What v2.1 changed in response to type checker findings on v2.0.2.

• v2.0.2, v2.1: findings on that release's src/ and tests/, both checked with v2.1's settings (tox.ini, pyproject.toml). "v2.0.2" is commit c298694: v2.0.2 plus the component bumps that preceded this work.
• Actionable: v2.0.2 findings resolved by a change in v2.1.
• Bugs, Design, Minor: how many of the changes listed under Bug fixes, Design and Minor the checker spotted.
• basedpyright counts include its warnings: 110 errors + 2,869 warnings on v2.0.2, 5 + 2,571 on v2.1. Its 5 remaining errors are import cycles (__init__ ↔ versions ↔ cpython ↔ inspector). basedpyright is available locally (tox -e basedpyright), see CI/CD for which checkers gate CI.
• v2.1's zeros need runez 5.10.1, which fixed an annotation portable-python tripped on (see Fixed in runez).
• v2.0.2 had 3 # type: comments, v2.1 has none.

A checker pointed at code that misbehaved.

• With cpython-use-github: true, a failed GitHub API call (rate limiting, network error) crashed with a TypeError: RestClient.get() returns None on failure, and the response was iterated as-is [zuban, once get_available_versions() had a return annotation: mypy-style checkers skip the body of unannotated functions]
• When bin/python couldn't be found after make install, a configured cpython-validate-script or cpython-additional-packages ran None as the python executable before the "Can't find bin/python" check happened: bin_python is now always a Path, and aborts with that message on first use [pyrefly, pyright, basedpyright, zuban]

portable-python's invariants are now stated in its types, and enforced where they used to be assumed.

• BuildSetup takes a PythonSpec, the new required_python_spec() turns CLI text (or None/"latest") into one, with a clear error when it isn't a full X.Y.Z version [ty, pyrefly, pyright, basedpyright]
• VersionFamily is an ABC (get_available_versions() and get_builder() are abstract): latest is always a Version, aborting with "Could not determine latest cpython version" instead of the puzzling "Invalid python spec: None", and available_versions is always a dict [all six]
• Folders: build, destdir, sources and ppp-marker are required (clear error when not configured), only dist and logs are optional, and folders are Paths [pyrefly, pyright, basedpyright, zuban]
• PPG.family() always aborts for an unknown family (its fatal= parameter is gone) [all six]
• m_telltale is a plain str (several files are space-separated), instead of a mix of str and ClassVar[list] [all six]
• Library tracking: Trackable is an ABC declaring relative_path and tracked_category, LibType moved to tracking.py (the only enum Tracker was ever used with), and Tracker.report() no longer overrides represented() with a different return type [ty, pyrefly, pyright, basedpyright]

portable-python tripped on this runez annotation, fixed in runez 5.10.1 rather than worked around.

• to_path(None) returns None: it always did at runtime, but runez 5.10.0's annotation only allowed str | Path [all six]

A checker flagged code that turned out not to be needed.

• The __main__ block of cli.py re-imported main from its own module [ty, pyrefly, zuban]

The checker was right, the fix changes little in practice.

• Attributes say what they hold, including None (ModuleBuilder.m_*, parent_module, ModuleCollection, _bin_python, BuildSetup.build_context, ...) [all six]
• Base class methods declare their return type, so overrides agree (url, auto_select_reason(), candidate_modules(), get_problem(), xenv_LDFLAGS()) [all six]
• config.py: ConfigSource.get_value() walks the key in a loop, SingleFileMatch sets its attributes in __init__, and is_match() returns a bool [all six]
• # type: comments became annotations [pyrefly, pyright, basedpyright, zuban]
• Inspector: report lists hold strings, relative_path() returns a str, no x and x.y chains [pyrefly, mypy, zuban]
• Version listing checks v.patch truthiness instead of v.patch > 0 [ty, pyrefly, pyright, basedpyright]
• Tests: no poking at Config._sources, the mock's patcher is created in __init__ [ty, pyrefly, pyright, basedpyright]
• runez.ActivateColors instead of runez.colors.ActivateColors [pyright, basedpyright]
• recompress takes family and version from a spec only when the path names one [pyright, basedpyright]
• run_make(cpu_count=...) is annotated [ty]

• Folder paths containing a space are refused by portable-python itself, with the reason spelled out ("escapes too complex with makefiles, shell scripts etc"), instead of relying on a niche runez helper
• New tests: missing bin/python, python.org listing no versions, folder path with a space