diff --git a/apps/server/package.json b/apps/server/package.json
index 4bf0185..c20dff6 100644
--- a/apps/server/package.json
+++ b/apps/server/package.json
@@ -9,7 +9,8 @@
     "start": "node --env-file-if-exists=.env dist/index.js",
     "seed-admin": "node --env-file-if-exists=.env scripts/seed-admin.mjs",
     "typecheck": "tsc --noEmit",
-    "lint": "tsc --noEmit"
+    "lint": "tsc --noEmit",
+    "test": "vitest run"
   },
   "dependencies": {
     "@fastify/cookie": "^11.0.2",
@@ -28,6 +29,7 @@
     "@types/bcrypt": "6.0.0",
     "@types/node": "25.9.3",
     "tsx": "4.22.4",
-    "typescript": "6.0.3"
+    "typescript": "6.0.3",
+    "vitest": "^4.1.9"
   }
 }
diff --git a/apps/server/src/event-log.test.ts b/apps/server/src/event-log.test.ts
new file mode 100644
index 0000000..389e0db
--- /dev/null
+++ b/apps/server/src/event-log.test.ts
@@ -0,0 +1,129 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { createTestDb } from "@parking/db/testing";
+import { ledgerEvents, eq, type Db } from "@parking/db";
+import { EventLog, canonicalize, hashEvent } from "./event-log.js";
+import { SoftwareSigner, buildVerifier } from "./signer.js";
+
+// The append-only, hash-chained, signed event log is THE anti-fraud primitive
+// (threat model: the operator at the booth). These tests pin every integrity rule:
+// monotonic index, prevHash linkage, payload-in-signature, and that verifyChain()
+// catches each class of tamper (content edit, reorder, deletion gap, forged sig,
+// missing key). No live DB is touched — a fresh in-memory SQLite per test.
+
+const SECRET = "test-event-signing-key-0123456789";
+
+let db: Db;
+let close: () => void;
+let log: EventLog;
+
+beforeEach(() => {
+  const t = createTestDb();
+  db = t.db;
+  close = t.close;
+  log = new EventLog(db, new SoftwareSigner(SECRET), buildVerifier);
+});
+
+afterEach(() => close());
+
+describe("EventLog.append — chain construction", () => {
+  it("assigns a monotonic index starting at 1", async () => {
+    const a = await log.append({ type: "vehicle_entry", identity: "T1" });
+    const b = await log.append({ type: "vehicle_exit", identity: "T1" });
+    expect(a.index).toBe(1);
+    expect(b.index).toBe(2);
+  });
+
+  it("genesis event has a null prevHash; the next chains to it", async () => {
+    const a = await log.append({ type: "vehicle_entry", identity: "T1" });
+    const b = await log.append({ type: "vehicle_exit", identity: "T1" });
+    expect(a.prevHash).toBeNull();
+    expect(b.prevHash).toBe(hashEvent(canonicalize(a)));
+  });
+
+  it("signs each row under the active keyId", async () => {
+    const row = await log.append({ type: "payment", identity: "T1", payload: { amountMinor: 100 } });
+    expect(row.keyId).toBe("sw-hmac-v2");
+    expect(new SoftwareSigner(SECRET).verify(canonicalize(row), row.signature)).toBe(true);
+  });
+
+  it("serializes concurrent appends without index collisions", async () => {
+    const rows = await Promise.all(
+      Array.from({ length: 25 }, (_, i) => log.append({ type: "vehicle_entry", identity: `T${i}` })),
+    );
+    const indices = rows.map((r) => r.index).sort((a, b) => a - b);
+    expect(indices).toEqual(Array.from({ length: 25 }, (_, i) => i + 1));
+  });
+});
+
+describe("EventLog.verifyChain — integrity", () => {
+  async function seed() {
+    await log.append({ type: "vehicle_entry", identity: "T1", direction: "entry" });
+    await log.append({ type: "payment", identity: "T1", payload: { amountMinor: 200, tariffVersionId: "tv1" } });
+    await log.append({ type: "vehicle_exit", identity: "T1", direction: "exit" });
+  }
+
+  it("accepts an untampered chain", async () => {
+    await seed();
+    expect(log.verifyChain()).toEqual({ ok: true });
+  });
+
+  it("accepts an empty chain", () => {
+    expect(log.verifyChain()).toEqual({ ok: true });
+  });
+
+  it("detects a tampered payload (the money amount)", async () => {
+    await seed();
+    // Rewrite the payment amount directly in the DB — exactly the booth-operator
+    // fraud the signed payload defends against.
+    db.update(ledgerEvents).set({ payload: { amountMinor: 1, tariffVersionId: "tv1" } }).where(eq(ledgerEvents.index, 2)).run();
+    const r = log.verifyChain();
+    expect(r.ok).toBe(false);
+    if (!r.ok) {
+      expect(r.index).toBe(2);
+      expect(r.reason).toMatch(/signature invalid/);
+    }
+  });
+
+  it("detects a deleted row as an index gap", async () => {
+    await seed();
+    db.delete(ledgerEvents).where(eq(ledgerEvents.index, 2)).run();
+    const r = log.verifyChain();
+    expect(r.ok).toBe(false);
+    if (!r.ok) expect(r.reason).toMatch(/index gap/);
+  });
+
+  it("detects a broken prevHash link (reordering / re-chaining)", async () => {
+    await seed();
+    db.update(ledgerEvents).set({ prevHash: "0".repeat(64) }).where(eq(ledgerEvents.index, 3)).run();
+    const r = log.verifyChain();
+    expect(r.ok).toBe(false);
+    if (!r.ok) {
+      expect(r.index).toBe(3);
+      expect(r.reason).toMatch(/prevHash/);
+    }
+  });
+
+  it("detects an event signed under a key that is no longer configured", async () => {
+    await seed();
+    // Re-sign row 2 under an unknown keyId — buildVerifier can't resolve it.
+    db.update(ledgerEvents).set({ keyId: "atecc608-slot9" }).where(eq(ledgerEvents.index, 2)).run();
+    const r = log.verifyChain();
+    expect(r.ok).toBe(false);
+    if (!r.ok) expect(r.reason).toMatch(/no signer for keyId/);
+  });
+});
+
+describe("canonicalize — byte-stability", () => {
+  it("is independent of payload key order (sorted recursively)", () => {
+    const base = { index: 1, type: "payment", direction: null, source: null, identity: "T1", occurredAt: "2026-06-21T10:00:00.000Z", prevHash: null };
+    const a = canonicalize({ ...base, payload: { amountMinor: 100, tariffVersionId: "tv1" } });
+    const b = canonicalize({ ...base, payload: { tariffVersionId: "tv1", amountMinor: 100 } });
+    expect(a).toBe(b);
+  });
+
+  it("changes when any signed field changes", () => {
+    const base = { index: 1, type: "payment" as const, direction: null, source: null, identity: "T1", payload: { amountMinor: 100 }, occurredAt: "2026-06-21T10:00:00.000Z", prevHash: null };
+    expect(canonicalize(base)).not.toBe(canonicalize({ ...base, payload: { amountMinor: 101 } }));
+    expect(canonicalize(base)).not.toBe(canonicalize({ ...base, identity: "T2" }));
+  });
+});
diff --git a/apps/server/src/signer.test.ts b/apps/server/src/signer.test.ts
new file mode 100644
index 0000000..fd636c9
--- /dev/null
+++ b/apps/server/src/signer.test.ts
@@ -0,0 +1,77 @@
+import { describe, expect, it } from "vitest";
+import { SoftwareSigner, buildSigner, buildVerifier } from "./signer.js";
+
+// The signer is half of the anti-fraud chain (the other half is event-log's hashing).
+// These tests pin: a sign/verify round-trip, rejection of any tamper, constant-time
+// length handling, and the keyId rotation contract that lets one chain span keys.
+
+describe("SoftwareSigner", () => {
+  it("verifies its own signature (round-trip)", () => {
+    const s = new SoftwareSigner("a-test-secret-key");
+    const sig = s.sign("hello world");
+    expect(s.verify("hello world", sig)).toBe(true);
+  });
+
+  it("rejects a signature over different content (tamper-evidence)", () => {
+    const s = new SoftwareSigner("a-test-secret-key");
+    const sig = s.sign("amount=100");
+    // Flip the signed content — the whole point of signing the payload.
+    expect(s.verify("amount=9999", sig)).toBe(false);
+  });
+
+  it("rejects a signature made under a different key (forgery)", () => {
+    const real = new SoftwareSigner("the-real-host-key");
+    const forger = new SoftwareSigner("an-attacker-guess");
+    const forged = forger.sign("amount=100");
+    expect(real.verify("amount=100", forged)).toBe(false);
+  });
+
+  it("rejects a malformed / wrong-length signature without throwing", () => {
+    const s = new SoftwareSigner("a-test-secret-key");
+    // timingSafeEqual throws on length mismatch; verify() must guard it.
+    expect(() => s.verify("x", "deadbeef")).not.toThrow();
+    expect(s.verify("x", "deadbeef")).toBe(false);
+    expect(s.verify("x", "")).toBe(false);
+  });
+
+  it("is deterministic — same key + payload yields the same signature", () => {
+    const a = new SoftwareSigner("k").sign("p");
+    const b = new SoftwareSigner("k").sign("p");
+    expect(a).toBe(b);
+  });
+
+  it("defaults to the v2 keyId", () => {
+    expect(new SoftwareSigner("k").keyId).toBe("sw-hmac-v2");
+  });
+});
+
+describe("buildSigner", () => {
+  // vitest.config.ts sets EVENT_SIGNING_KEY + JWT_SECRET for the whole run.
+  it("prefers EVENT_SIGNING_KEY (keyId sw-hmac-v2)", () => {
+    const s = buildSigner();
+    expect(s.keyId).toBe("sw-hmac-v2");
+    const sig = s.sign("x");
+    expect(s.verify("x", sig)).toBe(true);
+  });
+});
+
+describe("buildVerifier (key rotation)", () => {
+  it("returns a working verifier for the configured v2 key", () => {
+    const v = buildVerifier("sw-hmac-v2");
+    expect(v).toBeDefined();
+    const signer = new SoftwareSigner(process.env.EVENT_SIGNING_KEY!, "sw-hmac-v2");
+    expect(v!.verify("x", signer.sign("x"))).toBe(true);
+  });
+
+  it("resolves the jwtfallback key when present", () => {
+    const v = buildVerifier("sw-hmac-jwtfallback");
+    expect(v).toBeDefined();
+    const signer = new SoftwareSigner(process.env.JWT_SECRET!, "sw-hmac-jwtfallback");
+    expect(v!.verify("x", signer.sign("x"))).toBe(true);
+  });
+
+  it("returns undefined for an unknown keyId (key gone, not a false tamper)", () => {
+    expect(buildVerifier("atecc608-slot0")).toBeUndefined();
+    expect(buildVerifier("nonsense")).toBeUndefined();
+  });
+});
diff --git a/apps/server/tsconfig.json b/apps/server/tsconfig.json
index c432d9e..f68c250 100644
--- a/apps/server/tsconfig.json
+++ b/apps/server/tsconfig.json
@@ -9,5 +9,6 @@
     { "path": "../../packages/db" },
     { "path": "../../packages/devices" }
   ],
-  "include": ["src/**/*"]
+  "include": ["src/**/*"],
+  "exclude": ["src/**/*.test.ts"]
 }
diff --git a/apps/server/vitest.config.ts b/apps/server/vitest.config.ts
new file mode 100644
index 0000000..66aa278
--- /dev/null
+++ b/apps/server/vitest.config.ts
@@ -0,0 +1,15 @@
+import { defineConfig } from "vitest/config";
+
+// Server tests live next to the code under test (src/**/*.test.ts). They run against
+// a fresh in-memory SQLite from @parking/db/testing — never the live parking.sqlite.
+// A test signing key is set here so the SoftwareSigner/buildSigner path works without
+// a real .env (the value is irrelevant — tests assert self-consistency, not secrecy).
+export default defineConfig({
+  test: {
+    include: ["src/**/*.test.ts"],
+    env: {
+      EVENT_SIGNING_KEY: "test-event-signing-key-0123456789",
+      JWT_SECRET: "test-jwt-secret-0123456789abcdef",
+    },
+  },
+});
diff --git a/packages/db/package.json b/packages/db/package.json
index 13903fc..f9b0b8c 100644
--- a/packages/db/package.json
+++ b/packages/db/package.json
@@ -11,6 +11,10 @@
     "./schema": {
       "types": "./dist/schema.d.ts",
       "default": "./dist/schema.js"
+    },
+    "./testing": {
+      "types": "./dist/testing.d.ts",
+      "default": "./dist/testing.js"
     }
   },
   "main": "./dist/index.js",
diff --git a/packages/db/src/testing.ts b/packages/db/src/testing.ts
new file mode 100644
index 0000000..05bbae2
--- /dev/null
+++ b/packages/db/src/testing.ts
@@ -0,0 +1,32 @@
+import { fileURLToPath } from "node:url";
+import { dirname, resolve } from "node:path";
+import Database from "better-sqlite3";
+import { drizzle } from "drizzle-orm/better-sqlite3";
+import { migrate } from "drizzle-orm/better-sqlite3/migrator";
+import * as schema from "./schema.js";
+import type { Db } from "./index.js";
+
+// Test-only helper: a fresh, fully-migrated SQLite database with NO live-DB risk.
+// Every server/integration test spins one of these so suites are isolated and
+// deterministic — never the real parking.sqlite. Not exported from the package
+// root (`@parking/db`); import it from `@parking/db/testing` in test code only.
+
+// The migrations live next to this package's compiled output. From dist/testing.js
+// that's ../drizzle; resolve it off import.meta.url so it works regardless of the
+// caller's cwd (tests run from apps/server, packages/devices, etc.).
+const MIGRATIONS_DIR = resolve(dirname(fileURLToPath(import.meta.url)), "../drizzle");
+
+/**
+ * Open an in-memory SQLite (or a temp file if `url` is given), apply every Drizzle
+ * migration in order, and return a typed Drizzle handle plus the raw better-sqlite3
+ * connection (so a test can assert raw rows or `.close()` it). The schema matches
+ * production exactly because it's the SAME migration set, not a hand-rolled DDL.
+ */
+export function createTestDb(url = ":memory:"): { db: Db; sqlite: Database.Database; close: () => void } {
+  const sqlite = new Database(url);
+  sqlite.pragma("journal_mode = WAL");
+  sqlite.pragma("foreign_keys = ON");
+  const db = drizzle(sqlite, { schema }) as Db;
+  migrate(db, { migrationsFolder: MIGRATIONS_DIR });
+  return { db, sqlite, close: () => sqlite.close() };
+}
diff --git a/packages/shared/tsconfig.json b/packages/shared/tsconfig.json
index bfdb609..1d607f2 100644
--- a/packages/shared/tsconfig.json
+++ b/packages/shared/tsconfig.json
@@ -5,5 +5,6 @@
     "outDir": "./dist",
     "composite": true
   },
-  "include": ["src/**/*"]
+  "include": ["src/**/*"],
+  "exclude": ["src/**/*.test.ts"]
 }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 22ade16..635801e 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -79,6 +79,9 @@ importers:
       typescript:
         specifier: 6.0.3
         version: 6.0.3
+      vitest:
+        specifier: ^4.1.9
+        version: 4.1.9(@types/node@25.9.3)(vite@8.0.16(@types/node@25.9.3)(esbuild@0.28.1)(jiti@2.7.0)(tsx@4.22.4))
 
   apps/vision: {}