Fix zigbuild detection: use cargo zigbuild --help

cargo-zigbuild --version doesn't work reliably in all PATH configs.
Use cargo zigbuild --help instead, which uses cargo's subcommand
discovery to find the cargo-zigbuild binary. Also verify zigbuild
actually works in CI after installation.

https://claude.ai/code/session_01EcsZDNeWn56wFqryb4Wq7r

.github/workflows/ci.yml

@@ -51,7 +51,8 @@ jobs:
         # ziglang pip package installs as python-zig, symlink to zig for cargo-zigbuild
         sudo ln -sf "$(which python-zig)" /usr/local/bin/zig
         zig version
-        command -v cargo-zigbuild || cargo install cargo-zigbuild
+        cargo-zigbuild --version 2>/dev/null || cargo install cargo-zigbuild
+        cargo-zigbuild --version
 
     - run: make check-fmt
     - run: make lint

src/builder/mod.rs

@@ -32,8 +32,8 @@ impl RustBuilder {
 
     /// Check that cargo-zigbuild is available, or bail with install instructions.
     fn require_zigbuild() -> Result<()> {
-        let available = Command::new("cargo-zigbuild")
-            .arg("--version")
+        let available = Command::new("cargo")
+            .args(["zigbuild", "--help"])
             .stdout(std::process::Stdio::null())
             .stderr(std::process::Stdio::null())
             .status()