feat: reject socket-scoped tokens on REST (the other half of realtime delegation)

The delegated socket token (aud=IIOS_REALTIME_AUDIENCE) was only narrow in one direction: the
gateway accepts ONLY that audience, but REST never checked the actor token's audience — so a
leaked browser socket token still drove privileged REST, i.e. a full actor token with extra steps.

RealtimeTokenRestGuard closes it, registered GLOBALLY (APP_GUARD) because every REST route is a
target — only 2 of 15 controllers sit behind ContextAttestationGuard, so inbox/media/interactions/
ai/... would otherwise stay open.

It is a decode-only REJECT filter, never an authenticator:
- does not verify signatures (controllers still call SessionVerifier); stripping `aud` to bypass it
  invalidates the signature downstream,
- no bearer -> pass through (health, metrics, HMAC adapter webhooks),
- ws context -> pass through (the gateway enforces the mirror rule),
- unset IIOS_REALTIME_AUDIENCE -> no-op, the same switch that turns on the socket half.

So one env now enables the whole boundary: socket accepts only iios-message, REST refuses it.
8 tests; typecheck + build green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/platform/realtime-token.guard.ts

@@ -0,0 +1,43 @@
+import { CanActivate, ExecutionContext, ForbiddenException, Injectable } from '@nestjs/common';
+import jwt from 'jsonwebtoken';
+import type { Request } from 'express';
+
+/**
+ * Realtime delegation — the REST half.
+ *
+ * The browser's socket token is deliberately narrow: `aud = IIOS_REALTIME_AUDIENCE` (e.g.
+ * iios-message), minutes-long, and good for the /message socket ONLY. The gateway enforces the
+ * mirror of this rule (it accepts ONLY that audience). Without this guard the narrowing is
+ * one-directional: REST doesn't check the actor token's audience, so a leaked socket token would
+ * still drive privileged REST — i.e. it would be a full actor token with extra steps.
+ *
+ * Applied GLOBALLY (APP_GUARD) on purpose: every REST route is a target, not just the ones behind
+ * ContextAttestationGuard (inbox, media, interactions, ai, … would otherwise stay open).
+ *
+ * It is a decode-only REJECT filter, never an authenticator:
+ *  - it does not verify signatures (each controller still calls SessionVerifier) — cheap, and it
+ *    can't be bypassed by stripping `aud`, because that invalidates the signature downstream;
+ *  - no bearer token → pass through (health, metrics, HMAC adapter webhooks are not its business);
+ *  - unset IIOS_REALTIME_AUDIENCE → no-op (same switch that turns on the socket half).
+ */
+@Injectable()
+export class RealtimeTokenRestGuard implements CanActivate {
+  canActivate(context: ExecutionContext): boolean {
+    if (context.getType() !== 'http') return true; // the socket enforces its own (mirror) rule
+
+    const socketAudience = process.env.IIOS_REALTIME_AUDIENCE?.trim();
+    if (!socketAudience) return true;
+
+    const auth = context.switchToHttp().getRequest<Request>().headers['authorization'];
+    const raw = Array.isArray(auth) ? auth[0] : auth;
+    if (typeof raw !== 'string' || !/^Bearer\s+/i.test(raw)) return true;
+
+    const decoded = jwt.decode(raw.replace(/^Bearer\s+/i, ''), { json: true });
+    const aud = decoded?.aud;
+    const isSocketToken = aud === socketAudience || (Array.isArray(aud) && aud.includes(socketAudience));
+    if (isSocketToken) {
+      throw new ForbiddenException(`socket-scoped token (aud="${socketAudience}") cannot be used for REST`);
+    }
+    return true;
+  }
+}