Better accounting of orphaned attachments

Co-authored-by: trevor-signal <131492920+trevor-signal@users.noreply.github.com>

app/attachment_channel.main.ts

@@ -19,6 +19,8 @@ import z from 'zod';
 import GrowingFile from 'growing-file';
 import lodash from 'lodash';
 import { pathExists } from 'fs-extra';
+import pMap from 'p-map';
+import { access } from 'node:fs/promises';
 
 import {
   type DecryptAttachmentToSinkOptionsType,
@@ -462,6 +464,22 @@ function deleteOrphanedAttachments({
       `cleanupOrphanedAttachments: ${totalAttachmentsFound} attachments and \
       ${totalDownloadsFound} downloads found on disk`
     );
+    const attachmentsFolder = getAttachmentsPath(userDataPath);
+
+    // It's possible that messages and attachments have been deleted since we first
+    // checked the contents of the attachments folder, so for better accounting, we
+    // check once more that they still exist.
+    await pMap(
+      orphanedAttachments,
+      async path => {
+        try {
+          await access(join(attachmentsFolder, path));
+        } catch (e) {
+          orphanedAttachments.delete(path);
+        }
+      },
+      { concurrency: 20 }
+    );
 
     if (orphanedAttachments.size > 0) {
       log.error(`${orphanedAttachments.size} orphaned attachment(s) found`);