Fix deterministic live weather rewind

src/render/Viewer.cpp

@@ -407,12 +407,12 @@ void Viewer::liveStepForward() {
     liveAdvance(liveRate, liveRate);
 }
 
-// Step everything back: restore the most recent snapshot strictly before the current time (clock +
+// Step everything back: restore the newest snapshot at or before the current time (clock +
 // weather + storms) -- so storms reverse whether they were born while stepping or during a run. If
 // the history is exhausted, fall back to rewinding the deterministic sky only.
 void Viewer::liveStepBack() {
     paused = true;
-    while (!wxUndo.empty() && wxUndo.back().t >= liveTime - 1e-6) wxUndo.pop_back();  // drop any future frames
+    while (!wxUndo.empty() && wxUndo.back().t > liveTime + 1e-6) wxUndo.pop_back();   // drop only true future frames
     if (!wxUndo.empty()) {
         WxFrame f = wxUndo.back(); wxUndo.pop_back();
         liveTime = f.t;

src/sim/Planet.hpp

@@ -220,7 +220,7 @@ private:
     // Weather (Live World; saved v10). sHasWeather latches once spun up/loaded.
     std::vector<double>  sHumidity, sCloud, sRain;
     bool                 sHasWeather = false;
-    // Moving weather systems (transient agents; not saved). Separate RNG keeps tectonic
+    // Moving weather systems (saved with weather state). Separate RNG keeps tectonic
     // determinism intact (seeded from cfg.seed in initWeather).
     std::vector<WeatherSystem> sStorms;
     uint32_t                   sWeatherRng  = 1;

src/sim/PlanetTypes.hpp

@@ -28,7 +28,7 @@ enum class PlateType { Oceanic, Continental };
 // A moving weather system (Live World): a drifting low-pressure disturbance that travels with the
 // steering wind and stamps clouds & rain onto the weather fields. Geometry is fixed, so this is a
 // world-object agent (a point on the sphere, like a moon), not a cell. The intense tropical ones
-// (strength past weatherHurricaneStrength) are hurricanes/typhoons. Transient -- not saved.
+// (strength past weatherHurricaneStrength) are hurricanes/typhoons. Saved with the weather state.
 struct WeatherSystem {
     uint32_t id = 0;         // stable id (for the viewer follow-cam; assigned at spawn)
     Vec3   pos;              // unit position on the sphere

test_weather.cpp

@@ -22,6 +22,24 @@ static void check(bool cond, const char* what) {
     if (!cond) ++failures;
 }
 
+static bool sameStorms(const std::vector<WeatherSystem>& a, const std::vector<WeatherSystem>& b) {
+    if (a.size() != b.size()) return false;
+    for (size_t i = 0; i < a.size(); ++i) {
+        if (a[i].id != b[i].id
+            || a[i].pos.x != b[i].pos.x || a[i].pos.y != b[i].pos.y || a[i].pos.z != b[i].pos.z
+            || a[i].strength != b[i].strength || a[i].radius != b[i].radius
+            || a[i].age != b[i].age || a[i].life != b[i].life || a[i].spin != b[i].spin
+            || a[i].tropical != b[i].tropical) return false;
+    }
+    return true;
+}
+
+static bool sameWeatherSnapshot(const WeatherSnapshot& a, const WeatherSnapshot& b) {
+    return a.humidity == b.humidity && a.cloud == b.cloud && a.rain == b.rain
+        && sameStorms(a.storms, b.storms)
+        && a.rng == b.rng && a.nextId == b.nextId;
+}
+
 // Run a fixed weather sequence on a planet (returns whether rain ever fell, max cloud + storms).
 static void runWeather(Planet& p, bool& everRained, double& maxCloud, int& maxStorms) {
     p.initWeather();
@@ -139,6 +157,19 @@ int main() {
         check(rt, "captureWeather/restoreWeather round-trips the full weather state");
     }
 
+    std::printf("Weather: snapshot deterministic replay\n");
+    {
+        Planet wc; wc.generate(cfg); wc.initWeather();
+        for (int k = 0; k < 90; ++k) { wc.computeInsolation(0.25, std::fmod(0.2 + 0.01 * k, 1.0)); wc.stepWeather(1.0); }
+        WeatherSnapshot snap = wc.captureWeather();
+        for (int k = 0; k < 180; ++k) { wc.computeInsolation(0.25, std::fmod(0.4 + 0.01 * k, 1.0)); wc.stepWeather(1.0); }
+        WeatherSnapshot first = wc.captureWeather();
+        wc.restoreWeather(snap);
+        for (int k = 0; k < 180; ++k) { wc.computeInsolation(0.25, std::fmod(0.4 + 0.01 * k, 1.0)); wc.stepWeather(1.0); }
+        WeatherSnapshot second = wc.captureWeather();
+        check(sameWeatherSnapshot(first, second), "restored weather snapshot replays storms and RNG exactly");
+    }
+
     std::printf(failures ? "\nSOME WEATHER CHECKS FAILED (%d)\n" : "\nALL WEATHER CHECKS PASSED\n", failures);
     return failures ? 1 : 0;
 }