Feature request: configurable auto-compact threshold (e.g. autoCompactThreshold in settings.json)

Summary

Currently there is no way to configure when auto-compact triggers. Claude Code manages context automatically, but users cannot set a threshold to control this behavior.

Current behavior

• Auto-compact fires at an undocumented internal threshold with no user control
• No setting in settings.json, no environment variable, no CLI flag
• The only option is manual /compact

Requested behavior

Add a configurable threshold in settings.json, for example:

{
  "autoCompactThreshold": 0.9
}

Or alternatively an environment variable: CLAUDE_AUTOCOMPACT_THRESHOLD=90

This would let users define at what context percentage auto-compact triggers (e.g. 80%, 90%).

Why this matters

Users working on large, long-running sessions need to predict and control when compaction happens. An unexpected auto-compact mid-task can disrupt workflow. A configurable threshold gives users control without requiring manual /compact every session.

Alternatives considered

Implementing a Stop hook that reads context % and triggers /compact — this works as a local workaround but requires custom scripting and is not as clean as a native setting.