Two defects shipped with a green suite: button.py imported a helper that had
been deleted (no harness ever loaded the file), and the drift sweep only judged
`homeassistant.*`, so a relative import of a name that no longer exists was
invisible to it. Both are now impossible to ship silently.
* tests/test_module_coverage.py loads EVERY *.py file of the package, in a clean
interpreter, under the stub harness — exhaustive by construction (a new
platform is covered the moment the file exists; there is no list and no
special case). It asserts the reported set equals the files on disk, so a
silently skipped module fails too;
* entity_stublib.load_entity_modules() now also loads button.py (the named gap);
the sweep is what keeps that list from needing to be complete;
* ha_api_drift gained pass 5: the package's own relative imports. Pure AST,
no homeassistant required, with its own entry point
`scan_package_imports()` for the fast suite — it checks the target file exists
and defines every imported name (submodule imports still resolve), instead of
trusting that the modules a harness happened to load are the ones that matter;
* the file walk in both AST passes is recursive, and the non-vacuity floors moved
with it (modules 10 → 20, relative_imports ≥ 100 — a shallow-glob regression
trips the floor instead of looking green);
* two permanent red proofs, both on a copy of the tree with the reverted
`from .helpers import discover_adb_host` reference in button.py: the stub-harness
sweep fails with "FAIL button.py", and the static pass fails with
"button.py:1: broken-relative-import: … not defined in helpers.py". Manual runs
confirm the engine's other direction on the real pre-fix tree (c588a7c: exit 1
with the t40 entity-contract finding) and exit 0 on HEAD.
No Home-Assistant API drift (23 modules, 58 imports, 148 relative imports, 36
call arguments, 6 awaited HA calls). Verified: 334 passed / 2 skipped, 335 / 1
with androidtvremote2, ruff clean.
Note (pre-existing, not introduced here): running a SUBSET of test files in an
order the suite was not written for (e.g. test_init.py alone after
test_standalone_setup.py) fails 3 import-step tests with
"ModuleNotFoundError: No module named 'voluptuous'" — the per-file stub scoping
assumes the suite's order. Verified identical on the pre-t41 tree (60d884b), so
it is left alone here.
