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-sdk/src/config.ts

@@ -1,5 +1,6 @@
 import type { StorageProvider } from '@shade/core';
 import { ConfigurationError } from '@shade/core';
+import type { ObservabilityHook } from '@shade/observability';
 
 /**
  * Shade SDK configuration.
@@ -56,6 +57,43 @@ export interface ShadeConfig {
     /** Path prefix to mount under (default: "/shade-observer") */
     basePath?: string;
   };
+
+  /**
+   * Optional OpenTelemetry observability hook. Build with
+   * `withTracer(otelTracer)` from `@shade/observability`. Default: off.
+   *
+   * The hook propagates to the session manager (encrypt/decrypt spans),
+   * transfer engine (upload/download), and `@shade/files` (per-op).
+   * `withTracer()` is itself a no-op unless `SHADE_OTEL_ENABLED` is set,
+   * so leaving this configured in code stays free in production until
+   * the env-var flips it on.
+   */
+  observability?: ObservabilityHook;
+
+  /**
+   * Optional Key-Transparency verifier (V3.12). When set, every
+   * `fetchBundle` validates the server's inclusion proof against the
+   * pinned `logPublicKey` and feeds the STH into a `LightWitness` for
+   * split-view detection.
+   *
+   * Modes:
+   *  - `'observe'`        — verify proofs when present, do not fail when missing.
+   *  - `'observe-strict'` — require a proof on every successful and 404 response.
+   *
+   * Default: KT verification disabled. Set this to enable.
+   */
+  keyTransparency?: ShadeKTConfig;
+}
+
+/** Public configuration shape for `Shade.keyTransparency`. */
+export interface ShadeKTConfig {
+  mode: 'observe' | 'observe-strict';
+  /** Operator's pinned signing public key (32-byte Ed25519) — base64 or raw bytes. */
+  logPublicKey: Uint8Array | string;
+  /** Reject STHs older than this many ms. Default 24h. */
+  maxStaleMs?: number;
+  /** Cap on observed-STH cache. Default 1024. */
+  witnessMaxStored?: number;
 }
 
 export interface ResolvedConfig {
@@ -69,6 +107,15 @@ export interface ResolvedConfig {
     port?: number | undefined;
     basePath: string;
   };
+  observability?: ObservabilityHook;
+  keyTransparency?: ResolvedKTConfig;
+}
+
+export interface ResolvedKTConfig {
+  mode: 'observe' | 'observe-strict';
+  logPublicKey: Uint8Array;
+  maxStaleMs: number;
+  witnessMaxStored: number;
 }
 
 /** Parse and validate a ShadeConfig, resolving defaults and env var overrides */
@@ -104,6 +151,42 @@ export function resolveConfig(input: ShadeConfig): ResolvedConfig {
     };
   }
 
+  if (input.observability !== undefined) {
+    resolved.observability = input.observability;
+  }
+
+  if (input.keyTransparency !== undefined) {
+    const kt = input.keyTransparency;
+    if (kt.mode !== 'observe' && kt.mode !== 'observe-strict') {
+      throw new ConfigurationError(
+        `keyTransparency.mode must be 'observe' or 'observe-strict'`,
+      );
+    }
+    let logKey: Uint8Array;
+    if (typeof kt.logPublicKey === 'string') {
+      try {
+        logKey = new Uint8Array(Buffer.from(kt.logPublicKey, 'base64'));
+      } catch {
+        throw new ConfigurationError(
+          'keyTransparency.logPublicKey must be base64 or Uint8Array',
+        );
+      }
+    } else {
+      logKey = kt.logPublicKey;
+    }
+    if (logKey.length !== 32) {
+      throw new ConfigurationError(
+        `keyTransparency.logPublicKey must be 32 bytes (got ${logKey.length})`,
+      );
+    }
+    resolved.keyTransparency = {
+      mode: kt.mode,
+      logPublicKey: logKey,
+      maxStaleMs: kt.maxStaleMs ?? 24 * 60 * 60 * 1000,
+      witnessMaxStored: kt.witnessMaxStored ?? 1024,
+    };
+  }
+
   return resolved;
 }