diff --git a/server/src/nest/storage/drivers/local.driver.ts b/server/src/nest/storage/drivers/local.driver.ts
new file mode 100644
index 000000000..35ae0e333
--- /dev/null
+++ b/server/src/nest/storage/drivers/local.driver.ts
@@ -0,0 +1,198 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { randomUUID } from 'node:crypto';
+import { pipeline } from 'node:stream/promises';
+import type { Readable } from 'node:stream';
+import { assertValidKey, assertValidPrefix } from '../storage-keys';
+import {
+  isLocalTempFile,
+  StorageBackendError,
+  StorageInvalidKeyError,
+  StorageNotFoundError,
+  type ByteRange,
+  type LocalTempFile,
+  type ObjectStat,
+  type StorageDriver,
+} from '../storage.types';
+
+const SPOOL_DIR_NAME = '.tmp';
+
+function errnoCode(err: unknown): string | undefined {
+  return (err as NodeJS.ErrnoException).code;
+}
+
+/** ENOENT on the path or any parent segment being a file — both are a miss. */
+function isMissing(err: unknown): boolean {
+  const code = errnoCode(err);
+  return code === 'ENOENT' || code === 'ENOTDIR';
+}
+
+/**
+ * The only real driver type in v1: plain files under a root directory.
+ *
+ * `put` is atomic — stream sources spool into the hidden `<root>/.tmp` and
+ * commit with a single same-volume `rename()`; caller-owned temp files rename
+ * directly with an EXDEV copy-fallback for the cross-volume edge case. The
+ * root is realpath'd at `init()` because in Docker both storage anchors are
+ * symlinks (Dockerfile: `/app/server/uploads → /app/uploads`,
+ * `/app/server/data → /app/data`) and a naive `startsWith` containment check
+ * misbehaves on symlinked roots — the trap backup.impl.ts:423 and
+ * nest/plugins/paths.ts already work around with `realpathSync`.
+ */
+export class LocalDriver implements StorageDriver {
+  readonly id: string;
+  private readonly configuredRoot: string;
+  private realRoot: string | null = null;
+
+  constructor(opts: { id: string; root: string }) {
+    this.id = opts.id;
+    this.configuredRoot = opts.root;
+  }
+
+  /**
+   * Ensure root + spool + category prefix dirs exist and resolve the real
+   * root. Runs on every registry load (boot and reload()) so a newly
+   * configured backend is usable immediately; `cleanSpool` is passed at boot
+   * only — on a reload it could delete an in-flight upload's spool file.
+   */
+  init(opts: { ensurePrefixes?: string[]; cleanSpool?: boolean } = {}): void {
+    fs.mkdirSync(this.configuredRoot, { recursive: true });
+    this.realRoot = fs.realpathSync(this.configuredRoot);
+    fs.mkdirSync(this.spoolDir(), { recursive: true });
+    for (const prefix of opts.ensurePrefixes ?? []) {
+      assertValidPrefix(prefix);
+      if (prefix) fs.mkdirSync(path.join(this.realRoot, prefix), { recursive: true });
+    }
+    if (opts.cleanSpool) {
+      for (const entry of fs.readdirSync(this.spoolDir())) {
+        fs.rmSync(path.join(this.spoolDir(), entry), { recursive: true, force: true });
+      }
+    }
+  }
+
+  private root(): string {
+    if (!this.realRoot) {
+      throw new StorageBackendError(`LocalDriver '${this.id}' used before init()`);
+    }
+    return this.realRoot;
+  }
+
+  private spoolDir(): string {
+    return path.join(this.root(), SPOOL_DIR_NAME);
+  }
+
+  getSpoolDir(): string {
+    return this.spoolDir();
+  }
+
+  /**
+   * Central key validation plus defense-in-depth containment: even a key that
+   * somehow passed validation must resolve inside the real root.
+   */
+  private resolvePath(key: string): string {
+    assertValidKey(key);
+    const resolved = path.resolve(this.root(), key);
+    if (!resolved.startsWith(this.root() + path.sep)) {
+      throw new StorageInvalidKeyError(key);
+    }
+    return resolved;
+  }
+
+  getLocalPath(key: string): string {
+    return this.resolvePath(key);
+  }
+
+  async put(key: string, source: Readable | LocalTempFile): Promise<void> {
+    const dest = this.resolvePath(key);
+    await fs.promises.mkdir(path.dirname(dest), { recursive: true });
+
+    if (isLocalTempFile(source)) {
+      try {
+        await fs.promises.rename(source.tmpPath, dest);
+      } catch (err) {
+        if (errnoCode(err) !== 'EXDEV') {
+          throw new StorageBackendError(`put failed for '${key}' on '${this.id}'`, err);
+        }
+        await fs.promises.copyFile(source.tmpPath, dest);
+        await fs.promises.unlink(source.tmpPath);
+      }
+      return;
+    }
+
+    const spool = path.join(this.spoolDir(), randomUUID());
+    try {
+      await pipeline(source, fs.createWriteStream(spool));
+      await fs.promises.rename(spool, dest);
+    } catch (err) {
+      await fs.promises.rm(spool, { force: true });
+      throw err instanceof Error && !errnoCode(err)
+        ? err // source-stream failure: surface the caller's own error untouched
+        : new StorageBackendError(`put failed for '${key}' on '${this.id}'`, err);
+    }
+  }
+
+  async getStream(key: string, range?: ByteRange): Promise<{ stream: Readable; stat: ObjectStat }> {
+    const resolved = this.resolvePath(key);
+    const stat = await this.stat(key);
+    if (!stat) throw new StorageNotFoundError(key);
+    const stream = fs.createReadStream(
+      resolved,
+      range ? { start: range.start, end: range.end } : undefined,
+    );
+    return { stream, stat };
+  }
+
+  async stat(key: string): Promise<ObjectStat | null> {
+    const resolved = this.resolvePath(key);
+    try {
+      const st = await fs.promises.stat(resolved);
+      if (!st.isFile()) return null;
+      return { key, size: st.size, mtimeMs: st.mtimeMs };
+    } catch (err) {
+      if (isMissing(err)) return null;
+      throw new StorageBackendError(`stat failed for '${key}' on '${this.id}'`, err);
+    }
+  }
+
+  async delete(key: string): Promise<void> {
+    const resolved = this.resolvePath(key);
+    try {
+      await fs.promises.unlink(resolved);
+    } catch (err) {
+      if (isMissing(err)) return; // idempotent
+      throw new StorageBackendError(`delete failed for '${key}' on '${this.id}'`, err);
+    }
+  }
+
+  async *list(prefix: string): AsyncIterable<ObjectStat> {
+    assertValidPrefix(prefix);
+    const root = this.root();
+    yield* this.walk(prefix ? path.resolve(root, prefix) : root, root);
+  }
+
+  private async *walk(dir: string, root: string): AsyncIterable<ObjectStat> {
+    let entries: fs.Dirent[];
+    try {
+      entries = await fs.promises.readdir(dir, { withFileTypes: true });
+    } catch (err) {
+      if (isMissing(err)) return; // unpopulated prefix — empty, not an error
+      throw new StorageBackendError(`list failed under '${dir}' on '${this.id}'`, err);
+    }
+    for (const entry of entries) {
+      // Skips the .tmp spool (and any dotfile) defensively — key validation
+      // already makes dot segments unreachable, but list walks the real disk.
+      if (entry.name.startsWith('.')) continue;
+      const entryPath = path.join(dir, entry.name);
+      if (entry.isDirectory()) {
+        yield* this.walk(entryPath, root);
+      } else if (entry.isFile()) {
+        const st = await fs.promises.stat(entryPath);
+        yield {
+          key: path.relative(root, entryPath).split(path.sep).join('/'),
+          size: st.size,
+          mtimeMs: st.mtimeMs,
+        };
+      }
+    }
+  }
+}
diff --git a/server/src/nest/storage/storage-keys.ts b/server/src/nest/storage/storage-keys.ts
new file mode 100644
index 000000000..32bb7a5ce
--- /dev/null
+++ b/server/src/nest/storage/storage-keys.ts
@@ -0,0 +1,48 @@
+import { StorageInvalidKeyError } from './storage.types';
+
+/**
+ * Central key validation — the ONE place storage keys are checked, replacing
+ * the scattered per-route guards (`path.basename` + `startsWith` shapes in
+ * files.service.ts / platform.routes.ts / journey-public.controller.ts) as
+ * call sites migrate. Drivers still confine resolved paths to their root as
+ * defense in depth, but no driver or route re-implements these rules.
+ *
+ * Rejected: `..` segments, absolute paths, backslashes, empty segments,
+ * leading-dot segments (matches `express.static`'s default
+ * `dotfiles: 'ignore'` and keeps the `.tmp` spool unreachable), and control
+ * characters. Spaces are valid — legacy `photos/<filename>` keys are
+ * user-named flat files.
+ */
+
+const MAX_KEY_LENGTH = 1024;
+
+function hasControlChars(value: string): boolean {
+  for (let i = 0; i < value.length; i++) {
+    const code = value.charCodeAt(i);
+    if (code < 0x20 || code === 0x7f) return true;
+  }
+  return false;
+}
+
+export function isValidKey(key: string): boolean {
+  if (!key || key.length > MAX_KEY_LENGTH) return false;
+  if (key.includes('\\') || hasControlChars(key)) return false;
+  for (const segment of key.split('/')) {
+    if (segment === '' || segment.startsWith('.')) return false;
+  }
+  return true;
+}
+
+export function assertValidKey(key: string): void {
+  if (!isValidKey(key)) throw new StorageInvalidKeyError(key);
+}
+
+/** Prefixes additionally allow `''` (list everything) and a trailing `/`. */
+export function isValidPrefix(prefix: string): boolean {
+  if (prefix === '') return true;
+  return isValidKey(prefix.endsWith('/') ? prefix.slice(0, -1) : prefix);
+}
+
+export function assertValidPrefix(prefix: string): void {
+  if (!isValidPrefix(prefix)) throw new StorageInvalidKeyError(prefix);
+}
diff --git a/server/src/nest/storage/storage-paths.ts b/server/src/nest/storage/storage-paths.ts
new file mode 100644
index 000000000..493ca3c4e
--- /dev/null
+++ b/server/src/nest/storage/storage-paths.ts
@@ -0,0 +1,20 @@
+import path from 'node:path';
+
+/**
+ * The storage domain's one `__dirname` anchor (the uploads-root.ts idiom, and
+ * eventually its replacement: the registry's defaults make this the single
+ * source of truth the other 16 copies collapse onto in later slices).
+ *
+ * `__dirname` moves with the file — `server/{src,dist}/nest/storage` sits
+ * three levels under `server/`, so three `..` hops resolve to `<server>/`
+ * under both the src (vitest) and dist (runtime) layouts. The depth is stated
+ * rather than counted by hand and pinned by storage-keys.test.ts, exactly
+ * like uploads-root.test.ts pins UPLOADS_ROOT. In Docker both anchors are
+ * symlinks (`/app/server/uploads → /app/uploads`, `/app/server/data →
+ * /app/data`), which is why LocalDriver realpaths its root at init.
+ */
+export const DEFAULT_UPLOADS_ROOT = path.resolve(__dirname, '..', '..', '..', 'uploads');
+export const DATA_ROOT = path.resolve(__dirname, '..', '..', '..', 'data');
+export const DEFAULT_BACKUPS_ROOT = path.join(DATA_ROOT, 'backups');
+/** Driver-agnostic global scratch space (`data/tmp`) — see StorageService.tempDir(). */
+export const GLOBAL_TEMP_DIR = path.join(DATA_ROOT, 'tmp');
diff --git a/server/src/nest/storage/storage.types.ts b/server/src/nest/storage/storage.types.ts
new file mode 100644
index 000000000..ddbb81524
--- /dev/null
+++ b/server/src/nest/storage/storage.types.ts
@@ -0,0 +1,100 @@
+import type { Readable } from 'node:stream';
+
+/**
+ * The storage abstraction's contract surface (spec:
+ * docs/superpowers/specs/2026-07-20-storage-backend-abstraction-design.md).
+ *
+ * S3 constraints are baked into the driver contract, not the implementation:
+ * keys are opaque POSIX-style strings, no rename/append/partial writes, no
+ * directory semantics. Adding a backend later means one driver file that
+ * passes the contract suite (tests/unit/nest/storage/storage-driver.contract.ts)
+ * — zero changes to controllers or services.
+ */
+
+export const STORAGE_CATEGORIES = [
+  'files',
+  'journey',
+  'covers',
+  'avatars',
+  'places',
+  'photos',
+  'photos-google',
+  'photos-trek',
+  'backups',
+] as const;
+export type StorageCategory = (typeof STORAGE_CATEGORIES)[number];
+
+export interface ObjectStat {
+  key: string;
+  size: number;
+  mtimeMs: number;
+}
+
+/** Inclusive byte range, `fs.createReadStream` semantics; `end` omitted = to EOF. */
+export interface ByteRange {
+  start: number;
+  end?: number;
+}
+
+/** Ignored by local drivers; a future S3 driver needs it for the PUT. */
+export interface PutOptions {
+  contentType?: string;
+}
+
+/**
+ * A temp file whose OWNERSHIP transfers to `put()`: the driver moves or
+ * consumes it (rename into place locally; upload-then-delete remotely).
+ * Callers must not touch the path afterwards.
+ */
+export interface LocalTempFile {
+  tmpPath: string;
+}
+
+export function isLocalTempFile(source: Readable | LocalTempFile): source is LocalTempFile {
+  return typeof (source as LocalTempFile).tmpPath === 'string';
+}
+
+export interface StorageDriver {
+  /** Backend instance name, e.g. 'uploads-local'. */
+  readonly id: string;
+  /** Atomic: spool + single rename locally; single/multipart PUT remotely. */
+  put(key: string, source: Readable | LocalTempFile, opts?: PutOptions): Promise<void>;
+  getStream(key: string, range?: ByteRange): Promise<{ stream: Readable; stat: ObjectStat }>;
+  stat(key: string): Promise<ObjectStat | null>;
+  /** Idempotent; resolving on a missing key is success. */
+  delete(key: string): Promise<void>;
+  list(prefix: string): AsyncIterable<ObjectStat>;
+  /** Fast-path for local drivers; `null`/absent is exactly the remote-driver branch every caller must handle. */
+  getLocalPath?(key: string): string | null;
+  /** Same-filesystem spool dir (LocalDriver: `<root>/.tmp`), or null for drivers with no local filesystem. */
+  getSpoolDir?(): string | null;
+}
+
+/**
+ * Typed error set so route handlers map storage failures to their existing
+ * bespoke envelopes without string-matching driver internals.
+ */
+export class StorageBackendError extends Error {
+  constructor(
+    message: string,
+    readonly cause?: unknown,
+  ) {
+    super(message);
+    this.name = 'StorageBackendError';
+  }
+}
+
+export class StorageNotFoundError extends Error {
+  constructor(readonly key: string) {
+    super(`storage object not found: ${key}`);
+    this.name = 'StorageNotFoundError';
+  }
+}
+
+/** Serving slices map this to a miss (404/next()), never a 500. */
+export class StorageInvalidKeyError extends Error {
+  constructor(readonly key: string) {
+    super(`invalid storage key: ${key}`);
+    this.name = 'StorageInvalidKeyError';
+  }
+}
diff --git a/server/tests/unit/nest/storage/local.driver.test.ts b/server/tests/unit/nest/storage/local.driver.test.ts
new file mode 100644
index 000000000..776d3e0aa
--- /dev/null
+++ b/server/tests/unit/nest/storage/local.driver.test.ts
@@ -0,0 +1,125 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { Readable } from 'node:stream';
+import { LocalDriver } from '../../../../src/nest/storage/drivers/local.driver';
+import { StorageInvalidKeyError } from '../../../../src/nest/storage/storage.types';
+import { describeStorageDriver, type DriverHarness } from './storage-driver.contract';
+
+function makeTmpDir(): string {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'trek-storage-'));
+}
+
+async function makeHarness(): Promise<DriverHarness> {
+  const root = makeTmpDir();
+  const tmpFiles = makeTmpDir();
+  const driver = new LocalDriver({ id: 'test-local', root });
+  driver.init({ cleanSpool: true });
+  let counter = 0;
+  return {
+    driver,
+    makeTempFile: async (contents) => {
+      const p = path.join(tmpFiles, `src-${counter++}.tmp`);
+      fs.writeFileSync(p, contents);
+      return p;
+    },
+    cleanup: async () => {
+      fs.rmSync(root, { recursive: true, force: true });
+      fs.rmSync(tmpFiles, { recursive: true, force: true });
+    },
+  };
+}
+
+describeStorageDriver('LocalDriver', makeHarness);
+
+describe('LocalDriver specifics', () => {
+  const dirs: string[] = [];
+  const tmp = (): string => {
+    const d = makeTmpDir();
+    dirs.push(d);
+    return d;
+  };
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    while (dirs.length) fs.rmSync(dirs.pop()!, { recursive: true, force: true });
+  });
+
+  it('realpaths a symlinked root and confines keys to the real directory', async () => {
+    // Docker symlinks BOTH storage anchors (/app/server/uploads → /app/uploads,
+    // /app/server/data → /app/data), so this is the deployed shape, not an edge.
+    const realdir = tmp();
+    const link = path.join(tmp(), 'uploads-link');
+    fs.symlinkSync(realdir, link);
+
+    const driver = new LocalDriver({ id: 'sym', root: link });
+    driver.init();
+    await driver.put('files/x.bin', Readable.from('sym'));
+
+    const local = driver.getLocalPath('files/x.bin');
+    expect(local.startsWith(fs.realpathSync(realdir) + path.sep)).toBe(true);
+    expect(fs.readFileSync(local, 'utf8')).toBe('sym');
+    expect(() => driver.getLocalPath('../escape')).toThrow(StorageInvalidKeyError);
+  });
+
+  it('cleans spool leftovers only at boot, never on reload-style init', () => {
+    const driver = new LocalDriver({ id: 'spool', root: tmp() });
+    driver.init();
+    const stray = path.join(driver.getSpoolDir(), 'leftover.part');
+    fs.writeFileSync(stray, 'in-flight upload');
+
+    driver.init(); // reload(): must NOT delete an in-flight upload's spool file
+    expect(fs.existsSync(stray)).toBe(true);
+
+    driver.init({ cleanSpool: true }); // boot: crash leftovers are reclaimed
+    expect(fs.existsSync(stray)).toBe(false);
+  });
+
+  it('creates its root, spool, and category prefix dirs at init', () => {
+    const root = path.join(tmp(), 'nested', 'uploads');
+    const driver = new LocalDriver({ id: 'pfx', root });
+    driver.init({ ensurePrefixes: ['files', 'photos/trek'] });
+
+    expect(fs.statSync(path.join(root, '.tmp')).isDirectory()).toBe(true);
+    expect(fs.statSync(path.join(root, 'files')).isDirectory()).toBe(true);
+    expect(fs.statSync(path.join(root, 'photos/trek')).isDirectory()).toBe(true);
+  });
+
+  it('falls back to copy+unlink when a temp-file rename crosses volumes (EXDEV)', async () => {
+    const root = tmp();
+    const driver = new LocalDriver({ id: 'exdev', root });
+    driver.init();
+    const src = path.join(tmp(), 'other-volume.bin');
+    fs.writeFileSync(src, 'exdev payload');
+
+    vi.spyOn(fs.promises, 'rename').mockRejectedValueOnce(
+      Object.assign(new Error('EXDEV: cross-device link not permitted'), { code: 'EXDEV' }),
+    );
+
+    await driver.put('files/moved.bin', { tmpPath: src });
+    expect(fs.readFileSync(path.join(root, 'files/moved.bin'), 'utf8')).toBe('exdev payload');
+    expect(fs.existsSync(src)).toBe(false);
+  });
+
+  it('commits stream puts via a same-volume spool rename', async () => {
+    const root = tmp();
+    const driver = new LocalDriver({ id: 'samevol', root });
+    driver.init();
+
+    const renameSpy = vi.spyOn(fs.promises, 'rename');
+    await driver.put('files/spooled.bin', Readable.from('data'));
+
+    const [from, to] = renameSpy.mock.calls.at(-1)!;
+    expect(String(from).startsWith(path.join(fs.realpathSync(root), '.tmp') + path.sep)).toBe(true);
+    expect(String(to)).toBe(path.join(fs.realpathSync(root), 'files/spooled.bin'));
+  });
+
+  it('lists a missing prefix as empty', async () => {
+    const driver = new LocalDriver({ id: 'empty', root: tmp() });
+    driver.init();
+    const seen: unknown[] = [];
+    for await (const stat of driver.list('nope/')) seen.push(stat);
+    expect(seen).toEqual([]);
+  });
+});
diff --git a/server/tests/unit/nest/storage/storage-driver.contract.ts b/server/tests/unit/nest/storage/storage-driver.contract.ts
new file mode 100644
index 000000000..338e43543
--- /dev/null
+++ b/server/tests/unit/nest/storage/storage-driver.contract.ts
@@ -0,0 +1,140 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { Readable } from 'node:stream';
+import fs from 'node:fs';
+import path from 'node:path';
+import {
+  StorageInvalidKeyError,
+  StorageNotFoundError,
+  type ObjectStat,
+  type StorageDriver,
+} from '../../../../src/nest/storage/storage.types';
+
+/**
+ * The parameterized driver contract suite — the groundwork's real product
+ * (spec, Testing). Every driver must pass it: LocalDriver and MirrorDriver in
+ * v1; a future S3 driver imports this same suite (against MinIO/localstack)
+ * and must pass before touching TREK code.
+ *
+ * Not a `.test.ts` on purpose: vitest only collects files matching the
+ * `*.test.ts` include, so this suite runs exclusively through a driver's own
+ * spec file.
+ */
+
+export interface DriverHarness {
+  driver: StorageDriver;
+  /** Create a temp file whose ownership put() may take (LocalTempFile source). */
+  makeTempFile(contents: string | Buffer): Promise<string>;
+  cleanup(): Promise<void>;
+}
+
+const INVALID_KEYS = ['../x', '/abs', 'a\\b', 'a//b', '.tmp/x', 'a/.h', 'a\u0000b'];
+
+export function describeStorageDriver(name: string, makeHarness: () => Promise<DriverHarness>): void {
+  describe(`storage driver contract: ${name}`, () => {
+    let h: DriverHarness;
+
+    beforeEach(async () => {
+      h = await makeHarness();
+    });
+    afterEach(async () => {
+      await h.cleanup();
+    });
+
+    async function readAll(key: string, range?: { start: number; end?: number }): Promise<Buffer> {
+      const { stream } = await h.driver.getStream(key, range);
+      const chunks: Buffer[] = [];
+      for await (const chunk of stream) chunks.push(Buffer.from(chunk as Buffer));
+      return Buffer.concat(chunks);
+    }
+
+    async function listAll(prefix: string): Promise<ObjectStat[]> {
+      const out: ObjectStat[] = [];
+      for await (const stat of h.driver.list(prefix)) out.push(stat);
+      return out;
+    }
+
+    it('roundtrips a stream source and stats its size', async () => {
+      await h.driver.put('a/stream.bin', Readable.from(Buffer.from('hello storage')));
+      expect((await readAll('a/stream.bin')).toString()).toBe('hello storage');
+      const stat = await h.driver.stat('a/stream.bin');
+      expect(stat).toMatchObject({ key: 'a/stream.bin', size: 13 });
+      expect(stat!.mtimeMs).toBeGreaterThan(0);
+    });
+
+    it('roundtrips a LocalTempFile source and consumes the temp file', async () => {
+      const tmp = await h.makeTempFile('from tmp file');
+      await h.driver.put('a/tmpfile.bin', { tmpPath: tmp });
+      expect((await readAll('a/tmpfile.bin')).toString()).toBe('from tmp file');
+      expect(fs.existsSync(tmp)).toBe(false); // ownership transferred
+    });
+
+    it('overwrites an existing key', async () => {
+      await h.driver.put('a/over.bin', Readable.from('first'));
+      await h.driver.put('a/over.bin', Readable.from('second!'));
+      expect((await readAll('a/over.bin')).toString()).toBe('second!');
+      expect((await h.driver.stat('a/over.bin'))!.size).toBe(7);
+    });
+
+    it('serves closed and open-ended byte ranges', async () => {
+      await h.driver.put('a/range.bin', Readable.from('0123456789'));
+      expect((await readAll('a/range.bin', { start: 2, end: 5 })).toString()).toBe('2345');
+      expect((await readAll('a/range.bin', { start: 7 })).toString()).toBe('789');
+    });
+
+    it('rejects getStream on a missing key with StorageNotFoundError', async () => {
+      await expect(h.driver.getStream('a/nope.bin')).rejects.toBeInstanceOf(StorageNotFoundError);
+    });
+
+    it('stats a missing key as null', async () => {
+      expect(await h.driver.stat('a/nope.bin')).toBeNull();
+    });
+
+    it('deletes idempotently', async () => {
+      await h.driver.put('a/gone.bin', Readable.from('x'));
+      await h.driver.delete('a/gone.bin');
+      expect(await h.driver.stat('a/gone.bin')).toBeNull();
+      await expect(h.driver.delete('a/gone.bin')).resolves.toBeUndefined();
+    });
+
+    it('lists by prefix with full keys and sizes', async () => {
+      await h.driver.put('a/one.bin', Readable.from('11'));
+      await h.driver.put('a/sub/two.bin', Readable.from('222'));
+      await h.driver.put('b/three.bin', Readable.from('3'));
+
+      const underA = await listAll('a/');
+      expect(underA.map((s) => s.key).sort()).toEqual(['a/one.bin', 'a/sub/two.bin']);
+      expect(underA.find((s) => s.key === 'a/sub/two.bin')!.size).toBe(3);
+
+      const everything = await listAll('');
+      expect(everything.map((s) => s.key).sort()).toEqual(['a/one.bin', 'a/sub/two.bin', 'b/three.bin']);
+    });
+
+    it.each(INVALID_KEYS)('rejects invalid key %j on every method', async (key) => {
+      await expect(h.driver.put(key, Readable.from('x'))).rejects.toBeInstanceOf(StorageInvalidKeyError);
+      await expect(h.driver.getStream(key)).rejects.toBeInstanceOf(StorageInvalidKeyError);
+      await expect(h.driver.stat(key)).rejects.toBeInstanceOf(StorageInvalidKeyError);
+      await expect(h.driver.delete(key)).rejects.toBeInstanceOf(StorageInvalidKeyError);
+    });
+
+    it('leaves no object and no visible partial when the source stream errors', async () => {
+      const boom = new Readable({
+        read() {
+          this.push('partial bytes');
+          this.destroy(new Error('source exploded'));
+        },
+      });
+      await expect(h.driver.put('a/broken.bin', boom)).rejects.toThrow();
+      expect(await h.driver.stat('a/broken.bin')).toBeNull();
+      expect((await listAll('')).map((s) => s.key)).toEqual([]);
+    });
+
+    it('honors the getSpoolDir contract', async () => {
+      const spool = h.driver.getSpoolDir?.() ?? null;
+      if (spool === null) return; // drivers with no local filesystem
+      expect(fs.existsSync(spool)).toBe(true);
+      // Spool contents are invisible to the abstraction by construction.
+      fs.writeFileSync(path.join(spool, 'leftover.part'), 'junk');
+      expect((await listAll('')).map((s) => s.key)).toEqual([]);
+    });
+  });
+}
diff --git a/server/tests/unit/nest/storage/storage-keys.test.ts b/server/tests/unit/nest/storage/storage-keys.test.ts
new file mode 100644
index 000000000..910f44950
--- /dev/null
+++ b/server/tests/unit/nest/storage/storage-keys.test.ts
@@ -0,0 +1,90 @@
+import { describe, it, expect } from 'vitest';
+import path from 'node:path';
+import {
+  isValidKey,
+  assertValidKey,
+  isValidPrefix,
+  assertValidPrefix,
+} from '../../../../src/nest/storage/storage-keys';
+import { StorageInvalidKeyError } from '../../../../src/nest/storage/storage.types';
+import {
+  DEFAULT_UPLOADS_ROOT,
+  DEFAULT_BACKUPS_ROOT,
+  GLOBAL_TEMP_DIR,
+} from '../../../../src/nest/storage/storage-paths';
+
+// Central key validation (spec: storage-keys.ts owns the rules; drivers and
+// routes never re-implement them). Every rejected shape here replaces one of
+// the scattered per-route guards the refactor retires.
+describe('storage keys', () => {
+  const validKeys = [
+    'files/a.pdf',
+    'journey/thumbs/ab12.jpg',
+    'backup-2026.zip', // backups category uses bare keys (spec rev 3.1)
+    'photos/trek/deadbeef.bin',
+    // legacy photos/<filename> keys are user-named flat files — spaces stay valid
+    'photos/my holiday pic.jpg',
+  ];
+
+  const invalidKeys = [
+    '', // empty
+    '/abs', // absolute
+    'a\\b', // backslash
+    'a//b', // empty segment
+    'a/', // trailing slash = empty segment
+    '../x', // traversal
+    'a/../b', // embedded traversal
+    '.', // dot segment
+    '..', // dot-dot segment
+    '.tmp/x', // leading-dot segment (spool must be unreachable)
+    'a/.hidden', // dotfile segment
+    'a\u0000b', // control character
+    `a/${'x'.repeat(1024)}`, // over length cap
+  ];
+
+  it.each(validKeys)('accepts %j', (key) => {
+    expect(isValidKey(key)).toBe(true);
+    expect(() => assertValidKey(key)).not.toThrow();
+  });
+
+  it.each(invalidKeys)('rejects %j', (key) => {
+    expect(isValidKey(key)).toBe(false);
+    expect(() => assertValidKey(key)).toThrow(StorageInvalidKeyError);
+  });
+
+  it('caps keys at 1024 chars (boundary)', () => {
+    const exactly1024 = `a/${'x'.repeat(1022)}`;
+    expect(exactly1024.length).toBe(1024);
+    expect(isValidKey(exactly1024)).toBe(true);
+    expect(isValidKey(`${exactly1024}x`)).toBe(false);
+  });
+
+  describe('prefixes', () => {
+    it.each(['', 'thumbs/', 'thumbs', 'photos/google/'])('accepts %j', (prefix) => {
+      expect(isValidPrefix(prefix)).toBe(true);
+      expect(() => assertValidPrefix(prefix)).not.toThrow();
+    });
+
+    it.each(['../', '/abs', '.tmp/', 'a//b/', 'a\\b'])('rejects %j', (prefix) => {
+      expect(isValidPrefix(prefix)).toBe(false);
+      expect(() => assertValidPrefix(prefix)).toThrow(StorageInvalidKeyError);
+    });
+  });
+});
+
+// Depth contract for the storage domain's one __dirname anchor, same guard as
+// tests/unit/nest/uploads-root.test.ts: the resolved defaults must equal the
+// paths the server has always used, under both src (vitest) and dist layouts.
+describe('storage default paths', () => {
+  it('anchors the default uploads root at <server>/uploads', () => {
+    expect(DEFAULT_UPLOADS_ROOT).toBe(path.resolve(process.cwd(), 'uploads'));
+  });
+
+  it('anchors the default backups root at <server>/data/backups', () => {
+    expect(DEFAULT_BACKUPS_ROOT).toBe(path.resolve(process.cwd(), 'data/backups'));
+  });
+
+  it('anchors the global temp dir at <server>/data/tmp', () => {
+    expect(GLOBAL_TEMP_DIR).toBe(path.resolve(process.cwd(), 'data/tmp'));
+  });
+});