feat(third_party): add Basecamp plugin

[jeremy]

Adds a basecamp plugin that connects to Basecamp's official remote MCP server, built and run by 37signals.

What's included

• third_party/basecamp/mcp.json: HTTP server at https://mcp.basecamp.com/mcp, "placement": "server" (same as Trello, beehiiv and PostHog MCP, so Grok Bot dials it through the hosted path)
• plugin.json, README, CHANGELOG, LICENSE, and a 192×192 logo (Basecamp's official mark)
• Marketplace and root README entries

Auth

OAuth 2.1 with Dynamic Client Registration and PKCE. There's no API key or client ID to configure. Basecamp accepts DCR redirects for Cursor desktop (cursor://anysphere.cursor-mcp/oauth/callback) and the hosted callback (https://www.cursor.com/agents/mcp/oauth/callback). Cursor desktop and Cursor cloud agents have both connected in production. On the consent screen the person picks the Basecamp account and Read-only or Full access.

Notes for reviewers

• Tools cover projects, to-dos, cards, messages, comments, documents, schedules, Campfire, check-ins, assignments and Hey! notifications, and search. Each tool is annotated as one of three kinds: read-only, additive (create_*: not read-only, not destructive) or destructive. The server can write as well as read, and the README says so.
• Tool calls run as the signed-in Basecamp person, with their permissions. People can revoke access from Connected apps in Basecamp.
• We're 37signals, the company that makes Basecamp, so this submits our own server.

Validation

• node scripts/validate-plugins.mjs passes

Docs: https://basecamp.com/ai

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Note

Low Risk
Marketplace and documentation-only addition following existing third-party MCP plugin structure; no changes to core plugin validation or shared runtime code in this diff.

Overview
Adds a new Basecamp Cursor marketplace plugin under third_party/basecamp/ so agents can connect to 37signals’ hosted MCP at https://mcp.basecamp.com/mcp with "placement": "server" (same hosted-path pattern as Trello and beehiiv).

The plugin ships plugin.json (v1.0.0, minClientVersions.cursor 3.13.0), mcp.json, README, CHANGELOG, LICENSE, and logo assets. OAuth (DCR + PKCE) is documented—no API keys in the manifest. Marketplace (marketplace.json) and root README plugin tables gain a basecamp row describing find/read/update for projects, to-dos, cards, messages, docs, and schedules.

^{Reviewed by Cursor Bugbot for commit 99db365. Bugbot is set up for automated code reviews on this repo. Configure here.}

[Copilot]

🟢 Approval recommended

The new plugin is complete, internally consistent, and follows established hosted MCP integration patterns.

0 open findings

What changed in this PR

Adds the official Basecamp hosted MCP integration to the plugin marketplace.

Changes:

• Configures Basecamp’s remote MCP server with hosted placement.
• Documents OAuth, capabilities, installation, and licensing.
• Registers the plugin in marketplace and repository listings.

File	Description
.cursor-plugin/​marketplace.json	Registers Basecamp in the marketplace.
README.md	Adds Basecamp to the plugin table.
third_party/​basecamp/​.cursor-plugin/​plugin.json	Defines plugin metadata.
third_party/​basecamp/​mcp.json	Configures the hosted MCP endpoint.
third_party/​basecamp/​README.md	Documents installation, authentication, and capabilities.
third_party/​basecamp/​CHANGELOG.md	Records the initial release.
third_party/​basecamp/​LICENSE	Adds the MIT license.
third_party/​basecamp/​assets/​logo.png	Adds the validated 192×192 Basecamp logo.

🧠 Review effort: Balanced

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