Load engines from TOML and improve scenario audio and carb tuning

Migrate 32 engine definitions into validated startup-loaded TOML files and separate configuration and snapshots from scenario assembly. Add camera-based stereo propagation from shared pipe geometry, preserve exhaust character, tune carburetor mixtures and idle, use ignition cuts for carb engines, and support returning to the scenario menu.

Validation: full Windows build and all 14 CTest checks passed.

tests/outdoor_audio_tests.cpp

@@ -1,5 +1,9 @@
 #include "FluidSim/OutdoorAudio.hpp"
 #include "FluidSim/ReedValve.hpp"
+#include "FluidSim/Scenario.hpp"
+#include "FluidSim/ScenarioGeometry.hpp"
+#include "FluidSim/DesktopScenario.hpp"
+#include "FluidSim/ScenarioCatalog.hpp"
 #include <algorithm>
 #include <cmath>
 #include <iostream>
@@ -98,6 +102,85 @@ int main() {
     }
     check(right < left, "source on right does not reach right ear first");
 
+    // A moved listener must converge to the same propagation as one created
+    // there, including the reversed ear orientation and the reflected field.
+    auto moved_config=stereo_config;
+    moved_config.listener={-.5f,1.5f,4};
+    moved_config.listener_right={-1,0,0};
+    OutdoorAudio moving(44100,stereo_config),destination(44100,moved_config);
+    moving.set_listener({moved_config.listener,moved_config.listener_right});
+    for(auto* p:{&moving,&destination})p->set_monitor_filter(false);
+    for(int i=0;i<44100;++i) {moving.process(0,0);destination.process(0,0);}
+    for(int i=0;i<6000;++i) {
+        const auto a=moving.process(0,.001f),b=destination.process(0,.001f);
+        check(std::abs(a.left-b.left)<2e-7f && std::abs(a.right-b.right)<2e-7f,
+              "moving listener does not update direct/reflected stereo paths");
+    }
+    // Exercise rapid pose changes while a wet tail is still ringing.
+    for(int i=0;i<22050;++i) {
+        if(i%735==0) {
+            const float angle=i*.0002f;
+            moving.set_listener({{3*std::sin(angle),1,3*std::cos(angle)},
+                                 {std::cos(angle),0,-std::sin(angle)}});
+        }
+        const auto a=moving.process(0,.001f);
+        check(std::isfinite(a.left) && std::isfinite(a.right) &&
+              std::abs(a.left)<1 && std::abs(a.right)<1,"moving wet paths became unstable");
+    }
+
+    // Source relocation must use geometry without resetting audio state.
+    auto source_config=config();source_config.exhaust_position={2,1,-1};
+    OutdoorAudio relocated(44100,config()),fixed_source(44100,source_config);
+    relocated.set_source_positions({source_config.intake_position,source_config.exhaust_position,
+                                   source_config.second_exhaust_position});
+    for(int i=0;i<44100;++i) {relocated.process(0,0);fixed_source.process(0,0);}
+    for(int i=0;i<3000;++i) {
+        const auto a=relocated.process(0,.001f),b=fixed_source.process(0,.001f);
+        check(std::abs(a.left-b.left)<2e-7f && std::abs(a.right-b.right)<2e-7f,
+              "relocated mouth does not match world source position");
+    }
+    ScenarioSnapshot geometry;
+    geometry.two_stroke=true;
+    auto mouths=scenario_sound_sources(geometry);
+    check(mouths[0].x==-1.05f && mouths[1].x==1.45f && mouths[1].y==.23f,
+          "two-stroke mouths are not on the drawn pipe ends");
+    geometry.two_stroke=false;geometry.cylinder_count=8;geometry.layout=EngineLayout::V;
+    geometry.v8_headers=true;geometry.dual_exhaust=true;
+    mouths=scenario_sound_sources(geometry);
+    check(mouths[1].x==2.94f && mouths[1].z==-.39f && mouths[2].z==.39f,
+          "dual V8 outlets are not at their separate tailpipe mouths");
+    geometry.v8_headers=false;geometry.dual_exhaust=false;geometry.silencers=true;
+    geometry.cylinder_count=4;geometry.layout=EngineLayout::Inline;
+    const auto& e=geometry.exhaust_config;
+    mouths=scenario_sound_sources(geometry);
+    check(std::abs(mouths[1].x-(.74f+e.inlet_length+e.resonator.length+e.connecting_length+
+                              e.muffler.length+e.outlet_length))<1e-6f,
+          "silenced exhaust source does not follow the configured pipe length");
+    // Crossing a reflecting plane must not turn its virtual image into a
+    // source that arrives before the actual pipe mouth.
+    auto behind_config=config();behind_config.listener={-4,1,0};
+    OutdoorAudio behind_wall(44100,behind_config);
+    behind_wall.set_monitor_filter(false);
+    for(int i=0;i<4410;++i)behind_wall.process(0,0);
+    int first_behind=-1;
+    for(int i=0;i<1000;++i) {
+        const auto a=behind_wall.process(0,.001f);
+        if(first_behind<0 && std::abs(a.left)>1e-9f)first_behind=i;
+    }
+    check(first_behind==514,"reflection crosses wall and precedes the physical source");
+
+    for(const auto& example:scenario_examples()) {
+        DesktopScenario scenario(example.kind,example.two,example.exhaust,example.junctions,example.engine);
+        scenario.set_listener({{2,1,3},{1,0,0}});
+        const auto snapshot=scenario.snapshot();
+        const auto sources=scenario_sound_sources(snapshot);
+        for(auto source:sources)
+            check(std::isfinite(source.x) && std::isfinite(source.y) && std::isfinite(source.z),
+                  "catalog scenario has an invalid sound source");
+        const auto frame=scenario.process();
+        check(std::isfinite(frame.left) && std::isfinite(frame.right),"catalog listener wiring failed");
+    }
+
     ReedValve reed;
     for (int i = 0; i < 10000; i++)
         reed.step(1.f / 44100, 100);