Claude Code on the web: cloud sessions don't load user-configured MCP servers (only first-party GitHub works)

Summary

In Claude Code on the web (Research Preview, cloud sessions), only the first-party GitHub MCP integration is available. There appears to be no working path for users to add additional MCP servers to a cloud session.

What I tried

1. Project-scoped .mcp.json committed at the repo root on the session's branch:

``json
{"mcpServers": {"sentry": {"type": "sse", "url": "https://mcp.sentry.dev/mcp"}}}
`
Started a fresh cloud session on the branch. The file is present in the working tree but no mcp__sentry__ tools are registered. Only mcp__github__` tools are available.

This contradicts the docs at https://code.claude.com/docs/en/claude-code-on-the-web, which state that repo .mcp.json servers are loaded as "part of the clone".

1. Account-level Connectors at https://claude.ai/customize/connectors. Connected the Sentry connector (15 read-only tools, OAuth completed successfully, shows as Connected). Started a fresh Claude Code web session afterward — Sentry tools still not present. Connectors appear to be a claude.ai chat feature only, not surfaced to Code-on-web sessions.

What I observed in the cloud session

The harness injects only the GitHub MCP via a session-scoped config at /tmp/mcp-config-cse_<session-id>.json pointing at https://api.anthropic.com/v2/ccr-sessions/.../github/mcp. There is no equivalent injection for any other server, regardless of how it's configured upstream.

Expected

Either (a) project .mcp.json should be honored in cloud sessions as documented, or (b) account-level Connectors from claude.ai/customize/connectors should sync to Code-on-web sessions, or (c) the docs should clearly state that user-configurable MCPs are not yet supported on Code-on-web.

Environment

• Claude Code on the web (Research Preview), cloud session
• Date: 2026-04-28