fix: address review comments - add runtime enforcement and remove unused code

- Remove unused 'import asyncio' from test file
- Remove unused 'original_execute_sync' variable from test
- Add defensive sorted() by _execution_index in _execute_tasks and _aexecute_tasks
  so the field is actively used at runtime, not just metadata

Co-Authored-By: João <joao@crewai.com>

lib/crewai/src/crewai/crew.py

@@ -999,7 +999,10 @@ class Crew(FlowTrackable, BaseModel):
         **Ordering contract**: tasks are dispatched in the exact order they
         appear in *tasks* (i.e. their insertion / list order).  Each task
         carries an ``_execution_index`` stamped at crew-construction time
-        that locks this order deterministically.
+        that locks this order deterministically.  As a defensive measure
+        the task list is sorted by ``_execution_index`` before iteration
+        so ordering is enforced even if the list is mutated after
+        construction.
 
         Args:
             tasks: List of tasks to execute (preserves insertion order).
@@ -1009,6 +1012,10 @@ class Crew(FlowTrackable, BaseModel):
         Returns:
             CrewOutput: Final output of the crew.
         """
+        tasks = sorted(
+            tasks,
+            key=lambda t: t._execution_index if t._execution_index is not None else 0,
+        )
         task_outputs: list[TaskOutput] = []
         pending_tasks: list[tuple[Task, asyncio.Task[TaskOutput], int]] = []
         last_sync_output: TaskOutput | None = None
@@ -1203,7 +1210,10 @@ class Crew(FlowTrackable, BaseModel):
         **Ordering contract**: tasks are dispatched in the exact order they
         appear in *tasks* (i.e. their insertion / list order).  Each task
         carries an ``_execution_index`` stamped at crew-construction time
-        that locks this order deterministically.
+        that locks this order deterministically.  As a defensive measure
+        the task list is sorted by ``_execution_index`` before iteration
+        so ordering is enforced even if the list is mutated after
+        construction.
 
         Args:
             tasks: List of tasks to execute (preserves insertion order).
@@ -1213,6 +1223,10 @@ class Crew(FlowTrackable, BaseModel):
         Returns:
             CrewOutput: Final output of the crew.
         """
+        tasks = sorted(
+            tasks,
+            key=lambda t: t._execution_index if t._execution_index is not None else 0,
+        )
         custom_start = self._get_execution_start_index(tasks)
         if custom_start is not None:
             start_index = custom_start

lib/crewai/tests/crew/test_deterministic_task_ordering.py

@@ -9,7 +9,6 @@ See: https://github.com/crewAIInc/crewAI/issues/4664
 
 from __future__ import annotations
 
-import asyncio
 from unittest.mock import patch
 
 import pytest
@@ -129,7 +128,6 @@ class TestDeterministicSyncOrder:
 
         for _ in range(ITERATIONS):
             dispatch_order: list[str] = []
-            original_execute_sync = Task.execute_sync
 
             def tracking_execute_sync(self_task, *args, **kwargs):
                 dispatch_order.append(self_task.description)