Consolidate Odysseus agent harness and tool contracts

static/js/editor/tools/lasso.js

@@ -13,6 +13,7 @@
  * }} deps
  */
 import { state } from '../state.js';
+import { selectionModeForEvent } from '../selection-modifiers.js';
 import { canvasCoords } from '../canvas-coords.js';
 import { buildLassoMask } from './lasso-mask.js';
 
@@ -23,9 +24,7 @@ export function createLassoTool({
   let pendingMode = 'replace';
   return {
     begin(e) {
-      pendingMode = state.wandMode || 'replace';
-      if (e.shiftKey) pendingMode = 'add';
-      else if (e.altKey) pendingMode = 'subtract';
+      pendingMode = selectionModeForEvent(e, state.wandMode || 'replace');
       state.lassoPoints = [];
       state.lassoActive = true;
       const coords = canvasCoords(e, state.mainCanvas);

static/js/editor/tools/marquee.js

@@ -1,6 +1,7 @@
 /** Rectangle and ellipse marquee interaction producing a document-space mask. */
 
 import { state } from '../state.js';
+import { selectionModeForEvent } from '../selection-modifiers.js';
 import { canvasCoords } from '../canvas-coords.js';
 import {
   createMarqueeMask,
@@ -60,9 +61,7 @@ export function createMarqueeTool({
         gesture.begin(e, { mode: 'move' }, { captureTarget: e.currentTarget });
         return;
       }
-      pendingMode = state.wandMode || 'replace';
-      if (e.shiftKey) pendingMode = 'add';
-      else if (e.altKey) pendingMode = 'subtract';
+      pendingMode = selectionModeForEvent(e, state.wandMode || 'replace');
       state.marqueeStart = coords;
       state.marqueeRect = normalizeConstrainedSelectionRect(
         coords,

static/js/editor/tools/wand.js

@@ -18,6 +18,7 @@
  * }} deps
  */
 import { state } from '../state.js';
+import { selectionModeForEvent } from '../selection-modifiers.js';
 import { canvasCoords } from '../canvas-coords.js';
 
 export function createWandTool({ activeLayer, saveState, composite, wandHits, runMagicWand, deselectSelection }) {
@@ -28,9 +29,7 @@ export function createWandTool({ activeLayer, saveState, composite, wandHits, ru
       const coords = canvasCoords(e, state.mainCanvas);
       // Persistent toggle sets the default mode; Shift forces add, Alt
       // forces subtract regardless of the toggle (modifiers always win).
-      let mode = state.wandMode || 'replace';
-      if (e.shiftKey) mode = 'add';
-      else if (e.altKey) mode = 'subtract';
+      const mode = selectionModeForEvent(e, state.wandMode || 'replace');
       // Click INSIDE the existing selection with no modifier → deselect.
       if (mode === 'replace' && wandHits(coords.x, coords.y)) {
         if (deselectSelection) {