fix: reject checkpoint resume for a different task ID

src/fara/core/run_context.py

@@ -53,6 +53,12 @@ def create(
         output_path = Path(output_dir)
         if output_path.exists() and (output_path / "task.json").exists():
             writer = DataPointWriter.resume(output_path)
+            if writer.data_point.task.task_id != task.task_id:
+                raise ValueError(
+                    "Cannot resume task: checkpoint task_id "
+                    f"{writer.data_point.task.task_id!r} does not match requested "
+                    f"task_id {task.task_id!r}"
+                )
         else:
             writer = DataPointWriter.create(output_path, task, run_id=run_id)
         ctx = cls(

tests/test_run_context_resume_identity.py

@@ -0,0 +1,46 @@
+"""Native, no-browser tests for resume task identity invariants."""
+import sys
+from pathlib import Path
+from types import ModuleType
+
+import pytest
+
+# Load first-party core modules without Fara's package-level agent/OpenAI imports.
+source = Path(__file__).resolve().parents[1] / "src" / "fara"
+fara_package = ModuleType("fara")
+fara_package.__path__ = [str(source)]
+core_package = ModuleType("fara.core")
+core_package.__path__ = [str(source / "core")]
+sys.modules.setdefault("fara", fara_package)
+sys.modules.setdefault("fara.core", core_package)
+from fara.core.data_point import Task
+from fara.core.run_context import RunContext
+
+
+def test_resume_rejects_different_task_id(tmp_path):
+    original = Task(task_id="experiment-1", instruction="collect A")
+    different = Task(task_id="experiment-2", instruction="collect B")
+    RunContext.create(environment=object(), task=original, output_dir=tmp_path)
+
+    with pytest.raises(ValueError, match="task"):
+        RunContext.create(environment=object(), task=different, output_dir=tmp_path)
+
+    # Denial must not overwrite the recorded identity.
+    assert Task.load(tmp_path / "task.json").task_id == original.task_id
+
+
+def test_resume_same_task_id_keeps_original_checkpoint(tmp_path):
+    task = Task(task_id="experiment-1", instruction="collect A")
+    first = RunContext.create(environment=object(), task=task, output_dir=tmp_path)
+    first.set_state("stage", "complete")
+    first.checkpoint()
+
+    resumed = RunContext.create(environment=object(), task=task, output_dir=tmp_path)
+    assert resumed.task.task_id == task.task_id
+    assert resumed.get_state("stage") == "complete"
+
+
+def test_new_directory_keeps_requested_task_identity(tmp_path):
+    task = Task(task_id="experiment-2", instruction="new task")
+    created = RunContext.create(environment=object(), task=task, output_dir=tmp_path)
+    assert created.task.task_id == "experiment-2"