Implemented the urgent stability/performance pass.

What I fixed:
Removed the warning-calculation N+1 queries. Occupancy warnings now use one floor-plan participant query instead of per-scene character/asset lookups.
Added SceneFloorPlanParticipant_ListByFloorPlan to the existing migration script with SET ANSI_NULLS ON and SET QUOTED_IDENTIFIER ON.
Reapplied the migration locally.
Confirmed FloorPlanBlock_Save, FloorPlan_GetEditor, and the new participant proc have quoted identifiers enabled.
Reduced drag/resize freeze risk by throttling expensive geometry recalculation to animation frames instead of every pointer event.
Added a final geometry refresh on pointer-up/cancel before autosave.
Improved autosave failure visibility by showing the real error in the editor, not just leaving status stuck.
Made Occupancy mode view/staging only:Blocks no longer start drag/resize in Occupancy mode.
Resize handles are hidden.
Structural toolbox is hidden.
Plan canvas expands to use the freed width.
Structure mode restores normal editing.

Verification:
dotnet build PlotLine.slnx passes with 0 warnings and 0 errors.
Non-destructive SQL smoke test of FloorPlanBlock_Save against the Lounge block passed inside a transaction and rolled back.
Confirmed the Lounge block stayed unchanged after the rollback.
Reapplied 081_FloorPlanFloorDescriptionAndOccupancyWarnings.sql successfully.
Files changed:
[Repositories.cs](C:/Source/PlotLine/PlotLine/Data/Repositories.cs)
[CoreModels.cs](C:/Source/PlotLine/PlotLine/Models/CoreModels.cs)
[CoreServices.cs](C:/Source/PlotLine/PlotLine/Services/CoreServices.cs)
[081 SQL migration](C:/Source/PlotLine/PlotLine/Sql/081_FloorPlanFloorDescriptionAndOccupancyWarnings.sql)
[Edit.cshtml](C:/Source/PlotLine/PlotLine/Views/FloorPlans/Edit.cshtml)
[site.css](C:/Source/PlotLine/PlotLine/wwwroot/css/site.css)
[site.min.css](C:/Source/PlotLine/PlotLine/wwwroot/css/site.min.css)
Manual browser QA still needed for the exact drag/add/reload flow, but the code path and SQL save path are now stabilized.

PlotLine/Data/Repositories.cs

@@ -89,6 +89,7 @@ public interface ISceneFloorPlanOccupancyRepository
 {
     Task<IReadOnlyList<SceneFloorPlanOccupancy>> ListBySceneAsync(int sceneId);
     Task<IReadOnlyList<SceneFloorPlanOccupancy>> ListByFloorPlanAsync(int floorPlanId);
+    Task<IReadOnlyList<FloorPlanOccupancyParticipant>> ListParticipantsByFloorPlanAsync(int floorPlanId);
     Task SaveAsync(int sceneId, int? floorPlanId, int? initialFloorPlanFloorId, IEnumerable<SceneFloorPlanOccupancy> occupancyRows);
 }
 
@@ -2649,6 +2650,16 @@ public sealed class SceneFloorPlanOccupancyRepository(ISqlConnectionFactory conn
         return rows.ToList();
     }
 
+    public async Task<IReadOnlyList<FloorPlanOccupancyParticipant>> ListParticipantsByFloorPlanAsync(int floorPlanId)
+    {
+        using var connection = connectionFactory.CreateConnection();
+        var rows = await connection.QueryAsync<FloorPlanOccupancyParticipant>(
+            "dbo.SceneFloorPlanParticipant_ListByFloorPlan",
+            new { FloorPlanID = floorPlanId },
+            commandType: CommandType.StoredProcedure);
+        return rows.ToList();
+    }
+
     public async Task SaveAsync(int sceneId, int? floorPlanId, int? initialFloorPlanFloorId, IEnumerable<SceneFloorPlanOccupancy> occupancyRows)
     {
         using var connection = connectionFactory.CreateConnection();

PlotLine/Models/CoreModels.cs

@@ -1274,6 +1274,14 @@ public sealed class SceneFloorPlanOccupancy
     public DateTime? ModifiedDate { get; set; }
 }
 
+public sealed class FloorPlanOccupancyParticipant
+{
+    public int SceneID { get; set; }
+    public string EntityType { get; set; } = string.Empty;
+    public int EntityID { get; set; }
+    public string DisplayName { get; set; } = string.Empty;
+}
+
 public static class FloorPlanTransitionPositions
 {
     public const string Centre = "Centre";

PlotLine/Services/CoreServices.cs

@@ -7733,8 +7733,6 @@ public sealed class FloorPlanService(
     IProjectRepository projects,
     ISceneRepository scenes,
     ISceneFloorPlanOccupancyRepository sceneOccupancy,
-    ICharacterRepository characters,
-    IAssetRepository assets,
     IFloorPlanRepository floorPlans,
     ILocationRepository locations,
     IFloorPlanBackgroundImageService backgroundImages,
@@ -7771,6 +7769,7 @@ public sealed class FloorPlanService(
         var orderedFloors = data.Floors.OrderBy(x => x.SortOrder).ThenBy(x => x.Name).ToList();
         var occupancyScenes = await scenes.ListByFloorPlanAsync(floorPlanId);
         var occupancyRows = await sceneOccupancy.ListByFloorPlanAsync(floorPlanId);
+        var occupancyParticipants = await sceneOccupancy.ListParticipantsByFloorPlanAsync(floorPlanId);
         var firstBlockByLocation = data.Blocks
             .GroupBy(x => x.LocationID)
             .ToDictionary(x => x.Key, x => x.OrderBy(block => block.Y).ThenBy(block => block.X).First());
@@ -7863,12 +7862,12 @@ public sealed class FloorPlanService(
                 .Where(x => x is not null)
                 .Cast<FloorPlanOccupancyTokenViewModel>()
                 .ToList(),
-            OccupancyWarnings = await BuildFloorPlanOccupancyWarningsAsync(occupancyScenes, occupancyRows, data.Blocks, data.Transitions)
+            OccupancyWarnings = BuildFloorPlanOccupancyWarnings(occupancyParticipants, occupancyRows, data.Blocks, data.Transitions)
         };
     }
 
-    private async Task<IReadOnlyList<FloorPlanOccupancyWarningViewModel>> BuildFloorPlanOccupancyWarningsAsync(
+    private static IReadOnlyList<FloorPlanOccupancyWarningViewModel> BuildFloorPlanOccupancyWarnings(
-        IReadOnlyList<Scene> occupancyScenes,
+        IReadOnlyList<FloorPlanOccupancyParticipant> participants,
         IReadOnlyList<SceneFloorPlanOccupancy> occupancyRows,
         IReadOnlyList<FloorPlanBlock> blocks,
         IReadOnlyList<FloorPlanTransition> transitions)
@@ -7881,37 +7880,38 @@ public sealed class FloorPlanService(
             .SelectMany(x => new[] { x.FromLocationID, x.ToLocationID })
             .ToHashSet();
 
-        foreach (var scene in occupancyScenes)
+        foreach (var sceneGroup in participants.GroupBy(x => x.SceneID))
         {
-            var sceneRows = occupancyRows.Where(x => x.SceneID == scene.SceneID).ToList();
+            var sceneId = sceneGroup.Key;
+            var sceneRows = occupancyRows.Where(x => x.SceneID == sceneId).ToList();
             var occupiedCharacterIds = sceneRows.Where(x => x.CharacterID.HasValue).Select(x => x.CharacterID!.Value).ToHashSet();
             var occupiedAssetIds = sceneRows.Where(x => x.StoryAssetID.HasValue).Select(x => x.StoryAssetID!.Value).ToHashSet();
 
-            var sceneCharacters = await characters.ListSceneCharactersAsync(scene.SceneID);
+            foreach (var character in sceneGroup
-            foreach (var character in sceneCharacters
+                .Where(x => string.Equals(x.EntityType, "Character", StringComparison.OrdinalIgnoreCase))
-                .GroupBy(x => x.CharacterID)
+                .GroupBy(x => x.EntityID)
                 .Select(x => x.First())
-                .Where(x => !occupiedCharacterIds.Contains(x.CharacterID)))
+                .Where(x => !occupiedCharacterIds.Contains(x.EntityID)))
             {
                 warnings.Add(new FloorPlanOccupancyWarningViewModel
                 {
-                    SceneID = scene.SceneID,
+                    SceneID = sceneId,
                     Severity = "warning",
-                    Message = $"{character.CharacterName} appears in this scene but has no floor-plan location."
+                    Message = $"{character.DisplayName} appears in this scene but has no floor-plan location."
                 });
             }
 
-            var sceneAssets = await assets.ListEventsBySceneAsync(scene.SceneID);
+            foreach (var asset in sceneGroup
-            foreach (var asset in sceneAssets
+                .Where(x => string.Equals(x.EntityType, "Asset", StringComparison.OrdinalIgnoreCase))
-                .GroupBy(x => x.StoryAssetID)
+                .GroupBy(x => x.EntityID)
                 .Select(x => x.First())
-                .Where(x => !occupiedAssetIds.Contains(x.StoryAssetID)))
+                .Where(x => !occupiedAssetIds.Contains(x.EntityID)))
             {
                 warnings.Add(new FloorPlanOccupancyWarningViewModel
                 {
-                    SceneID = scene.SceneID,
+                    SceneID = sceneId,
                     Severity = "warning",
-                    Message = $"{asset.AssetName} appears in this scene but has no floor-plan location."
+                    Message = $"{asset.DisplayName} appears in this scene but has no floor-plan location."
                 });
             }
 
@@ -7919,7 +7919,7 @@ public sealed class FloorPlanService(
             {
                 warnings.Add(new FloorPlanOccupancyWarningViewModel
                 {
-                    SceneID = scene.SceneID,
+                    SceneID = sceneId,
                     Severity = "warning",
                     Message = $"{OccupantName(row)} is assigned to {row.LocationName}, but that location is not placed on this floor plan."
                 });
@@ -7934,7 +7934,7 @@ public sealed class FloorPlanService(
             {
                 warnings.Add(new FloorPlanOccupancyWarningViewModel
                 {
-                    SceneID = scene.SceneID,
+                    SceneID = sceneId,
                     FloorPlanFloorID = floorId,
                     Severity = "info",
                     Message = "Some occupants are on other floors."
@@ -7947,7 +7947,7 @@ public sealed class FloorPlanService(
                 {
                     warnings.Add(new FloorPlanOccupancyWarningViewModel
                     {
-                        SceneID = scene.SceneID,
+                        SceneID = sceneId,
                         FloorPlanFloorID = floorId,
                         Severity = "info",
                         Message = $"{row.LocationName} has no visible entrance."

PlotLine/Sql/081_FloorPlanFloorDescriptionAndOccupancyWarnings.sql

@@ -1,3 +1,8 @@
+SET ANSI_NULLS ON;
+GO
+SET QUOTED_IDENTIFIER ON;
+GO
+
 IF COL_LENGTH(N'dbo.FloorPlanFloors', N'Description') IS NULL
     ALTER TABLE dbo.FloorPlanFloors ADD Description nvarchar(max) NULL;
 GO
@@ -119,6 +124,38 @@ BEGIN
 END;
 GO
 
+CREATE OR ALTER PROCEDURE dbo.SceneFloorPlanParticipant_ListByFloorPlan
+    @FloorPlanID int
+AS
+BEGIN
+    SET NOCOUNT ON;
+
+    SELECT DISTINCT
+        s.SceneID,
+        N'Character' AS EntityType,
+        sc.CharacterID AS EntityID,
+        c.CharacterName AS DisplayName
+    FROM dbo.Scenes s
+    INNER JOIN dbo.SceneCharacters sc ON sc.SceneID = s.SceneID
+    INNER JOIN dbo.Characters c ON c.CharacterID = sc.CharacterID
+    WHERE s.FloorPlanID = @FloorPlanID
+      AND s.IsArchived = 0
+
+    UNION
+
+    SELECT DISTINCT
+        s.SceneID,
+        N'Asset' AS EntityType,
+        ae.StoryAssetID AS EntityID,
+        sa.AssetName AS DisplayName
+    FROM dbo.Scenes s
+    INNER JOIN dbo.AssetEvents ae ON ae.SceneID = s.SceneID
+    INNER JOIN dbo.StoryAssets sa ON sa.StoryAssetID = ae.StoryAssetID
+    WHERE s.FloorPlanID = @FloorPlanID
+      AND s.IsArchived = 0;
+END;
+GO
+
 CREATE OR ALTER PROCEDURE dbo.FloorPlanFloor_Get
     @FloorPlanFloorID int
 AS

PlotLine/Views/FloorPlans/Edit.cshtml

@@ -1059,6 +1059,7 @@
             let saveInFlight = false;
             let saveAgain = false;
             let refreshAfterSave = false;
+            let geometryRefreshQueued = false;
             const backgroundTimers = new Map();
             const gridCoordinatesStorageKey = "floorPlan.showGridCoordinates";
             const referenceFloorStorageKey = "floorPlan.referenceFloor";
@@ -1124,6 +1125,11 @@
                 saveButtons.forEach(button => {
                     button.hidden = isOccupancy;
                 });
+                if (isOccupancy) {
+                    pointerState = null;
+                    blocks.forEach(item => item.classList.remove("selected"));
+                    if (noSelection) noSelection.classList.remove("d-none");
+                }
                 refreshOccupancyTrays();
             }
 
@@ -1295,6 +1301,10 @@
                 alert.textContent = message || "Save failed";
             }
 
+            function clearWorkspaceError() {
+                editor.querySelector("[data-workspace-error]")?.remove();
+            }
+
             function cleanupModalArtifacts() {
                 document.querySelectorAll(".modal-backdrop").forEach(backdrop => backdrop.remove());
                 document.body.classList.remove("modal-open");
@@ -1407,6 +1417,7 @@
                         throw new Error(result.message || "Unable to save layout.");
                     }
 
+                    clearWorkspaceError();
                     setSaveStatus("saved");
                     if (refreshAfterSave) {
                         refreshAfterSave = false;
@@ -1414,6 +1425,7 @@
                     }
                 } catch (error) {
                     setSaveStatus("failed", error.message || "Save failed");
+                    showWorkspaceError(error.message || "Save failed");
                 } finally {
                     saveInFlight = false;
                     saveButtons.forEach(button => button.disabled = false);
@@ -1562,6 +1574,7 @@
 
             function attachBlockEvents(block) {
                 block.addEventListener("pointerdown", event => {
+                    if (editor.classList.contains("floor-plan-editor--occupancy")) return;
                     selectBlock(block);
                     const grid = gridFor(block);
                     if (!grid) return;
@@ -1819,7 +1832,16 @@
                 if (fields.y) fields.y.value = next.y;
                 if (fields.w) fields.w.value = next.w;
                 if (fields.h) fields.h.value = next.h;
+                scheduleGeometryRefresh();
+            }
+
+            function scheduleGeometryRefresh() {
+                if (geometryRefreshQueued) return;
+                geometryRefreshQueued = true;
+                window.requestAnimationFrame(() => {
+                    geometryRefreshQueued = false;
                     checkOverlaps();
+                });
             }
 
             function rangesOverlap(aStart, aLength, bStart, bLength) {
@@ -2445,6 +2467,10 @@
 
             editor.addEventListener("pointermove", event => {
                 if (!pointerState) return;
+                if (editor.classList.contains("floor-plan-editor--occupancy")) {
+                    pointerState = null;
+                    return;
+                }
                 const currentCell = cellFromPointer(pointerState.grid, event);
                 const dx = currentCell.x - pointerState.start.x;
                 const dy = currentCell.y - pointerState.start.y;
@@ -2466,6 +2492,7 @@
             editor.addEventListener("pointerup", () => {
                 if (pointerState) {
                     const floorId = pointerState.block.dataset.floorId;
+                    checkOverlaps();
                     markDirty();
                     refreshTransitionDestination(floorId);
                 }
@@ -2474,6 +2501,7 @@
             editor.addEventListener("pointercancel", () => {
                 if (pointerState) {
                     const floorId = pointerState.block.dataset.floorId;
+                    checkOverlaps();
                     markDirty();
                     refreshTransitionDestination(floorId);
                 }

PlotLine/wwwroot/css/site.css

@@ -4510,6 +4510,10 @@ body.dragging-location [data-drag-type="location"] {
   grid-template-columns: minmax(0, 1fr) minmax(320px, 360px);
 }
 
+.floor-plan-editor--occupancy .floor-plan-layout {
+  grid-template-columns: minmax(0, 1fr);
+}
+
 .floor-plan-editor-toolbar {
   background: rgba(255, 255, 255, .92);
   border: 1px solid var(--border-color, #d8ded9);
@@ -5341,12 +5345,17 @@ body.dragging-location [data-drag-type="location"] {
 
 .floor-plan-editor--occupancy .floor-plan-block {
   cursor: default;
+  touch-action: auto;
 }
 
 .floor-plan-editor--occupancy .floor-plan-resize-handle {
   display: none;
 }
 
+.floor-plan-editor--occupancy .floor-plan-side-panel {
+  display: none;
+}
+
 .floor-plan-occupancy-tray {
   position: absolute;
   z-index: 14;