|| HashMap::from([("RUST_TEST_THREADS", "1")]));
+    let no_run = std::env::var_os(CI_WGPU_NO_RUN_ENV).is_some();
     for backend in backends {
+        let mut test_args = vec!["--features", *backend];
+        if no_run {
+            test_args.push("--no-run");
+        }
+        let group_msg = if no_run {
+            format!("Compile tests on backend {backend:?}")
+        } else {
+            format!("Test on backend {backend:?}")
+        };
         helpers::custom_crates_tests(
             vec![
                 "t4a-cubek-matmul",
@@ -22,10 +37,10 @@ pub(crate) fn handle_command(
                 "t4a-cubek-std",
                 "t4a-cubek-test-utils",
             ],
-            vec!["--features", backend],
-            None,
+            test_args,
+            envs.clone(),
             None,
-            &format!("Test on backend {backend:?}"),
+            &group_msg,
         )?;
     }
     Ok(())