`homeassistant.util.diagnostic` does not exist — verified against a real
install: `import homeassistant.util.diagnostic` raises ModuleNotFoundError, and
the helper has always lived in `homeassistant.helpers.redact`. The import sat
inside a `try/except ImportError` that set the helper to None, so the
documented G14 pass — the one carrying `_TO_REDACT`, hosts included — silently
did nothing; only the marker scan (pairing-/key-shaped names) masked anything,
which is why the existing test's pairing-code assertion stayed green.
The helper is now imported at MODULE scope from homeassistant.helpers.redact and
applied unconditionally after the marker-name pass. A missing module is a loud
import error at integration load instead of a silent downgrade.
* the diagnostics test now asserts `adb_host` and `protocol_host` really are
masked in the emitted payload (options and a nested data value);
* TestFaithfulHaStubs asserts the module USES the helper from that path
(`nsh.diagnostics.async_redact_data is homeassistant.helpers.redact.async_redact_data`),
that no production module imports the non-existent module (AST), and that the
try/except ImportError fallback is gone;
* `entity_stublib` gains a faithful `homeassistant.helpers.redact` stub (same
masking, same nested mapping/list recursion, same None/empty-string skip) so
the harness meets the import the way a real install does.
Verified: 287 passed, 2 skipped (D2 stage); ruff clean. Full gate re-run on the
completed branch: 289 passed / 2 skipped and 290 passed / 1 skipped.
James Mackay