Feature Request: Add compaction threshold percentage option

[smnuman]

Description

Would be helpful to have a configurable percentage threshold for when auto-compaction triggers, rather than only at ~100% context usage.

Use Case

Proactively compact context at 50-62% usage to avoid unexpected compaction during critical work.

Proposed Solution

Add threshold option to oh-my-opencode config:

{
  \"compaction\": {
    \"threshold\": 0.55,  // 55% - midpoint of 50-62%
    \"auto\": true,
    \"prune\": true
  }
}

Or expose OpenCode's existing hooks (context-window-monitor, compaction-context-injector) to allow plugins to control trigger threshold.

Context

• Using google/antigravity-claude-opus-4-6-thinking (200k context)
• Current workaround in opencode.json with high reserved value isn't precise enough

Thank you!