diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 88c2ee0c76..49b158bb58 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -339,7 +339,10 @@ def _payload_chars(value: Any, image_cost: int) -> int:
     if value is None:
         return 0
     if isinstance(value, dict):
-        if value.get("type") in _IMAGE_PART_TYPES and any(k in value for k in ("image_url", "image", "source", "file_id")):
+        part_type = value.get("type")
+        # JSON-Schema nodes may hold a sub-schema (``properties.type``) or a multi-type list
+        # under the "type" key; only scalar content-part types can ever match (#104793).
+        if isinstance(part_type, str) and part_type in _IMAGE_PART_TYPES and any(k in value for k in ("image_url", "image", "source", "file_id")):
             return _image_part_chars(value, image_cost)
         return sum(len(str(k)) + 6 + _payload_chars(v, image_cost) for k, v in value.items())
     if isinstance(value, list):
diff --git a/tests/agent/test_context_estimator_multimodal.py b/tests/agent/test_context_estimator_multimodal.py
index 8a320f4eee..a8661e4768 100644
--- a/tests/agent/test_context_estimator_multimodal.py
+++ b/tests/agent/test_context_estimator_multimodal.py
@@ -31,3 +31,24 @@ def test_text_payloads_and_tool_schemas_keep_the_legacy_estimate():
                "tools": [{"type": "function", "function": {"name": "vision", "parameters": {"type": "image"}}}]}
     legacy = (sum(len(str(m)) for m in payload["messages"]) + len(str(payload["tools"]))) // 4
     assert abs(estimate_request_context_tokens(payload) - legacy) < legacy * 0.02
+
+
+def test_schema_nodes_with_structured_type_values_keep_the_legacy_estimate():
+    """A JSON-Schema ``properties`` dict whose ``type`` KEY holds a sub-schema dict, or a multi-type
+    list like ``["string", "null"]``, is payload data — not an image part. The membership test must
+    not raise ``TypeError: unhashable type`` before the request reaches the provider (#104793)."""
+    def _tools(param_name):
+        return [{"type": "function", "function": {"name": "memory_search", "parameters": {"type": "object", "properties": {
+            param_name: {"type": "string", "enum": ["episode", "semantic"]},
+            "maybe": {"type": ["string", "null"]},
+        }}}}]
+    messages = [{"role": "user", "content": "hi"}]
+    payload = {"messages": messages, "tools": _tools("type")}
+    renamed = {"messages": messages, "tools": _tools("kind")}  # equal-length key: identical walk
+    assert estimate_request_context_tokens(payload) == estimate_request_context_tokens(renamed)
+    # A real image part in the same request is still priced at the learned cost.
+    chat = {"messages": [{"role": "user", "content": [
+        {"type": "text", "text": "look"},
+        {"type": "image_url", "image_url": {"url": _B64}},
+    ]}], "tools": _tools("type")}
+    assert DEFAULT_IMAGE_TOKEN_COST <= estimate_request_context_tokens(chat) < DEFAULT_IMAGE_TOKEN_COST + 400