Bug: streamTo parameter in sessions_spawn breaks subagent runtime

Environment

• OpenClaw version: 2026.3.8 (also affects 3.7+)
• OS: macOS (Apple Silicon)
• Runtime: subagent (default)
• Model: aiberm/openai/gpt-5.4

Description

The streamTo parameter was added to the sessions_spawn tool schema for ACP runtime support. However, this parameter is visible to all runtime modes in the tool schema. When using models like gpt-5.4 that strictly follow tool schemas, the model automatically includes streamTo: "parent" in every sessions_spawn call.

For runtime=subagent (the default), this triggers a 400 error:

streamTo is only supported for runtime=acp; got runtime=subagent

This makes sessions_spawn completely unusable for subagent-mode agents using schema-following models.

Steps to Reproduce

1. Configure an agent with runtime=subagent (or default) using gpt-5.4
2. Have the agent call sessions_spawn with any task
3. The model will include streamTo: "parent" because it's in the tool schema
4. API returns 400 error

Expected Behavior

Either:

• streamTo should not appear in the tool schema when runtime != acp
• Or streamTo should be silently ignored (not error) for non-ACP runtimes

Workaround

Patched 10 dist files to silently ignore streamTo for non-ACP runtime:

// Before (error):
if (streamTo && runtime !== "acp") return jsonResult({ status: "error", error: `streamTo is only supported...` });
// After (noop):
if (streamTo && runtime !== "acp") { /* noop */ }

Impact

• All agents using subagent runtime + schema-following models are affected
• 90%+ of sessions_spawn calls fail (115/127 in our testing)
• Agents fall back to doing work themselves instead of delegating