Omit sensitive process inputs from spawn trace logs (#60034)

## Why

Command arguments and environment variables can contain credentials. Logging them when spawning a child process can expose those credentials in trace output.

## What changed

Replace argument, `arg0`, and environment contents in `spawn_child_async` trace logs with argument and environment counts and a flag indicating whether `arg0` is overridden. Keep the program, working directory, network sandbox policy, and stdio policy in the trace.

## Testing

Add a regression test that captures trace output and verifies that argument, `arg0`, and environment canaries are omitted while the program path remains visible.

GitOrigin-RevId: c317e7dcc6fd8b4eafb6fcfe98dc8634807c813d

codex-rs/core/src/spawn_tests.rs

@@ -0,0 +1,33 @@
+#![cfg(test)]
+
+use super::*;
+use std::sync::Arc;
+
+#[tokio::test]
+async fn spawn_trace_omits_sensitive_inputs() -> std::io::Result<()> {
+    let dir = tempfile::tempdir()?;
+    let capture = tempfile::NamedTempFile::new()?;
+    let subscriber = tracing_subscriber::fmt()
+        .with_max_level(tracing::Level::TRACE)
+        .with_writer(Arc::new(capture.reopen()?))
+        .finish();
+    let _guard = tracing::subscriber::set_default(subscriber);
+
+    let result = spawn_child_async(SpawnChildRequest {
+        program: dir.path().join("missing-test-program"),
+        args: vec!["canary-argument".into()],
+        arg0: Some("canary-arg0"),
+        cwd: AbsolutePathBuf::from_absolute_path(dir.path())?,
+        network_sandbox_policy: NetworkSandboxPolicy::Enabled,
+        network: None,
+        stdio_policy: StdioPolicy::RedirectForShellTool,
+        env: HashMap::from([("SETTING".into(), "canary-env-value".into())]),
+    })
+    .await;
+    assert!(result.is_err());
+
+    let logs = std::fs::read_to_string(capture.path())?;
+    assert!(logs.contains("missing-test-program"));
+    assert!(!logs.contains("canary-"));
+    Ok(())
+}