Gmail MCP Connector: add threadId support to create_draft so Claude can reply within existing email threads

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When Claude uses the built-in Cowork Gmail connector to create a draft email, it has no way to attach the draft to an existing thread. Every draft Claude creates appears as a new standalone email, even when it is clearly intended as a reply to an ongoing conversation. This breaks the workflow for any email follow-up task.

Proposed Solution

Add a threadId parameter to the create_draft tool in the Gmail MCP connector. The Gmail API already supports this natively — passing a threadId along with In-Reply-To and References headers is all that is needed for the draft to land correctly inside an existing thread, exactly as it would if a user hit Reply in Gmail.

Alternative Solutions

Currently the only workaround is to open Gmail manually, find the thread, hit Reply, and paste in the draft Claude created. This defeats much of the purpose of having Claude draft emails on your behalf.

Priority

High - Significant impact on productivity

Feature Category

MCP server integration

Use Case Example

I asked Claude to draft a reply to my lawyer in an existing email thread. Claude created the draft correctly but it landed as a new standalone email rather than a reply in the thread. I had to manually copy the draft text and paste it as a reply in Gmail. This happens every time Claude drafts a reply to any ongoing conversation.

Additional Context

This is a small, well-scoped change on the API side. The Gmail API drafts.create endpoint already accepts threadId — it just needs to be exposed in the MCP tool schema. Third-party Gmail MCP servers (e.g. CharlesAD/gmail-mcp-server-claude) already implement this pattern successfully.