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-recovery/tests/shamir.test.ts

@@ -0,0 +1,147 @@
+import { describe, test, expect } from 'bun:test';
+import fc from 'fast-check';
+import {
+  combineShares,
+  decodeShare,
+  encodeShare,
+  splitSecret,
+  type ShamirShare,
+} from '../src/shamir.js';
+
+const cryptoRandom = (n: number): Uint8Array => {
+  const out = new Uint8Array(n);
+  globalThis.crypto.getRandomValues(out);
+  return out;
+};
+
+describe('Shamir Secret Sharing', () => {
+  test('split + combine roundtrip restores the secret (k=3, n=5)', () => {
+    const secret = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]);
+    const shares = splitSecret(secret, 3, 5, cryptoRandom);
+    expect(shares.length).toBe(5);
+    // Pick first 3 shares — any 3 should work.
+    const subset = shares.slice(0, 3);
+    const combined = combineShares(subset);
+    expect(Array.from(combined)).toEqual(Array.from(secret));
+  });
+
+  test('any threshold-sized subset reconstructs', () => {
+    const secret = cryptoRandom(32);
+    const shares = splitSecret(secret, 3, 5, cryptoRandom);
+    // All 10 possible 3-subsets must reconstruct.
+    for (let i = 0; i < 5; i++) {
+      for (let j = i + 1; j < 5; j++) {
+        for (let k = j + 1; k < 5; k++) {
+          const combined = combineShares([shares[i]!, shares[j]!, shares[k]!]);
+          expect(Array.from(combined)).toEqual(Array.from(secret));
+        }
+      }
+    }
+  });
+
+  test('exactly threshold shares reconstruct (k=2, n=2)', () => {
+    const secret = new Uint8Array([0xde, 0xad, 0xbe, 0xef]);
+    const shares = splitSecret(secret, 2, 2, cryptoRandom);
+    const combined = combineShares(shares);
+    expect(Array.from(combined)).toEqual(Array.from(secret));
+  });
+
+  test('k-1 shares yield a wrong (random-looking) result', () => {
+    const secret = cryptoRandom(32);
+    const shares = splitSecret(secret, 3, 5, cryptoRandom);
+    const truncated = shares.slice(0, 2); // 2 < k=3
+    const combined = combineShares(truncated);
+    // We can't reliably assert "looks random", but we can assert
+    // it's not equal to the secret (passing 2 shares to a polynomial
+    // of degree 2 yields a different polynomial with prob ≈ 1).
+    expect(Array.from(combined)).not.toEqual(Array.from(secret));
+  });
+
+  test('split rejects k < 1, n < k, n > 255', () => {
+    expect(() => splitSecret(new Uint8Array([1]), 0, 5, cryptoRandom)).toThrow();
+    expect(() => splitSecret(new Uint8Array([1]), 6, 5, cryptoRandom)).toThrow();
+    expect(() => splitSecret(new Uint8Array([1]), 1, 256, cryptoRandom)).toThrow();
+  });
+
+  test('split rejects empty secret', () => {
+    expect(() => splitSecret(new Uint8Array(0), 1, 1, cryptoRandom)).toThrow();
+  });
+
+  test('combine rejects empty share set', () => {
+    expect(() => combineShares([])).toThrow();
+  });
+
+  test('combine rejects duplicate x-coordinates', () => {
+    const secret = new Uint8Array([1, 2, 3]);
+    const shares = splitSecret(secret, 2, 3, cryptoRandom);
+    const dup: ShamirShare[] = [shares[0]!, { x: shares[0]!.x, y: shares[1]!.y }];
+    expect(() => combineShares(dup)).toThrow(/duplicate x-coordinate/);
+  });
+
+  test('combine rejects mismatched share lengths', () => {
+    const a: ShamirShare = { x: 1, y: new Uint8Array([1, 2, 3]) };
+    const b: ShamirShare = { x: 2, y: new Uint8Array([1, 2]) };
+    expect(() => combineShares([a, b])).toThrow(/length mismatch/);
+  });
+
+  test('encode + decode share roundtrip', () => {
+    const share: ShamirShare = { x: 7, y: new Uint8Array([1, 2, 3, 4, 5]) };
+    const bytes = encodeShare(share);
+    expect(bytes.length).toBe(6);
+    expect(bytes[0]).toBe(7);
+    const decoded = decodeShare(bytes);
+    expect(decoded.x).toBe(7);
+    expect(Array.from(decoded.y)).toEqual([1, 2, 3, 4, 5]);
+  });
+
+  test('encodeShare rejects x out of range', () => {
+    expect(() => encodeShare({ x: 0, y: new Uint8Array([1]) })).toThrow();
+    expect(() => encodeShare({ x: 256, y: new Uint8Array([1]) })).toThrow();
+  });
+
+  test('decodeShare rejects x=0', () => {
+    const bad = new Uint8Array([0, 1, 2, 3]);
+    expect(() => decodeShare(bad)).toThrow();
+  });
+
+  test('property: random-secret roundtrip preserves bytes for arbitrary k/n', () => {
+    fc.assert(
+      fc.property(
+        fc.uint8Array({ minLength: 1, maxLength: 64 }),
+        fc.integer({ min: 1, max: 8 }),
+        fc.integer({ min: 0, max: 8 }),
+        (secret, k, extra) => {
+          const n = k + extra;
+          if (n > 16) return;
+          const shares = splitSecret(secret, k, n, cryptoRandom);
+          // Pick the first k shares — any k will do.
+          const reconstructed = combineShares(shares.slice(0, k));
+          expect(Array.from(reconstructed)).toEqual(Array.from(secret));
+        },
+      ),
+      { numRuns: 50 },
+    );
+  });
+
+  test('property: any k-1 share subset yields a different output than the secret', () => {
+    // This is a probabilistic statement: with random secrets and
+    // random polynomials, P(reconstruction collides with the secret
+    // by accident) is ≈ 1/256^len, vanishingly small for 32-byte
+    // secrets.
+    fc.assert(
+      fc.property(
+        fc.uint8Array({ minLength: 16, maxLength: 32 }),
+        fc.integer({ min: 2, max: 6 }),
+        (secret, k) => {
+          const n = k + 2;
+          if (n > 16) return;
+          const shares = splitSecret(secret, k, n, cryptoRandom);
+          const subset = shares.slice(0, k - 1); // k-1 < threshold
+          const combined = combineShares(subset);
+          expect(Array.from(combined)).not.toEqual(Array.from(secret));
+        },
+      ),
+      { numRuns: 30 },
+    );
+  });
+});