test(server): Phase 1 — server-core suites (occupancy, pay, exit, shift)

Completes the anti-fraud/safety core coverage on a fresh in-memory DB:

- occupancy.test.ts (12): the ledger-fold count, the capacity/full gate, and the
  reserved-subscriber-spots model — never double-count a parked subscriber, reserve
  tightens only the TRANSIENT gate.
- pay-station.test.ts (12): quote math against the frozen tariff, the signed-payment
  side effect (+ chain verify), no-session / no-tariff errors, the booth lookup view,
  active-session listing.
- exit-flow.test.ts (9): the GATE — refuse unknown / unpaid / grace-expired (no exit
  signed); a paid-within-grace session signs the exit; the booth transient path has NO
  subscription bypass; a prepaid subscriber leaves via the assist (reopenBarrier) path.
- shift-service.test.ts (14): site-wide single-open invariant, the takings SPLIT by
  source (subscription sales vs out-of-window vs transient tickets), drawer carry-
  forward + cash_in/out vouchers, Z-report sign + listShifts read-back.
- entry-flow.test.ts (5): the exported validateTicketCode Luhn typo-guard. (The
  capacity-gate/print-hold/sign-before-open paths need device fakes — covered in the
  device + route phases.)

Adds test-helpers.ts (real EventLog, silent logger, tariff seeder). server 68/68 green.

Note: apps/vision has 2 PRE-EXISTING failures (test_app.py) — environment drift now
that fast_alpr + the ONNX model are installed (the "stub mode" assertions are stale).
Untouched here; to be fixed in the vision phase.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/server/src/occupancy.test.ts

@@ -0,0 +1,133 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { createTestDb } from "@parking/db/testing";
+import { ledgerEvents, siteConfig, subscriptions, type Db } from "@parking/db";
+import { getOccupancy, occupancyCount, reservedSubscriberSpots } from "./occupancy.js";
+
+// Occupancy is a FOLD over the signed ledger, never a stored counter. These tests
+// pin: the entries-minus-exits count, the capacity/full gate, and the reserved-
+// subscriber-spots model (its trickiest invariant — never double-count a parked
+// subscriber, and never gate the subscriber's own entry).
+
+let db: Db;
+let close: () => void;
+
+beforeEach(() => {
+  const t = createTestDb();
+  db = t.db;
+  close = t.close;
+});
+afterEach(() => close());
+
+// Insert a ledger row directly (these fns read raw rows; signing is event-log's job).
+let idx = 0;
+function entry(identity: string, payload?: Record<string, unknown>) {
+  idx += 1;
+  db.insert(ledgerEvents).values({
+    id: `e${idx}`, index: idx, type: "vehicle_entry", direction: "entry",
+    identity, payload: payload ?? null, occurredAt: new Date().toISOString(),
+    signature: "x", keyId: "test",
+  }).run();
+}
+function exit(identity: string) {
+  idx += 1;
+  db.insert(ledgerEvents).values({
+    id: `e${idx}`, index: idx, type: "vehicle_exit", direction: "exit",
+    identity, payload: null, occurredAt: new Date().toISOString(),
+    signature: "x", keyId: "test",
+  }).run();
+}
+function setSite(v: Partial<typeof siteConfig.$inferInsert>) {
+  db.insert(siteConfig).values({ id: 1, ...v }).onConflictDoUpdate({ target: siteConfig.id, set: v }).run();
+}
+
+describe("occupancyCount", () => {
+  beforeEach(() => { idx = 0; });
+
+  it("is 0 with no events", () => {
+    expect(occupancyCount(db)).toBe(0);
+  });
+
+  it("counts open sessions (entries minus matching exits)", () => {
+    entry("A"); entry("B"); entry("C");
+    exit("B");
+    expect(occupancyCount(db)).toBe(2);
+  });
+
+  it("a re-entry after exit counts again", () => {
+    entry("A"); exit("A"); entry("A");
+    expect(occupancyCount(db)).toBe(1);
+  });
+});
+
+describe("getOccupancy — capacity + full gate", () => {
+  beforeEach(() => { idx = 0; });
+
+  it("uncapped: never full, free/effectiveFree null", () => {
+    setSite({ capacity: null });
+    entry("A");
+    const o = getOccupancy(db);
+    expect(o.full).toBe(false);
+    expect(o.free).toBeNull();
+    expect(o.effectiveFree).toBeNull();
+  });
+
+  it("capped: full when count reaches capacity", () => {
+    setSite({ capacity: 2 });
+    entry("A");
+    expect(getOccupancy(db).full).toBe(false);
+    entry("B");
+    const o = getOccupancy(db);
+    expect(o.full).toBe(true);
+    expect(o.free).toBe(0);
+  });
+});
+
+describe("reservedSubscriberSpots", () => {
+  beforeEach(() => { idx = 0; });
+
+  function addSub(id: string, opts: Partial<typeof subscriptions.$inferInsert> = {}) {
+    db.insert(subscriptions).values({ id, status: "active", quantity: 1, period: "month", ...opts }).run();
+  }
+
+  it("is 0 when the toggle is off (default)", () => {
+    setSite({ capacity: 10, reserveSubscriberSpots: false });
+    addSub("s1", { quantity: 2 });
+    expect(reservedSubscriberSpots(db)).toBe(0);
+  });
+
+  it("holds quantity spots for an active, not-parked subscription", () => {
+    setSite({ capacity: 10, reserveSubscriberSpots: true });
+    addSub("s1", { quantity: 2 });
+    expect(reservedSubscriberSpots(db)).toBe(2);
+  });
+
+  it("does NOT double-count a subscriber already parked (holds only the rest)", () => {
+    setSite({ capacity: 10, reserveSubscriberSpots: true });
+    addSub("s1", { quantity: 2 });
+    // One of the family's two cars is inside (occurrence entry carries permitId = sub id).
+    entry("SUBSESS-1", { permitId: "s1" });
+    expect(reservedSubscriberSpots(db)).toBe(1); // 2 quantity − 1 inside
+  });
+
+  it("ignores suspended/revoked and out-of-window subscriptions", () => {
+    setSite({ capacity: 10, reserveSubscriberSpots: true });
+    addSub("active", { quantity: 1 });
+    addSub("suspended", { quantity: 5, status: "suspended" });
+    addSub("expired", { quantity: 5, validTo: "2000-01-01T00:00:00.000Z" });
+    expect(reservedSubscriberSpots(db)).toBe(1);
+  });
+});
+
+describe("getOccupancy — reserved tightens the transient gate", () => {
+  beforeEach(() => { idx = 0; });
+
+  it("transient sees full once count + reserved ≥ capacity", () => {
+    setSite({ capacity: 3, reserveSubscriberSpots: true });
+    db.insert(subscriptions).values({ id: "s1", status: "active", quantity: 2, period: "month" }).run();
+    entry("A"); // 1 inside + 2 reserved = 3 ≥ capacity 3
+    const o = getOccupancy(db);
+    expect(o.reserved).toBe(2);
+    expect(o.effectiveFree).toBe(0);
+    expect(o.full).toBe(true);
+  });
+});