Add Agent execution guidelines & trim AGENTS.md

Introduce a new detailed Agent handbook (docs/【协作规范】Agent工作入口与执行准则-2026-06-22.md) and refactor AGENTS.md to be an entry-only navigation page. Update documentation cross-references (docs/README.md, project-memory README, document-map, team-conventions, development-workflow, decision-log and project-overview) to point to the new file and clarify reading/order rules, submission/validation constraints, and SpacetimeDB/back-end wording. Also adjust image canvas generation placement rules in the frontend doc and apply related changes to image-editor hooks/tests (src/components/image-editor/*). Purpose: separate high-level entry rules from complex execution details to reduce startup cost for complex tasks and centralize execution practices in a single guideline document.

src/components/image-editor/useImageCanvasGenerationSubmissionWorkflow.ts

@@ -44,6 +44,7 @@ import {
   createQuickEditResultLayer,
   createVideoResultLayer,
 } from './ImageCanvasGenerationLayerModel';
+import { chooseGenerationPlacement } from './ImageCanvasGenerationPlacementModel';
 import {
   buildCharacterAnimationGenerationInputs,
   buildEditGenerationInputs,
@@ -98,6 +99,7 @@ type GenerationSubmissionWorkflowOptions = {
   quickEditPanel: QuickEditPanelState | null;
   quickEditSourceLayer: CanvasLayer | null;
   quickEditSelectionState: UiAssetExtractionState | null;
+  canvasGenerationDialogs: CanvasGenerationDialogState[];
   setQuickEditPanel: Dispatch<SetStateAction<QuickEditPanelState | null>>;
   characterAnimationPanel: CharacterAnimationPanelState | null;
   characterAnimationDialog: CanvasGenerationDialogState | null;
@@ -165,6 +167,7 @@ export function useImageCanvasGenerationSubmissionWorkflow({
   quickEditPanel,
   quickEditSourceLayer,
   quickEditSelectionState,
+  canvasGenerationDialogs,
   setQuickEditPanel,
   characterAnimationPanel,
   characterAnimationDialog,
@@ -741,21 +744,33 @@ export function useImageCanvasGenerationSubmissionWorkflow({
           );
     let quickEditDialogId: string | undefined;
     if (panelMode === 'quick-edit') {
-      quickEditDialogId = openCanvasGenerationDialog(
-        createQuickEditGenerationDialogDraft({
-          sourceLayer: quickEditSourceLayer,
-          prompt: normalizedPrompt,
-          status: 'generating',
-          references: quickEditReferences,
-          model: quickEditPanel.model,
-          aspectRatio: quickEditAspectRatio,
-          imageSize: quickEditImageSize,
-          frame: {
-            width: quickEditOutputSize.width,
-            height: quickEditOutputSize.height,
-          },
-        }),
-      );
+      const quickEditDraft = createQuickEditGenerationDialogDraft({
+        sourceLayer: quickEditSourceLayer,
+        prompt: normalizedPrompt,
+        status: 'generating',
+        references: quickEditReferences,
+        model: quickEditPanel.model,
+        aspectRatio: quickEditAspectRatio,
+        imageSize: quickEditImageSize,
+        frame: {
+          width: quickEditOutputSize.width,
+          height: quickEditOutputSize.height,
+        },
+      });
+      const quickEditPlacement = quickEditDraft.placeholder
+        ? chooseGenerationPlacement({
+            canvasSize,
+            viewport,
+            frame: quickEditDraft.placeholder,
+            layers,
+            generationDialogs: canvasGenerationDialogs,
+          })
+        : quickEditDraft.placeholder;
+      quickEditDialogId = openCanvasGenerationDialog({
+        ...quickEditDraft,
+        // 中文注释：快速编辑生成结果复用新建图片的避让落点，避免覆盖已有素材。
+        placeholder: quickEditPlacement,
+      });
       setQuickEditPanel(null);
       selectSingleLayer(null);
     } else {
@@ -956,7 +971,10 @@ export function useImageCanvasGenerationSubmissionWorkflow({
     addCharacterAnimationResultLayer,
     addQuickEditResultLayer,
     addVideoResultLayer,
+    canvasGenerationDialogs,
+    canvasSize,
     getGeneratingDialogPlaceholder,
+    layers,
     openCanvasGenerationDialog,
     projectId,
     assetFolderId,
@@ -966,6 +984,7 @@ export function useImageCanvasGenerationSubmissionWorkflow({
     selectSingleLayer,
     setQuickEditPanel,
     updateCanvasGenerationDialogById,
+    viewport,
   ]);
 
   const submitImageGeneration = useCallback(