[Bug]: `anyOf: [false, X]` converts to `{"not": {}}`, clobbering the concrete branch

Is there an existing issue for the same bug?

• I have searched existing issues and this is not a duplicate.

Bug Description

_process_schema_node in openhands-sdk/openhands/sdk/tool/schema.py picks the wrong anyOf member when a boolean false schema appears in the list. Its filter keeps every non-dict member:

non_null_types = [
    t
    for t in node["anyOf"]
    if not isinstance(t, dict) or t.get("type") != "null"
]

not isinstance(False, dict) is True, so false survives the filter, and only the first survivor is used. anyOf: [false, {"type": "string"}] therefore converts to {"not": {}} — a schema no value can satisfy — while the reversed anyOf: [{"type": "string"}, false] converts to {"type": "string"}. The conversion is order-dependent.

The same filter is the only thing standing between a malformed member (5, "string", None, [], 1.5) and an uncaught TypeError/AttributeError out of to_openai_tool(), which takes down the whole tool list rather than one tool.

This is reachable from untrusted input: MCPToolDefinition._get_tool_schema deep-copies the server-provided inputSchema and feeds it straight into _process_schema_node, so whatever an MCP server advertises reaches this code verbatim.

Expected Behavior

anyOf is a disjunction, so a false branch contributes nothing and the concrete branch should win regardless of position:

• anyOf: [false, {"type": "string"}] → {"type": "string"}
• anyOf: [{"type": "string"}, false] → {"type": "string"}

Degenerate unions with no viable branch must keep their reject-all meaning (anyOf: [false] → {"not": {}}), and a member that is not a schema at all should be ignored rather than raising.

Actual Behavior

Running this against the current main with uv run python -c ... shows the order dependence:

uv run python -c "
from openhands.sdk.tool.schema import _process_schema_node
print(_process_schema_node({'anyOf': [False, {'type': 'string'}]}, {}))
print(_process_schema_node({'anyOf': [{'type': 'string'}, False]}, {}))
print(_process_schema_node({'anyOf': ['string', {'type': 'string'}]}, {}))
"

prints

{'not': {}}
{'type': 'string'}
AttributeError: 'str' object has no attribute 'get'

The first line should be {'type': 'string'} like the second, and the third case should not raise.

Steps to Reproduce

1. uv sync in a checkout of this repository.
2. Run the uv run python -c ... snippet above.
3. Observe {'not': {}} for the [false, {"type": "string"}] union and an AttributeError for the non-schema member.

Acceptance Criteria

• anyOf: [false, {"type": "string"}] and anyOf: [{"type": "string"}, false] both convert to {"type": "string"}.
• anyOf: [false] and anyOf: [false, {"type": "null"}] still convert to {"not": {}}.
• anyOf: [true, X] keeps converting to {} (unchanged behavior).
• An anyOf member that is not a schema (5, "string", None, [], 1.5) is ignored instead of raising TypeError/AttributeError.
• Regression tests covering the above live in tests/sdk/tool/test_mcp_schema.py and pass with uv run pytest tests/sdk/tool/test_mcp_schema.py -q.

Installation Method

Source checkout (uv sync)

Start in openhands-sdk/openhands/sdk/tool/schema.py at _process_schema_node, then run the reproduction command from the issue. Add regression coverage in tests/sdk/tool/test_mcp_schema.py for false, true, null, and malformed anyOf members, and run uv run pytest tests/sdk/tool/test_mcp_schema.py -q to confirm the expected conversions and no exceptions.