Add sem MCP extension (entity-level code intelligence)

[rs545837]

What this adds

This adds sem to the extensions registry, plus a tutorial page, following the same pattern as recent extension PRs (Scholar Sidekick, Rendex).

sem is an entity-level code-intelligence MCP server. It indexes a codebase into functions/classes/methods and builds a real cross-file call and import graph, then exposes:

• sem_context: pack a target entity plus its real callers and callees into a token budget (instead of dumping whole files)
• sem_impact: deterministic "what breaks if I change this," answered from the graph so the agent can check blast radius before editing
• sem_entities: find code by intent (ranked structural search), or list entities in a file/dir
• sem_diff / sem_blame / sem_log: entity-level change review, authorship, history

Why

goose agents reason about code structure mostly through reads and grep, which miss cross-file callers and can infer edges that are not real. sem is deterministic and cross-file, so it complements the built-in developer tools rather than overlapping them.

Changes

• documentation/static/servers.json: one new entry (endorsed: false, is_builtin: false)
• documentation/docs/mcp/sem-mcp.md: tutorial page

It runs with no API key via npx -y @ataraxy-labs/sem mcp (verified the MCP handshake locally). Happy to adjust copy or the entry fields.

[DOsinga]

Thanks for the contribution and for the clean, well-documented PR!

We're currently not adding new MCP servers to the extensions registry, as we're looking for a more scalable solution to manage extensions going forward. Because of that, we're going to close this for now rather than grow the registry by hand.

Nothing wrong with the work here — please keep an eye out for the new approach, and we'd welcome resubmitting sem once that's in place.

[rs545837]

Hi @DOsinga, thanks again for the kind words when closing this.

I noticed v1.40.0 shipped MCP extension discovery via open plugins (#9471). Is that the more scalable approach you mentioned? If so, is publishing sem to open-plugins.com the right path now, or is there anything else planned for the registry that I should wait for?

Happy to close the loop on our side either way. sem is already in the official MCP registry as io.github.Ataraxy-Labs/sem if that helps with discovery.