write the review-classifier fake agent scripts from a child process

swarm-review-classifier/src/acp.rs

@@ -274,8 +274,6 @@ impl Sink for FinalText {
 
 #[cfg(test)]
 mod tests {
-    use std::os::unix::fs::PermissionsExt as _;
-
     use swarm_wire::review_classifier::Prices;
 
     use super::*;
@@ -347,12 +345,10 @@ done
     fn acp(dir: &Path) -> (Acp<Arc<Costs>>, Arc<Costs>) {
         let script = dir.join("agent.sh");
         let log = dir.join("log");
-        std::fs::write(
+        crate::test_script::write_executable(
             &script,
-            AGENT.replacen("log=\"$1\"", &format!("log='{}'", log.display()), 1),
-        )
-        .expect("written");
-        std::fs::set_permissions(&script, std::fs::Permissions::from_mode(0o755)).expect("chmod");
+            &AGENT.replacen("log=\"$1\"", &format!("log='{}'", log.display()), 1),
+        );
         let costs = Arc::new(Costs::default());
         let acp = Acp {
             program: PathBuf::from("/nix/store/x-opencode/bin/opencode"),

swarm-review-classifier/src/main.rs

@@ -25,6 +25,8 @@ mod child_env;
 mod cost;
 mod prompt;
 mod run;
+#[cfg(test)]
+mod test_script;
 
 /// The cert-auth role this service logs in to the store as. `swarm-bao.nix`
 /// writes it, matching the leaf's subject.

swarm-review-classifier/src/run.rs

@@ -856,12 +856,9 @@ printf '{"type":"result","subtype":"success","is_error":false,"result":"ok"}\n'
 
     #[tokio::test]
     async fn claude_reads_the_shared_context_and_the_question_as_separate_blocks() {
-        use std::os::unix::fs::PermissionsExt as _;
-
         let tmp = tempfile::tempdir().expect("a dir");
         let script = tmp.path().join("claude.sh");
-        std::fs::write(&script, CLAUDE).expect("written");
-        std::fs::set_permissions(&script, std::fs::Permissions::from_mode(0o755)).expect("chmod");
+        crate::test_script::write_executable(&script, CLAUDE);
         let claude = Claude {
             program: PathBuf::from("claude"),
             trampoline: script.clone(),

swarm-review-classifier/src/test_script.rs

@@ -0,0 +1,25 @@
+//! Fake agent scripts for the tests.
+
+use std::path::Path;
+
+/// Write the script `body` to `path` as an executable, from a child process
+/// rather than from this one: a write fd on it held here could be inherited
+/// by a child another test thread forks, and exec'ing a file some process
+/// still holds open for writing fails with `ETXTBSY`.
+///
+/// # Panics
+///
+/// If `/bin/sh` cannot run or the write fails.
+pub fn write_executable(path: &Path, body: &str) {
+    let status = std::process::Command::new("/bin/sh")
+        .args([
+            "-c",
+            r#"printf '%s' "$1" > "$2" && chmod 755 "$2""#,
+            "sh",
+            body,
+        ])
+        .arg(path)
+        .status()
+        .expect("run /bin/sh");
+    assert!(status.success(), "writing {} failed", path.display());
+}