Surface dead filters, and name board and stacks in the moved-card mail

A filter whose entries have all been deleted from the board was the one
failure mode of this app that was completely invisible: the workflow kept
running, kept updating last_run and matched nothing, forever. It happens
with deleted labels and just as easily when a filtered user loses board
access, because Deck's BoardService::deleteAcl() calls
assignedUsersMapper->deleteByParticipantOnBoard() and wipes that user's
card assignments.

Two low-stakes signals, no new column and no migration:

- WorkflowRunner::warnAboutDeadFilters() logs a warning on every run.
- workflowIssues in PersonalSettings.vue marks the row red.

Deliberately no mail and no `enabled = false`. One deleted label out of
three is harmless, and even a fully dead filter can be one board edit away
from being live again.

Both obey the rule the disable path already follows: only positive
knowledge. DeckIntegrationService::findFilterOptions() therefore throws
instead of degrading to [], unlike listLabels()/listParticipants(), where
an empty list only means an empty dropdown.

That also fixes an existing false positive of the same family:
loadStacksFor() stored [] when the request failed, so a single failed
fetch reported "Quell-Stapel und Ziel-Stapel nicht mehr vorhanden" for an
untouched board. Failed requests now store null and are read as "unknown".

The comparison itself lives in WorkflowRunner::findDeadFilters(), static
and side-effect free like cardMatchesFilters(), with unit tests -- notably
that an empty filter is never dead, which would otherwise flag every
unfiltered workflow.

Separately, the moved-card mail now names the board and both stacks.
DeckIntegrationService::describeTargets() resolves the titles at most once
per workflow run, and only when a card actually moved and the workflow
wants a mail; unreadable titles degrade to #<id> rather than costing the
user their notification.

CLAUDE.md

@@ -27,7 +27,7 @@ In cron that is *never* the user being impersonated: `null` if any Deck-owned ba
 
 Consequence for `getUserBoards()`: `listBoardsForCurrentUser()` stays **request-only** anyway — Deck may already have cached board lists behind that field, and the job has no use for a board *list*; it asks `findStackIds()` about one known board id. Before using any other `OCA\Deck\*` service from the runner, check whether it carries a frozen `$userId` — the failure mode is silent and user-crossing, not an error.
 
-The filter-matching logic (`WorkflowRunner::cardMatchesFilters()`, `::isOverdue()`) is deliberately `static` and side-effect-free so it's unit-testable without a real Deck installation — see `tests/Unit/Service/WorkflowRunnerFilterTest.php`.
+The filter logic (`WorkflowRunner::cardMatchesFilters()`, `::isOverdue()`, `::findDeadFilters()`) is deliberately `static` and side-effect-free so it's unit-testable without a real Deck installation — see `tests/Unit/Service/WorkflowRunnerFilterTest.php`. Keep new pure logic in that shape; it is the only part of this app that has tests at all.
 
 ## Workflows are auto-disabled when their Deck targets vanish
 
@@ -40,6 +40,21 @@ The filter-matching logic (`WorkflowRunner::cardMatchesFilters()`, `::isOverdue(
 
 Archived boards deliberately do *not* trigger this (they stay readable, so `findStackIds()` succeeds), even though they're filtered out of the settings dropdowns.
 
+## Dead filters are surfaced, never disabled
+
+`findBrokenTarget()` covers the board and the two stacks — **not** `filter_user_ids` / `filter_label_ids`. Those are plain id lists compared with `array_intersect()` in `cardMatchesFilters()`, so an entry that no longer exists simply stops matching. With three labels of which one was deleted that is exactly right, and disabling would be wrong.
+
+The pathological case is a filter whose entries are *all* gone: the workflow keeps running, updates `last_run`, and matches nothing — forever, with no mail, no log line and a healthy-looking row. It happens on deleted labels and just as easily on a user losing board access, because Deck's `BoardService::deleteAcl()` calls `assignedUsersMapper->deleteByParticipantOnBoard()` and wipes that user's card assignments.
+
+Two low-stakes signals, no state and no migration:
+
+- `WorkflowRunner::warnAboutDeadFilters()` logs a warning on every run.
+- `workflowIssues` in `src/PersonalSettings.vue` marks the row red.
+
+Both obey the same rule as the disable path: **only positive knowledge**. `DeckIntegrationService::findFilterOptions()` therefore *throws* instead of degrading to `[]` — unlike its siblings `listLabels()`/`listParticipants()`, which are wrapped in `call(…, [])` for the dropdowns, where an empty list is harmless. On the JS side the per-board caches store `null` for a failed request, and `isDeadFilter()` returns false for `null`; storing `[]` there would report every stack and filter of the board as deleted the moment one request fails. Don't collapse those two states back together.
+
+Deliberately no mail and no `enabled = false`: one board edit can revive the filter, and there is no "already warned" column to keep a mail one-off with (unlike the disable case, which is one-off for free because a disabled workflow is never picked up again).
+
 ## The job has no interval — one run per cron pass
 
 `RunWorkflowsJob` extends `OCP\BackgroundJob\Job`, **not** `TimedJob`, so it runs every time cron picks it up. There is no interval and no knob: the cadence *is* the instance's cron cadence. Don't reintroduce one — an earlier version read `workflow_deck_automation.interval` from `config.php` (default 300, 60s floor), and that config key is gone as of v0.2.0. `TimedJob` with `setInterval(0)` would behave nearly identically but keeps an interval concept nothing uses.

README.md

@@ -48,6 +48,19 @@ Ein Workflow verweist per ID auf ein Board und zwei Stapel. Wird eines davon in
 
 Ist Deck vorübergehend nicht erreichbar, wird **nicht** deaktiviert — der Job überspringt den Workflow und versucht es beim nächsten Lauf erneut. Archivierte Boards lösen die Deaktivierung ebenfalls nicht aus, sie sind nur in den Auswahlfeldern ausgeblendet.
 
+### Gelöschte Labels und entfernte Benutzer
+
+Filter sind ein anderer Fall: Sie werden **nicht** deaktiviert. Wird eines von drei ausgewählten Labels gelöscht, greifen die anderen beiden weiter — das abzuschalten wäre falsch.
+
+Problematisch ist nur der Grenzfall, dass **alle** Einträge eines Filters verschwunden sind. Der Workflow läuft dann weiter, kann aber keine einzige Karte mehr treffen. Das passiert bei gelöschten Labels und ebenso, wenn ein gefilterter Benutzer die Board-Freigabe verliert — Deck entfernt dabei alle seine Kartenzuweisungen auf diesem Board.
+
+Damit dieser Zustand nicht unsichtbar bleibt:
+
+- **In der Übersicht** wird der Workflow rot markiert („Label-Filter trifft keine Karte mehr", „Benutzer-Filter trifft keine Karte mehr").
+- **Im Hintergrundjob** landet bei jedem Lauf eine Warnung im `nextcloud.log`.
+
+Keine E-Mail und keine Deaktivierung: Ein einziger Board-Klick kann den Filter wieder lebendig machen. Und wie bei Board und Stapel gilt auch hier — lässt sich das Board gerade nicht abfragen, wird nichts gemeldet statt etwas Falsches.
+
 ## Ausführungstakt
 
 Der Hintergrundjob hat **kein eigenes Intervall** und ist auch nicht konfigurierbar: Er läuft bei **jedem** Cron-Durchlauf von Nextcloud. Der Takt ist damit exakt der des System-Crons — üblicherweise alle 5 Minuten, bei einem häufiger eingerichteten Cron entsprechend öfter.

lib/Service/DeckIntegrationService.php

@@ -315,17 +315,80 @@ class DeckIntegrationService {
 	 * @return array<int, array{id: int, title: string, color: string|null}>
 	 */
 	public function listLabels(int $boardId): array {
-		$labels = $this->call(function () use ($boardId) {
+		$labels = $this->call(fn () => $this->readLabels($boardId), []);
-			$board = $this->resolve(BoardService::class)->find($boardId, true);
-			return $board->getLabels() ?? [];
-		}, []);
 
 		return array_map(
-			static fn ($label) => ['id' => $label->getId(), 'title' => $label->getTitle(), 'color' => $label->getColor()],
+			static fn ($label) => ['id' => (int)$label->getId(), 'title' => $label->getTitle(), 'color' => $label->getColor()],
 			$labels,
 		);
 	}
 
+	/**
+	 * What a workflow's filters *could* legitimately refer to on this board.
+	 *
+	 * Unlike listLabels()/listParticipants() this throws instead of degrading
+	 * to an empty list, because its only caller draws a conclusion from
+	 * emptiness ("this filter cannot match anything any more"). Same rule as
+	 * findStackIds(): a Deck hiccup must never be read as positive knowledge.
+	 *
+	 * @return array{labelIds: int[], participantUids: string[]}
+	 * @throws DeckUnavailableException
+	 */
+	public function findFilterOptions(int $boardId): array {
+		try {
+			$board = $this->readBoard($boardId);
+
+			return [
+				'labelIds' => array_map(
+					static fn ($label) => (int)$label->getId(),
+					$board->getLabels() ?? [],
+				),
+				'participantUids' => array_values(array_unique($this->collectParticipantUids($board))),
+			];
+		} catch (DeckUnavailableException $e) {
+			throw $e;
+		} catch (Throwable $e) {
+			$this->logger->error('Could not read filter options of board ' . $boardId . ': ' . $e->getMessage(), [
+				'app' => 'workflow_deck_automation',
+				'exception' => $e,
+			]);
+			throw new DeckUnavailableException('Deck call failed: ' . $e->getMessage(), 0, $e);
+		}
+	}
+
+	/**
+	 * Titles of a workflow's board and stacks, for the notification mail.
+	 *
+	 * Best effort by design: this only decorates a mail that is being sent
+	 * because a card *was* already moved, so anything unreadable degrades to
+	 * `#<id>` rather than costing the user their notification.
+	 *
+	 * @return array{board: string, sourceStack: string, targetStack: string}
+	 */
+	public function describeTargets(int $boardId, int $sourceStackId, int $targetStackId): array {
+		$titles = $this->call(function () use ($boardId) {
+			$stackTitles = [];
+			foreach ($this->resolve(StackMapper::class)->findAll($boardId) as $stack) {
+				$stackTitles[(int)$stack->getId()] = (string)$stack->getTitle();
+			}
+
+			return [
+				'board' => (string)$this->resolve(BoardMapper::class)->find($boardId)->getTitle(),
+				'stacks' => $stackTitles,
+			];
+		}, ['board' => '', 'stacks' => []]);
+
+		return [
+			'board' => self::titleOr($titles['board'], $boardId),
+			'sourceStack' => self::titleOr($titles['stacks'][$sourceStackId] ?? '', $sourceStackId),
+			'targetStack' => self::titleOr($titles['stacks'][$targetStackId] ?? '', $targetStackId),
+		];
+	}
+
+	private static function titleOr(string $title, int $id): string {
+		return $title !== '' ? $title : ('#' . $id);
+	}
+
 	/**
 	 * Everyone who can hold a card on this board: the board owner (who is
 	 * *not* part of the ACL — a private board has an empty ACL) plus every
@@ -334,9 +397,39 @@ class DeckIntegrationService {
 	 * @return array<int, array{uid: string, displayName: string}>
 	 */
 	public function listParticipants(int $boardId): array {
-		$uids = $this->call(function () use ($boardId) {
+		$uids = $this->call(fn () => $this->collectParticipantUids($this->readBoard($boardId)), []);
-			$board = $this->resolve(BoardService::class)->find($boardId, true);
 
+		$participants = [];
+		foreach ($uids as $uid) {
+			if (isset($participants[$uid])) {
+				continue;
+			}
+			$participants[$uid] = [
+				'uid' => $uid,
+				'displayName' => $this->userManager->get($uid)?->getDisplayName() ?? $uid,
+			];
+		}
+
+		return array_values($participants);
+	}
+
+	/**
+	 * The enriched board — `$fullDetails = true` is what populates labels and
+	 * the ACL. Shared by every caller that needs one so a single Deck read
+	 * serves them all.
+	 */
+	private function readBoard(int $boardId): mixed {
+		return $this->resolve(BoardService::class)->find($boardId, true);
+	}
+
+	private function readLabels(int $boardId): array {
+		return $this->readBoard($boardId)->getLabels() ?? [];
+	}
+
+	/**
+	 * @return string[] may contain duplicates
+	 */
+	private function collectParticipantUids(mixed $board): array {
 		$uids = [];
 		$owner = $this->unwrapUid($board->getOwner());
 		if ($owner !== null) {
@@ -359,20 +452,6 @@ class DeckIntegrationService {
 		}
 
 		return $uids;
-		}, []);
-
-		$participants = [];
-		foreach ($uids as $uid) {
-			if (isset($participants[$uid])) {
-				continue;
-			}
-			$participants[$uid] = [
-				'uid' => $uid,
-				'displayName' => $this->userManager->get($uid)?->getDisplayName() ?? $uid,
-			];
-		}
-
-		return array_values($participants);
 	}
 
 	/**

lib/Service/NotificationMailer.php

@@ -30,7 +30,11 @@ class NotificationMailer {
 	) {
 	}
 
-	public function sendCardMovedNotification(IUser $user, Workflow $workflow, Card $card): void {
+	/**
+	 * @param array{board: string, sourceStack: string, targetStack: string} $targets
+	 *        titles resolved by DeckIntegrationService::describeTargets()
+	 */
+	public function sendCardMovedNotification(IUser $user, Workflow $workflow, Card $card, array $targets): void {
 		$email = $user->getEMailAddress();
 		if ($email === null || $email === '') {
 			$this->logger->info('Skipping notification for workflow ' . $workflow->getId() . ': user ' . $user->getUID() . ' has no email address', [
@@ -55,6 +59,13 @@ class NotificationMailer {
 				'The card "%1$s" was moved because it is overdue (workflow "%2$s").',
 				[$card->getTitle(), $workflow->getTitle()],
 			));
+			// Single-argument addBodyText() runs htmlspecialchars() itself, so
+			// these board- and stack-titles (user input) are safe as-is —
+			// unlike the description below, which passes both parts.
+			$template->addBodyText($this->l10n->t(
+				'Board "%1$s": moved from "%2$s" to "%3$s".',
+				[$targets['board'], $targets['sourceStack'], $targets['targetStack']],
+			));
 			$this->addCardDescription($template, $card);
 			$template->addBodyButton($this->l10n->t('Open card'), $cardLink);
 			$template->addFooter();

lib/Service/WorkflowRunner.php

@@ -159,6 +159,11 @@ class WorkflowRunner {
 
 		$filterUserIds = $workflow->getFilterUserIdsArray();
 		$filterLabelIds = $workflow->getFilterLabelIdsArray();
+		$this->warnAboutDeadFilters($workflow, $filterUserIds, $filterLabelIds);
+
+		// Resolved at most once per run, and only if a card actually moves
+		// and the workflow wants a mail — this is decoration, not a check.
+		$targets = null;
 
 		foreach ($cards as $card) {
 			if (!self::isOverdue($card->getDaysUntilDue())) {
@@ -171,7 +176,18 @@ class WorkflowRunner {
 				continue;
 			}
 
-			$this->moveAndNotify($user, $workflow, $card);
+			if (!$this->moveCard($workflow, $card)) {
+				continue;
+			}
+
+			if ($workflow->getNotifyEmail()) {
+				$targets ??= $this->deckService->describeTargets(
+					$workflow->getBoardId(),
+					$workflow->getSourceStackId(),
+					$workflow->getTargetStackId(),
+				);
+				$this->mailer->sendCardMovedNotification($user, $workflow, $card, $targets);
+			}
 		}
 
 		$workflow->setLastRun($this->timeFactory->getDateTime());
@@ -226,7 +242,7 @@ class WorkflowRunner {
 		$this->mailer->sendWorkflowDisabledNotification($user, $workflow, $brokenTarget);
 	}
 
-	private function moveAndNotify(IUser $user, Workflow $workflow, Card $card): void {
+	private function moveCard(Workflow $workflow, Card $card): bool {
 		try {
 			$this->deckService->moveCard($card->getId(), $workflow->getTargetStackId());
 		} catch (Throwable $e) {
@@ -235,11 +251,55 @@ class WorkflowRunner {
 				'card' => $card->getId(),
 				'id' => $workflow->getId(),
 			]);
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * A filter whose every entry has been deleted from the board is not an
+	 * error — the workflow still runs, it just cannot match a single card any
+	 * more, forever, without anything in the UI or the log saying so. That is
+	 * the one failure mode of this app that is completely invisible, so it
+	 * gets a log line on every run.
+	 *
+	 * Explicitly *not* a reason to disable the workflow or mail the user: a
+	 * filter with three labels of which one was deleted still works as
+	 * intended, and even a fully dead filter may be one board edit away from
+	 * being live again. The settings page shows the same condition in red.
+	 *
+	 * @param string[] $filterUserIds
+	 * @param int[] $filterLabelIds
+	 */
+	private function warnAboutDeadFilters(Workflow $workflow, array $filterUserIds, array $filterLabelIds): void {
+		if ($filterUserIds === [] && $filterLabelIds === []) {
 			return;
 		}
 
-		if ($workflow->getNotifyEmail()) {
+		try {
-			$this->mailer->sendCardMovedNotification($user, $workflow, $card);
+			$options = $this->deckService->findFilterOptions($workflow->getBoardId());
+		} catch (DeckUnavailableException $e) {
+			// Same rule as everywhere else: no answer is not a bad answer.
+			$this->logger->debug('Could not check the filters of workflow {id}: ' . $e->getMessage(), [
+				'app' => 'workflow_deck_automation',
+				'id' => $workflow->getId(),
+			]);
+			return;
+		}
+
+		$dead = self::findDeadFilters($filterUserIds, $filterLabelIds, $options['participantUids'], $options['labelIds']);
+
+		if ($dead !== []) {
+			$this->logger->warning(
+				'Workflow {id} can no longer match any card: none of its ' . implode('/', $dead)
+				. ' filter entries exists on board {board} any more',
+				[
+					'app' => 'workflow_deck_automation',
+					'id' => $workflow->getId(),
+					'board' => $workflow->getBoardId(),
+				],
+			);
 		}
 	}
 
@@ -247,6 +307,38 @@ class WorkflowRunner {
 		return $daysUntilDue !== null && $daysUntilDue < 0;
 	}
 
+	/**
+	 * Which filters cannot match anything any more, because not one of their
+	 * entries is still offered by the board. An empty filter is not dead, it
+	 * is "no restriction on this dimension" — the same reading as in
+	 * cardMatchesFilters(), and getting it backwards would report every
+	 * unfiltered workflow as broken.
+	 *
+	 * Static and side-effect free for the same reason as the matching logic:
+	 * testable without a Deck installation.
+	 *
+	 * @param string[] $filterUserIds
+	 * @param int[] $filterLabelIds
+	 * @param string[] $boardUserIds everyone who can hold a card on the board
+	 * @param int[] $boardLabelIds the board's remaining labels
+	 * @return string[] any of 'label', 'user', in that order
+	 */
+	public static function findDeadFilters(
+		array $filterUserIds,
+		array $filterLabelIds,
+		array $boardUserIds,
+		array $boardLabelIds,
+	): array {
+		$dead = [];
+		if ($filterLabelIds !== [] && array_intersect($filterLabelIds, $boardLabelIds) === []) {
+			$dead[] = 'label';
+		}
+		if ($filterUserIds !== [] && array_intersect($filterUserIds, $boardUserIds) === []) {
+			$dead[] = 'user';
+		}
+		return $dead;
+	}
+
 	/**
 	 * Pure filter-matching logic (kept static/side-effect free so it can
 	 * be unit tested without real Deck objects). Both filters are OR

src/PersonalSettings.vue

@@ -159,7 +159,10 @@ const loading = ref(true)
 const loadError = ref('')
 const workflows = ref([])
 const boards = ref([])
+// Per board, and `null` whenever the request failed — see loadStacksFor().
 const stacksByBoard = reactive({})
+const labelsByBoard = reactive({})
+const participantsByBoard = reactive({})
 
 const showForm = ref(false)
 const saving = ref(false)
@@ -181,9 +184,15 @@ const sourceStackOptions = computed(() => stackOptions.value.filter((option) =>
 const targetStackOptions = computed(() => stackOptions.value.filter((option) => option.value !== form.sourceStackId))
 
 /**
- * Workflows whose board or stacks were deleted in Deck, keyed by id. The
+ * Workflows that stopped working, keyed by id. Two different kinds:
- * background job switches these off by itself, but a row that just stopped
+ *
- * working needs to say so instead of looking healthy.
+ * - Board or stacks deleted in Deck. The background job switches these off
+ *   by itself, but a row that just stopped working needs to say so instead
+ *   of looking healthy.
+ * - Every entry of a filter deleted from the board. Nothing switches those
+ *   off — deliberately, since one deleted label out of three is harmless —
+ *   yet a filter that cannot match a single card any more is otherwise
+ *   completely invisible: the workflow keeps running and moves nothing.
  */
 const workflowIssues = computed(() => {
 	const issues = {}
@@ -195,10 +204,7 @@ const workflowIssues = computed(() => {
 		}
 
 		const stacks = stacksByBoard[workflow.boardId]
-		if (!stacks) {
+		if (stacks) {
-			continue
-		}
-
 			const missing = []
 			if (!stacks.some((stack) => stack.id === workflow.sourceStackId)) {
 				missing.push('Quell-Stapel')
@@ -208,12 +214,39 @@ const workflowIssues = computed(() => {
 			}
 			if (missing.length) {
 				issues[workflow.id] = `${missing.join(' und ')} nicht mehr vorhanden`
+				continue
+			}
+		}
+
+		const dead = []
+		if (isDeadFilter(workflow.filterLabelIds, labelsByBoard[workflow.boardId], 'id')) {
+			dead.push('Label-Filter')
+		}
+		if (isDeadFilter(workflow.filterUserIds, participantsByBoard[workflow.boardId], 'uid')) {
+			dead.push('Benutzer-Filter')
+		}
+		if (dead.length > 1) {
+			issues[workflow.id] = `${dead.join(' und ')} treffen keine Karte mehr`
+		} else if (dead.length) {
+			issues[workflow.id] = `${dead[0]} trifft keine Karte mehr`
 		}
 	}
 
 	return issues
 })
 
+/**
+ * True only on positive knowledge: the filter has entries, the board's list
+ * was actually loaded, and not one entry is still on it. A failed request
+ * (null) says nothing and must not turn a healthy row red.
+ */
+function isDeadFilter(selected, available, key) {
+	if (!selected.length || !available) {
+		return false
+	}
+	return !selected.some((value) => available.some((entry) => entry[key] === value))
+}
+
 const form = reactive(emptyForm())
 
 function emptyForm() {
@@ -242,11 +275,27 @@ async function loadStacksFor(boardId) {
 	if (!boardId || stacksByBoard[boardId]) {
 		return
 	}
-	try {
+	// `null`, not `[]` — "could not ask Deck" has to stay distinguishable
-		stacksByBoard[boardId] = await fetchStacks(boardId)
+	// from "this board has none", or a single failed request reports every
-	} catch (e) {
+	// stack of the board as deleted.
-		stacksByBoard[boardId] = []
+	stacksByBoard[boardId] = await fetchStacks(boardId).catch(() => null)
+}
+
+/**
+ * Labels and participants of a board — needed only to judge whether a stored
+ * filter can still match anything, so this is fetched just for the boards of
+ * workflows that actually use filters.
+ */
+async function loadFiltersFor(boardId) {
+	if (!boardId || labelsByBoard[boardId]) {
+		return
 	}
+	const [labels, participants] = await Promise.all([
+		fetchLabels(boardId).catch(() => null),
+		fetchParticipants(boardId).catch(() => null),
+	])
+	labelsByBoard[boardId] = labels
+	participantsByBoard[boardId] = participants
 }
 
 async function loadAll() {
@@ -256,7 +305,13 @@ async function loadAll() {
 		const [loadedWorkflows, loadedBoards] = await Promise.all([fetchWorkflows(), fetchBoards()])
 		workflows.value = loadedWorkflows
 		boards.value = loadedBoards
-		await Promise.all(loadedWorkflows.map((workflow) => loadStacksFor(workflow.boardId)))
+		await Promise.all(loadedWorkflows.flatMap((workflow) => {
+			const pending = [loadStacksFor(workflow.boardId)]
+			if (workflow.filterLabelIds.length || workflow.filterUserIds.length) {
+				pending.push(loadFiltersFor(workflow.boardId))
+			}
+			return pending
+		}))
 	} catch (e) {
 		loadError.value = 'Konnte Workflows oder Deck-Boards nicht laden. Ist die Deck-App aktiviert?'
 	} finally {
@@ -281,15 +336,20 @@ async function loadBoardOptions(boardId) {
 
 	// One failing endpoint must not take the other two dropdowns down with it.
 	const [stacks, labels, participants] = await Promise.all([
-		fetchStacks(boardId).catch(() => []),
+		fetchStacks(boardId).catch(() => null),
-		fetchLabels(boardId).catch(() => []),
+		fetchLabels(boardId).catch(() => null),
-		fetchParticipants(boardId).catch(() => []),
+		fetchParticipants(boardId).catch(() => null),
 	])
 
+	// Feed the overview's caches too, so its red markers agree with what the
+	// form just loaded. `null` propagates on purpose: it means "unknown".
 	stacksByBoard[boardId] = stacks
-	stackOptions.value = stacks.map((stack) => ({ value: stack.id, label: stack.title }))
+	labelsByBoard[boardId] = labels
-	labelOptions.value = labels.map((label) => ({ value: label.id, label: label.title }))
+	participantsByBoard[boardId] = participants
-	participantOptions.value = participants.map((participant) => ({ value: participant.uid, label: participant.displayName }))
+
+	stackOptions.value = (stacks ?? []).map((stack) => ({ value: stack.id, label: stack.title }))
+	labelOptions.value = (labels ?? []).map((label) => ({ value: label.id, label: label.title }))
+	participantOptions.value = (participants ?? []).map((participant) => ({ value: participant.uid, label: participant.displayName }))
 }
 
 /**

tests/Unit/Service/WorkflowRunnerFilterTest.php

@@ -43,4 +43,28 @@ class WorkflowRunnerFilterTest extends TestCase {
 		// both match -> true
 		$this->assertTrue(WorkflowRunner::cardMatchesFilters(['alice'], [1], ['alice'], [1]));
 	}
+
+	public function testEmptyFiltersAreNeverDead(): void {
+		// "no restriction" must not be reported as a broken filter, however
+		// little the board has left to offer.
+		$this->assertSame([], WorkflowRunner::findDeadFilters([], [], [], []));
+		$this->assertSame([], WorkflowRunner::findDeadFilters([], [], ['alice'], [1]));
+	}
+
+	public function testFilterSurvivesAsLongAsOneEntryRemains(): void {
+		$this->assertSame([], WorkflowRunner::findDeadFilters(['alice', 'bob'], [1, 2], ['bob'], [2]));
+	}
+
+	public function testFilterIsDeadWhenEveryEntryIsGone(): void {
+		$this->assertSame(['label'], WorkflowRunner::findDeadFilters([], [1, 2], [], [3]));
+		$this->assertSame(['user'], WorkflowRunner::findDeadFilters(['alice'], [], ['bob'], []));
+		$this->assertSame(
+			['label', 'user'],
+			WorkflowRunner::findDeadFilters(['alice'], [1], ['bob'], [2]),
+		);
+	}
+
+	public function testAnEmptyBoardKillsOnlyTheFiltersThatAreSet(): void {
+		$this->assertSame(['label'], WorkflowRunner::findDeadFilters([], [1], [], []));
+	}
 }