Bug

PR #58003 (commit e394262, merged 2026-03-31) reordered the fallback chain in resolveSubagentConfiguredModelSelection to prefer agentConfig.model (the agent's own model) over agents.defaults.subagents.model (the global subagent default).

This is correct for named agents with an explicit subagents.model override, but it introduces a regression for the common case: the main agent.

Reproduction

Config:

agents:
  defaults:
    model:
      primary: anthropic/claude-opus-4-6
    subagents:
      model:
        primary: openai/gpt-5.4
  list:
    - id: main
      model:
        primary: anthropic/claude-opus-4-6

Expected: subagents spawned from the main agent use openai/gpt-5.4 (the global subagent default).

Actual: subagents use anthropic/claude-opus-4-6 (the main agent's own model), because the agent's own model is checked before the global subagent default.

Root cause

In src/agents/model-selection.ts, resolveSubagentConfiguredModelSelection:

// After PR #58003 (buggy):
agentConfig?.subagents?.model   // per-agent subagent config → null for main
?? agentConfig?.model           // agent's OWN model → Opus (shadows global default)
?? cfg.agents.defaults.subagents.model  // global subagent default → never reached

An agent's own model (what model runs the agent) is conceptually different from what model its subagents should use. The agent's own model should only be a last-resort fallback, not take priority over an explicitly configured global subagent default.

The same issue exists in src/cron/isolated-agent/model-selection.ts.

Correct precedence

1. agentConfig.subagents.model — explicit per-agent subagent config (highest priority)
2. cfg.agents.defaults.subagents.model — global subagent default
3. agentConfig.model — agent's own model (last-resort fallback only)

Related

• Agents: fix subagent model precedence #58003 (introduced the regression)
• [Bug]: Per-agent model override not inherited by embedded/subagent runs #48255 (original subagent model resolution issue)