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-transport-webrtc/tests/signaling.test.ts

@@ -0,0 +1,76 @@
+import { describe, expect, it } from 'bun:test';
+import {
+  MemoryShadeBridge,
+  WebRtcSignalingChannel,
+} from '../src/signaling.js';
+
+describe('WebRtcSignalingChannel', () => {
+  it('routes typed signaling messages through the bridge', async () => {
+    const { a, b } = MemoryShadeBridge.linked('alice', 'bob');
+    const aliceSig = new WebRtcSignalingChannel(a);
+    const bobSig = new WebRtcSignalingChannel(b);
+
+    const received: Array<{ from: string; kind: string }> = [];
+    bobSig.onSignal((from, msg) => {
+      received.push({ from, kind: msg.kind });
+    });
+
+    await aliceSig.sendOffer('bob', 'sess-1', 'v=0\nfake-sdp');
+    await aliceSig.sendIce('bob', 'sess-1', {
+      candidate: 'candidate:1 1 udp 0 1.2.3.4 1234 typ host',
+      sdpMid: '0',
+      sdpMLineIndex: 0,
+    });
+    await aliceSig.sendBye('bob', 'sess-1', 'no longer needed');
+
+    expect(received).toEqual([
+      { from: 'alice', kind: 'shade.webrtc-offer/v1' },
+      { from: 'alice', kind: 'shade.webrtc-ice/v1' },
+      { from: 'alice', kind: 'shade.webrtc-bye/v1' },
+    ]);
+
+    aliceSig.destroy();
+    bobSig.destroy();
+  });
+
+  it('passes non-signaling messages through to the passthrough hook', async () => {
+    const { a, b } = MemoryShadeBridge.linked('alice', 'bob');
+    const passthrough: string[] = [];
+    const bobSig = new WebRtcSignalingChannel(b, {
+      passthrough: (_from, plaintext) => passthrough.push(plaintext),
+    });
+    const seen: string[] = [];
+    bobSig.onSignal((_from, msg) => seen.push(msg.kind));
+
+    await a.send('bob', 'hello world (not signaling)');
+    await a.send('bob', JSON.stringify({ kind: 'shade.fs.cancel/v1' }));
+
+    expect(passthrough).toContain('hello world (not signaling)');
+    expect(seen).toEqual([]);
+    bobSig.destroy();
+  });
+
+  it('preserves causal order — offer awaited before ICE handler runs', async () => {
+    const { a, b } = MemoryShadeBridge.linked('alice', 'bob');
+    const aliceSig = new WebRtcSignalingChannel(a);
+    const bobSig = new WebRtcSignalingChannel(b);
+    const order: string[] = [];
+
+    bobSig.onSignal(async (_from, msg) => {
+      if (msg.kind === 'shade.webrtc-offer/v1') {
+        // Slow handler — must complete before ICE arrives.
+        await new Promise<void>((resolve) => setTimeout(resolve, 25));
+        order.push('offer-done');
+      } else if (msg.kind === 'shade.webrtc-ice/v1') {
+        order.push('ice');
+      }
+    });
+
+    await aliceSig.sendOffer('bob', 's', 'sdp');
+    await aliceSig.sendIce('bob', 's', null);
+
+    expect(order).toEqual(['offer-done', 'ice']);
+    aliceSig.destroy();
+    bobSig.destroy();
+  });
+});