audit: validate ancestry before buffering, tighten nested ordering test

docs/superpowers/specs/2026-09-04-foreach-back-edge-design.md

@@ -432,9 +432,10 @@ may independently return and complete the item.
 ## State and Failure Behavior
 
 Back-edge return changes control representation, not state semantics.
-Iteration writes remain buffered in the item lineage. Serial behavior and the
+Concurrent iteration writes remain buffered in the item lineage for the
-concurrent barrier continue to commit or merge those writes according to the
+barrier to merge, while serial owners pass writes outward to the scope
-accepted concurrent-foreach ADR and declared reducers. One shared helper
+root, which commits them according to the accepted concurrent-foreach ADR
+and declared reducers. One shared helper
 routes every item write: it climbs through each serial owner to the scope
 root, where it commits, or stops at the first concurrent item boundary,
 where it buffers for that barrier to merge (the concurrent barrier finish

src/wf_core/runtime/lineage.py

@@ -98,8 +98,11 @@ def commit_foreach_aware_patch(
     climbs through every serial item owner until it reaches either the
     workflow/subgraph scope root, where it commits, or a concurrent item
     boundary, where it buffers in that item lineage for the barrier to
-    merge. Malformed ownership, missing parents, parent cycles, and closed
+    merge. The whole ancestry is validated first: the write lands only
-    or superseded activations fail closed.
+    after the chain reaches an acyclic non-item ancestor, so a parent
+    cycle fails closed even when it passes through a concurrent
+    boundary. Malformed ownership, missing parents, parent cycles, and
+    closed or superseded activations fail closed.
     """
     from wf_core.runtime.foreach_state import (
         item_frame_owner,
@@ -108,10 +111,11 @@ def commit_foreach_aware_patch(
 
     current = frame
     seen: set[str] = set()
+    buffer_in: ExecutionFrame | None = None
     while True:
         owner = item_frame_owner(current)
         if owner is None:
-            return commit_patch_for_frame(run, current, patch)
+            break
         if current.id in seen:
             raise WorkflowExecutionError(
                 f"cycle detected in foreach parent chain at frame {current.id!r}"
@@ -126,15 +130,18 @@ def commit_foreach_aware_patch(
         activation = require_foreach_activation(
             parent_frame, owner.foreach_node_id, owner.activation_id
         )
-        if activation.barrier.mode == "concurrent":
+        if buffer_in is None and activation.barrier.mode == "concurrent":
-            append_lineage_writes(
+            buffer_in = current
-                run,
-                scope_id=current.scope_id,
-                lineage_id=current.lineage_id,
-                writes=patch.writes,
-            )
-            return {}
         current = parent_frame
+    if buffer_in is not None:
+        append_lineage_writes(
+            run,
+            scope_id=buffer_in.scope_id,
+            lineage_id=buffer_in.lineage_id,
+            writes=patch.writes,
+        )
+        return {}
+    return commit_patch_for_frame(run, current, patch)
 
 
 def scope_state_for_frame(run: RunState, frame: ExecutionFrame) -> dict[str, Any]:

tests/core/test_foreach_back_edges.py

@@ -497,22 +497,26 @@ def _nested_mode_workflow(*, outer_mode: str, inner_mode: str) -> Workflow:
 
 
 @pytest.mark.parametrize(
-    ("outer_mode", "inner_mode"),
+    ("outer_mode", "inner_mode", "exact_order"),
     [
-        ("serial", "serial"),
+        ("serial", "serial", True),
-        ("serial", "concurrent"),
+        ("serial", "concurrent", True),
-        ("concurrent", "serial"),
+        ("concurrent", "serial", False),
-        ("concurrent", "concurrent"),
+        ("concurrent", "concurrent", False),
     ],
 )
 def test_nested_foreach_preserves_inner_writes_in_all_modes(
-    outer_mode: str, inner_mode: str
+    outer_mode: str, inner_mode: str, exact_order: bool
 ) -> None:
     """Inner writes must reach root state whatever the nesting modes are.
 
     Serial owners commit through the scope root; concurrent owners buffer
     for their barrier. Every inner write (1, 2 per outer item) must survive
     even with no intermediate writer to replay-rescue stranded lineages.
+
+    Serial outer admission is strictly ordered, so the sequence is exactly
+    [1, 2, 1, 2]. Concurrent outer completion order depends on scheduling,
+    so only the multiset is contractual there.
     """
     workflow = _nested_mode_workflow(outer_mode=outer_mode, inner_mode=inner_mode)
 
@@ -528,9 +532,11 @@ def test_nested_foreach_preserves_inner_writes_in_all_modes(
     )
 
     assert run.status == RunStatus.COMPLETED
-    assert sorted(run.state.get("seen") or [], key=repr) == sorted(
+    seen = run.state.get("seen") or []
-        [1, 2, 1, 2], key=repr
+    if exact_order:
-    )
+        assert seen == [1, 2, 1, 2]
+    else:
+        assert sorted(seen, key=repr) == sorted([1, 2, 1, 2], key=repr)
 
 
 def test_item_frame_owner_rejects_missing_parent_frame() -> None:
@@ -595,6 +601,98 @@ def test_foreach_aware_patch_rejects_parent_cycle() -> None:
         commit_foreach_aware_patch(run, frame_a, StatePatch(changes={}))
 
 
+def test_foreach_aware_patch_rejects_concurrent_self_cycle() -> None:
+    """A self-parented item with a concurrent owner must fail, not buffer."""
+    from wf_core.run_state import LineageState
+    from wf_core.runtime.foreach_state import load_or_begin_foreach_activation
+    from wf_core.runtime.lineage import commit_foreach_aware_patch
+    from wf_core.runtime.ops.state import StatePatch
+
+    frame = ExecutionFrame(
+        id="self",
+        kind="foreach_iteration",
+        node_id="work",
+        scope_id="root",
+        lineage_id="root",
+    )
+    activation = load_or_begin_foreach_activation(frame, "each", mode="concurrent")
+    frame.parent_frame_id = "self"
+    frame.metadata.update(
+        {
+            "foreach_node_id": "each",
+            "activation_id": activation.id,
+            "loop_index": 0,
+            "loop_item": "a",
+            "loop_alias": "item",
+        }
+    )
+    run = RunState(
+        workflow_name="concurrent_self_cycle",
+        status=RunStatus.RUNNING,
+        workflow_input={},
+        state={},
+        frames={"self": frame},
+        lineages={"root": LineageState(id="root", scope_id="root")},
+    )
+
+    with pytest.raises(WorkflowExecutionError, match="cycle"):
+        commit_foreach_aware_patch(run, frame, StatePatch(changes={}))
+    assert run.lineages["root"].writes == []
+
+
+def test_foreach_aware_patch_rejects_cycle_through_concurrent_boundary() -> None:
+    """A parent cycle spanning a concurrent boundary must fail, not buffer."""
+    from wf_core.run_state import LineageState
+    from wf_core.runtime.foreach_state import load_or_begin_foreach_activation
+    from wf_core.runtime.lineage import commit_foreach_aware_patch
+    from wf_core.runtime.ops.state import StatePatch
+
+    frame_a = ExecutionFrame(
+        id="frame-a",
+        kind="foreach_iteration",
+        node_id="work",
+        scope_id="root",
+        lineage_id="root",
+    )
+    frame_b = ExecutionFrame(id="frame-b", kind="foreach_iteration", node_id="work")
+    activation_on_b = load_or_begin_foreach_activation(
+        frame_b, "each", mode="concurrent"
+    )
+    activation_on_a = load_or_begin_foreach_activation(frame_a, "each", mode="serial")
+    frame_a.parent_frame_id = "frame-b"
+    frame_a.metadata.update(
+        {
+            "foreach_node_id": "each",
+            "activation_id": activation_on_b.id,
+            "loop_index": 0,
+            "loop_item": "a",
+            "loop_alias": "item",
+        }
+    )
+    frame_b.parent_frame_id = "frame-a"
+    frame_b.metadata.update(
+        {
+            "foreach_node_id": "each",
+            "activation_id": activation_on_a.id,
+            "loop_index": 0,
+            "loop_item": "a",
+            "loop_alias": "item",
+        }
+    )
+    run = RunState(
+        workflow_name="mixed_mode_cycle",
+        status=RunStatus.RUNNING,
+        workflow_input={},
+        state={},
+        frames={"frame-a": frame_a, "frame-b": frame_b},
+        lineages={"root": LineageState(id="root", scope_id="root")},
+    )
+
+    with pytest.raises(WorkflowExecutionError, match="cycle"):
+        commit_foreach_aware_patch(run, frame_a, StatePatch(changes={}))
+    assert run.lineages["root"].writes == []
+
+
 def test_reentering_foreach_uses_fresh_activation_and_item_frames() -> None:
     workflow = Workflow(
         name="foreach_reentry",