Fixes email reply threading for Gmail and Office365

[RazvanMitrica]

Problem
Workflow reply steps were not threading correctly:

• Gmail: threadId was never passed to the Gmail send API, so replies always created a new thread.

• Office365: createReply was called with the RFC internetMessageId instead of the Microsoft Graph message id, causing an immediate 404 on every reply attempt. Additionally, stored Graph ids were mutable and would become invalid once a message moved from Drafts to Sent Items.

Changes
Adds a params.replyTo object ({ emailMessageId, serviceThreadId/serviceMessageId, references }) as the preferred reply target for both providers. Existing flat params (inReplyTo, threadId) remain as fallbacks — no breaking changes.
Gmail: populates In-Reply-To, References, and threadId from replyTo.
Office365: routes createReply to replyTo.serviceMessageId (the Graph id). Adds Prefer: IdType="ImmutableId" to draft creation and reply draft calls so stored ids survive the Drafts → Sent Items move.
Adds options.returnMetadata to both providers: returns { email_message_id, service_message_id, service_thread_id } instead of a plain string, letting the Server store provider ids immediately without waiting for sent webhooks.

[cursor]

PR Summary

Medium Risk
Touches outbound send/reply paths for both providers (thread ids, Graph createReply, and id stability); behavior is backward compatible but errors in reply targeting would affect production email workflows.

Overview
Fixes workflow reply threading for Gmail and Office365 by introducing a preferred params.replyTo object while keeping legacy inReplyTo, references, and threadId as fallbacks.

Gmail now maps replyTo into RFC In-Reply-To / References, passes replyTo.serviceThreadId (or legacy threadId) on send, and supports options.returnMetadata so callers get { email_message_id, service_message_id, service_thread_id } (including partial ids when post-send getMessage fails).

Office365 routes replies through replyTo.serviceMessageId for createReply (instead of treating RFC ids as Graph ids), tightens legacy inReplyTo so it is not used when replyTo is present, sends Prefer: IdType="ImmutableId" on draft create/reply PATCH so stored message ids survive Drafts → Sent Items, and mirrors the same returnMetadata callback shape on send and reply paths.

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[cursor]

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