fix: merging consecutive user messages corrupts multimodal (image) content (#1277)

* fix: preserve multimodal content blocks when merging consecutive user messages

* test: consecutive user-message merge keeps multimodal image blocks

src/llm_core.py

@@ -576,6 +576,20 @@ def _parse_anthropic_response(data: dict) -> str:
     )
 
 
+def _as_content_blocks(content) -> List[Dict]:
+    """Coerce a message `content` into a list of content blocks.
+
+    A list (multimodal: text + image parts) passes through; a non-empty string
+    becomes a single text block; None/empty yields no blocks. Used when merging
+    consecutive user messages so multimodal content isn't str()-ed away.
+    """
+    if isinstance(content, list):
+        return content
+    if content:
+        return [{"type": "text", "text": str(content)}]
+    return []
+
+
 def _sanitize_llm_messages(messages: List[Dict]) -> List[Dict]:
     """Strip Odysseus-only metadata before sending messages to providers.
 
@@ -689,13 +703,25 @@ def _sanitize_llm_messages(messages: List[Dict]) -> List[Dict]:
         last = merged[-1]
         if last.get("role") == "user" and item.get("role") == "user":
             last_copy = dict(last)
-            last_str = str(last_copy.get("content")) if last_copy.get("content") is not None else ""
-            item_str = str(item.get("content")) if item.get("content") is not None else ""
-            new_content = "\n\n".join(part for part in (last_str, item_str) if part)
-            if new_content:
-                last_copy["content"] = new_content
+            lc = last_copy.get("content")
+            ic = item.get("content")
+            if isinstance(lc, list) or isinstance(ic, list):
+                # Preserve multimodal content blocks (e.g. an image part) by
+                # concatenating the block lists. str()-ing a list turned an
+                # image message into its Python repr and dropped the image.
+                merged_blocks = _as_content_blocks(lc) + _as_content_blocks(ic)
+                if merged_blocks:
+                    last_copy["content"] = merged_blocks
+                else:
+                    last_copy.pop("content", None)
             else:
-                last_copy.pop("content", None)
+                last_str = str(lc) if lc is not None else ""
+                item_str = str(ic) if ic is not None else ""
+                new_content = "\n\n".join(part for part in (last_str, item_str) if part)
+                if new_content:
+                    last_copy["content"] = new_content
+                else:
+                    last_copy.pop("content", None)
             merged[-1] = last_copy
         else:
             merged.append(item)