diff --git a/Core/Scripts/MapDataParser.cs b/Core/Scripts/MapDataParser.cs
index b91f73a..8f05503 100644
--- a/Core/Scripts/MapDataParser.cs
+++ b/Core/Scripts/MapDataParser.cs
@@ -163,6 +163,24 @@ namespace IslaApocalypse.Core
 	{
 		public static WorldBlueprint LoadMapData(string seedStr)
 		{
+			// ISLA_BLUEPRINT_PATH (task 25, FILE SAFETY): load an explicit blueprint
+			// FILE instead of the seed-named one in the runtime root. Capture and A/B
+			// tooling points this straight at a batch folder, so it never has to copy
+			// a blueprint over — or delete — the file the developer has staged at the
+			// root to view a world in 3D. Loud, so a forgotten env var cannot be
+			// mistaken for the root blueprint.
+			string envPath = OS.GetEnvironment("ISLA_BLUEPRINT_PATH");
+			if (!string.IsNullOrEmpty(envPath))
+			{
+				if (File.Exists(envPath))
+				{
+					GD.Print($"[MapDataParser] ⚠ ISLA_BLUEPRINT_PATH override: loading '{envPath}' " +
+						"(NOT the runtime-root blueprint).");
+					return LoadMapDataFromPath(envPath);
+				}
+				GD.PrintErr($"[MapDataParser] ISLA_BLUEPRINT_PATH set but '{envPath}' does not exist — " +
+					"falling back to the runtime-root blueprint.");
+			}
 			string filePath = ProjectSettings.GlobalizePath($"user://MapData_Seed_{seedStr}.dat");
 			return LoadMapDataFromPath(filePath);
 		}
diff --git a/Tools/Scripts/MapGenerator.cs b/Tools/Scripts/MapGenerator.cs
index af9f073..eaa8b7c 100644
--- a/Tools/Scripts/MapGenerator.cs
+++ b/Tools/Scripts/MapGenerator.cs
@@ -335,12 +335,12 @@ public partial class MapGenerator : TextureRect
 		// 6. Pull the image from the invisible monitor and save it!
 		Image capture = offscreenVP.GetTexture().GetImage();
 		string seedStr = _noise.Seed.ToString();
-		string fileName = $"user://Map_Seed_{seedStr}_{label}.png";
+		string fileName = System.IO.Path.Combine(OutputDir(), $"Map_Seed_{seedStr}_{label}.png");
 
 		Error saveResult = capture.SavePng(fileName);
 
 		if (saveResult == Error.Ok)
-			GD.Print($"{T()} Map saved: {ProjectSettings.GlobalizePath(fileName)}");
+			GD.Print($"{T()} Map saved: {fileName}");
 		else
 			GD.PrintErr($"{T()} Failed to save map. Godot Error code: {saveResult}");
 
@@ -348,18 +348,40 @@ public partial class MapGenerator : TextureRect
 		offscreenVP.QueueFree();
 	}
 	
+	/// <summary>
+	/// Where generated artifacts go. Normally the runtime root (`user://`), but
+	/// ISLA_EXPORT_DIR redirects EVERYTHING this run writes — blueprints and stage
+	/// snapshots — into a task folder instead (task 25, FILE SAFETY). Batch and A/B
+	/// tooling sets it so a generation can never overwrite the blueprint the
+	/// developer has staged at the root to view a world in 3D, and so no cleanup
+	/// move/delete is needed afterwards. Loud on use.
+	/// </summary>
+	private string OutputDir()
+	{
+		string dir = OS.GetEnvironment("ISLA_EXPORT_DIR");
+		if (!string.IsNullOrEmpty(dir))
+		{
+			if (System.IO.Directory.Exists(dir)) return dir;
+			GD.PrintErr($"[MapGenerator] ISLA_EXPORT_DIR '{dir}' does not exist — writing to the runtime root instead.");
+		}
+		return ProjectSettings.GlobalizePath("user://");
+	}
+
 	private void ExportMapData()
 	{
 		string seedStr = _noise.Seed.ToString();
+		string outDir = OutputDir();
+		if (outDir != ProjectSettings.GlobalizePath("user://"))
+			GD.Print($"{T()} ⚠ ISLA_EXPORT_DIR override: writing artifacts to '{outDir}' (NOT the runtime root).");
 
 		// PRIMARY: the v2 tagged-section container (Core/Scripts/BLUEPRINT_FORMAT.md),
 		// under the name the server looks for.
-		string v2Path = ProjectSettings.GlobalizePath($"user://MapData_Seed_{seedStr}.dat");
+		string v2Path = System.IO.Path.Combine(outDir, $"MapData_Seed_{seedStr}.dat");
 		BlueprintWriter.WriteV2(v2Path, BuildBlueprint());
 
 		// SAFETY NET: the legacy v1 format beside it, until the developer has lived
 		// with v2 across several regenerations. Removal is a future task.
-		ExportMapDataV1(ProjectSettings.GlobalizePath($"user://MapData_Seed_{seedStr}_v1.dat"));
+		ExportMapDataV1(System.IO.Path.Combine(outDir, $"MapData_Seed_{seedStr}_v1.dat"));
 	}
 
 	/// <summary>
@@ -869,6 +891,9 @@ public partial class MapGenerator : TextureRect
 			SeaMarginM = ConfigManager.RiverSeaMargin,
 			TribWaterMinFlowPx = ConfigManager.RiverTribWaterMinFlow,
 			TribTaperPx = ConfigManager.RiverTribTaperPx,
+			FillFraction = ConfigManager.RiverFillFraction,
+			BankFlare = ConfigManager.RiverBankFlare,
+			BankMaxCutM = ConfigManager.RiverBankMaxCutM,
 			LakeMinTargetPx = ConfigManager.RiverLakeMinTargetPx
 		};
 		var st = RiverCarvePass.Apply(_heightMap, MapSize, isOcean, isClassifyWater,
@@ -898,7 +923,8 @@ public partial class MapGenerator : TextureRect
 			nextBodyId, st.Carved, seaMap, seaFlat,
 			_impactCenter.X, _impactCenter.Y,
 			_impactRadius * ConfigManager.CraterErosionCore,
-			ConfigManager.RiverStepDropM, ConfigManager.RiverWaterDepthM);
+			ConfigManager.RiverStepDropM, ConfigManager.RiverWaterDepthM,
+			ConfigManager.RiverFillFraction);
 		long riverWetPx = 0;
 		foreach (var reach in reaches)
 		{
@@ -921,7 +947,8 @@ public partial class MapGenerator : TextureRect
 		GD.Print($"{T()} [Rivers] water: {reaches.Count} stepped reaches ({tribReaches} on tributaries) " +
 			$"across {mainCarved} mains + {tribCarved} tributaries, {riverWetPx} wet px " +
 			$"({tribWet} tributary), step drop {ConfigManager.RiverStepDropM:F2} m, depth {ConfigManager.RiverWaterDepthM:F1} m, " +
-			$"trib flow threshold {ConfigManager.RiverTribWaterMinFlow} px taper {ConfigManager.RiverTribTaperPx} px.");
+			$"trib flow threshold {ConfigManager.RiverTribWaterMinFlow} px taper {ConfigManager.RiverTribTaperPx} px, " +
+			$"fill {ConfigManager.RiverFillFraction:P0} of bed depth (min {ConfigManager.RiverWaterDepthM:F1} m), bank flare {ConfigManager.RiverBankFlare:F1}x (shoulder cut cap {ConfigManager.RiverBankMaxCutM:F1} m).");
 
 		GD.Print($"{T()} [Rivers] v1 '{ConfigManager.RiverRoutingStyle}': plan {st.AnalysisSeconds:F1}s, " +
 			$"routing {st.RoutingSeconds:F1}s, carve {st.CarveSeconds:F1}s " +