Add basedpyright language server support

[arikon]

Summary

• Add basedpyright as an alternative Python language server (experimental)
• basedpyright is a fork of pyright with additional features and stricter type checking
• Follows the same integration pattern as the existing pyright server

Changes

• New BasedPyrightServer class in src/solidlsp/language_servers/basedpyright_server.py
• PYTHON_BASEDPYRIGHT enum value in Language (marked as experimental)
• basedpyright==1.38.4 added as a bundled dependency
• Test repo alias and pytest marker added

Usage

In .serena/project.yml:

languages:
- python_basedpyright

Test plan

• Existing Python tests pass (pytest test -m python — 53 passed)
• ruff lint and format pass
• mypy type check passes (no new errors)

🤖 Generated with Claude Code

[MischaPanch]

Hi. We already support multiple python LS, including ty. What's the purpose of also supporting basedpyright?

[arikon]

@MischaPanch It is better to use with agent the same LSP Server as in IDE — shared configs and so on

[MischaPanch]

Ok, that makes sense. Pls adjust the PR to run basedpyright with uvx like I have recently done for ty, so it can be installed on the fly. Serena's users are essentially all uv users, and this way we can prevent having basedpyright as dependency. It's a fairly large package and offers no benefit to most users

[opcode81]

It is better to use with agent the same LSP Server as in IDE — shared configs and so on

Why though? Which problem is being solved? Why does the configuration even matter, and what, effectively, is the difference when using basedpyright instead of pyright as the Python language server with Serena?

[TyceHerrman]

@opcode81 it would help ensure agents are type checking the same way you are if you're using basedpyright.

Also why basedpyright vs pyright - it has new diagnostic rules pyright doesn't and reimplements some pylance features.

And why basedpyright vs other lsps - slower than others, but best conformance as of today (though other lsps are closing the gap: https://htmlpreview.github.io/?https://github.com/python/typing/blob/main/conformance/results/results.html).

As one data point, Zed editor has made basedpyright their default lsp and disabled pyright out of the box.