Close pass four: undetented host curve read, LiveValues guard, ordering assert, static-lane fix, docs

Points toPlain's exponent arm at the undetented curve map so host reads
match the editor; adds a sizeof guard plus field-poison test for
LiveValues::operator==; skips the model write when an automation value
hasn't moved; corrects five stale doc citations.

src/shell/instrument/processor_state.cpp

@@ -179,11 +179,12 @@ InstrumentParams ReaSamplerProcessor::instrumentParams(std::uint32_t& generation
     return params_;
 }
 
-void ReaSamplerProcessor::setInstrumentParams(const InstrumentParams& params) {
+std::uint32_t ReaSamplerProcessor::setInstrumentParams(const InstrumentParams& params) {
     // The exposed values alone, not the whole set: this funnel fires per mouse move on every live
     // knob and node drag, and InstrumentParams owns seven vectors — copying all of them to diff
     // 44 doubles is the cost, and the diff is what the notification actually needs.
     double before[kDeckParamSlots];
+    std::uint32_t generation;
     {
         std::lock_guard<std::mutex> lock(paramsMutex_);
         for (const instrument::param::ParamRow& row : instrument::param::exposedParams()) {
@@ -191,8 +192,10 @@ void ReaSamplerProcessor::setInstrumentParams(const InstrumentParams& params) {
         }
         params_ = params;
         // Bumped inside the lock with the write it names, so a reader taking the pair together
-        // can never see a generation that does not describe the set beside it.
-        ++paramsGeneration_;
+        // can never see a generation that does not describe the set beside it. Read back before
+        // the unlock for the same reason — a caller wanting ITS OWN write's generation must not
+        // race a second writer's bump between this function's unlock and its return.
+        generation = ++paramsGeneration_;
     }
     // Every writer of the parameter set — setState, the editor's commits, the bake's adopt —
     // funnels through here, so mirroring the limiter flag at this one point is what keeps the
@@ -214,6 +217,7 @@ void ReaSamplerProcessor::setInstrumentParams(const InstrumentParams& params) {
     // limiter mirror sits here: an internal write that skipped it would leave the host
     // displaying — and, on the next touch, re-imposing — the superseded value.
     notifyParamsFromModel(before, params);
+    return generation;
 }
 
 void ReaSamplerProcessor::flushLatencyRestart() {