refactor(workflow): delegate transition_state to TestEntity

transition_state() now hydrates a TestEntity from the ORM model and delegates state validation to entity.transition_to(). The entity is authoritative for which transitions are valid; VALID_TRANSITIONS and can_transition() are kept for backward compatibility.

Also adds public transition_to() method to TestEntity as the stable API surface for callers that need a single validated transition without lifecycle side-effects.

backend/app/services/test_workflow_service.py

@@ -19,6 +19,7 @@ from sqlalchemy.orm import Session
 
 from app.config import settings
 from app.domain.exceptions import InvalidOperationError, InvalidTransitionError
+from app.domain.test_entity import TestEntity
 from app.models.enums import TestState
 from app.models.test import Test
 from app.models.user import User
@@ -61,21 +62,18 @@ def transition_state(
     action_name: str = "transition_state",
     extra_details: dict | None = None,
 ) -> Test:
-    """Validate and perform a state transition, log it, and commit.
+    """Validate and perform a state transition, log it, and flush.
 
-    Raises :class:`InvalidTransitionError` when the transition is invalid.
+    Delegates validation to :class:`TestEntity` which raises
+    :class:`InvalidStateTransition` (aliased as ``InvalidTransitionError``)
+    when the transition is illegal.  The entity is authoritative for which
+    transitions are valid; the module-level ``VALID_TRANSITIONS`` dict is
+    kept temporarily for backward compatibility of ``can_transition()``.
     """
-    if not can_transition(test, target_state):
-        current = test.state if isinstance(test.state, TestState) else TestState(test.state)
-        valid = [s.value for s in VALID_TRANSITIONS.get(current, [])]
-        raise InvalidTransitionError(
-            current_state=current.value,
-            target_state=target_state.value,
-            valid_transitions=valid,
-        )
+    entity = TestEntity.from_orm(test)
+    previous_state = entity.transition_to(target_state)
 
-    previous_state = test.state.value if isinstance(test.state, TestState) else test.state
-    test.state = target_state
+    test.state = entity.state
     db.flush()
 
     details: dict = {
@@ -96,7 +94,6 @@ def transition_state(
         details=details,
     )
 
-    # Dispatch in-app notifications for the new state
     try:
         notify_test_state_change(db, test, target_state.value)
     except Exception as e: