External platform accessibility ranked by agent-friendliness: (1) GitLab — full CLI + API, MR automation, most agent-friendly; (2) GitHub — CLI + API, issue management; (3) Substack — browser-based but direct post/comment, no auth barriers; (4) YouTube — browser upload, Google SSO required, moderate friction; (5) Email — async, human-gated, slow; (6) Fourthwall — browser UI only, no API, designer tab crashes, least agent-friendly. The ranking correlates with agent productivity on each platform: GitLab (MR !9 resolved in 31 min) vs. Fourthwall (10 days, still UI-only).