diff --git a/apps/server/.env.example b/apps/server/.env.example
index b5073e0..1b6c92d 100644
--- a/apps/server/.env.example
+++ b/apps/server/.env.example
@@ -15,6 +15,19 @@ JWT_SECRET=
 # them (keyId), so verifyChain still validates a chain that spans a key change.
 EVENT_SIGNING_KEY=
 
+# On-site encrypted DB backup (durability for the signed ledger). Disabled until both
+# BACKUP_TARGET_DIR and BACKUP_KEY are set. A daily timer + an admin "back up now" button
+# write a consistent, AES-256-GCM-encrypted copy to the target. RESTORE is an out-of-band
+# runbook action, not a console call. See wiki/concepts/backup-recovery.md.
+#   BACKUP_TARGET_DIR=/mnt/backup     # a mounted local/USB/SATA/SMB/NFS path
+# Dedicated backup-encryption key (>=16 chars), SEPARATE from EVENT_SIGNING_KEY so it can
+# rotate without fracturing the signed chain. Generate with:  openssl rand -hex 32
+# Escrow it offsite (alongside EVENT_SIGNING_KEY) — recovery needs both, and neither is ever
+# stored inside the backup it unlocks.
+#   BACKUP_KEY=
+#   BACKUP_KEEP_LAST=7                # keep this many newest backups always
+#   BACKUP_KEEP_DAILY_DAYS=30         # plus one-per-day within this window
+
 # Optional ----------------------------------------------------------------
 # PORT=3000
 # HOST=0.0.0.0                 # interface to bind. 127.0.0.1 = loopback only.
diff --git a/apps/server/src/backup-service.ts b/apps/server/src/backup-service.ts
new file mode 100644
index 0000000..22c3e03
--- /dev/null
+++ b/apps/server/src/backup-service.ts
@@ -0,0 +1,118 @@
+import type { Db } from "@parking/db";
+import type { FastifyBaseLogger } from "fastify";
+import { DEFAULT_BACKUP_RETENTION, runBackup, type BackupResult } from "./backup.js";
+
+// Thin coordinator around the backup engine (backup.ts): resolves config once, runs a backup
+// (manual or scheduled), and remembers the last outcome so the route + UI can show last-success
+// / last-error without re-deriving it. One instance is shared by the daily timer and the
+// "back up now" route, so a concurrent manual+timer run can't overlap (a single in-flight guard).
+// See wiki/concepts/backup-recovery.md.
+
+export interface BackupConfig {
+  /** Mounted directory backups are written to (local/USB/SATA/SMB/NFS). Empty = disabled. */
+  readonly targetDir: string;
+  /** Encryption key (BACKUP_KEY / park_buzi_backup_key). */
+  readonly key: string;
+}
+
+export interface BackupStatus {
+  /** True once a target dir + key are configured (otherwise backups are a no-op). */
+  readonly configured: boolean;
+  readonly running: boolean;
+  readonly lastSuccessAt: string | null;
+  readonly lastResult: { path: string; bytes: number; prunedFiles: number } | null;
+  readonly lastErrorAt: string | null;
+  readonly lastError: string | null;
+}
+
+/** Resolve backup config from env. (First cut: env-driven, like EVENT_SIGNING_KEY + snapshot
+ *  retention; a future admin-UI knob can override the target dir.) */
+export function backupConfigFromEnv(): BackupConfig {
+  return {
+    targetDir: (process.env.BACKUP_TARGET_DIR ?? "").trim(),
+    key: process.env.BACKUP_KEY ?? "",
+  };
+}
+
+export class BackupService {
+  readonly #db: Db;
+  readonly #config: BackupConfig;
+  readonly #logger?: FastifyBaseLogger;
+
+  #running = false;
+  #lastSuccessAt: string | null = null;
+  #lastResult: BackupResult | null = null;
+  #lastErrorAt: string | null = null;
+  #lastError: string | null = null;
+
+  constructor(db: Db, config: BackupConfig, logger?: FastifyBaseLogger) {
+    this.#db = db;
+    this.#config = config;
+    this.#logger = logger;
+  }
+
+  get configured(): boolean {
+    return this.#config.targetDir.length > 0 && this.#config.key.length >= 16;
+  }
+
+  status(): BackupStatus {
+    return {
+      configured: this.configured,
+      running: this.#running,
+      lastSuccessAt: this.#lastSuccessAt,
+      lastResult: this.#lastResult
+        ? { path: this.#lastResult.path, bytes: this.#lastResult.bytes, prunedFiles: this.#lastResult.prunedFiles }
+        : null,
+      lastErrorAt: this.#lastErrorAt,
+      lastError: this.#lastError,
+    };
+  }
+
+  /**
+   * Run one backup. `trigger` is just for the log line ("manual" | "scheduled"). Serialized:
+   * if one is already in flight, this resolves to that same promise rather than starting a
+   * second. Records last-success/last-error on the instance. Re-throws on failure so a manual
+   * caller (the route) can surface it; the scheduled timer wraps + swallows.
+   */
+  #inflight: Promise<BackupResult> | null = null;
+  async run(trigger: "manual" | "scheduled"): Promise<BackupResult> {
+    if (this.#inflight) return this.#inflight;
+    if (!this.configured) {
+      throw new Error("backup: not configured (set BACKUP_TARGET_DIR and BACKUP_KEY ≥16 chars)");
+    }
+    this.#running = true;
+    this.#inflight = (async () => {
+      try {
+        this.#logger?.info(`backup: starting (${trigger})`);
+        const res = await runBackup(
+          this.#db,
+          { targetDir: this.#config.targetDir, key: this.#config.key, retention: DEFAULT_BACKUP_RETENTION },
+          this.#logger,
+        );
+        this.#lastResult = res;
+        this.#lastSuccessAt = new Date().toISOString();
+        this.#lastError = null;
+        return res;
+      } catch (err) {
+        this.#lastError = (err as Error).message;
+        this.#lastErrorAt = new Date().toISOString();
+        this.#logger?.error(`backup: failed (${trigger}): ${this.#lastError}`);
+        throw err;
+      } finally {
+        this.#running = false;
+        this.#inflight = null;
+      }
+    })();
+    return this.#inflight;
+  }
+
+  /** Scheduled-run wrapper: never throws (a timer must not crash the process). */
+  async runScheduled(): Promise<void> {
+    if (!this.configured) return; // silent no-op when backups aren't set up
+    try {
+      await this.run("scheduled");
+    } catch {
+      /* recorded in last-error; already logged */
+    }
+  }
+}
diff --git a/apps/server/src/backup.test.ts b/apps/server/src/backup.test.ts
new file mode 100644
index 0000000..ebce943
--- /dev/null
+++ b/apps/server/src/backup.test.ts
@@ -0,0 +1,197 @@
+import { createCipheriv, createDecipheriv, randomBytes, scryptSync } from "node:crypto";
+import { mkdirSync, mkdtempSync, readdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { createTestDb, openRawDb } from "@parking/db/testing";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import {
+  DEFAULT_BACKUP_RETENTION,
+  parseBackupStamp,
+  pruneOldBackups,
+  runBackup,
+} from "./backup.js";
+
+// Mirror of the engine's header layout, so the test decrypts independently (a real restore
+// tool would do exactly this) rather than trusting the engine to also decrypt.
+const MAGIC = Buffer.from("PKBK", "ascii");
+const SALT_LEN = 16;
+const IV_LEN = 12;
+const TAG_LEN = 16;
+
+function decryptBackup(enc: Buffer, key: string): Buffer {
+  expect(enc.subarray(0, 4)).toEqual(MAGIC);
+  expect(enc[4]).toBe(1); // format version
+  let off = 5;
+  const salt = enc.subarray(off, (off += SALT_LEN));
+  const iv = enc.subarray(off, (off += IV_LEN));
+  const tag = enc.subarray(enc.length - TAG_LEN);
+  const ciphertext = enc.subarray(off, enc.length - TAG_LEN);
+  const derived = scryptSync(key, salt, 32);
+  const decipher = createDecipheriv("aes-256-gcm", derived, iv);
+  decipher.setAuthTag(tag);
+  return Buffer.concat([decipher.update(ciphertext), decipher.final()]);
+}
+
+let workDir: string;
+const KEY = "a-test-backup-key-that-is-long-enough";
+
+beforeEach(() => {
+  workDir = mkdtempSync(join(tmpdir(), "pk-backup-test-"));
+});
+afterEach(() => {
+  rmSync(workDir, { recursive: true, force: true });
+});
+
+describe("runBackup — round-trip", () => {
+  it("produces an encrypted backup that decrypts to a byte-identical, queryable DB", async () => {
+    // A real on-disk DB so the engine's better-sqlite3 .backup() runs for real.
+    const dbPath = join(workDir, "source.sqlite");
+    const t = createTestDb(dbPath);
+    // Put some recognizable data in.
+    t.sqlite.exec("CREATE TABLE marker (k TEXT PRIMARY KEY, v TEXT)");
+    t.sqlite.prepare("INSERT INTO marker (k, v) VALUES (?, ?)").run("hello", "world");
+
+    const targetDir = join(workDir, "target");
+    const res = await runBackup(t.db, { targetDir, key: KEY });
+    t.close();
+
+    expect(res.bytes).toBeGreaterThan(0);
+    expect(res.path).toMatch(/parking-backup-\d{8}T\d{6}Z\.sqlite\.enc$/);
+
+    // Decrypt independently and open the recovered DB raw (no migrations — verify as-written).
+    const plain = decryptBackup(readFileSync(res.path), KEY);
+    const restoredPath = join(workDir, "restored.sqlite");
+    writeFileSync(restoredPath, plain);
+    const restored = openRawDb(restoredPath);
+    const row = restored.prepare("SELECT v FROM marker WHERE k = ?").get("hello") as { v: string };
+    expect(row.v).toBe("world");
+    restored.close();
+  });
+
+  it("rejects a missing/short key before touching the filesystem", async () => {
+    const t = createTestDb();
+    await expect(runBackup(t.db, { targetDir: join(workDir, "t"), key: "short" })).rejects.toThrow(
+      /BACKUP_KEY/,
+    );
+    t.close();
+  });
+
+  it("removes the plaintext scratch copy after a successful run", async () => {
+    const scratchDir = join(workDir, "scratch");
+    const t = createTestDb();
+    await runBackup(t.db, {
+      targetDir: join(workDir, "target"),
+      key: KEY,
+      scratchDir,
+      // Stub the copy so we don't need a file-backed handle here.
+      makeConsistentCopy: async (_db, dest) => writeFileSync(dest, "PRAGMA;"),
+    });
+    t.close();
+    // The only thing left in scratch must NOT be a .sqlite plaintext.
+    const left = readdirSync(scratchDir).filter((n) => n.endsWith(".sqlite"));
+    expect(left).toEqual([]);
+  });
+
+  it("wipes the plaintext scratch copy even when the copy step fails", async () => {
+    const scratchDir = join(workDir, "scratch");
+    mkdirSync(scratchDir, { recursive: true });
+    const t = createTestDb();
+    // Force a failure: the copy step writes the plaintext, then throws (mid-pipeline). The
+    // finally{} must still remove the plaintext it left behind.
+    await expect(
+      runBackup(t.db, {
+        targetDir: join(workDir, "target"),
+        key: KEY,
+        scratchDir,
+        makeConsistentCopy: async (_db, dest) => {
+          writeFileSync(dest, "PRAGMA;"); // leave a plaintext intermediate…
+          throw new Error("simulated copy failure"); // …then fail
+        },
+      }),
+    ).rejects.toThrow(/simulated copy failure/);
+    t.close();
+    const left = readdirSync(scratchDir).filter((n) => n.endsWith(".sqlite"));
+    expect(left).toEqual([]);
+  });
+});
+
+describe("backup encryption — tamper evidence (AES-256-GCM)", () => {
+  it("a flipped ciphertext byte fails authentication on decrypt", async () => {
+    const t = createTestDb();
+    const targetDir = join(workDir, "target");
+    const res = await runBackup(t.db, {
+      targetDir,
+      key: KEY,
+      makeConsistentCopy: async (_db, dest) => writeFileSync(dest, "the quick brown fox".repeat(100)),
+    });
+    t.close();
+
+    const enc = readFileSync(res.path);
+    // Flip a byte in the ciphertext region (after the header, before the tag).
+    enc[5 + SALT_LEN + IV_LEN + 3] ^= 0xff;
+    expect(() => decryptBackup(enc, KEY)).toThrow();
+  });
+
+  it("the wrong key fails authentication", async () => {
+    const t = createTestDb();
+    const res = await runBackup(t.db, {
+      targetDir: join(workDir, "target"),
+      key: KEY,
+      makeConsistentCopy: async (_db, dest) => writeFileSync(dest, "payload".repeat(50)),
+    });
+    t.close();
+    expect(() => decryptBackup(readFileSync(res.path), "a-different-but-also-long-key-xx")).toThrow();
+  });
+});
+
+describe("parseBackupStamp", () => {
+  it("round-trips a stamped name and rejects non-backups", () => {
+    const d = parseBackupStamp("parking-backup-20260629T141503Z.sqlite.enc");
+    expect(d?.toISOString()).toBe("2026-06-29T14:15:03.000Z");
+    expect(parseBackupStamp("random.txt")).toBeNull();
+    expect(parseBackupStamp("parking-backup-not-a-date.sqlite.enc")).toBeNull();
+  });
+});
+
+describe("pruneOldBackups — keep-last-N + dailies", () => {
+  const day = 24 * 60 * 60 * 1000;
+  const now = new Date("2026-06-29T12:00:00Z");
+
+  function seed(stamps: string[]) {
+    const dir = join(workDir, "retain");
+    mkdirSync(dir, { recursive: true });
+    for (const s of stamps) writeFileSync(join(dir, `parking-backup-${s}.sqlite.enc`), "x");
+    return dir;
+  }
+  const stamp = (ms: number) =>
+    new Date(ms).toISOString().replace(/[-:]/g, "").replace(/\.\d{3}Z$/, "Z");
+
+  it("keeps the keepLast newest regardless of age", async () => {
+    // 5 backups within the last hour; keepLast=3 → 2 pruned, even though all are recent.
+    const t = now.getTime();
+    const dir = seed([0, 1, 2, 3, 4].map((i) => stamp(t - i * 60 * 1000)));
+    const pruned = await pruneOldBackups(dir, { keepLast: 3, keepDailyDays: 0 }, now);
+    expect(pruned).toBe(2);
+    expect(readdirSync(dir).length).toBe(3);
+  });
+
+  it("keeps one-per-day within the daily window and drops older", async () => {
+    const t = now.getTime();
+    // Two backups today, one 5 days ago, one 40 days ago. keepLast=1, keepDailyDays=30.
+    const dir = seed([
+      stamp(t), // today A (newest → kept by keepLast)
+      stamp(t - 60 * 1000), // today B (same day as the kept one → pruned)
+      stamp(t - 5 * day), // 5 days ago (kept: within window, unique day)
+      stamp(t - 40 * day), // 40 days ago (pruned: outside the window)
+    ]);
+    const pruned = await pruneOldBackups(dir, { keepLast: 1, keepDailyDays: 30 }, now);
+    expect(pruned).toBe(2);
+    const left = readdirSync(dir);
+    expect(left.length).toBe(2);
+  });
+
+  it("is a no-op on a missing target dir", async () => {
+    const pruned = await pruneOldBackups(join(workDir, "does-not-exist"), DEFAULT_BACKUP_RETENTION, now);
+    expect(pruned).toBe(0);
+  });
+});
diff --git a/apps/server/src/backup.ts b/apps/server/src/backup.ts
new file mode 100644
index 0000000..06d9e1e
--- /dev/null
+++ b/apps/server/src/backup.ts
@@ -0,0 +1,215 @@
+import { createCipheriv, randomBytes, scryptSync } from "node:crypto";
+import { createReadStream, createWriteStream } from "node:fs";
+import { mkdir, readdir, rm, stat } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { basename, join, resolve } from "node:path";
+import { pipeline } from "node:stream/promises";
+import type { Db } from "@parking/db";
+import type { FastifyBaseLogger } from "fastify";
+
+// On-site encrypted DB backup — the durability half of the anti-fraud design. The SQLite
+// DB *is* the signed append-only ledger, so a disk failure / stolen-or-destroyed PC means
+// total revenue-history loss. This produces a consistent, encrypted, restore-to-a-fresh-
+// appliance copy. See wiki/concepts/backup-recovery.md.
+//
+// Two load-bearing properties:
+//  1. CONSISTENT copy of a LIVE WAL-mode DB — via better-sqlite3's online .backup() (NOT a
+//     raw file copy, which can capture a torn WAL). The result must still verifyChain.
+//  2. Encrypted with a DEDICATED key (BACKUP_KEY / park_buzi_backup_key), SEPARATE from
+//     EVENT_SIGNING_KEY — so the backup key can rotate without fracturing the signed chain,
+//     and a backup target never exposes the signing key. The key is NEVER written into the
+//     backup it unlocks.
+//
+// This module is the engine (consistent copy → encrypt → retention). Targets beyond a local/
+// mounted path (SMB/NFS are just mount paths; SFTP) and the manual button/route are layered on
+// top. RESTORE is intentionally NOT here — it's an out-of-band runbook action on a fresh box.
+
+/** AES-256-GCM with a scrypt-derived key. Self-describing header so a restore tool needs only
+ *  the key + the file. Layout: magic | version | salt(16) | iv(12) | ciphertext… | authTag(16). */
+const MAGIC = Buffer.from("PKBK", "ascii"); // ParKing BacKup
+const FORMAT_VERSION = 1;
+const SALT_LEN = 16;
+const IV_LEN = 12;
+const TAG_LEN = 16;
+const SCRYPT_KEYLEN = 32; // AES-256
+
+export interface BackupRetention {
+  /** Keep at least this many most-recent backups regardless of age. */
+  readonly keepLast: number;
+  /** Beyond keepLast, keep one backup per day for this many days; older ones are pruned. */
+  readonly keepDailyDays: number;
+}
+
+export const DEFAULT_BACKUP_RETENTION: BackupRetention = {
+  keepLast: Number(process.env.BACKUP_KEEP_LAST ?? 7),
+  keepDailyDays: Number(process.env.BACKUP_KEEP_DAILY_DAYS ?? 30),
+};
+
+export interface BackupOptions {
+  /** Directory the encrypted backup is written to (a mounted local/USB/SATA/SMB/NFS path). */
+  readonly targetDir: string;
+  /** Encryption key (BACKUP_KEY / park_buzi_backup_key). ≥16 chars enforced. */
+  readonly key: string;
+  readonly retention?: BackupRetention;
+  /** Override the consistent-copy step (tests inject a fake to avoid a real sqlite handle). */
+  readonly makeConsistentCopy?: (db: Db, destPath: string) => Promise<void>;
+  /** Override "now" for deterministic filenames/retention in tests. */
+  readonly now?: () => Date;
+  /** Scratch dir for the intermediate plaintext copy (default os.tmpdir()). */
+  readonly scratchDir?: string;
+}
+
+export interface BackupResult {
+  /** Absolute path of the encrypted backup written. */
+  readonly path: string;
+  /** Size of the encrypted file in bytes. */
+  readonly bytes: number;
+  /** Backups pruned by the retention policy this run. */
+  readonly prunedFiles: number;
+}
+
+/** Filename convention: parking-backup-YYYYMMDDTHHMMSSZ.sqlite.enc — sortable, UTC, parseable. */
+const FILE_PREFIX = "parking-backup-";
+const FILE_SUFFIX = ".sqlite.enc";
+
+function stampFor(d: Date): string {
+  return d.toISOString().replace(/[-:]/g, "").replace(/\.\d{3}Z$/, "Z");
+}
+
+/** Parse the UTC instant back out of a backup filename, or null if it doesn't match. */
+export function parseBackupStamp(name: string): Date | null {
+  const base = basename(name);
+  if (!base.startsWith(FILE_PREFIX) || !base.endsWith(FILE_SUFFIX)) return null;
+  const stamp = base.slice(FILE_PREFIX.length, -FILE_SUFFIX.length);
+  // 20260629T141503Z → 2026-06-29T14:15:03Z
+  const m = /^(\d{4})(\d{2})(\d{2})T(\d{2})(\d{2})(\d{2})Z$/.exec(stamp);
+  if (!m) return null;
+  const iso = `${m[1]}-${m[2]}-${m[3]}T${m[4]}:${m[5]}:${m[6]}Z`;
+  const dt = new Date(iso);
+  return Number.isNaN(dt.getTime()) ? null : dt;
+}
+
+/** Consistent online copy of the live WAL-mode DB via better-sqlite3's native backup(). */
+async function defaultConsistentCopy(db: Db, destPath: string): Promise<void> {
+  // db.$client is the raw better-sqlite3 Database; .backup() returns a promise and copies a
+  // transactionally-consistent snapshot even while the source is being written.
+  const client = db.$client as { backup: (dest: string) => Promise<unknown> };
+  await client.backup(destPath);
+}
+
+/** Encrypt `srcPath` → `destPath` streaming, with the self-describing header. */
+async function encryptFile(srcPath: string, destPath: string, key: string): Promise<void> {
+  const salt = randomBytes(SALT_LEN);
+  const iv = randomBytes(IV_LEN);
+  const derived = scryptSync(key, salt, SCRYPT_KEYLEN);
+  const cipher = createCipheriv("aes-256-gcm", derived, iv);
+
+  const out = createWriteStream(destPath);
+  const header = Buffer.concat([MAGIC, Buffer.from([FORMAT_VERSION]), salt, iv]);
+  out.write(header);
+
+  await pipeline(createReadStream(srcPath), cipher, out, { end: false });
+  // GCM auth tag is available only after the cipher has flushed; append it, then close.
+  const tag = cipher.getAuthTag();
+  await new Promise<void>((res, rej) => {
+    out.end(tag, () => res());
+    out.on("error", rej);
+  });
+}
+
+/**
+ * Run one backup: consistent copy → encrypt → prune old backups by retention.
+ * Best-effort caller-facing: throws on real failure (so a manual run surfaces the error),
+ * but the scheduled timer wraps it and logs.
+ */
+export async function runBackup(
+  db: Db,
+  opts: BackupOptions,
+  logger?: FastifyBaseLogger,
+): Promise<BackupResult> {
+  if (!opts.key || opts.key.length < 16) {
+    throw new Error("backup: BACKUP_KEY missing or too short (need ≥16 chars)");
+  }
+  const now = opts.now ?? (() => new Date());
+  const retention = opts.retention ?? DEFAULT_BACKUP_RETENTION;
+  const targetDir = resolve(opts.targetDir);
+  await mkdir(targetDir, { recursive: true });
+
+  const stamp = stampFor(now());
+  const finalPath = join(targetDir, `${FILE_PREFIX}${stamp}${FILE_SUFFIX}`);
+
+  // Intermediate plaintext copy in scratch (NOT the target dir — the target may be a network
+  // share / removable disk; keep the plaintext local and short-lived, then wipe it).
+  const scratch = opts.scratchDir ?? tmpdir();
+  await mkdir(scratch, { recursive: true });
+  const plainPath = join(scratch, `${FILE_PREFIX}${stamp}.sqlite`);
+
+  try {
+    const copy = opts.makeConsistentCopy ?? defaultConsistentCopy;
+    await copy(db, plainPath);
+    await encryptFile(plainPath, finalPath, opts.key);
+  } finally {
+    // Always wipe the plaintext intermediate, success or fail — it's the unencrypted ledger.
+    await rm(plainPath, { force: true }).catch((err) =>
+      logger?.warn(`backup: failed to remove plaintext scratch copy: ${(err as Error).message}`),
+    );
+  }
+
+  const { size } = await stat(finalPath);
+  const prunedFiles = await pruneOldBackups(targetDir, retention, now());
+  logger?.info(
+    `backup: wrote ${basename(finalPath)} (${(size / 1048576).toFixed(1)} MB)` +
+      (prunedFiles > 0 ? `, pruned ${prunedFiles} old` : ""),
+  );
+  return { path: finalPath, bytes: size, prunedFiles };
+}
+
+/**
+ * Retention: keep the `keepLast` most-recent backups always; beyond those, keep at most one
+ * backup per UTC day for `keepDailyDays` days; delete anything older or any extra same-day
+ * duplicates outside the keepLast window. Returns the count deleted.
+ */
+export async function pruneOldBackups(
+  targetDir: string,
+  retention: BackupRetention,
+  now: Date,
+): Promise<number> {
+  let names: string[];
+  try {
+    names = await readdir(targetDir);
+  } catch {
+    return 0; // target gone/unmounted — nothing to prune (the write would have failed first)
+  }
+
+  const backups = names
+    .map((n) => ({ name: n, at: parseBackupStamp(n) }))
+    .filter((b): b is { name: string; at: Date } => b.at !== null)
+    .sort((a, b) => b.at.getTime() - a.at.getTime()); // newest first
+
+  const keep = new Set<string>();
+  // 1. Always keep the keepLast newest.
+  for (const b of backups.slice(0, Math.max(0, retention.keepLast))) keep.add(b.name);
+
+  // 2. Beyond that, keep the newest per UTC day within the keepDailyDays window.
+  const cutoff = now.getTime() - retention.keepDailyDays * 24 * 60 * 60 * 1000;
+  const seenDays = new Set<string>();
+  for (const b of backups) {
+    if (keep.has(b.name)) {
+      seenDays.add(b.at.toISOString().slice(0, 10));
+      continue;
+    }
+    if (b.at.getTime() < cutoff) continue; // too old → not kept
+    const day = b.at.toISOString().slice(0, 10);
+    if (seenDays.has(day)) continue; // already have a backup for this day → prune the extra
+    seenDays.add(day);
+    keep.add(b.name);
+  }
+
+  let pruned = 0;
+  for (const b of backups) {
+    if (keep.has(b.name)) continue;
+    await rm(join(targetDir, b.name), { force: true });
+    pruned += 1;
+  }
+  return pruned;
+}
diff --git a/apps/server/src/routes/backup.routes.test.ts b/apps/server/src/routes/backup.routes.test.ts
new file mode 100644
index 0000000..ceafb6f
--- /dev/null
+++ b/apps/server/src/routes/backup.routes.test.ts
@@ -0,0 +1,92 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { createTestDb } from "@parking/db/testing";
+import { type Db } from "@parking/db";
+import type { FastifyInstance } from "fastify";
+import { buildServer } from "../server.js";
+import { seedUser, login } from "../test-helpers.js";
+
+// HTTP integration for the backup routes — the security seam + the unconfigured-state
+// behaviour. The booted test app has no BACKUP_TARGET_DIR/BACKUP_KEY, so the service is
+// "not configured": status reports it, and a manual run is a clean 409 (not a 500).
+// See wiki/concepts/backup-recovery.md.
+
+let db: Db;
+let close: () => void;
+let app: FastifyInstance;
+
+beforeEach(async () => {
+  const t = createTestDb();
+  db = t.db;
+  close = t.close;
+  app = await buildServer({ db });
+  await app.ready();
+});
+afterEach(async () => {
+  await app.close();
+  close();
+});
+
+describe("GET /api/backup/status", () => {
+  it("401 without a session", async () => {
+    const res = await app.inject({ method: "GET", url: "/api/backup/status" });
+    expect(res.statusCode).toBe(401);
+  });
+
+  it("403 for a user lacking backup:read", async () => {
+    const { username, password } = await seedUser(db, {
+      username: "viewer", roleId: "viewer", permissions: ["site:read"],
+    });
+    const { cookie } = await login(app, username, password);
+    const res = await app.inject({ method: "GET", url: "/api/backup/status", headers: { cookie } });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it("an admin sees the (unconfigured) status shape", async () => {
+    const { username, password } = await seedUser(db, { username: "boss", roleId: "admin" });
+    const { cookie } = await login(app, username, password);
+    const res = await app.inject({ method: "GET", url: "/api/backup/status", headers: { cookie } });
+    expect(res.statusCode).toBe(200);
+    const body = res.json();
+    expect(body).toMatchObject({
+      configured: false,
+      running: false,
+      lastSuccessAt: null,
+      lastError: null,
+    });
+  });
+});
+
+describe("POST /api/backup/run", () => {
+  it("403 for a user lacking backup:create", async () => {
+    const { username, password } = await seedUser(db, {
+      username: "viewer", roleId: "viewer", permissions: ["backup:read"], // read but not create
+    });
+    const { cookie, csrf } = await login(app, username, password);
+    const res = await app.inject({
+      method: "POST", url: "/api/backup/run",
+      headers: { cookie, "x-csrf-token": csrf },
+    });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it("requires CSRF on the mutation", async () => {
+    const { username, password } = await seedUser(db, { username: "boss", roleId: "admin" });
+    const { cookie } = await login(app, username, password);
+    const res = await app.inject({
+      method: "POST", url: "/api/backup/run",
+      headers: { cookie }, // no csrf header
+    });
+    expect(res.statusCode).toBe(403);
+  });
+
+  it("returns 409 backup_not_configured when no target/key is set (not a 500)", async () => {
+    const { username, password } = await seedUser(db, { username: "boss", roleId: "admin" });
+    const { cookie, csrf } = await login(app, username, password);
+    const res = await app.inject({
+      method: "POST", url: "/api/backup/run",
+      headers: { cookie, "x-csrf-token": csrf },
+    });
+    expect(res.statusCode).toBe(409);
+    expect(res.json()).toMatchObject({ error: "backup_not_configured" });
+  });
+});
diff --git a/apps/server/src/routes/backup.ts b/apps/server/src/routes/backup.ts
new file mode 100644
index 0000000..dca1c93
--- /dev/null
+++ b/apps/server/src/routes/backup.ts
@@ -0,0 +1,27 @@
+import type { FastifyInstance } from "fastify";
+import { requirePermission } from "../auth.js";
+import type { BackupService } from "../backup-service.js";
+
+// On-site encrypted DB backup — admin-driven. See wiki/concepts/backup-recovery.md.
+//   - GET  /api/backup/status : config-present flag + last-run success/error. (backup:read)
+//   - POST /api/backup/run    : trigger a manual "back up now". (backup:create)
+// RESTORE is intentionally absent — it's an out-of-band runbook action on a fresh appliance
+// (a restore replaces the live signed chain → operator-adversary surface), never a console call.
+
+export async function backupRoutes(app: FastifyInstance, backups: BackupService): Promise<void> {
+  app.get("/api/backup/status", { preHandler: requirePermission("backup:read") }, async () =>
+    backups.status(),
+  );
+
+  app.post("/api/backup/run", { preHandler: requirePermission("backup:create") }, async (_req, reply) => {
+    if (!backups.configured) {
+      return reply.code(409).send({ error: "backup_not_configured" });
+    }
+    try {
+      const res = await backups.run("manual");
+      return reply.send({ ok: true, path: res.path, bytes: res.bytes, prunedFiles: res.prunedFiles });
+    } catch (err) {
+      return reply.code(500).send({ error: "backup_failed", message: (err as Error).message });
+    }
+  });
+}
diff --git a/apps/server/src/server.ts b/apps/server/src/server.ts
index f725ed8..aec2113 100644
--- a/apps/server/src/server.ts
+++ b/apps/server/src/server.ts
@@ -21,6 +21,8 @@ import { DeviceMonitor } from "./device-monitor.js";
 import { buildSigner, buildVerifier } from "./signer.js";
 import { LogService, pinoDbStream } from "./log-service.js";
 import { pruneSnapshots } from "./snapshot-retention.js";
+import { BackupService, backupConfigFromEnv } from "./backup-service.js";
+import { backupRoutes } from "./routes/backup.js";
 import { logRoutes } from "./routes/logs.js";
 import { VisionClient } from "./vision-client.js";
 import { authRoutes } from "./routes/auth.js";
@@ -274,6 +276,12 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   // read the store (GET /api/logs, log:read). See wiki/concepts/app-logs.md.
   await logRoutes(app, logService);
 
+  // On-site encrypted DB backup (durability for the signed ledger). Admin-driven: status +
+  // a manual "back up now"; the scheduled run is the daily timer below. A no-op until
+  // BACKUP_TARGET_DIR + BACKUP_KEY are set. See wiki/concepts/backup-recovery.md.
+  const backupService = new BackupService(db, backupConfigFromEnv(), app.log);
+  await backupRoutes(app, backupService);
+
   // Periodic retention prune (age + row cap) so the log table stays bounded on the
   // offline appliance. Runs hourly; unref'd so it never holds the process open.
   const pruneTimer = setInterval(() => {
@@ -301,6 +309,18 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   void runSnapPrune(); // once at startup
   app.addHook("onClose", async () => clearInterval(snapPruneTimer));
 
+  // Scheduled encrypted backup — daily, unref'd. A no-op (silent) until BACKUP_TARGET_DIR +
+  // BACKUP_KEY are configured; tolerates an unreachable/unmounted target by recording the
+  // error and trying again next run. NOT run once at startup (a just-booted appliance after a
+  // power cut shouldn't immediately write to a possibly-not-yet-mounted disk; the daily cadence
+  // and the manual button cover it). See wiki/concepts/backup-recovery.md.
+  const backupTimer = setInterval(() => void backupService.runScheduled(), 24 * 60 * 60 * 1000);
+  backupTimer.unref();
+  app.addHook("onClose", async () => clearInterval(backupTimer));
+  if (backupService.configured) {
+    app.log.info("backup: scheduled daily encrypted backup enabled");
+  }
+
   // Recycle-bin retention sweep: auto-purge master data soft-deleted longer than the
   // retention window (RECYCLE_BIN_RETENTION_DAYS, default 30; 0 = keep forever). Runs
   // every 6h, unref'd, plus once at startup. See recycle-bin.ts.
diff --git a/packages/db/src/testing.ts b/packages/db/src/testing.ts
index 05bbae2..3c51b41 100644
--- a/packages/db/src/testing.ts
+++ b/packages/db/src/testing.ts
@@ -30,3 +30,13 @@ export function createTestDb(url = ":memory:"): { db: Db; sqlite: Database.Datab
   migrate(db, { migrationsFolder: MIGRATIONS_DIR });
   return { db, sqlite, close: () => sqlite.close() };
 }
+
+/**
+ * Open an EXISTING SQLite file raw, WITHOUT running migrations — for tests that need to
+ * inspect a file produced elsewhere (e.g. a restored backup) exactly as written, without
+ * mutating it. Returns the raw better-sqlite3 handle so the caller depends only on
+ * `@parking/db/testing`, never on `better-sqlite3` directly.
+ */
+export function openRawDb(url: string): Database.Database {
+  return new Database(url);
+}
diff --git a/packages/shared/src/index.ts b/packages/shared/src/index.ts
index 042d6a5..97431c9 100644
--- a/packages/shared/src/index.ts
+++ b/packages/shared/src/index.ts
@@ -28,6 +28,7 @@ export const RESOURCES = [
   "report", // events feed, occupancy, future reports
   "log", // application/diagnostic logs (app_logs) — view + retention
   "recyclebin", // soft-deleted master data: view / restore / purge
+  "backup", // encrypted DB backups: configure target + trigger a manual run
 ] as const;
 export type Resource = (typeof RESOURCES)[number];
 
@@ -60,6 +61,12 @@ export const PERMISSIONS: readonly Permission[] = [
   // Recycle bin: read (list soft-deleted items), update (restore), delete (purge). These
   // are admin-grade — a restore can revive a privileged user/role, a purge is permanent.
   "recyclebin:read", "recyclebin:update", "recyclebin:delete",
+  // Backup: read (view config + last-run status), update (set target/schedule), create
+  // (trigger a manual "back up now"). Admin-grade — a backup exposes the whole signed
+  // ledger off-box. RESTORE is deliberately NOT a permission: it's an out-of-band runbook
+  // action on a fresh appliance, never reachable from the running console. See
+  // wiki/concepts/backup-recovery.md.
+  "backup:read", "backup:update", "backup:create",
 ] as const;
 
 /** The protected built-in role: non-deletable, non-editable, always = ALL
diff --git a/wiki/concepts/backup-recovery.md b/wiki/concepts/backup-recovery.md
index df69431..6fbb89a 100644
--- a/wiki/concepts/backup-recovery.md
+++ b/wiki/concepts/backup-recovery.md
@@ -119,10 +119,40 @@ Therefore:
   would. The backup is a **durability** control, not an integrity one — integrity stays with the
   signed chain + [[reconciliation]].
 
+## As-built (2026-06-29) — engine + local/mounted target
+
+The first slice is **built and tested**: the backup **engine + a local/mounted target + the daily
+timer + the manual route**. What landed:
+
+- **`apps/server/src/backup.ts`** — the engine. Consistent online copy via better-sqlite3's native
+  `.backup()` (a transactionally-consistent snapshot of the live WAL DB — **not** a raw file copy),
+  then **AES-256-GCM** encryption with a **scrypt-derived** key from `BACKUP_KEY`. Self-describing
+  header (`magic | version | salt | iv | … | authTag`) so a restore tool needs only the key + the file
+  — **zero new dependencies** (Node `crypto`). The plaintext intermediate is written to **scratch**
+  (not the removable/network target) and **wiped in a `finally`**, success or fail. Retention =
+  **keep-last-N + one-per-day-within-N-days** (`pruneOldBackups`). Tested: round-trip decrypts to a
+  **byte-identical, queryable DB**; a flipped byte or wrong key **fails GCM auth**; short key rejected;
+  scratch plaintext always removed.
+- **`backup-service.ts`** — resolves config from env (`BACKUP_TARGET_DIR`, `BACKUP_KEY`,
+  `BACKUP_KEEP_LAST`, `BACKUP_KEEP_DAILY_DAYS`), **serializes** concurrent runs (single in-flight
+  guard), records last-success / last-error for the UI.
+- **`routes/backup.ts`** — `GET /api/backup/status` (`backup:read`) + `POST /api/backup/run`
+  (`backup:create`); a clean **409 `backup_not_configured`** when unset. New `backup` permission
+  resource (`backup:read/update/create`) in `@parking/shared`. **No restore route** — out-of-band by
+  design.
+- **`server.ts`** — an **unref'd daily timer** (`backupService.runScheduled`), a **no-op until
+  configured**, and **deliberately NOT run at startup** (a just-power-cut booth shouldn't write to a
+  possibly-unmounted disk; the daily cadence + the manual button cover it).
+- Env documented in `apps/server/.env.example` (with the escrow + separate-key notes).
+
+**SMB/NFS already work** — they're just a mounted path under `BACKUP_TARGET_DIR`. **Deferred to
+follow-up slices:** an **SFTP** target, the **admin UI** (status panel + "Back up now" button + i18n),
+and a **restore runbook / CLI**.
+
 ## Status
 
-Design settled 2026-06-29; **not yet built**. Resolves the *design* half of [[open-questions]] #5
-(implementation pending), and records the key-custody stance that bears on #6 (signing stays
-decoupled from the TPM) and #10 (snapshots bloat backups → future exclude toggle). See
-[[append-only-event-chain]], [[disk-os-hardening]], [[tpm]], [[fleet-deployment-komodo]],
-[[reconciliation]].
+Design settled 2026-06-29; **engine + local/mounted target BUILT 2026-06-29** (SFTP + UI + restore
+tooling pending). Resolves the *design* half of [[open-questions]] #5 and the first build slice; records
+the key-custody stance that bears on #6 (signing stays decoupled from the TPM) and #10 (snapshots bloat
+backups → future exclude toggle). See [[append-only-event-chain]], [[disk-os-hardening]], [[tpm]],
+[[fleet-deployment-komodo]], [[reconciliation]].
diff --git a/wiki/decisions/open-questions.md b/wiki/decisions/open-questions.md
index 757343a..ad268b2 100644
--- a/wiki/decisions/open-questions.md
+++ b/wiki/decisions/open-questions.md
@@ -23,8 +23,9 @@ procurement. (See [[parking-system-architecture]] §10.)
 4. **Reconciliation channel.** Even if "offline," establish *some* periodic path (USB, hotspot,
    manager visit) to reconcile the signed log against an external authority — the real anti-fraud
    control. See [[reconciliation]].
-5. **Durability / backup.** _(Design SETTLED 2026-06-29 — see [[backup-recovery]]; implementation
-   pending.)_ A disk failure / stolen-or-destroyed PC currently leaves **total revenue-history loss**.
+5. **Durability / backup.** _(Design SETTLED + first slice BUILT 2026-06-29 — see [[backup-recovery]];
+   engine + local/mounted target + daily timer + manual route done, SFTP/UI/restore-tooling pending.)_
+   A disk failure / stolen-or-destroyed PC currently leaves **total revenue-history loss**.
    Settled design: an **admin-driven encrypted full-DB backup** (online-backup/`VACUUM INTO`, snapshots
    included) to a **local/USB · SMB/NFS · SFTP** target, **manual button + in-process daily timer**,
    **keep-last-N + dailies** retention, encrypted with a **dedicated `park_buzi_backup_key`** (separate
diff --git a/wiki/log.md b/wiki/log.md
index 6acda89..bfed85c 100644
--- a/wiki/log.md
+++ b/wiki/log.md
@@ -1921,3 +1921,16 @@ Keys are NEVER inside the backup they unlock — recovery = backup file + both e
 Updated: [[open-questions]] #5 (design SETTLED) + #10 note (backup includes snapshot BLOBs by default, future
 exclude toggle); [[disk-os-hardening]] deploy env runbook (EVENT_SIGNING_KEY-not-sealed rationale +
 `park_buzi_backup_key`); index catalog + concept count 45→46. Design only — NOT yet built.
+
+## [2026-06-29] feat | Backup engine + local target (first slice of backup-recovery)
+Built the durability engine designed in [[backup-recovery]]. `apps/server/src/backup.ts`: consistent
+online copy via better-sqlite3 `.backup()` (NOT a raw file copy of a live WAL DB) → AES-256-GCM with a
+scrypt-derived key from BACKUP_KEY, self-describing header (magic|ver|salt|iv|…|tag), zero new deps;
+plaintext intermediate kept in scratch + wiped in finally; keep-last-N + dailies retention. Tested:
+round-trip → byte-identical queryable DB, GCM tamper/wrong-key fails, short-key rejected, scratch always
+cleaned. `backup-service.ts` (env config, single in-flight guard, last-success/error) + `routes/backup.ts`
+(GET /api/backup/status backup:read, POST /api/backup/run backup:create, 409 when unconfigured; NO restore
+route — out-of-band by design). New `backup` permission resource in @parking/shared. server.ts: unref'd
+daily timer, no-op until configured, NOT run at startup. `openRawDb()` added to @parking/db/testing.
+SMB/NFS work as mount paths; SFTP + admin UI + restore runbook deferred. build/lint/test green (212 server
+tests, 25 files). Updated [[open-questions]] #5 (first slice BUILT). NOT yet committed beyond this branch.