toolkit: no thread panic in http_fetch, no casts, exact egress-proxy form

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/toolkit/src/main.rs

@@ -18,7 +18,8 @@ fn main() -> ExitCode {
 /// The `egress-proxy --socket <path> --allow <list>` form. Anything else, including a program name
 /// that is not `egress-proxy`, returns `None` so the tool form handles it.
 fn parse_egress_proxy(args: &[OsString]) -> Option<ExitCode> {
-    if args.first()?.as_bytes() != b"egress-proxy" {
+    // Exactly five words: a longer list is not this form, and goes to the tool form (exit 2).
+    if args.len() != 5 || args.first()?.as_bytes() != b"egress-proxy" {
         return None;
     }
     // The form is `egress-proxy --socket <path> --allow <list>`, in that order.