fix(timeline): harden curator event precision field

- Validate the submitted precision against the DatePrecision allow-list in
  parseEventForm (falls back to DAY) so an untrusted token can't flow into
  the request body — symmetric with the existing `type` narrowing.
- Parameterize the precision input name via DatePrecisionField's new
  precisionInputName prop; the timeline form now submits `precision` instead
  of the misleading document-domain `metaDatePrecision`. Document form keeps
  the default, so its behaviour is unchanged.
- Capture EventTypeSelect's onchange into EventForm's `type` state so it no
  longer goes stale (the submitted value was already correct via the hidden
  input; this keeps the local state in sync).

Addresses PR #832 review (#781).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/shared/primitives/DatePrecisionField.svelte

@@ -16,7 +16,9 @@ import type { DatePrecision } from '$lib/shared/utils/documentDate';
  * Exposed (shared contract — both WhoWhenSection and EventForm depend on it):
  *   - dateIso, precision, endDateIso  — $bindable; the parent's binding IS the
  *     state (no redundant $state mirror).
- *   - dateInputName / endDateInputName — names of the hidden ISO inputs.
+ *   - dateInputName / endDateInputName / precisionInputName — submitted field
+ *     names; defaults match the document form (`metaDatePrecision`), the timeline
+ *     form overrides precisionInputName to `precision`.
  *   - initialDateIso / suggestedDateIso — seeding inputs (see onMount + $effect).
  *   - dateTestId / precisionTestId / endDateInnerTestId — forwarded data-testid
  *     attributes so existing WhoWhenSection selectors survive the extraction.
@@ -28,6 +30,7 @@ let {
 	endDateIso = $bindable(''),
 	dateInputName = 'documentDate',
 	endDateInputName = 'metaDateEnd',
+	precisionInputName = 'metaDatePrecision',
 	initialDateIso = '',
 	suggestedDateIso = '',
 	dateLabel = m.form_label_date(),
@@ -41,6 +44,7 @@ let {
 	endDateIso?: string;
 	dateInputName?: string;
 	endDateInputName?: string;
+	precisionInputName?: string;
 	initialDateIso?: string;
 	suggestedDateIso?: string;
 	dateLabel?: string;
@@ -145,7 +149,7 @@ $effect(() => {
 	</label>
 	<select
 		id="{dateInputName}Precision"
-		name="metaDatePrecision"
+		name={precisionInputName}
 		bind:value={precision}
 		class="block min-h-[48px] w-full rounded border border-line px-2 py-3 text-sm shadow-sm focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
 	>

frontend/src/lib/timeline/EventForm.svelte

@@ -62,7 +62,7 @@ let selectedDocuments = $state<DocumentOption[]>(
 	event?.documents
 		? event.documents.map((d) => ({
 				// Graceful degradation: DocumentRef has no precision fields. formatDocumentOption
-				// falls back to the bare title when documentDate is the only date info present.
+				// defaults a missing precision to DAY, so the chip shows the full documentDate.
 				id: d.id,
 				title: d.title,
 				documentDate: d.documentDate
@@ -196,7 +196,10 @@ async function confirmDelete(e: SubmitEvent) {
 						<span class="mb-1 block text-sm font-medium text-ink-2"
 							>{m.event_editor_type_label()}</span
 						>
-						<EventTypeSelect value={type} name="type" onchange={() => markDirty()} />
+						<EventTypeSelect value={type} name="type" onchange={(t) => {
+								type = t;
+								markDirty();
+							}} />
 					</div>
 
 					<div class="grid grid-cols-1 gap-5 md:grid-cols-2">
@@ -206,6 +209,7 @@ async function confirmDelete(e: SubmitEvent) {
 							bind:endDateIso={endDateIso}
 							dateInputName="eventDate"
 							endDateInputName="eventDateEnd"
+							precisionInputName="precision"
 							dateLabel={m.form_label_date()}
 							dateTestId="event-date"
 							precisionTestId="event-precision"

frontend/src/lib/timeline/eventFormServer.ts

@@ -8,6 +8,20 @@ type TimelineEventRequest = components['schemas']['TimelineEventRequest'];
 // Prevents open redirect: validate before constructing /persons/{id}. See OWASP CWE-601.
 const UUID_RE = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
 
+// Whitelist of accepted precision tokens — mirrors the DatePrecision union. Any
+// other submitted value falls back to DAY rather than flowing untrusted into the
+// request body (the backend enum is the hard gate; this keeps the two symmetric
+// with the `type` narrowing below).
+const VALID_PRECISIONS: readonly DatePrecision[] = [
+	'DAY',
+	'MONTH',
+	'SEASON',
+	'YEAR',
+	'RANGE',
+	'APPROX',
+	'UNKNOWN'
+];
+
 /**
  * Resolves the context-aware post-save / post-delete redirect target. Returns
  * the originating person page only when `originPersonIdRaw` is a strict UUID;
@@ -33,7 +47,9 @@ export interface ParsedEventForm {
 export function parseEventForm(formData: FormData): ParsedEventForm {
 	const rawType = formData.get('type')?.toString();
 	const type = rawType === 'HISTORICAL' ? 'HISTORICAL' : 'PERSONAL';
-	const precision = (formData.get('metaDatePrecision')?.toString() as DatePrecision) || 'DAY';
+	const rawPrecision = formData.get('precision')?.toString() as DatePrecision | undefined;
+	const precision: DatePrecision =
+		rawPrecision && VALID_PRECISIONS.includes(rawPrecision) ? rawPrecision : 'DAY';
 	const endRaw = formData.get('eventDateEnd')?.toString().trim() ?? '';
 	// Off-RANGE submits an empty string → null so a stale end-date never persists.
 	const eventDateEnd = precision === 'RANGE' && endRaw ? endRaw : null;

frontend/src/routes/zeitstrahl/events/new/page.server.spec.ts

@@ -119,7 +119,7 @@ describe('zeitstrahl/events/new save action (REQ-004/009/010/015)', () => {
 					title: 'Umzug',
 					type: 'PERSONAL',
 					eventDate: '1925-04-01',
-					metaDatePrecision: 'YEAR',
+					precision: 'YEAR',
 					eventDateEnd: '1925-05-01'
 				})
 			);
@@ -129,6 +129,27 @@ describe('zeitstrahl/events/new save action (REQ-004/009/010/015)', () => {
 		expect(post.mock.calls[0][1].body.eventDateEnd).toBeNull();
 	});
 
+	it('falls back to DAY precision when an unknown precision token is submitted (REQ-009 hardening)', async () => {
+		const post = vi
+			.fn()
+			.mockResolvedValue({ response: { ok: true, status: 200 }, data: { id: 'e-new' } });
+		vi.mocked(createApiClient).mockReturnValue({ POST: post } as never);
+
+		try {
+			await actions.save(
+				saveEvent({
+					title: 'Umzug',
+					type: 'PERSONAL',
+					eventDate: '1925-04-01',
+					precision: 'NOT_A_REAL_PRECISION'
+				})
+			);
+		} catch {
+			// redirect throws on success
+		}
+		expect(post.mock.calls[0][1].body.precision).toBe('DAY');
+	});
+
 	it('returns fail(400) with preserved picker arrays on blank title', async () => {
 		const post = vi.fn();
 		vi.mocked(createApiClient).mockReturnValue({ POST: post } as never);