pyright gate resolves a different tree-sitter-language-pack than the documented dev install

[cdeust]

What

The pyright gate resolves a different tree-sitter-language-pack than the
documented developer install, so a contributor sees one diagnostic that CI never
reports.

Measurement (2026-07-29, worktree at f606c37)

Environment	How it is built	tree-sitter-language-pack	pyright 1.1.410 mcp_server/
CI (ci.yml:430-437)	python -m venv .venv + pip install -e ".[dev,postgresql,sqlite,codebase,otel]" flashrank	1.13.5	0 errors, 0 warnings, 0 informations
Developer (CLAUDE.md:21, uv sync)	resolved from uv.lock	1.6.2	1 error

The diagnostic:

mcp_server/core/ast_parser.py:88:23 - error: Argument of type "str" cannot be
assigned to parameter "name" of type "SupportedLanguage" in function "get_parser"

Confirmed pre-existing by a paired control: it reproduces on an unmodified
origin/main tree in the same venv, and disappears on the same tree in the
CI-equivalent venv.

Why this matters

pyproject.toml:77 pins tree-sitter-language-pack>=0.24.0,<1.14, a range wide
enough that the two install paths land 7 minor versions apart. The pyright gate
is a zero-diagnostic gate (issue #197); a gate whose result depends on which
installer you used cannot be trusted in either direction — today it costs a
contributor a phantom error, tomorrow it can hide a real one.

Filed per coding-standards §14.3: outside the #239 DTZ family's blast radius —
ast_parser.py is untouched by that diff and the divergence is an environment
resolution issue, not a source defect.

Acceptance criteria

1. The pyright job and the documented developer install resolve the same
   tree-sitter-language-pack (either CI installs from the lockfile, or the
   lockfile is refreshed and the pin narrowed).
2. pyright mcp_server/ reports 0 errors in BOTH environments, evidenced by
   quoted output from each.
3. mcp_server/core/ast_parser.py:88 narrows language to the
   SupportedLanguage literal, or documents why the widening is safe.