ix-mcp Python sessions run on one pinned interpreter

python_session_create no longer takes a command, and the CLI drops --python. Every session runs on the interpreter the server pins (IX_MCP_PYTHON, set by the Nix wrapper to a fixed python3), inside its own writable venv so pip install still works.

Bring-your-own interpreter sounded flexible but bought little. It made each session depend on the host’s ambient Python, and its failure modes (missing interpreter, wrong version, no pip) all read as “your environment is weird.” One pinned interpreter makes every session reproducible and deletes that whole class of failure.

cwd stays, so a session can still root itself in a project directory:

{ "name": "python_session_create", "arguments": { "cwd": "/path/to/project" } }

What you give up: a session can’t use a project’s own resolved dependencies (a uv or poetry env). If that need comes back, the right shape is a typed “project env” door: the caller names a project and the server resolves the interpreter, no raw command vector.