diff --git a/openspec/changes/audit-mixin-coverage-guard/tasks.md b/openspec/changes/audit-mixin-coverage-guard/tasks.md
index a17986e..865a778 100644
--- a/openspec/changes/audit-mixin-coverage-guard/tasks.md
+++ b/openspec/changes/audit-mixin-coverage-guard/tasks.md
@@ -2,10 +2,10 @@ One task group = one GitHub ticket = one PR, merged before the next group starts
 
 ## 1. Coverage guard tests — depends on audit-mixin-auto-population, audit-mixin-rollout-tier3, audit-mixin-rollout-tier4 all being merged
 
-- [ ] 1.1 Confirm the full model inventory is at 100% `AuditMixin`/`AuditColumnsMixin` coverage post-Tier 4 (re-run the original survey); identify any remaining genuine exemptions.
-- [ ] 1.2 Add `services/ai/tests/test_audit_mixin_coverage.py`: walk `Base.registry.mappers`, assert each mapped class inherits `AuditMixin`/`AuditColumnsMixin` or is in a documented exemption set.
-- [ ] 1.3 Add the equivalent test in `services/budget/tests/`.
-- [ ] 1.4 Add the equivalent test in `services/chat/tests/`.
-- [ ] 1.5 Add the equivalent test in `services/users/tests/`.
-- [ ] 1.6 Verify each guard test fails as expected when a temporary non-compliant model is added locally (sanity-check the assertion actually catches the failure mode, then remove the temporary model).
+- [x] 1.1 Confirm the full model inventory is at 100% `AuditMixin`/`AuditColumnsMixin` coverage post-Tier 4 (re-run the original survey); identify any remaining genuine exemptions.
+- [x] 1.2 Add `services/ai/tests/test_audit_mixin_coverage.py`: walk `Base.registry.mappers`, assert each mapped class inherits `AuditMixin`/`AuditColumnsMixin` or is in a documented exemption set.
+- [x] 1.3 Add the equivalent test in `services/budget/tests/`.
+- [x] 1.4 Add the equivalent test in `services/chat/tests/`.
+- [x] 1.5 Add the equivalent test in `services/users/tests/`.
+- [x] 1.6 Verify each guard test fails as expected when a temporary non-compliant model is added locally (sanity-check the assertion actually catches the failure mode, then remove the temporary model).
 - [ ] 1.7 Run all 4 services' test suites clean; PR merged.
diff --git a/services/ai/tests/test_audit_mixin_coverage.py b/services/ai/tests/test_audit_mixin_coverage.py
new file mode 100644
index 0000000..5c6af5c
--- /dev/null
+++ b/services/ai/tests/test_audit_mixin_coverage.py
@@ -0,0 +1,11 @@
+"""Every model on this service's Base must inherit an audit mixin, or be in _EXEMPT."""
+
+import app.models
+from app.models.base import Base
+from shared.tests.audit_mixin_coverage import assert_full_audit_mixin_coverage
+
+_EXEMPT: dict[str, str] = {}
+
+
+def test_every_model_inherits_audit_mixin():
+    assert_full_audit_mixin_coverage(app.models, Base, _EXEMPT)
diff --git a/services/budget/tests/test_audit_mixin_coverage.py b/services/budget/tests/test_audit_mixin_coverage.py
new file mode 100644
index 0000000..a3abbbd
--- /dev/null
+++ b/services/budget/tests/test_audit_mixin_coverage.py
@@ -0,0 +1,13 @@
+"""Every model on this service's Base must inherit an audit mixin, or be in _EXEMPT."""
+
+import app.models
+from app.models.base import Base
+from shared.tests.audit_mixin_coverage import assert_full_audit_mixin_coverage
+
+_EXEMPT: dict[str, str] = {
+    "UserProfileModel": "denormalized cache of users-service state, not independently editable",
+}
+
+
+def test_every_model_inherits_audit_mixin():
+    assert_full_audit_mixin_coverage(app.models, Base, _EXEMPT)
diff --git a/services/chat/tests/test_audit_mixin_coverage.py b/services/chat/tests/test_audit_mixin_coverage.py
new file mode 100644
index 0000000..5c6af5c
--- /dev/null
+++ b/services/chat/tests/test_audit_mixin_coverage.py
@@ -0,0 +1,11 @@
+"""Every model on this service's Base must inherit an audit mixin, or be in _EXEMPT."""
+
+import app.models
+from app.models.base import Base
+from shared.tests.audit_mixin_coverage import assert_full_audit_mixin_coverage
+
+_EXEMPT: dict[str, str] = {}
+
+
+def test_every_model_inherits_audit_mixin():
+    assert_full_audit_mixin_coverage(app.models, Base, _EXEMPT)
diff --git a/services/users/tests/test_audit_mixin_coverage.py b/services/users/tests/test_audit_mixin_coverage.py
new file mode 100644
index 0000000..72db5d7
--- /dev/null
+++ b/services/users/tests/test_audit_mixin_coverage.py
@@ -0,0 +1,13 @@
+"""Every model on this service's Base must inherit an audit mixin, or be in _EXEMPT."""
+
+import app.models
+from app.models.base import Base
+from shared.tests.audit_mixin_coverage import assert_full_audit_mixin_coverage
+
+_EXEMPT: dict[str, str] = {
+    "SessionModel": "system-issued auth session tied 1:1 to user_id, not a user-edited resource",
+}
+
+
+def test_every_model_inherits_audit_mixin():
+    assert_full_audit_mixin_coverage(app.models, Base, _EXEMPT)
diff --git a/shared/tests/audit_mixin_coverage.py b/shared/tests/audit_mixin_coverage.py
new file mode 100644
index 0000000..d3d988f
--- /dev/null
+++ b/shared/tests/audit_mixin_coverage.py
@@ -0,0 +1,21 @@
+import importlib
+import pkgutil
+from types import ModuleType
+
+from shared.db.audit_mixin import AuditColumnsMixin
+
+
+def assert_full_audit_mixin_coverage(
+    models_package: ModuleType, base, exempt: dict[str, str]
+) -> None:
+    """Imports every module under models_package so a missing __init__.py import can't hide it."""
+    prefix = models_package.__name__ + "."
+    for module_info in pkgutil.iter_modules(models_package.__path__, prefix):
+        importlib.import_module(module_info.name)
+
+    missing = sorted(
+        mapper.class_.__name__
+        for mapper in base.registry.mappers
+        if not issubclass(mapper.class_, AuditColumnsMixin) and mapper.class_.__name__ not in exempt
+    )
+    assert not missing, f"Models missing AuditMixin/AuditColumnsMixin: {missing}"