v0.3.3: consumer post-sync verify даже для v0.3 per-slot events

Bug: cudaEventRecord(event[slot]) overwrites previous state каждый publish.
Когда producer wraps ring (~640ms при ring=16), event[slot] re-recorded для
new content. Consumer's pending cudaStreamWaitEvent satisfied новым signal —
consumer reads slot[slot_idx] thinking it's target_seq, реально получает
seq+ring_size content (stale-by-1-wrap drift).

После 50k+ wraps в long-running pipeline (9h uptime) drift накапливается:
output stream имеет 60-70% duplicate frames (vs 10% сразу после restart).

Симптом: TV picture freezes на 1-2 sec периодически. Encoder fps=25 stable
(content duplicates same PTS-advance), но motion choppy на 8-9 fps real.

Fix: unconditional post-sync verify (atomic re-read slot.seq после event wait).
Если producer wrap occurred — slot.seq != target_seq → continue к новому
target_seq. Cheap (one atomic load), correctness > perf.

Verified: после deploy с fresh pipeline, 18-sec sample = 4% duplicates
(vs 8.4% при том же setup но без fix).

Proper v0.4 fix: per-slot+per-publish event pool с unique handle per cycle.
Текущий v0.3.3 — sufficient mitigation для current production scale.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

libcuframes/src/consumer.c

@@ -322,15 +322,22 @@ int cuframes_subscriber_next(cuframes_subscriber_t *sub,
                 if (cerr != cudaSuccess) return CUFRAMES_ERR_CUDA;
             }
 
-            /* TOCTOU защита (v0.2 fallback only): legacy single event signals
-             * для последнего published frame. v0.3 per-slot events не нужны
-             * этой проверки — event[slot] = strict slot ordering guarantee. */
-            if (!sub->has_slot_events) {
-                uint64_t verify_seq = atomic_load_explicit(&sub->hdr->slots[slot_idx].seq,
-                                                           memory_order_acquire);
-                if (verify_seq != target_seq) {
-                    continue;
-                }
+            /* TOCTOU защита — unconditional (v0.2 и v0.3 обa). v0.3 per-slot
+             * events НЕ guaranty ordering: cudaEventRecord overwrites previous
+             * state каждый publish. Если producer wrapped ring пока consumer
+             * ждал event sync, slot[slot_idx] уже содержит seq > target.
+             * Event signal от nового publish satisfies stale wait — consumer
+             * читает new content thinking it's old (lazy consumption).
+             *
+             * Симптом в long-running pipeline: 50k+ ring wraps накапливают drift,
+             * output stream duplicates 60-70% frames despite stable encoder fps.
+             *
+             * Proper v0.4 fix: per-slot+per-publish event handle (event pool).
+             * Сейчас — post-sync verify catches main race window. */
+            uint64_t verify_seq = atomic_load_explicit(&sub->hdr->slots[slot_idx].seq,
+                                                       memory_order_acquire);
+            if (verify_seq != target_seq) {
+                continue;
             }
 
             /* Fill frame_out */