fix(server): CLIENT TRACKING unreachable on monoio runtime (H-3 reorder regression)

CHANGELOG.md

@@ -6,6 +6,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed — CLIENT TRACKING dead on the monoio runtime (H-3 reorder regression)
+
+- Since the H-3 ACL reorder (#258), `CLIENT TRACKING ON|OFF` answered
+  `ERR unknown subcommand 'TRACKING'` on the monoio runtime (the production
+  default) at every shard count: `try_handle_client_admin` runs before
+  `try_handle_client_tracking` in the frame loop and its unknown-subcommand
+  fallback consumed TRACKING before the dedicated handler could see it.
+  RESP3 invalidation push was therefore entirely unavailable. Invisible to CI
+  because the test matrix exercises the tokio handler (`handler_sharded`),
+  whose intercept ordering differs.
+- `try_handle_client_admin` now falls through for TRACKING (both handlers are
+  post-ACL, so the H-3 deniability guarantee is unchanged). Re-greens all 5
+  `client_tracking_invalidation` black-box tests on monoio.
+
 ### Fixed — `txn_kv_wiring` integration test port-collision flake
 
 - `start_txn_server` picked a port from a throwaway `bind(:0)` probe, dropped

src/server/conn/handler_monoio/dispatch.rs

@@ -854,6 +854,14 @@ pub(super) fn try_handle_client_admin(
     }
     if let Some(sub) = cmd_args.first() {
         if let Some(sub_bytes) = extract_bytes(sub) {
+            // TRACKING is owned by `try_handle_client_tracking`, which runs
+            // AFTER this handler in the frame loop (both are post-ACL). The
+            // unknown-subcommand fallback below must not swallow it — that
+            // regression (H-3 reorder, #258) made CLIENT TRACKING answer
+            // "unknown subcommand" on the entire monoio runtime.
+            if sub_bytes.eq_ignore_ascii_case(b"TRACKING") {
+                return false;
+            }
             if sub_bytes.eq_ignore_ascii_case(b"LIST") {
                 crate::client_registry::update(client_id, |e| {
                     e.live.touch(