Implement unique filename generation to prevent overwriting existing session files

handler.ts

@@ -197,6 +197,26 @@ function buildSlugExcerpt(full: string): string {
   return tail.slice(-3000);
 }
 
+async function getUniqueFilePath(dir: string, filename: string): Promise<string> {
+  const candidate = path.join(dir, filename);
+  try {
+    await fs.access(candidate);
+  } catch {
+    return candidate;
+  }
+
+  const parsed = path.parse(filename);
+  for (let i = 1; ; i += 1) {
+    const name = `${parsed.name}-${i}${parsed.ext}`;
+    const p = path.join(dir, name);
+    try {
+      await fs.access(p);
+    } catch {
+      return p;
+    }
+  }
+}
+
 async function generateSlug(params: {
   excerpt: string;
   cfg: AnyObj;
@@ -274,7 +294,7 @@ const handler = async (event: {
     await fs.mkdir(memoryDir, { recursive: true });
 
     const filename = `${dateStr}-${slug}.md`;
-    const memoryFilePath = path.join(memoryDir, filename);
+    const memoryFilePath = await getUniqueFilePath(memoryDir, filename);
 
     const source = typeof context.commandSource === "string" ? context.commandSource : "unknown";