feat(sdk): P5.1 @insignia/iios-adapter-sdk — ChannelAdapter contract + HMAC webhook adapter + sandbox + fixtures
Contract (capability incl. requiresFollowupFetch seam, verifySignature, normalize,
fetch?, send), HMAC-SHA256 sign/verify (timing-safe), reference WebhookAdapter
(normalize→IngestInteractionRequest), SandboxSink (no network), email/whatsapp
fixtures. CJS build (consumed by the NestJS service). 4 tests; boundary updated.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
maaz519
d70c7ea47b