fix: Automerge undefined rejection + thread not synced to server

- tweetImages and imageUrl set to null instead of undefined when empty
  (Automerge rejects undefined as invalid JSON)
- Updated ThreadData schema to allow null for optional fields
- This was the root cause of the 404 on image generation: saveDraft
  threw on undefined, so the thread never synced to the server, and
  the server-side route returned "Thread not found"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/rsocials/components/folk-thread-builder.ts

@@ -441,8 +441,8 @@ export class FolkThreadBuilder extends HTMLElement {
 			handle: handleInput.value || '@yourhandle',
 			title: titleInput.value || tweets[0].substring(0, 60),
 			tweets,
-			tweetImages: Object.keys(this._tweetImages).length ? { ...this._tweetImages } : undefined,
-			imageUrl: this._thread?.imageUrl,
+			tweetImages: Object.keys(this._tweetImages).length ? { ...this._tweetImages } : null,
+			imageUrl: this._thread?.imageUrl || null,
 			createdAt: this._thread?.createdAt || Date.now(),
 			updatedAt: Date.now(),
 		};
@@ -716,7 +716,7 @@ export class FolkThreadBuilder extends HTMLElement {
 			await fetch(this.basePath + 'api/threads/' + this._threadId + '/tweet/' + index + '/image', { method: 'DELETE' });
 			delete this._tweetImages[index];
 			if (this._thread) {
-				this._thread.tweetImages = Object.keys(this._tweetImages).length ? { ...this._tweetImages } : undefined;
+				this._thread.tweetImages = Object.keys(this._tweetImages).length ? { ...this._tweetImages } : null;
 				await this.saveToAutomerge(this._thread);
 			}
 			this.renderPreview();

modules/rsocials/mod.ts

@@ -216,7 +216,7 @@ routes.post("/api/threads/:id/upload-image", async (c) => {
 	const ext = safeExtension(file.name);
 	const filename = `thread-${id}.${ext}`;
 
-	await deleteOldImage(thread.imageUrl, filename);
+	if (thread.imageUrl) await deleteOldImage(thread.imageUrl, filename);
 
 	const buffer = Buffer.from(await file.arrayBuffer());
 	const imageUrl = await saveUploadedFile(buffer, filename);

modules/rsocials/schemas.ts

@@ -17,8 +17,8 @@ export interface ThreadData {
 	handle: string;
 	title: string;
 	tweets: string[];
-	imageUrl?: string;
-	tweetImages?: Record<string, string>;
+	imageUrl?: string | null;
+	tweetImages?: Record<string, string> | null;
 	createdAt: number;
 	updatedAt: number;
 }