fix(shared): tag filter SQL precedence, balance cards filter by tag

src/app/api/participants/balances/route.ts

@@ -6,6 +6,8 @@ export async function GET(req: NextRequest) {
   const user = await getCurrentUser(req);
   if (!user) return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
 
-  const balances = await getParticipantBalances(user.id);
+  const tagParam = req.nextUrl.searchParams.get("tag_ids");
+  const tagIds = tagParam ? tagParam.split(",").map(Number).filter(Boolean) : undefined;
+  const balances = await getParticipantBalances(user.id, tagIds);
   return NextResponse.json(balances);
 }

src/app/shared/page.tsx

@@ -259,7 +259,7 @@ function PaymentHistory({ participantId, currentUserId }: { participantId: numbe
 export default function SharedPage() {
   const [tagIds, setTagIds] = useState<string[]>([]);
   const { data: transactions = [], isLoading: txLoading } = useSharedTransactions(tagIds);
-  const { data: balances = [], isLoading: balLoading } = useParticipantBalances();
+  const { data: balances = [], isLoading: balLoading } = useParticipantBalances(tagIds);
   const { data: me } = useCurrentUser();
   const [addingParticipant, setAddingParticipant] = useState(false);
   const [paymentModal, setPaymentModal] = useState<{ id: number; name: string; balance: number } | null>(null);

src/lib/hooks.ts

@@ -198,11 +198,12 @@ export function useParticipants() {
   });
 }
 
-export function useParticipantBalances() {
+export function useParticipantBalances(tagIds?: string[]) {
   return useQuery<{ id: number; name: string; total_owed: number; unsettled_count: number }[]>({
-    queryKey: ["participant-balances"],
+    queryKey: ["participant-balances", tagIds],
     queryFn: async () => {
-      const res = await fetch("/api/participants/balances");
+      const params = tagIds?.length ? `?tag_ids=${tagIds.join(",")}` : "";
+      const res = await fetch(`/api/participants/balances${params}`);
       return res.json();
     },
   });

src/lib/queries.ts

@@ -273,7 +273,14 @@ export interface ParticipantBalance {
   unsettled_count: number;
 }
 
-export async function getParticipantBalances(ownerId: number) {
+export async function getParticipantBalances(ownerId: number, tagIds?: number[]) {
+  const params: unknown[] = [ownerId];
+  let tagFilter = "";
+  if (tagIds?.length) {
+    params.push(tagIds);
+    tagFilter = `AND EXISTS (SELECT 1 FROM transaction_tags tt WHERE tt.transaction_id = t.id AND tt.tag_id = ANY($2::int[]))`;
+  }
+
   return queryRaw<ParticipantBalance>(`
     SELECT p.id, p.name,
       COALESCE(SUM(splits.signed_amount), 0)::numeric(12,2)
@@ -281,7 +288,6 @@ export async function getParticipantBalances(ownerId: number) {
       COALESCE(SUM(splits.split_count), 0)::int AS unsettled_count
     FROM participants p
 
-    -- All split obligations (settled flag ignored — payments are the source of truth)
     LEFT JOIN (
       -- They owe me: their splits on transactions I own
       SELECT ts.participant_id AS pid,
@@ -291,6 +297,7 @@ export async function getParticipantBalances(ownerId: number) {
       JOIN transactions t ON t.id = ts.transaction_id
       LEFT JOIN statements s ON s.id = t.statement_id
       WHERE COALESCE(t.owner_id, s.owner_id) = $1 AND ts.participant_id != $1
+      ${tagFilter}
 
       UNION ALL
 
@@ -302,9 +309,10 @@ export async function getParticipantBalances(ownerId: number) {
       JOIN transactions t ON t.id = ts.transaction_id
       LEFT JOIN statements s ON s.id = t.statement_id
       WHERE ts.participant_id = $1 AND COALESCE(t.owner_id, s.owner_id) != $1
+      ${tagFilter}
     ) splits ON splits.pid = p.id
 
-    -- Net payments: positive = they paid me, negative = I paid them
+    -- Net payments always unfiltered (payments are against total debt, not per-tag)
     LEFT JOIN (
       SELECT
         CASE WHEN sp.from_participant_id != $1 THEN sp.from_participant_id ELSE sp.to_participant_id END AS pid,
@@ -317,7 +325,7 @@ export async function getParticipantBalances(ownerId: number) {
     WHERE p.id != $1
     GROUP BY p.id, p.name, payments.net_paid
     ORDER BY p.name
-  `, [ownerId]);
+  `, params);
 }
 
 export interface SharedTransactionRow extends TransactionRow {
@@ -365,12 +373,14 @@ export async function getSharedTransactions(ownerId: number, tagIds?: number[])
     LEFT JOIN statements s ON s.id = t.statement_id
     LEFT JOIN participants p_owner ON p_owner.id = COALESCE(t.owner_id, s.owner_id)
     WHERE (
+        (
           COALESCE(t.owner_id, s.owner_id) = $1
           AND EXISTS (SELECT 1 FROM transaction_splits ts2 WHERE ts2.transaction_id = t.id AND ts2.participant_id != $1)
         ) OR (
           COALESCE(t.owner_id, s.owner_id) != $1
           AND EXISTS (SELECT 1 FROM transaction_splits ts_me WHERE ts_me.transaction_id = t.id AND ts_me.participant_id = $1)
         )
+      )
     ${tagClause}
     GROUP BY t.id, o.category_override, o.merchant_normalized, o.notes, s.bank_name, s.owner_id, p_owner.name
     ORDER BY t.transaction_date DESC