topology: early-exit resolve_recipient before topology.json read (argus on #703)

hive-c0re/src/topology.rs

@@ -76,11 +76,20 @@ pub fn parent_of(name: &str) -> Option<String> {
 ///
 /// Returns an owned `String` for the rewritten recipient so callers
 /// can plug it straight into [`crate::broker::Broker::send`] without
-/// borrow-juggling around the temporary lookup. Cheap — the resolved
-/// path clones twice in the worst case (parent name + return), no-op
-/// in the common case (recipient already a real label).
+/// borrow-juggling around the temporary lookup.
+///
+/// Fast path: ordinary recipient names (the overwhelming majority of
+/// sends) short-circuit before touching the disk — only `<parent>`
+/// triggers the `read()` of `topology.json`. Sentinel-free traffic
+/// pays a single string compare; the disk read is amortised across
+/// every `<parent>` send (per argus on #703#issuecomment-8750).
 #[must_use]
 pub fn resolve_recipient(sender: &str, to: &str) -> String {
+    // Early exit: only sentinel recipients need topology lookup. This
+    // keeps the cost of a normal `send` at one string comparison.
+    if to != hive_sh4re::PARENT_RECIPIENT {
+        return to.to_owned();
+    }
     resolve_recipient_in(&read(), sender, to)
 }