From f35eb1e51501471bf6c5673c4d42315dbbf445b6 Mon Sep 17 00:00:00 2001
From: openhands <openhands@all-hands.dev>
Date: Fri, 31 Jul 2026 11:34:43 +0000
Subject: [PATCH] fix(sdk): exclude boolean false from anyOf non-null type
 selection

PR #4185 added boolean JSON Schema node handling but introduced a bug in
the anyOf filter: the condition `not isinstance(t, dict)` treats `False`
as a non-null type because `not isinstance(False, dict)` is `True`. This
causes `_process_schema_node(False)` to return `{"not": {}}` (rejects
everything), which then becomes the selected type for the parameter.

When an MCP server's schema contains `anyOf: [false, {"type": "string"}]`
(a pattern common in TypeScript-generated schemas where `false` represents
an impossible branch), the processor picks `{"not": {}}` as the parameter
type, making it impossible for the LLM to provide a valid value.

Fix: change the filter to `isinstance(t, dict) and t.get("type") != "null"`
so non-dict values (booleans True/False) are excluded from the non-null
type list, and only actual schema objects with a non-null type are
considered.

Co-authored-by: openhands <openhands@all-hands.dev>
---
 openhands-sdk/openhands/sdk/tool/schema.py |  4 +---
 tests/sdk/tool/test_mcp_schema.py          | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/openhands-sdk/openhands/sdk/tool/schema.py b/openhands-sdk/openhands/sdk/tool/schema.py
index e5d6033ecb..bfe3de1247 100644
--- a/openhands-sdk/openhands/sdk/tool/schema.py
+++ b/openhands-sdk/openhands/sdk/tool/schema.py
@@ -139,9 +139,7 @@ def _process_schema_node(
     # Handle anyOf (often used for optional fields with None)
     if "anyOf" in node:
         non_null_types = [
-            t
-            for t in node["anyOf"]
-            if not isinstance(t, dict) or t.get("type") != "null"
+            t for t in node["anyOf"] if isinstance(t, dict) and t.get("type") != "null"
         ]
         if non_null_types:
             # Process the first non-null type
diff --git a/tests/sdk/tool/test_mcp_schema.py b/tests/sdk/tool/test_mcp_schema.py
index 05967fbb65..e31dc07089 100644
--- a/tests/sdk/tool/test_mcp_schema.py
+++ b/tests/sdk/tool/test_mcp_schema.py
@@ -432,3 +432,25 @@ def test_boolean_schema_nodes_are_normalized(node, expected):
 
     assert result == expected
     json.dumps(result)
+
+
+def test_anyof_with_false_does_not_clobber_concrete_type():
+    """A ``false`` member in ``anyOf`` must not become the representative type.
+
+    JSON Schema ``false`` means "reject everything."  When it appears as one
+    branch of an ``anyOf`` alongside a concrete type (common in schemas emitted
+    by TypeScript/MCP servers), the processor must pick the concrete type, not
+    ``false``.  Previously the filter ``not isinstance(t, dict)`` treated
+    ``False`` as a non-null type, so ``_process_schema_node(False)`` returned
+    ``{"not": {}}`` — making the parameter impossible for the LLM to satisfy.
+    """
+    schema = {
+        "type": "object",
+        "properties": {
+            "value": {
+                "anyOf": [False, {"type": "string"}],
+            },
+        },
+    }
+    result = _process_schema_node(schema, {})
+    assert result["properties"]["value"] == {"type": "string"}