fix(bedrock): place cache point before non-PDF document blocks

src/strands/models/bedrock.py

@@ -362,7 +362,20 @@ def _inject_cache_point(self, messages: list[dict[str, Any]]) -> None:
                 last_user_idx = msg_idx
 
         if last_user_idx is not None and messages[last_user_idx].get("content"):
-            messages[last_user_idx]["content"].append({"cachePoint": {"type": "default"}})
+            content = messages[last_user_idx]["content"]
+
+            # Insert before non-PDF document blocks to avoid Bedrock ValidationException
+            first_non_pdf_doc_idx = None
+            for i, block in enumerate(content):
+                if "document" in block and block["document"].get("format", "") != "pdf":
+                    first_non_pdf_doc_idx = i
+                    break
+
+            if first_non_pdf_doc_idx is not None:
+                content.insert(first_non_pdf_doc_idx, {"cachePoint": {"type": "default"}})
+            else:
+                content.append({"cachePoint": {"type": "default"}})
+
             logger.debug("msg_idx=<%s> | added cache point to last user message", last_user_idx)
 
     def _find_last_user_text_message_index(self, messages: Messages) -> int | None:

tests/strands/models/test_bedrock.py

@@ -2683,6 +2683,82 @@ def test_inject_cache_point_strips_existing_cache_points(bedrock_client):
     assert "cachePoint" in cleaned_messages[2]["content"][-1]
 
 
+def test_inject_cache_point_before_non_pdf_document(bedrock_client):
+    """Test that cache point is inserted before non-PDF document blocks."""
+    model = BedrockModel(
+        model_id="us.anthropic.claude-sonnet-4-20250514-v1:0", cache_config=CacheConfig(strategy="auto")
+    )
+
+    cleaned_messages = [
+        {
+            "role": "user",
+            "content": [
+                {"text": "Analyze this file"},
+                {"document": {"format": "md", "name": "readme", "source": {"bytes": b"# Hello"}}},
+            ],
+        },
+    ]
+
+    model._inject_cache_point(cleaned_messages)
+
+    content = cleaned_messages[0]["content"]
+    assert len(content) == 3
+    assert content[0] == {"text": "Analyze this file"}
+    assert "cachePoint" in content[1]
+    assert "document" in content[2]
+
+
+def test_inject_cache_point_after_pdf_document(bedrock_client):
+    """Test that cache point is appended at end when only PDF documents are present."""
+    model = BedrockModel(
+        model_id="us.anthropic.claude-sonnet-4-20250514-v1:0", cache_config=CacheConfig(strategy="auto")
+    )
+
+    cleaned_messages = [
+        {
+            "role": "user",
+            "content": [
+                {"text": "Analyze this PDF"},
+                {"document": {"format": "pdf", "name": "report", "source": {"bytes": b"%PDF-1.4"}}},
+            ],
+        },
+    ]
+
+    model._inject_cache_point(cleaned_messages)
+
+    content = cleaned_messages[0]["content"]
+    assert len(content) == 3
+    assert "document" in content[1]
+    assert "cachePoint" in content[2]
+
+
+def test_inject_cache_point_mixed_pdf_and_non_pdf_documents(bedrock_client):
+    """Test that cache point is inserted before the first non-PDF document in mixed content."""
+    model = BedrockModel(
+        model_id="us.anthropic.claude-sonnet-4-20250514-v1:0", cache_config=CacheConfig(strategy="auto")
+    )
+
+    cleaned_messages = [
+        {
+            "role": "user",
+            "content": [
+                {"text": "Analyze these files"},
+                {"document": {"format": "pdf", "name": "report", "source": {"bytes": b"%PDF-1.4"}}},
+                {"document": {"format": "csv", "name": "data", "source": {"bytes": b"a,b,c"}}},
+            ],
+        },
+    ]
+
+    model._inject_cache_point(cleaned_messages)
+
+    content = cleaned_messages[0]["content"]
+    assert len(content) == 4
+    assert "text" in content[0]
+    assert "document" in content[1] and content[1]["document"]["format"] == "pdf"
+    assert "cachePoint" in content[2]
+    assert "document" in content[3] and content[3]["document"]["format"] == "csv"
+
+
 def test_inject_cache_point_anthropic_strategy_skips_model_check(bedrock_client):
     """Test that anthropic strategy injects cache point without model support check."""
     model = BedrockModel(