Make the uv bootstrap chain survive venv recreation

pyproject.toml

@@ -37,10 +37,16 @@ dependencies = [
 dev = [
   "coverage[toml]>=7.6,<8.0",
   "mypy>=1.10,<2.0",
+  # pip and uv must stay declared here: ./scripts/uv requires .venv/bin/uv and
+  # ./scripts/bootstrap.sh requires .venv/bin/pip, but `uv sync` makes the venv
+  # exactly match the lockfile (and recreates it on interpreter upgrades) —
+  # undeclared, both binaries vanish and the bootstrap chain breaks.
+  "pip>=24.0,<26.0",
   "pre-commit>=4.0,<5.0",
   "pytest>=8.3,<9.0",
   "pytest-asyncio>=0.24,<1.0",
   "ruff>=0.6,<1.0",
+  "uv>=0.4,<1.0",
 ]
 
 [project.scripts]

scripts/bootstrap.sh

@@ -144,6 +144,11 @@ PYTHON_BIN="$(find_python_312)"
 
 if [[ ! -d "${VENV_DIR}" ]]; then
   "${PYTHON_BIN}" -m venv "${VENV_DIR}"
+elif [[ ! -x "${PIP_BIN}" && ! -x "${UV_BIN}" ]]; then
+  # A uv-recreated venv (e.g. after a Homebrew Python upgrade) contains
+  # neither pip nor uv; rebuild it so the pip -> uv -> sync chain below works.
+  echo "Existing .venv has neither pip nor uv; rebuilding it." >&2
+  "${PYTHON_BIN}" -m venv --clear "${VENV_DIR}"
 fi
 
 if [[ ! -x "${UV_BIN}" ]]; then

tests/test_dev_env_contract.py

@@ -0,0 +1,26 @@
+"""Contract: the bootstrap chain depends on uv and pip living inside .venv.
+
+``uv sync`` makes the environment exactly match the lockfile, and uv
+recreates the venv outright when the base interpreter changes (e.g. a
+Homebrew Python upgrade). If ``uv`` and ``pip`` are not declared dev
+dependencies they vanish on the next sync or recreation, breaking
+``./scripts/uv`` (which requires ``.venv/bin/uv``) and
+``./scripts/bootstrap.sh`` (which uses ``.venv/bin/pip`` to install uv).
+"""
+
+from __future__ import annotations
+
+import re
+import tomllib
+from pathlib import Path
+
+_PYPROJECT = Path(__file__).resolve().parent.parent / "pyproject.toml"
+
+
+def test_dev_extras_pin_uv_and_pip_for_the_bootstrap_chain() -> None:
+    with open(_PYPROJECT, "rb") as handle:
+        data = tomllib.load(handle)
+    dev = data["project"]["optional-dependencies"]["dev"]
+    names = {re.split(r"[><=\[ ]", item, maxsplit=1)[0] for item in dev}
+    assert "uv" in names, "uv must stay a dev dependency or syncs strip .venv/bin/uv"
+    assert "pip" in names, "pip must stay a dev dependency or bootstrap.sh cannot recover"