fix(deprecation): validate v1 folder transition

.cursor/rules/suggestions-development.mdc

@@ -39,7 +39,7 @@ Users can configure suggestions via `useCopilotChatSuggestions` hook which regis
 - **@react-core**
   - [copilot-context.tsx](mdc:packages/react-core/src/v1-deprecated/context/copilot-context.tsx) - Where the actual suggestions are stored, the "provider" or "context"
   - [use-copilot-chat.ts](mdc:packages/react-core/src/v1-deprecated/hooks/use-copilot-chat.ts) - Hook that controls and contains logic for suggestions, often referred to as "headless UI"
-  - [suggestions.ts](mdc:packages/react-core/src/v1-deprecated/utils/suggestions.ts) - Core suggestion generation logic with streaming validation and error handling
+  - [use-configure-chat-suggestions.tsx](mdc:packages/react-core/src/v1-deprecated/hooks/use-configure-chat-suggestions.tsx) - V1 compatibility bridge that configures v2 suggestion generation and reloads suggestions when the target agent becomes available
   - [suggestions-constants.ts](mdc:packages/react-core/src/v1-deprecated/utils/suggestions-constants.ts) - Retry configuration constants
 
 ## How Suggestions Work

packages/runtime/tsdown.config.ts

@@ -10,7 +10,10 @@ import path from "node:path";
 // directory is added as a public package export.
 function preservePublishedV1Layout(distDir: string) {
   const v1DeprecatedDir = path.join(distDir, "v1-deprecated");
-  if (!fs.existsSync(v1DeprecatedDir)) return;
+  if (!fs.existsSync(v1DeprecatedDir)) {
+    // build:done runs for concurrent outputs; another callback may have already flattened it.
+    return;
+  }
   const movedFiles = new Map<string, string>();
 
   const moveTree = (source: string, destination: string) => {