Sub-Agent Model Routing Ignored

Summary

buildDirectChildSessionPatch() writes the model to session display metadata fields (model, modelProvider) but the execution engine reads override fields (modelOverride, providerOverride). Explicit sessions_spawn(model="...") calls and agents.defaults.subagents.model config are silently ignored, causing all sub-agents to fall back to the parent agent's primary model.

Environment

• OpenClaw: 2026.4.25
• File: dist/subagent-spawn-cbH-XgdN.js
• Function: buildDirectChildSessionPatch(patch)

Root Cause

What buildDirectChildSessionPatch() does:

function buildDirectChildSessionPatch(patch) {
    const entry = {};
    if (typeof patch.model === "string" && patch.model.trim()) {
        const { provider, model } = splitModelRef(patch.model.trim());
        if (model) {
            entry.model = model;
            if (provider) entry.modelProvider = provider;
        }
    }
    return entry;
}

What the execution engine reads:

return runEmbeddedPiAgent({
    provider: params.providerOverride,
    model: params.modelOverride,
    ...
});

The disconnect:

• model / modelProvider are display metadata (used by /subagents list)
• modelOverride / providerOverride are what the actual execution engine uses
• The spawn handler only populates display fields, never override fields
• Result: modelOverride is undefined → runtime falls back to parent primary model

Reproduction Steps

1. Parent agent configured with primary model = anthropic/claude-opus-4-7
2. Spawn sub-agent: sessions_spawn(model="local-qwen36/Qwen3.6-35B-A3B...", task="...")
3. Sub-agent runs on Opus 4.7 instead of specified local model
4. Explicit model= silently ignored (no warning, no error)

Expected Behavior

Sub-agent uses the explicitly specified model.

Actual Behavior

Sub-agent silently falls back to parent agent's primary model.

Fix

Add override fields in buildDirectChildSessionPatch():

if (typeof patch.model === "string" && patch.model.trim()) {
    const { provider, model } = splitModelRef(patch.model.trim());
    if (model) {
        entry.model = model;
        entry.modelOverride = model;
        if (provider) {
            entry.modelProvider = provider;
            entry.providerOverride = provider;
        }
    }
}

Impact

• All sub-agent model specifications are silently ignored
• sessions_spawn(model="...") never works as documented
• agents.defaults.subagents.model config never takes effect
• Sub-agents always use parent's primary model
• Cost impact: every sub-agent runs on expensive primary model

Files Affected

• dist/subagent-spawn-cbH-XgdN.js — buildDirectChildSessionPatch()

Verification

• Local patch applied and verified: sub-agents correctly route to specified model
• Trajectory logs confirm spawn params include correct model but execution uses parent model