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/inferproxy/src/main.rs

@@ -7,7 +7,11 @@ use std::process;
 use inferproxy::{Limits, serve};
 
 fn main() {
-    let args: Vec<String> = env::args().collect();
+    // `args_os`, because `args` panics on an argument that is not UTF-8.
+    let args: Vec<String> = match env::args_os().map(|a| a.into_string()).collect() {
+        Ok(args) => args,
+        Err(_) => usage(),
+    };
     let mut listen: Option<String> = None;
     let mut upstream: Option<String> = None;
     let mut i = 1;

crates/inferproxy/tests/args_os.rs

@@ -0,0 +1,14 @@
+//! An argument that is not UTF-8 is a usage error, not a panic (M3a review finding 7).
+
+use std::ffi::OsStr;
+use std::os::unix::ffi::OsStrExt;
+use std::process::Command;
+
+#[test]
+fn an_argument_that_is_not_utf8_is_a_usage_error() {
+    let out = Command::new(env!("CARGO_BIN_EXE_inferproxy"))
+        .args([OsStr::new("--listen"), OsStr::from_bytes(b"/tmp/\xff.sock")])
+        .output()
+        .unwrap();
+    assert_eq!(out.status.code(), Some(2));
+}