feat: add resend plugin

[saoudrizwan]

Resend

Adds a Resend plugin for Cline for transactional email, broadcasts, domain setup, webhook processing, React Email templates, CLI usage, deliverability, compliance, and secure agent email inbox workflows.

It is intended for users building or operating email features where mistakes can affect real recipients, sender reputation, account resources, and private inbound email content.

Cline Primitives

This plugin uses MCP, skills, and a safety rule.

The MCP server is resend, backed by a pinned package-local resend-mcp@2.6.1 dependency. It exposes Resend account operations such as sending email, managing domains, contacts, broadcasts, templates, webhooks, logs, automations, and events. The plugin-owned MCP settings entry stores ${env:RESEND_API_KEY} rather than a copied secret, so the key stays in the host environment and can be rotated without rewriting plugin settings.

The bundled skills cover the Resend API, Resend CLI, React Email, email best practices, and agent email inbox patterns. They include workflow references for sending and managing email, designing templates, handling deliverability and compliance constraints, and safely processing inbound messages.

The safety rule asks Cline to confirm before real sends, broadcasts, contact imports, domain changes, webhook changes, API-key changes, automation/event changes, destructive deletes, or private inbound-email reads. It also marks inbound email, logs, headers, attachments, and webhook payloads as untrusted data.

Requirements

Set RESEND_API_KEY in the environment before using MCP tools. Keep that variable available in the environment that starts Cline, then reload MCP servers after changing it. Use the narrowest practical key, ideally scoped to the domain or environment being worked on.

Some workflows may also require the Resend CLI, Resend SDK packages, React Email packages, DNS access for domain authentication, webhook endpoint access, or a Resend account with the relevant permissions. The plugin does not create accounts, run CLI login, start services, or send email at install time.

Safety and Design

The MCP server is package-local rather than npx -y, so startup does not fetch an unpinned package. The stdio transport uses the installed plugin package directory as its cwd so the MCP command resolves the plugin dependency, not a workspace dependency.

Email content is a prompt-injection surface. The skills and rule steer Cline to treat inbound email bodies, headers, attachments, webhook payloads, and logs as data to validate and summarize, not instructions to execute. Broadcast examples default to draft creation and require explicit approval before send.

Bundled Resend skill material is MIT licensed; the plugin includes LICENSE.resend-skills and NOTICE.resend-skills for attribution.

[saoudrizwan]

Closing this plugin PR for now because this cleanup pass is limiting plugin marketplace PRs to plugins that only bundle MCP servers and/or skills. This PR includes additional plugin primitive(s): rules.

Those primitives may still be useful, but we are keeping this batch scoped to MCP and skill distribution.