ae50f56404
Adds a canonical EmailInboundPayload + EmailAdapter implementing the ChannelAdapter contract: HMAC signature verify + normalize with email-native threading (whole reply chain → one IIOS thread via references/inReplyTo root), messageId as providerEventId for dedup, html→text fallback, Re:/Fwd: stripping. Plus emailInboundFixture/emailReplyFixture and unit tests. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>