Deduplicate incoming attachments on disk

ts/sql/migrations/1650-protected-attachments.std.ts

@@ -0,0 +1,53 @@
+// Copyright 2026 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+import type { WritableDB } from '../Interface.std.js';
+
+export default function updateToSchemaVersion1650(db: WritableDB): void {
+  db.exec(`
+      CREATE TABLE attachments_protected_from_deletion (
+        path TEXT NOT NULL,
+        UNIQUE (path)
+      ) STRICT;
+    `);
+
+  db.exec(`
+    CREATE INDEX message_attachments_plaintextHash ON message_attachments (plaintextHash);
+  `);
+  db.exec(`
+    CREATE INDEX message_attachments_path ON message_attachments (path);
+  `);
+  db.exec(`
+    CREATE INDEX message_attachments_thumbnailPath ON message_attachments (thumbnailPath);
+  `);
+  db.exec(`
+    CREATE INDEX message_attachments_screenshotPath ON message_attachments (screenshotPath);
+  `);
+  db.exec(`
+    CREATE INDEX message_attachments_backupThumbnailPath ON message_attachments (backupThumbnailPath);
+  `);
+
+  db.exec(`
+    CREATE TRIGGER stop_protecting_attachments_after_update 
+    AFTER UPDATE OF path, thumbnailPath, screenshotPath, backupThumbnailPath 
+    ON message_attachments
+    WHEN 
+      OLD.path IS NOT NEW.path OR
+      OLD.thumbnailPath IS NOT NEW.thumbnailPath OR
+      OLD.screenshotPath IS NOT NEW.screenshotPath OR
+      OLD.backupThumbnailPath IS NOT NEW.backupThumbnailPath
+    BEGIN
+      DELETE FROM attachments_protected_from_deletion 
+      WHERE path IN (NEW.path, NEW.thumbnailPath, NEW.screenshotPath, NEW.backupThumbnailPath);
+    END;
+  `);
+
+  db.exec(`
+    CREATE TRIGGER stop_protecting_attachments_after_insert 
+    AFTER INSERT 
+    ON message_attachments
+    BEGIN
+      DELETE FROM attachments_protected_from_deletion 
+      WHERE path IN (NEW.path, NEW.thumbnailPath, NEW.screenshotPath, NEW.backupThumbnailPath);
+    END;
+  `);
+}