Bug Description

The model parameter in sessions_spawn and the agents.defaults.subagents.model config setting are not being applied to spawned sub-agents. Sub-agents always inherit the main agent's model regardless of configuration.

Steps to Reproduce

1. Configure sub-agent default model in clawdbot.json:

{
  "agents": {
    "defaults": {
      "subagents": {
        "model": {
          "primary": "openai-codex/gpt-4o",
          "fallbacks": ["openai/gpt-4o"]
        }
      }
    }
  }
}

2. Spawn a sub-agent with explicit model override:

sessions_spawn(task="Test task", model="openai/gpt-4o")

3. Tool returns { "modelApplied": true }

4. Check the session transcript:

{"type":"model_change","provider":"anthropic","modelId":"claude-opus-4-5"}

Expected Behavior

Sub-agent should run on the specified model (openai/gpt-4o or openai-codex/gpt-4o).

Actual Behavior

Sub-agent runs on the main agent's model (anthropic/claude-opus-4-5) despite:

• Config setting agents.defaults.subagents.model
• Explicit model parameter in sessions_spawn
• Tool returning modelApplied: true

Environment

• Clawdbot version: 2026.1.24-3
• OS: macOS (Darwin 25.2.0 arm64)
• Main agent model: anthropic/claude-opus-4-5
• Attempted sub-agent models: openai-codex/gpt-4o, openai/gpt-4o

Additional Context

Gateway logs show config is being detected and applied:

[reload] config change applied (dynamic reads: agents.defaults.subagents.model)

But the actual model used in sub-agent sessions is always the main agent's model.