Fix defensive bounds checks found in review: plate indexing, war/diplomacy load, map zoom reset

- PlanetDrift.cpp: guard cells[i].plateId before indexing plates[] in advect(),
  matching the bounds-checking convention used elsewhere in plate lifecycle code.
- Panels.cpp: same guard in cellInfo() for the cell-info panel's plate lookup.
- PlanetIO.cpp: range-check War.attacker/.defender and DiploTie.a/.b against
  settlements.size() on load, matching the validation already done for
  sSettleAllegiance.
- Viewer.cpp: reset mapZoom/mapPanX/mapPanY in regenWorld() so a zoomed 2D map
  doesn't strand the view on reseed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/render/Panels.cpp

@@ -34,7 +34,8 @@ static int drawWrapped(const std::string& text, int x, int y, int font, Color co
 static std::vector<std::string> cellInfo(const Planet& p, int i, double elev, double age) {
     const Cell& c = p.cells[i];
     double lon, lat; dirToLonLat(c.unit, lon, lat);
-    const Plate& pl = p.plates[c.plateId];
+    static const Plate kUnknownPlate{};   // defensive: a cell should always own a valid plate
+    const Plate& pl = (c.plateId >= 0 && c.plateId < (int)p.plates.size()) ? p.plates[c.plateId] : kUnknownPlate;
     const int n = (int)p.cells.size();
     auto sized = [&](const std::vector<double>& v) { return (int)v.size() == n; };
     std::vector<std::string> L;

src/render/Viewer.cpp

@@ -284,6 +284,7 @@ void Viewer::regenWorld() {                 // after generate(): geometry change
     buildDriftArrows(planet, driftR, driftArrows, plateLabels);
     buildMap2D(planet, mapRect, map2D);
     selectedCell = -1; subgrids.clear();
+    mapZoom = 1.0; mapPanX = 0.0; mapPanY = 0.0;   // drop any 2D-map zoom/pan from the old world
     settled = false; settleRun = 0; formAccum = 0.0; stepCount = 0; paused = false;
     liveWorld = false; followId = 0; wxUndo.clear(); events.clear(); nextEventId = 1; // reseed/regen drops back to World Creation
     liveInfoTab = 0; eventRowRects.clear(); eventRowIndices.clear();

src/sim/PlanetDrift.cpp

@@ -34,8 +34,12 @@ void Planet::advect(double dtMy) {
     std::vector<Vec3>    vel(n);
     for (int i = 0; i < n; ++i) {
         oP[i] = cells[i].plateId; oE[i] = cells[i].elevation; oA[i] = cells[i].geoAge; oO[i] = cells[i].oceanic;
-        const Plate& p = plates[cells[i].plateId];
-        vel[i] = (p.driftAxis * p.angSpeed).cross(cells[i].unit) * R;
+        if (cells[i].plateId >= 0 && cells[i].plateId < (int)plates.size()) {
+            const Plate& p = plates[cells[i].plateId];
+            vel[i] = (p.driftAxis * p.angSpeed).cross(cells[i].unit) * R;
+        } else {
+            vel[i] = Vec3();   // defensive: a cell should always own a valid plate
+        }
     }
 
     for (int c = 0; c < n; ++c) {

src/sim/PlanetIO.cpp

@@ -756,6 +756,8 @@ bool Planet::readState(std::istream& is, bool hasBiome, bool hasBiota, bool hasM
             readPod(is, w.id); readPod(is, w.attacker); readPod(is, w.defender);
             readPod(is, w.startYear); readPod(is, w.warscore); readPod(is, w.battles);
             if (!is || !std::isfinite(w.warscore)) return false;
+            if (w.attacker < 0 || w.attacker >= (int)settlements.size()
+                || w.defender < 0 || w.defender >= (int)settlements.size()) return false;
         }
         readPod(is, sWarRng); readPod(is, sWarNextId);
         if (!sWarRng) sWarRng = cfg.seed ? (cfg.seed ^ 0x5A7B0A11u) : 0x5A7B0A11u;
@@ -771,6 +773,8 @@ bool Planet::readState(std::istream& is, bool hasBiome, bool hasBiota, bool hasM
             readPod(is, t.truceUntil); uint8_t k = 0; readPod(is, k);
             t.kind = (k <= (uint8_t)DiploKind::Rival) ? (DiploKind)k : DiploKind::Neutral;
             if (!is || !std::isfinite(t.attitude)) return false;
+            if (t.a < 0 || t.a >= (int)settlements.size()
+                || t.b < 0 || t.b >= (int)settlements.size()) return false;
         }
     }
     computeBiotaDensity();                  // derived density scalars for the colour views