diff --git a/tests/providers/test_anthropic_tool_result.py b/tests/providers/test_anthropic_tool_result.py
new file mode 100644
index 00000000..5860b8ba
--- /dev/null
+++ b/tests/providers/test_anthropic_tool_result.py
@@ -0,0 +1,57 @@
+"""Tests for AnthropicProvider._tool_result_block image_url conversion.
+
+Regression for: tool results containing OpenAI-format image_url blocks
+(e.g. from read_file on an image file, via build_image_content_blocks)
+were passed to Anthropic unconverted, causing silent image drops with a
+"Non-transient LLM error with image content, retrying without images"
+warning.
+"""
+
+from nanobot.providers.anthropic_provider import AnthropicProvider
+
+
+def test_tool_result_block_converts_image_url_in_list_content():
+    """image_url blocks inside tool_result list content must be translated
+    to Anthropic-native image blocks; sibling text blocks pass through."""
+    msg = {
+        "role": "tool",
+        "tool_call_id": "call_1",
+        "content": [
+            {
+                "type": "image_url",
+                "image_url": {"url": "data:image/png;base64,AAAA"},
+                "_meta": {"path": "/tmp/x.png"},
+            },
+            {"type": "text", "text": "(Image file: /tmp/x.png)"},
+        ],
+    }
+    block = AnthropicProvider._tool_result_block(msg)
+
+    assert block["type"] == "tool_result"
+    assert block["tool_use_id"] == "call_1"
+    content = block["content"]
+    assert isinstance(content, list)
+    assert content[0] == {
+        "type": "image",
+        "source": {
+            "type": "base64",
+            "media_type": "image/png",
+            "data": "AAAA",
+        },
+    }
+    assert content[1] == {"type": "text", "text": "(Image file: /tmp/x.png)"}
+
+
+def test_tool_result_block_preserves_string_content():
+    """String content must be passed through unchanged; the image-conversion
+    path for lists must not affect the string path."""
+    msg = {
+        "role": "tool",
+        "tool_call_id": "call_2",
+        "content": "plain tool output",
+    }
+    block = AnthropicProvider._tool_result_block(msg)
+
+    assert block["type"] == "tool_result"
+    assert block["tool_use_id"] == "call_2"
+    assert block["content"] == "plain tool output"