fix bug where selecting the same ship again in a shipyard clears the layout and resets the progress

src/lib/sim/BuildingSystem.cpp

@@ -419,6 +419,12 @@ void BuildingSystem::setRecipe(BuildingId id, const std::string& recipeId)
     {
         if (site.id == id)
         {
+            // No-op if the recipe is unchanged, so a redundant selection does
+            // not wipe an already-configured ship layout.
+            if (site.recipeId == recipeId)
+            {
+                return;
+            }
             site.recipeId = recipeId;
             site.shipLayout = std::nullopt;
             return;
@@ -430,6 +436,12 @@ void BuildingSystem::setRecipe(BuildingId id, const std::string& recipeId)
     {
         if (building.id == id)
         {
+            // No-op if the recipe is unchanged, so a redundant selection does
+            // not wipe an already-configured ship layout or reset buffers.
+            if (building.recipeId == recipeId)
+            {
+                return;
+            }
             building.recipeId = recipeId;
             building.shipLayout = std::nullopt;
             building.inputBuffer.counts.clear();

src/test/ShipModuleTest.cpp

@@ -292,6 +292,38 @@ TEST_CASE("Shipyard: setRecipe clears ship layout", "[modules][shipyard]")
     CHECK_FALSE(b2->shipLayout.has_value());
 }
 
+TEST_CASE("Shipyard: setRecipe with unchanged recipe keeps ship layout",
+          "[modules][shipyard]")
+{
+    Simulation sim(loadConfig(), 42);
+    const BuildingDef* yardDef = findShipyardDef(sim.config());
+    REQUIRE(yardDef != nullptr);
+
+    const BuildingId yardId = placeShipyard(sim, *yardDef);
+    SimulationTestAccess::buildings(sim).setRecipe(yardId,"interceptor");
+
+    ShipLayoutConfig layout;
+    PlacedModule pm;
+    pm.moduleId = "armor_plate";
+    pm.position = QPoint(0, 0);
+    pm.rotation = Rotation::East;
+    layout.placedModules.push_back(pm);
+    SimulationTestAccess::buildings(sim).setShipLayout(yardId, layout);
+
+    const Building* b1 = sim.buildings().findBuilding(yardId);
+    REQUIRE(b1 != nullptr);
+    REQUIRE(b1->shipLayout.has_value());
+
+    // Re-selecting the same recipe must be a no-op and preserve the layout.
+    SimulationTestAccess::buildings(sim).setRecipe(yardId,"interceptor");
+
+    const Building* b2 = sim.buildings().findBuilding(yardId);
+    REQUIRE(b2 != nullptr);
+    REQUIRE(b2->shipLayout.has_value());
+    REQUIRE(b2->shipLayout->placedModules.size() == 1);
+    CHECK(b2->shipLayout->placedModules[0].moduleId == "armor_plate");
+}
+
 // ---------------------------------------------------------------------------
 // Weapon modifier simulation tests
 // ---------------------------------------------------------------------------