diff --git a/lambda/workorder-sync/index.ts b/lambda/workorder-sync/index.ts
index b18340a..45100ab 100644
--- a/lambda/workorder-sync/index.ts
+++ b/lambda/workorder-sync/index.ts
@@ -52,9 +52,10 @@ interface WorkOrderComment {
   ingested_at?: string;
 }
 
-async function clearOldFiles(bucket: string): Promise<void> {
+/** List all existing S3 keys under the work-orders/ prefix. */
+async function listExistingKeys(bucket: string): Promise<Set<string>> {
+  const keys = new Set<string>();
   let continuationToken: string | undefined;
-  const toDelete: { Key: string }[] = [];
 
   do {
     const res = await s3.send(
@@ -65,23 +66,27 @@ async function clearOldFiles(bucket: string): Promise<void> {
       }),
     );
     for (const obj of res.Contents ?? []) {
-      if (obj.Key) toDelete.push({ Key: obj.Key });
+      if (obj.Key) keys.add(obj.Key);
     }
     continuationToken = res.NextContinuationToken;
   } while (continuationToken);
 
-  if (toDelete.length === 0) return;
+  return keys;
+}
 
-  // S3 DeleteObjects accepts up to 1000 keys per request
-  for (let i = 0; i < toDelete.length; i += 1000) {
+/** Delete S3 keys that no longer correspond to active records. */
+async function deleteStaleKeys(bucket: string, keys: string[]): Promise<void> {
+  if (keys.length === 0) return;
+
+  for (let i = 0; i < keys.length; i += 1000) {
     await s3.send(
       new DeleteObjectsCommand({
         Bucket: bucket,
-        Delete: { Objects: toDelete.slice(i, i + 1000) },
+        Delete: { Objects: keys.slice(i, i + 1000).map((Key) => ({ Key })) },
       }),
     );
   }
-  console.log(`Deleted ${toDelete.length} stale work order file(s) from S3`);
+  console.log(`Deleted ${keys.length} stale work order file(s) from S3`);
 }
 
 async function scanAllWorkOrders(): Promise<WorkOrder[]> {
@@ -194,44 +199,62 @@ export const handler = async (): Promise<void> => {
   const kbId = process.env.KNOWLEDGE_BASE_ID!;
   const dsId = process.env.DATA_SOURCE_ID!;
 
-  console.log('Clearing stale work order files from S3...');
-  await clearOldFiles(bucket);
+  console.log('Listing existing work order files in S3...');
+  const existingKeys = await listExistingKeys(bucket);
+  console.log(`Found ${existingKeys.size} existing file(s) in S3`);
 
   console.log('Scanning work orders from DynamoDB...');
   const workOrders = await scanAllWorkOrders();
   console.log(`Found ${workOrders.length} work order(s)`);
 
+  const writtenKeys = new Set<string>();
   let synced = 0;
   let failed = 0;
 
-  for (const wo of workOrders) {
-    try {
-      const comments = await getComments(wo.work_order_id);
-      const markdown = formatWorkOrderMarkdown(wo, comments);
+  // Upload in batches of 10 (each WO also queries comments, so keep concurrency moderate)
+  const CONCURRENCY = 10;
+  for (let i = 0; i < workOrders.length; i += CONCURRENCY) {
+    const batch = workOrders.slice(i, i + CONCURRENCY);
+    const results = await Promise.allSettled(
+      batch.map(async (wo) => {
+        const comments = await getComments(wo.work_order_id);
+        const markdown = formatWorkOrderMarkdown(wo, comments);
+        const key = `${WO_PREFIX}${wo.work_order_id}.md`;
 
-      await s3.send(
-        new PutObjectCommand({
-          Bucket: bucket,
-          Key: `${WO_PREFIX}${wo.work_order_id}.md`,
-          Body: markdown,
-          ContentType: 'text/markdown',
-          Metadata: {
-            'work-order-id': wo.work_order_id,
-            'site-code': (wo.site_code ?? '').slice(0, 256),
-          },
-        }),
-      );
+        await s3.send(
+          new PutObjectCommand({
+            Bucket: bucket,
+            Key: key,
+            Body: markdown,
+            ContentType: 'text/markdown',
+            Metadata: {
+              'work-order-id': wo.work_order_id,
+              'site-code': (wo.site_code ?? '').slice(0, 256),
+            },
+          }),
+        );
 
-      console.log(`Synced: ${wo.work_order_id} (${comments.length} comment(s))`);
-      synced++;
-    } catch (err) {
-      console.error(`Failed to sync work order ${wo.work_order_id}:`, err);
-      failed++;
+        return key;
+      }),
+    );
+
+    for (const r of results) {
+      if (r.status === 'fulfilled') {
+        writtenKeys.add(r.value);
+        synced++;
+      } else {
+        console.error(`Failed to sync work order:`, r.reason);
+        failed++;
+      }
     }
   }
 
   console.log(`Upload complete. ${synced} synced, ${failed} failed.`);
 
+  // Delete S3 files for records that no longer exist in DynamoDB
+  const staleKeys = [...existingKeys].filter((k) => !writtenKeys.has(k));
+  await deleteStaleKeys(bucket, staleKeys);
+
   console.log('Triggering Bedrock KB ingestion job...');
   const ingestionRes = await bedrockAgent.send(
     new StartIngestionJobCommand({