fix: 2026-06-09 full-codebase audit hardening

Validation: shared NaN-guarded Zod coercion helpers in schemas/common.ts replace
the raw number|string transform idiom across every schema (the root-cause NaN bug
class); emailOrEmpty + lenient isoDateString/timeString.

Security: roles privilege-escalation closed; refresh-token family revocation on
reuse; TOTP uses config params; read endpoints permission-guarded; received-invoices
gross VAT on all paths; orders-pdf custom-items authz.

Concurrency: $queryRaw SELECT...FOR UPDATE locks in ascending-id order (warehouse
confirm/cancel, attendance lockUserRow); uniqueness checks moved into create
transactions (TOCTOU -> 409); deterministic id tiebreak on second-precision
timestamp ordering (plan resolveCell/resolveGrid, warehouse FIFO).

Frontend: Rules-of-Hooks fixed across ~14 pages + PlanCellModal; UTC-date persisted
fields; dashboard invalidation gaps; stale-closure confirm bugs.

Tooling/tests: ESLint flat config (react-hooks/rules-of-hooks = error) + Prettier;
tsconfig.test.json so tsc -b type-checks the tests; removed 3 dead deps; npm audit
fix (8 -> 3). Suite 195 -> 247 (happy-path auth, FIFO oldest-first, flakiness fixes),
isolated on app_test via .env.test with a hard-throw setup guard.

Gates: tsc 0 | build 0 | vitest 247/247 | eslint 0 errors.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/__tests__/exchange-rates.test.ts

@@ -1,5 +1,9 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
-import { toCzk, getRate } from "../services/exchange-rates";
+import {
+  toCzk,
+  getRate,
+  __resetRateCacheForTest,
+} from "../services/exchange-rates";
 
 // Mock global fetch
 const mockFetch = vi.fn();
@@ -8,6 +12,11 @@ global.fetch = mockFetch;
 describe("exchange-rates", () => {
   beforeEach(() => {
     mockFetch.mockReset();
+    // The rate cache is module-level and persists across tests. Without this
+    // reset, the first test to populate "today" would short-circuit every
+    // later mockFetch resolution (cache hit), making assertions order-dependent
+    // and asserting stale rates. Reset it so each test gets a clean fetch.
+    __resetRateCacheForTest();
   });
 
   describe("toCzk", () => {
@@ -43,6 +52,21 @@ describe("exchange-rates", () => {
       const result = await toCzk(100, "EUR");
       expect(result).toBe(2500);
     });
+
+    it("honours amount != 1 (currency quoted per 100 units)", async () => {
+      // CNB quotes some currencies (e.g. HUF, JPY) per 100 units: the `rate`
+      // is for `amount` units, so the per-unit rate is rate/amount. Here the
+      // per-unit rate is 250/100 = 2.5 CZK; converting 100 units → 250 CZK.
+      // If the service ignored `amount` it would compute 100*250 = 25000.
+      mockFetch.mockResolvedValue({
+        ok: true,
+        json: async () => ({
+          rates: [{ currencyCode: "HUF", rate: 250, amount: 100 }],
+        }),
+      });
+      const result = await toCzk(100, "HUF");
+      expect(result).toBe(250);
+    });
   });
 
   describe("getRate", () => {
@@ -60,5 +84,17 @@ describe("exchange-rates", () => {
       });
       await expect(getRate("XYZ")).rejects.toThrow(/Neznámá měna: XYZ/);
     });
+
+    it("returns the per-unit rate for amount != 1", async () => {
+      // rate 250 for amount 100 → per-unit rate 2.5 (CZK per 1 unit).
+      mockFetch.mockResolvedValue({
+        ok: true,
+        json: async () => ({
+          rates: [{ currencyCode: "HUF", rate: 250, amount: 100 }],
+        }),
+      });
+      const result = await getRate("HUF");
+      expect(result).toBe(2.5);
+    });
   });
 });