diff --git a/tests/test_tool_dispatch_adversarial.py b/tests/test_tool_dispatch_adversarial.py
new file mode 100644
index 0000000..95afe42
--- /dev/null
+++ b/tests/test_tool_dispatch_adversarial.py
@@ -0,0 +1,147 @@
+"""Behavioral adversarial fixtures for ``_TOOL_RESULT_DISPATCH`` predicate overlap.
+
+Structural tuple-position guards live in ``test_tool_dispatch_ordering.py``.
+These tests construct ``toolUseResult`` JSON that satisfies multiple predicates
+and assert the classified winner via ``_parse_tool_result`` (first match wins).
+"""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+
+import pytest
+
+from tests.test_tool_dispatch_ordering import ORDERING_INVARIANT_IDS, ORDERING_INVARIANTS
+from utils import tool_dispatch
+from utils.tool_dispatch import _TOOL_RESULT_DISPATCH, _parse_tool_result
+
+# Overlap blobs: keys chosen so both predicates in each ORDERING_INVARIANTS pair match.
+PLAN_FILE_WRITE_OVERLAP: dict[str, object] = {
+    "plan": {"name": "sprint-plan", "steps": ["index", "search", "render"]},
+    "filePath": ".cursor/plans/week28.md",
+    "content": "Plan body that would also satisfy file_write.",
+}
+
+TASK_MESSAGE_RETRIEVAL_OVERLAP: dict[str, object] = {
+    "task_id": "task-overlap-retrieval",
+    "message": "polling retrieval",
+    "retrieval_status": "found",
+    "task": {"task_id": "task-overlap-retrieval", "description": "subagent scan"},
+}
+
+TASK_MESSAGE_COMPLETED_OVERLAP: dict[str, object] = {
+    "agentId": "agent-overlap-completed",
+    "totalDurationMs": 3200,
+    "totalTokens": 900,
+    "status": "completed",
+    "message": "task finished",
+}
+
+TASK_MESSAGE_ASYNC_OVERLAP: dict[str, object] = {
+    "agentId": "agent-overlap-async",
+    "isAsync": True,
+    "description": "explore auth handlers",
+    "message": "task launched",
+}
+
+# Narrow retrieval shape: only the downstream predicate matches (no task_id/message).
+TASK_RETRIEVAL_NARROW: dict[str, object] = {
+    "retrieval_status": "pending",
+    "task": {"task_id": "task-narrow", "description": "wait for result"},
+}
+
+AssertWinner = Callable[[dict[str, object]], None]
+
+
+def _assert_plan_beats_file_write(result: dict[str, object]) -> None:
+    assert result["result_type"] == "plan"
+    assert result.get("file_path") == ".cursor/plans/week28.md"
+
+
+def _assert_task_message_beats_retrieval(result: dict[str, object]) -> None:
+    assert result["result_type"] == "task"
+    assert result.get("task_id") == "task-overlap-retrieval"
+    assert "retrieval_status" not in result
+
+
+def _assert_task_message_beats_completed(result: dict[str, object]) -> None:
+    assert result["result_type"] == "task"
+    assert result.get("agent_id") is None
+    assert result.get("total_duration_ms") is None
+
+
+def _assert_task_message_beats_async(result: dict[str, object]) -> None:
+    assert result["result_type"] == "task"
+    assert result.get("agent_id") is None
+    assert result.get("description") is None
+
+
+_INVARIANT_BEHAVIOR: dict[str, tuple[dict[str, object], AssertWinner]] = {
+    "plan_before_file_write": (PLAN_FILE_WRITE_OVERLAP, _assert_plan_beats_file_write),
+    "task_message_before_task_retrieval": (
+        TASK_MESSAGE_RETRIEVAL_OVERLAP,
+        _assert_task_message_beats_retrieval,
+    ),
+    "task_message_before_task_completed": (
+        TASK_MESSAGE_COMPLETED_OVERLAP,
+        _assert_task_message_beats_completed,
+    ),
+    "task_message_before_task_async": (
+        TASK_MESSAGE_ASYNC_OVERLAP,
+        _assert_task_message_beats_async,
+    ),
+}
+
+_INVARIANT_PREDICATES = dict(zip(ORDERING_INVARIANT_IDS, ORDERING_INVARIANTS, strict=True))
+
+
+@pytest.mark.parametrize(
+    "fixture_id",
+    ORDERING_INVARIANT_IDS,
+)
+def test_adversarial_overlap_classifies_documented_winner(fixture_id: str) -> None:
+    blob, assert_winner = _INVARIANT_BEHAVIOR[fixture_id]
+    before, after, _ = _INVARIANT_PREDICATES[fixture_id]
+    assert before(blob), f"{fixture_id}: fixture no longer matches {before.__name__}"
+    assert after(blob), f"{fixture_id}: fixture no longer matches {after.__name__}"
+    result = _parse_tool_result(blob)
+    assert result is not None
+    assert_winner(result)
+
+
+def test_task_retrieval_narrow_shape_without_task_message_keys() -> None:
+    """Boundary: narrow retrieval wins when broad task_message keys are absent."""
+    result = _parse_tool_result(TASK_RETRIEVAL_NARROW)
+    assert result is not None
+    assert result["result_type"] == "task"
+    assert result.get("retrieval_status") == "pending"
+    assert result.get("task_id") == "task-narrow"
+
+
+def test_inverted_plan_file_write_dispatch_misclassifies_overlap(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Regression: swapping plan below file_write flips the overlap winner."""
+    table = list(_TOOL_RESULT_DISPATCH)
+    plan_idx = next(
+        i for i, (pred, _) in enumerate(table) if pred.__name__ == "is_plan_tool_result"
+    )
+    write_idx = next(
+        i for i, (pred, _) in enumerate(table) if pred.__name__ == "is_file_write_tool_result"
+    )
+    table[plan_idx], table[write_idx] = table[write_idx], table[plan_idx]
+    monkeypatch.setattr(tool_dispatch, "_TOOL_RESULT_DISPATCH", tuple(table))
+
+    result = _parse_tool_result(PLAN_FILE_WRITE_OVERLAP)
+    assert result is not None
+    assert result["result_type"] == "file_write"
+    assert result.get("file_path") == ".cursor/plans/week28.md"
+    with pytest.raises(AssertionError):
+        _assert_plan_beats_file_write(result)
+
+
+def test_ordering_invariants_have_adversarial_coverage() -> None:
+    """Every ORDERING_INVARIANTS row has a behavioral fixture (keeps tables in sync)."""
+    assert len(ORDERING_INVARIANTS) == len(ORDERING_INVARIANT_IDS)
+    assert len(ORDERING_INVARIANT_IDS) == len(_INVARIANT_BEHAVIOR)
+    assert set(_INVARIANT_BEHAVIOR.keys()) == set(ORDERING_INVARIANT_IDS)
diff --git a/tests/test_tool_dispatch_ordering.py b/tests/test_tool_dispatch_ordering.py
index ce6835e..008f644 100644
--- a/tests/test_tool_dispatch_ordering.py
+++ b/tests/test_tool_dispatch_ordering.py
@@ -44,6 +44,13 @@
     ),
 ]
 
+ORDERING_INVARIANT_IDS = [
+    "plan_before_file_write",
+    "task_message_before_task_retrieval",
+    "task_message_before_task_completed",
+    "task_message_before_task_async",
+]
+
 
 def _predicate_index(predicate: Predicate) -> int:
     for i, entry in enumerate(_TOOL_RESULT_DISPATCH):
@@ -57,12 +64,7 @@ def _predicate_index(predicate: Predicate) -> int:
 @pytest.mark.parametrize(
     "before,after,reason",
     ORDERING_INVARIANTS,
-    ids=[
-        "plan_before_file_write",
-        "task_message_before_task_retrieval",
-        "task_message_before_task_completed",
-        "task_message_before_task_async",
-    ],
+    ids=ORDERING_INVARIANT_IDS,
 )
 def test_tool_dispatch_ordering_invariant(
     before: Predicate,