fix: preserve stale task identity history

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a053ff-1d6f-7fe2-ac1c-a6eb40a42a0c

tests/test_forge_projection.py

@@ -1156,6 +1156,23 @@ class TestExistingWorkplanTasks:
         assert out.refused[0]["reason"].startswith("current workplan contains duplicate")
         assert session.added == []
 
+    @pytest.mark.asyncio
+    async def test_duplicate_stale_history_inside_current_workplan_does_not_block(self):
+        row = _Row(slug="demo-wp-0001", status="active", path="workplans/a.md")
+        desired = _TaskRow("DEMO-WP-0001-T01", status="todo", workplan_id=row.id)
+        stale_a = _TaskRow("DEMO-WP-0001-T09", status="done", workplan_id=row.id)
+        stale_b = _TaskRow("demo-wp-0001-t09", status="done", workplan_id=row.id)
+        session = _FakeSession(
+            repo=_Repo(), rows=[row], task_rows=[desired, stale_a, stale_b]
+        )
+        out = await fp.reset_repository_projection(
+            session,
+            "demo",
+            derived=self._derived(("DEMO-WP-0001-T01", "Do it", "todo")),
+        )
+        assert out.status in {"applied", "noop"}
+        assert out.refused == []
+
     @pytest.mark.asyncio
     async def test_derived_task_uuid_held_elsewhere_is_refused_before_insert(self):
         row = _Row(slug="demo-wp-0001", status="active", path="workplans/a.md")
@@ -1170,7 +1187,7 @@ class TestExistingWorkplanTasks:
         )
         out = await fp.reset_repository_projection(session, "demo", derived=derived)
         assert out.status == "refused"
-        assert out.refused[0]["reason"].startswith("task identity already belongs")
+        assert out.refused[0]["reason"].startswith("derived task identifier already belongs")
         assert session.added == []
 
     @pytest.mark.asyncio