From a499c28029000e824df678792e42a89554fed440 Mon Sep 17 00:00:00 2001
From: yucheng-berri <293926326+yucheng-berri@users.noreply.github.com>
Date: Sat, 17 Oct 2026 15:31:53 -0700
Subject: [PATCH] fix(guardrails): split a newline-joined Converse message back
 into its parts

A vendor that returns a multi-part message as one newline-joined string now has its masks written back to each part, guardContent included, when no part sent already holds a newline.
---
 .../guardrail_translation/structured_edits.py | 15 +++++-
 .../guardrail_translation/test_handler.py     | 47 ++++++++++++++++---
 2 files changed, 54 insertions(+), 8 deletions(-)

diff --git a/litellm/llms/bedrock/passthrough/guardrail_translation/structured_edits.py b/litellm/llms/bedrock/passthrough/guardrail_translation/structured_edits.py
index 7ce666457b5..61399f67ae1 100644
--- a/litellm/llms/bedrock/passthrough/guardrail_translation/structured_edits.py
+++ b/litellm/llms/bedrock/passthrough/guardrail_translation/structured_edits.py
@@ -166,12 +166,25 @@ def _carries_no_text(content: object) -> bool:
             return False
 
 
+def _content_texts(row: ConverseRow, returned: Mapping[str, object]) -> tuple[str, ...] | None:
+    content: Final = returned.get("content")
+    sent: Final = _text_parts(row.message)
+    if (
+        isinstance(content, str)
+        and len(row.content) > 1
+        and sent is not None
+        and all("\n" not in text for text in sent)
+    ):
+        return tuple(content.split("\n"))
+    return _text_parts(returned)
+
+
 def _content_edits(row: ConverseRow, original: object, returned: Mapping[str, object]) -> tuple[Edit, ...] | None:
     if returned.get("content") == original:
         return ()
     if not row.content and _carries_no_text(returned.get("content")):
         return ()
-    texts: Final = _text_parts(returned)
+    texts: Final = _content_texts(row, returned)
     if texts is None or len(texts) != len(row.content):
         return None
     return _merged(tuple(_slot_edits(slot, text) for slot, text in zip(row.content, texts)))
diff --git a/tests/unit/llms/bedrock/passthrough/guardrail_translation/test_handler.py b/tests/unit/llms/bedrock/passthrough/guardrail_translation/test_handler.py
index 2caec8ee06a..f35e1b61e92 100644
--- a/tests/unit/llms/bedrock/passthrough/guardrail_translation/test_handler.py
+++ b/tests/unit/llms/bedrock/passthrough/guardrail_translation/test_handler.py
@@ -1741,14 +1741,14 @@ class TestConverseRowEditWriteBack:
                 id="role-changed",
             ),
             pytest.param(
-                [
-                    {
-                        "role": "user",
-                        "content": [{"text": "card 4111"}, {"cachePoint": {"type": "default"}}, {"text": "thanks"}],
-                    }
-                ],
+                [{"role": "user", "content": [{"text": "card\n4111"}, {"text": "thanks"}]}],
+                [{"role": "user", "content": "card\n[CARD] thanks"}],
+                id="blocks-that-hold-newlines-joined-with-a-space",
+            ),
+            pytest.param(
+                [{"role": "user", "content": [{"text": "card 4111"}, {"text": "thanks"}, {"text": "bye"}]}],
                 [{"role": "user", "content": "card [CARD]\nthanks"}],
-                id="blocks-merged-around-a-cache-point",
+                id="newline-joined-blocks-with-one-missing",
             ),
             pytest.param([_pay_turn(_CARD_TOOL_CALL)], [_pay_row(content="added text")], id="text-added-to-a-call"),
             pytest.param([_pay_turn(_CARD_TOOL_CALL)], [_pay_row(call_id="t2")], id="tool-call-id-changed"),
@@ -1789,6 +1789,39 @@ class TestConverseRowEditWriteBack:
 
         assert data["data"] == original
 
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize(
+        ("last_block", "masked_last_block"),
+        [
+            ({"text": "thanks 4111"}, {"text": "thanks [CARD]"}),
+            ({"guardContent": {"text": {"text": "thanks 4111"}}}, {"guardContent": {"text": {"text": "thanks [CARD]"}}}),
+        ],
+        ids=["text", "guard-content"],
+    )
+    async def test_row_joined_with_newlines_is_split_back_into_its_blocks(self, last_block, masked_last_block):
+        cache_point = {"cachePoint": {"type": "default"}}
+        data = _converse_request(
+            {"messages": [{"role": "user", "content": [{"text": "card 4111"}, cache_point, last_block]}]}
+        )
+
+        result = await BedrockPassthroughGuardrailHandler().process_input_messages(
+            data, _replying({"structured_messages": [{"role": "user", "content": "card [CARD]\nthanks [CARD]"}]})
+        )
+
+        assert result["data"]["messages"] == [
+            {"role": "user", "content": [{"text": "card [CARD]"}, cache_point, masked_last_block]}
+        ]
+
+    @pytest.mark.asyncio
+    async def test_single_block_row_keeps_a_newline_the_guardrail_wrote(self):
+        data = _converse_request({"messages": [{"role": "user", "content": [{"text": "card 4111"}]}]})
+
+        result = await BedrockPassthroughGuardrailHandler().process_input_messages(
+            data, _replying({"structured_messages": [{"role": "user", "content": "card\n[CARD]"}]})
+        )
+
+        assert result["data"]["messages"] == [{"role": "user", "content": [{"text": "card\n[CARD]"}]}]
+
     @pytest.mark.asyncio
     @pytest.mark.parametrize("content", [None, "", []], ids=["none", "empty-string", "empty-list"])
     async def test_tool_call_argument_mask_in_a_row_is_written_back(self, content):