ci: build Rust on Windows as part of CI to ensure we guard platform-specific code appropriately

.github/workflows/rust-ci.yml

@@ -41,6 +41,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        # Note: While Codex CLI does not support Windows today, we include
+        # Windows in CI to ensure the code at least builds there.
         include:
           - runner: macos-14
             target: aarch64-apple-darwin
@@ -50,6 +52,8 @@ jobs:
             target: x86_64-unknown-linux-musl
           - runner: ubuntu-24.04
             target: x86_64-unknown-linux-gnu
+          - runner: windows-latest
+            target: x86_64-pc-windows-msvc
 
     steps:
       - uses: actions/checkout@v4