loopd, bxctl, inferproxy: read args_os instead of panicking

M3a review finding 7, for the other three roles. loopd keeps its config path
as a path; bxctl and inferproxy take text arguments and answer one that is
not UTF-8 with their usage.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/loopd/src/main.rs

@@ -16,11 +16,12 @@ use loopd::selftest::{SelfTestError, run};
 use loopd::tools::{Registry, ToolPort};
 
 fn main() -> ExitCode {
-    let args: Vec<String> = std::env::args().skip(1).collect();
-    let args: Vec<&str> = args.iter().map(String::as_str).collect();
-    match args.as_slice() {
-        ["selftest", "--config", path] => run_selftest(path),
-        ["serve", "--config", path] => run_serve(path),
+    // `args_os`: the config path need not be UTF-8, and `args` would panic on one that is not.
+    let args: Vec<std::ffi::OsString> = std::env::args_os().skip(1).collect();
+    let words: Vec<Option<&str>> = args.iter().map(|a| a.to_str()).collect();
+    match (words.as_slice(), args.get(2)) {
+        ([Some("selftest"), Some("--config"), _], Some(path)) => run_selftest(Path::new(path)),
+        ([Some("serve"), Some("--config"), _], Some(path)) => run_serve(Path::new(path)),
         _ => {
             eprintln!("usage: loopd selftest --config <path>");
             eprintln!("usage: loopd serve --config <path>");
@@ -46,8 +47,8 @@ fn run_selftest_check(client: &Client) -> Result<(), SelfTestError> {
     }
 }
 
-fn run_selftest(path: &str) -> ExitCode {
-    let cfg = match Config::load(Path::new(path)) {
+fn run_selftest(path: &Path) -> ExitCode {
+    let cfg = match Config::load(path) {
         Ok(cfg) => cfg,
         Err(e) => {
             eprintln!("loopd: {e}");
@@ -62,8 +63,8 @@ fn run_selftest(path: &str) -> ExitCode {
     }
 }
 
-fn run_serve(path: &str) -> ExitCode {
-    let cfg = match Config::load(Path::new(path)) {
+fn run_serve(path: &Path) -> ExitCode {
+    let cfg = match Config::load(path) {
         Ok(cfg) => cfg,
         Err(e) => {
             eprintln!("loopd: {e}");

crates/loopd/tests/args_os.rs

@@ -0,0 +1,36 @@
+//! A config path that is not UTF-8 is read as a path, not a panic (M3a review finding 7).
+
+use std::ffi::OsStr;
+use std::os::unix::ffi::OsStrExt;
+use std::process::Command;
+
+#[test]
+fn a_config_path_that_is_not_utf8_is_read_as_a_path() {
+    let path = std::env::temp_dir().join(OsStr::from_bytes(b"loopd-missing-\xff.toml"));
+    let out = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .args([
+            OsStr::new("selftest"),
+            OsStr::new("--config"),
+            path.as_os_str(),
+        ])
+        .output()
+        .unwrap();
+    assert_eq!(
+        out.status.code(),
+        Some(1),
+        "a config error, not a panic (101)"
+    );
+}
+
+#[test]
+fn a_flag_that_is_not_utf8_is_a_usage_error() {
+    let out = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .args([
+            OsStr::from_bytes(b"serve\xff"),
+            OsStr::new("--config"),
+            OsStr::new("x"),
+        ])
+        .output()
+        .unwrap();
+    assert_eq!(out.status.code(), Some(2));
+}