feat(bulk-upload): guard save() against concurrent invocations

Adds a saving $state flag that blocks re-entry while a chunk upload is
in flight. The UploadSaveBar save button is disabled via a new disabled
prop while saving is true. Tested: clicking Save twice fires fetch only
once.

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

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte

@@ -31,6 +31,7 @@ let {
 let files = new SvelteMap<string, FileEntry>();
 let activeId = $state<string | null>(null);
 let chunkProgress = $state<{ done: number; total: number } | undefined>(undefined);
+let saving = $state(false);
 
 // --- Shared metadata ---
 let senderId = $state(untrack(() => initialSenderId));
@@ -84,6 +85,8 @@ onDestroy(() => {
 
 // --- Save ---
 async function save() {
+	if (saving) return;
+	saving = true;
 	const entries = Array.from(files.values());
 	const chunkSize = 10;
 	const chunks: FileEntry[][] = [];
@@ -124,6 +127,7 @@ async function save() {
 		}
 		chunkProgress = { done: i + 1, total: chunks.length };
 	}
+	saving = false;
 	if (!hadErrors) goto('/documents');
 }
 </script>
@@ -276,6 +280,7 @@ async function save() {
 				chunkProgress={chunkProgress}
 				onSave={save}
 				onDiscard={discardAll}
+				disabled={saving}
 			/>
 		</div>
 	</div>

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte.spec.ts

@@ -206,6 +206,34 @@ describe('BulkDocumentEditLayout', () => {
 		);
 	});
 
+	it('save() does not call fetch a second time when already saving', async () => {
+		let resolveFirst: (() => void) | undefined;
+		const mockFetch = vi.fn().mockImplementation(
+			() =>
+				new Promise<Response>((resolve) => {
+					resolveFirst = () =>
+						resolve({
+							ok: true,
+							json: async () => ({ created: [], updated: [], errors: [] })
+						} as Response);
+				})
+		);
+		vi.stubGlobal('fetch', mockFetch);
+
+		const { container } = render(BulkDocumentEditLayout, {});
+		await addFilesViaInput(container, [makeFile('a.pdf')]);
+
+		const saveBtn = container.querySelector(
+			'button[data-testid="bulk-save-btn"]'
+		) as HTMLButtonElement;
+		saveBtn.click(); // first click — fetch is in-flight
+		saveBtn.click(); // second click — should be a no-op
+
+		resolveFirst?.();
+		await vi.waitFor(() => expect(mockFetch).toHaveBeenCalledTimes(1), { timeout: 3000 });
+		expect(mockFetch).toHaveBeenCalledTimes(1);
+	});
+
 	it('discard-all resets to N=0 state and shows drop zone', async () => {
 		const { container } = render(BulkDocumentEditLayout, {});
 		await addFilesViaInput(container, [makeFile('a.pdf'), makeFile('b.pdf')]);

frontend/src/lib/components/document/UploadSaveBar.svelte

@@ -5,12 +5,14 @@ let {
 	fileCount,
 	chunkProgress,
 	onSave,
-	onDiscard
+	onDiscard,
+	disabled = false
 }: {
 	fileCount: number;
 	chunkProgress?: { done: number; total: number };
 	onSave: () => void;
-	onDiscard: () => void;
+	onDiscard: () => void | Promise<void>;
+	disabled?: boolean;
 } = $props();
 </script>
 
@@ -37,7 +39,7 @@ let {
 		<button
 			type="button"
 			data-testid="bulk-save-btn"
-			disabled={fileCount === 0}
+			disabled={fileCount === 0 || disabled}
 			onclick={onSave}
 			class="min-h-[44px] rounded-sm bg-primary px-6 text-sm font-bold tracking-widest text-primary-fg uppercase transition-opacity hover:opacity-90 disabled:opacity-40"
 		>