fix(agent): shrink anthropic-native image history

Retry image-size rejections by rewriting Anthropic base64 image source blocks, not just OpenAI-style image_url parts.

agent/conversation_compression.py

@@ -805,10 +805,11 @@ def try_shrink_image_parts_in_messages(
     Pillow couldn't help (caller should surface the original error).
 
     Strategy: look for ``image_url`` / ``input_image`` parts carrying a
-    ``data:image/...;base64,...`` payload.  For each one whose encoded
-    size exceeds 4 MB (a safe target that slides under Anthropic's 5 MB
-    ceiling with header overhead) or whose longest side exceeds
-    ``max_dimension``, write the base64 to a tempfile, call
+    ``data:image/...;base64,...`` payload, plus Anthropic-native
+    ``{"type": "image", "source": {"type": "base64", ...}}`` blocks.
+    For each one whose encoded size exceeds 4 MB (a safe target that slides
+    under Anthropic's 5 MB ceiling with header overhead) or whose longest side
+    exceeds ``max_dimension``, write the base64 to a tempfile, call
     ``vision_tools._resize_image_for_vision`` to produce a smaller data
     URL, and substitute it in place.
 
@@ -964,6 +965,28 @@ def try_shrink_image_parts_in_messages(
             logger.warning("image-shrink recovery: re-encode failed — %s", exc)
             return None, triggered_by is not None
 
+    def _source_to_data_url(source: Any) -> Optional[str]:
+        if not isinstance(source, dict) or source.get("type") != "base64":
+            return None
+        data = source.get("data")
+        if not isinstance(data, str) or not data:
+            return None
+        media_type = str(source.get("media_type") or "image/jpeg").strip()
+        if not media_type.startswith("image/"):
+            media_type = "image/jpeg"
+        return f"data:{media_type};base64,{data}"
+
+    def _write_data_url_to_source(source: dict, data_url: str) -> None:
+        header, _, data = data_url.partition(",")
+        media_type = "image/jpeg"
+        if header.startswith("data:"):
+            candidate = header[len("data:"):].split(";", 1)[0].strip()
+            if candidate.startswith("image/"):
+                media_type = candidate
+        source["type"] = "base64"
+        source["media_type"] = media_type
+        source["data"] = data
+
     for msg in api_messages:
         if not isinstance(msg, dict):
             continue
@@ -974,6 +997,16 @@ def try_shrink_image_parts_in_messages(
             if not isinstance(part, dict):
                 continue
             ptype = part.get("type")
+            if ptype == "image":
+                source = part.get("source")
+                url = _source_to_data_url(source)
+                resized, unshrinkable = _shrink_data_url(url or "")
+                if resized and isinstance(source, dict):
+                    _write_data_url_to_source(source, resized)
+                    changed_count += 1
+                elif unshrinkable:
+                    unshrinkable_oversized += 1
+                continue
             if ptype not in {"image_url", "input_image"}:
                 continue
             image_value = part.get("image_url")

tests/run_agent/test_image_shrink_recovery.py

@@ -260,6 +260,52 @@ class TestShrinkImagePartsHelper:
         assert seen["max_dimension"] == 2000
         assert msgs[0]["content"][0]["image_url"]["url"] == shrunk
 
+    def test_anthropic_base64_image_source_rewritten(self, monkeypatch):
+        """Anthropic-native image blocks are shrinkable after adapter conversion."""
+        agent = _make_agent()
+        _install_fake_pillow(monkeypatch, (2501, 100), shrunk_size=(1500, 60))
+        original = _big_png_data_url(100)
+        _, _, original_data = original.partition(",")
+        shrunk = "data:image/jpeg;base64," + "N" * 1000
+        seen = {}
+
+        def _fake_resize(path, mime_type=None, max_base64_bytes=None, max_dimension=None):
+            seen["mime_type"] = mime_type
+            seen["max_dimension"] = max_dimension
+            return shrunk
+
+        monkeypatch.setattr(
+            "tools.vision_tools._resize_image_for_vision",
+            _fake_resize,
+            raising=False,
+        )
+
+        msgs = [{
+            "role": "user",
+            "content": [
+                {
+                    "type": "image",
+                    "source": {
+                        "type": "base64",
+                        "media_type": "image/png",
+                        "data": original_data,
+                    },
+                },
+            ],
+        }]
+        changed = agent._try_shrink_image_parts_in_messages(
+            msgs,
+            max_dimension=2000,
+        )
+        source = msgs[0]["content"][0]["source"]
+
+        assert changed is True
+        assert seen["mime_type"] == "image/png"
+        assert seen["max_dimension"] == 2000
+        assert source["type"] == "base64"
+        assert source["media_type"] == "image/jpeg"
+        assert source["data"] == "N" * 1000
+
     def test_oversized_input_image_string_shape_rewritten(self, monkeypatch):
         """OpenAI Responses shape: {type: input_image, image_url: "data:..."}."""
         agent = _make_agent()