refactor(media): fix stale Task-1 forward-ref comment + strengthen Reflex test 6

Fix 1: removes a Task-1 forward-reference comment in reflex.rs that
contradicted itself once Task 2 added the imports it claimed were
"intentionally absent."

Fix 2: MockPipe::on_pcm_frame was a no-op, so Test 6 could not
distinguish "delegated to inner" from "dropped on the floor." Add
last_inbound_frame: Option<PcmFrame> capture + assert delegation so
the reflex's inbound-passthrough guarantee is verified, not assumed.

Addresses the two Important findings from the Task 2 review.

Signed-off-by: Aaron D. Lee <himself@adlee.work>

crates/rutster-media/src/reflex.rs

@@ -31,13 +31,6 @@ use std::time::Instant;
 use crate::pcm::{AudioPipe, AudioSink, AudioSource, PcmFrame};
 use tokio::sync::mpsc;
 
-// Task 2 will reintroduce these when `Reflex<P>` lands: `Reflex` holds the
-// `mpsc::Receiver<AdvisoryEvent>` drained on each 20 ms tick, and the
-// `P: AudioPipe` generic bound names `AudioPipe`/`AudioSource`/`AudioSink`
-// (plus `PcmFrame` for the source/sink methods it delegates to). They are
-// intentionally absent here to keep Task 1 self-contained (no `tokio` dep
-// added yet — Task 2 adds it together with the type that consumes it).
-
 /// A turn-event advisory from the brain. The brain decodes its own
 /// speech-to-text / VAD results and forwards these; the FOB *owns*
 /// turn-taking and acts on them (slice-3 §4.3 — OpenAI Realtime
@@ -254,6 +247,10 @@ mod tests {
         queued: std::collections::VecDeque<PcmFrame>,
         flush_calls: usize,
         barge_calls: usize,
+        /// Last inbound frame observed via `on_pcm_frame` — proves the
+        /// reflex delegates caller→brain audio to the inner pipe rather
+        /// than dropping it on the floor (Test 6's delegation check).
+        last_inbound_frame: Option<PcmFrame>,
     }
 
     impl MockPipe {
@@ -262,6 +259,7 @@ mod tests {
                 queued: Default::default(),
                 flush_calls: 0,
                 barge_calls: 0,
+                last_inbound_frame: None,
             }
         }
         fn push_frame(&mut self, frame: PcmFrame) {
@@ -276,8 +274,8 @@ mod tests {
     }
 
     impl AudioSink for MockPipe {
-        fn on_pcm_frame(&mut self, _frame: PcmFrame) {
-            // capture count via separate test-side state if needed
+        fn on_pcm_frame(&mut self, frame: PcmFrame) {
+            self.last_inbound_frame = Some(frame);
         }
     }
 
@@ -416,6 +414,11 @@ mod tests {
         reflex.next_pcm_frame(); // drain + apply barge
         // Inbound frame arrives — must pass through to inner.
         reflex.on_pcm_frame(PcmFrame::zeroed());
-        // Inner captured it (no panic, no drop).
+        // The inbound frame is observable on the inner pipe — proof the
+        // reflex delegates to inner, never gates the caller→brain path.
+        assert!(
+            reflex.inner.last_inbound_frame.is_some(),
+            "inbound audio must reach inner even during barge"
+        );
     }
 }