Summary

Allow configuring a separate model for conversation compaction via agents.defaults.compaction.model (and per-agent overrides).

Motivation

Compaction currently uses the session's primary model. For users running an expensive primary model (e.g. Claude Opus) for conversation quality, compaction is a mechanical summarization task that doesn't need the same level of intelligence. Being able to route compaction to a cheaper model (e.g. Sonnet) would meaningfully reduce costs without affecting conversation quality.

Proposed Config

{
  "agents": {
    "defaults": {
      "compaction": {
        "mode": "safeguard",
        "model": "anthropic/claude-sonnet-4",
        "memoryFlush": {
          "enabled": true,
          "softThresholdTokens": 40000
        }
      }
    }
  }
}

Same pattern as heartbeat.model and subagents.model — override the model for a specific subsystem without changing the primary.

Current Workaround

None. Compaction always uses the primary model.