fix(node): bound the FFI advanced dispatch queue too

The conversion to dispatch_capacity covered three of four
CallbackDispatcher::spawn sites. node.rs's advanced (TransientLocal) arm
still passed DISPATCH_UNBOUNDED, so an FFI raw subscriber declaring
KeepLast(n) got an unbounded queue fed by remote samples -- the exact
defect the other three sites were changed to remove.

Two shipped doc comments and the PR description asserted 'both paths pass
dispatch_capacity'. There are four paths, and one did not.

Nothing caught it because the ffi feature is enabled by no crate, so this
arm is never compiled on the PR gate (#291). Found by an audit agent
reading the diff against its own description.

Author: YuanYuYuan

crates/hiroz/src/node.rs

@@ -642,7 +642,7 @@ impl ZNode {
         use crate::{
             entity::{EndpointEntity, EndpointKind},
             pubsub::{
-                CallbackDispatcher, DISPATCH_UNBOUNDED, SubscriberHandle,
+                CallbackDispatcher, SubscriberHandle,
                 apply_transient_local_sub, dispatch_capacity, qos_needs_advanced,
             },
             topic_name,
@@ -678,8 +678,11 @@ impl ZNode {
         // never runs on a thread that is inside a hiroz publish — see
         // `pubsub::CallbackDispatcher`.
         let subscriber = if qos_needs_advanced(&entity.qos) {
-            let dispatcher =
-                CallbackDispatcher::spawn(&qualified_topic, raw_callback, DISPATCH_UNBOUNDED)?;
+            let dispatcher = CallbackDispatcher::spawn(
+                &qualified_topic,
+                raw_callback,
+                dispatch_capacity(&entity.qos),
+            )?;
             let subscriber = self
                 .session
                 .declare_subscriber((*topic_ke).clone())

crates/hiroz/src/pubsub.rs

@@ -392,9 +392,15 @@ impl CallbackDispatcher {
     /// [`Self::local_only_shim`] to obtain the callback to hand to zenoh.
     ///
     /// `capacity` is the number of undelivered samples retained before the
-    /// oldest is dropped. Both paths pass [`dispatch_capacity`], so a callback
-    /// subscriber retains what its history QoS declares regardless of which
-    /// path it takes. See the "Backpressure" section.
+    /// oldest is dropped. **All four construction sites pass
+    /// [`dispatch_capacity`]** — the plain and advanced arms of both the typed
+    /// builder (this module) and the FFI raw subscriber (`node.rs`) — so a
+    /// callback subscriber retains what its history QoS declares regardless of
+    /// which path it takes. See the "Backpressure" section.
+    ///
+    /// The FFI advanced arm was missed when the other three were converted, and
+    /// nothing caught it: the `ffi` feature is enabled by no crate, so that arm
+    /// is not compiled on the PR gate at all (#291).
     pub(crate) fn spawn<F>(topic: &str, handler: Arc<F>, capacity: usize) -> Result<Self>
     where
         F: Fn(Sample) + Send + Sync + 'static,