Bug type

Regression (worked before, now fails)

Beta release blocker

No

Summary

After upgrading to OpenClaw v2026.4.27, the parameter-free MCP tool schema issue from #60158 appears to be back: openai/gpt-5.4 rejects flux-mcp__get_flux_instance with object schema missing properties.

Steps to reproduce

1. Run OpenClaw v2026.4.27.
2. Configure flux-operator-mcp.
3. Use model openai/gpt-5.4.
4. Trigger a request path that registers or uses flux-mcp__get_flux_instance.
5. Observe the request fail with an OpenAI schema validation error.

Expected behavior

Parameter-free MCP tool schemas should be normalized before being sent to OpenAI.

This worked after #60158 was fixed by #60176. That fix normalized truly empty MCP tool schemas {} into { type: "object", properties: {} }, so OpenAI should not reject parameter-free MCP tools with object schema missing properties.

Actual behavior

On OpenClaw v2026.4.27, the same schema validation failure is observed again for flux-mcp__get_flux_instance.

OpenClaw version

v2026.4.27

Operating system

node:24-bookworm / official OpenClaw image

Install method

Official OpenClaw image

Model

openai/gpt-5.4

Provider / routing chain

openclaw -> openai

Additional provider/model setup details

This appears to be a regression of #60158.

The issue was previously fixed by #60176, which handled truly empty MCP tool schemas returned by parameter-free MCP tools. The same MCP tool, flux-mcp__get_flux_instance, now fails again on v2026.4.27 with the same OpenAI schema validation error.

Logs, screenshots, and evidence

2026-04-30T18:36:26.268+00:00 [model-fallback/decision] model fallback decision: decision=candidate_failed requested=openai/gpt-5.4 candidate=openai/gpt-5.4-nano reason=format next=none detail=400 Invalid schema for function 'flux-mcp__get_flux_instance': In context=(), object schema missing properties.
Embedded agent failed before reply: All models failed (3): openai/gpt-5.4: 400 Invalid schema for function 'flux-mcp__get_flux_instance': In context=(), object schema missing properties. (format) | openai/gpt-5.4-mini: 400 Invalid schema for function 'flux-mcp__get_flux_instance': In context=(), object schema missing properties. (format) | openai/gpt-5.4-nano: 400 Invalid schema for function 'flux-mcp__get_flux_instance': In context=(), object schema missing properties. (format) | LLM request failed: provider rejected the request schema or tool payload.

Impact and severity

Affected: OpenClaw v2026.4.27 deployments using openai/gpt-5.4 with flux-operator-mcp and similar MCP servers exposing parameter-free tool schemas.

Severity: High, because the affected MCP tools cannot be registered or used with the OpenAI provider path.

Frequency: Observed after upgrading to v2026.4.27.

Consequence: Agent workflows depending on affected MCP tools fail.

Additional information

This looks like a regression of #60158.

#60176 fixed the previous occurrence by normalizing truly empty MCP tool schemas {} into { type: "object", properties: {} } before sending them to OpenAI. The same class of failure is now observed again on v2026.4.27.