Phase 4+5: WebAudio I/O shim + verify DAW checklist — live=export, order, fader, PDC, smoke

native_bridge/src/RenderFxJob.cpp

@@ -1144,6 +1144,12 @@ struct RealtimeFxChain::Impl {
     };
     struct Chain { std::vector<Entry> entries; };
 
+    // SET_PARAM chờ chain swap (setParam tới trước setChain): worker áp sau
+    // khi swap — không mất param race lúc khởi động.
+    struct PendingParam { int slot; std::string key; double value; };
+    std::mutex pmutex_;                    // guards pending_
+    std::vector<PendingParam> pending_;
+
     std::mutex mutex_;               // guards chain_ / retired_
     std::shared_ptr<Chain> chain_;
     std::shared_ptr<Chain> retired_; // dtor deferred to the worker thread
@@ -1224,9 +1230,14 @@ void RealtimeFxChain::setParam(int slot, const std::string& key, double value) {
     if (!impl_) return;
     std::shared_ptr<Impl::Chain> c;
     { std::lock_guard<std::mutex> lk(impl_->mutex_); c = impl_->chain_; }
-    if (!c || slot < 0 || (size_t)slot >= c->entries.size()) return;
-    auto& e = c->entries[(size_t)slot];
-    if (e.bfx) e.bfx->setParam(key, value);
+    if (c && slot >= 0 && (size_t)slot < c->entries.size()) {
+        auto& e = c->entries[(size_t)slot];
+        if (e.bfx) e.bfx->setParam(key, value);
+        return;
+    }
+    // Chain chưa swap (SET_PARAM tới trước setChain) — stash, worker áp sau swap.
+    std::lock_guard<std::mutex> lk(impl_->pmutex_);
+    impl_->pending_.push_back({slot, key, value});
 }
 
 uint64_t RealtimeFxChain::chainGen() {
@@ -1325,6 +1336,16 @@ void RealtimeFxChain::Impl::workerLoop() {
             retired_ = std::move(chain_);  // old chain destroyed on THIS thread
             chain_ = std::move(next);
         }
+        {
+            // Áp param chờ (đăng ký trước khi chain tồn tại).
+            std::lock_guard<std::mutex> lk(pmutex_);
+            for (const auto& p : pending_) {
+                if (p.slot < 0 || (size_t)p.slot >= chain_->entries.size()) continue;
+                auto& e = chain_->entries[(size_t)p.slot];
+                if (e.bfx) e.bfx->setParam(p.key, p.value);
+            }
+            pending_.clear();
+        }
         gen_.fetch_add(1, std::memory_order_release);  // loop báo lại latency
     }
 #ifdef _WIN32