diff --git a/tests/agent/test_learning_mutations.py b/tests/agent/test_learning_mutations.py
index 79afa4d1379..dc2f562d02f 100644
--- a/tests/agent/test_learning_mutations.py
+++ b/tests/agent/test_learning_mutations.py
@@ -112,3 +112,17 @@ def test_edit_skill_rewrites_and_validates(home):
 
 def test_missing_skill_detail(home):
     assert not lm.node_detail("nonexistent-skill")["ok"]
+
+
+def test_memory_writes_match_memory_tool_format(home):
+    """A journey mutation must leave the file byte-identical to what the memory
+    tool itself writes — same §-join, no trailing-newline drift — so the two
+    surfaces never fight over format and indices stay aligned."""
+    from tools.memory_tool import ENTRY_DELIMITER, MemoryStore
+
+    assert lm.edit_node("memory:memory:0", "alpha rewritten")["ok"]
+    path = home / "memories" / "MEMORY.md"
+    entries = MemoryStore._read_file(path)
+
+    assert entries == ["alpha rewritten", "beta note"]
+    assert path.read_text(encoding="utf-8") == ENTRY_DELIMITER.join(entries)