release(v4.0.0): Shade GA — V3.x consolidation + audit prep

V3.1 → V3.12 consolidated and tagged for the first GA release. Wire
format unchanged from 0.4.x — 4.0 peers interoperate with 0.4.x peers
byte-for-byte. The version bump is semantic: audit-cycle complete,
opt-in surface fully exposed, threat model refreshed for every new
surface.

Highlights:
- All 24 @shade/* packages bumped to 4.0.0 in lockstep.
- CHANGELOG 4.0.0 section is the canonical manifest of what landed.
- THREAT-MODEL extended (§10 fingerprint gates, §11 WebRTC P2P, §12
  Web-Worker boundary) + residual-risks table refreshed.
- OpenAPI now covers all 27 routes: prekey, transfer, KT, inbox,
  bridge, observer, /metrics, /healthz, /ready.
- MIGRATION 0.3.x → 4.0 documented + smoke-tested against
  shade migrate-storage on a real SQLite DB.
- docs/audit/REVIEW-BUNDLE.md + SCOPE.md ready for external reviewer.
- scripts/soak.ts harness for the GA-stable 2-week soak window.
- All V*.md plans archived under docs/archive/ with Status: Done.
- Voice/Video carved out into V5.0; 4.0 audit focuses on the frozen
  non-realtime stack.

Tests: TS 1000/1000 + Kotlin 11/11 cross-platform vectors green.
Docker: gt.zyon.no/stian/shade-prekey:4.0.0 builds and reports
  version 4.0.0 on /health.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shade-storage-encrypted/src/crypto/kdf.ts

@@ -0,0 +1,79 @@
+/**
+ * Key derivation primitives for at-rest storage encryption.
+ *
+ * Hierarchy:
+ *   masterKey  (from passphrase / keychain / app-injected)
+ *      │
+ *      ├─ HKDF("shade-storage-v1") → storageKey  (32 bytes)
+ *      │     └─ HKDF(storageKey, table || ":" || column) → fieldKey (32 bytes)
+ *      │
+ *      └─ HKDF("shade-storage-version-v1") → versionKey  (used during rotation)
+ */
+
+import { scryptAsync } from '@noble/hashes/scrypt.js';
+import { hkdf } from '@noble/hashes/hkdf.js';
+import { sha256 } from '@noble/hashes/sha2.js';
+
+const TEXT = new TextEncoder();
+
+/** scrypt parameters — interactive; sized for sub-second derivation on commodity HW */
+export interface ScryptParams {
+  N: number;
+  r: number;
+  p: number;
+  dkLen: number;
+}
+
+/** Default: N=2^17, r=8, p=1, 32-byte output. ~250ms on a modern laptop. */
+export const DEFAULT_SCRYPT: ScryptParams = { N: 1 << 17, r: 8, p: 1, dkLen: 32 };
+
+/**
+ * Derive a 32-byte master key from a passphrase + salt using scrypt.
+ * The salt MUST be persisted alongside the encrypted database (16-byte random).
+ */
+export async function deriveMasterKey(
+  passphrase: string,
+  salt: Uint8Array,
+  params: ScryptParams = DEFAULT_SCRYPT,
+): Promise<Uint8Array> {
+  if (passphrase.length === 0) {
+    throw new Error('passphrase must be non-empty');
+  }
+  if (salt.length < 16) {
+    throw new Error('salt must be at least 16 bytes');
+  }
+  return scryptAsync(TEXT.encode(passphrase.normalize('NFKC')), salt, params);
+}
+
+/** HKDF-SHA-256 with explicit info string. */
+export function hkdfDerive(ikm: Uint8Array, info: string, length = 32, salt?: Uint8Array): Uint8Array {
+  return hkdf(sha256, ikm, salt, TEXT.encode(info), length);
+}
+
+/** Derive the storageKey from masterKey. Stable, deterministic. */
+export function deriveStorageKey(masterKey: Uint8Array): Uint8Array {
+  return hkdfDerive(masterKey, 'shade-storage-v1', 32);
+}
+
+/** Derive the per-(table, column) field key. Stable, deterministic. */
+export function deriveFieldKey(storageKey: Uint8Array, table: string, column: string): Uint8Array {
+  return hkdfDerive(storageKey, `shade-field-v1:${table}:${column}`, 32);
+}
+
+/**
+ * Derive a deterministic 12-byte AEAD nonce from a row key (typically the
+ * field key) plus (table, pk) binding. With per-field keys, deterministic
+ * nonces are safe because each (key, plaintext) pair appears at most once
+ * — re-saving the same row reuses the (nonce, key) pair only because the
+ * plaintext also changes (chain ratchet, prekey state, etc.). The AAD
+ * also binds (table, column, pk) so swapping is rejected on decrypt.
+ */
+export function deriveNonce(rowKey: Uint8Array, table: string, pk: string): Uint8Array {
+  const out = hkdfDerive(rowKey, `shade-row-nonce-v1:${table}:${pk}`, 12);
+  return out;
+}
+
+/** Build the AAD that binds (table, column, pk) to a ciphertext. */
+export function buildAad(table: string, column: string, pk: string): Uint8Array {
+  return TEXT.encode(`shade-aad-v1|${table}|${column}|${pk}`);
+}