Purpose
-------
OI-531 regression coverage — the ``"optional"`` tier in
:data:`oct.git.policy.PROFILE_MATRIX` must be truly non-blocking:
the check runs and its failures are reported, but the CLI exit code
stays at 0 for that tier alone.
Before OI-531 the policy layer treated ``"optional"`` identically to
``"blocking"`` at [oct/oct/git/policy.py:381](oct/oct/git/policy.py#L381),
which meant ``oct git commit`` under the compact profile would exit 4
on any test failure. The user confirmed the intended semantics: compact
should flag test failures but let the commit through.
Responsibilities
----------------
- ``compact`` profile + test failures → exit code 0.
- ``strict`` profile + test failures → exit code 4 (still blocking).
- :data:`PROFILE_MATRIX` docstring documents all three tier values.
Diagnostics
-----------
Domain: GIT-TESTS
Levels:
L2 — test lifecycle
L3 — assertion details
L4 — deep tracing
Contracts
---------
- Tests use in-memory mock objects; no subprocess or filesystem writes.