Feature Request: Configurable Context Window Compaction Threshold

Summary

Add a user-configurable setting to control when auto-compaction triggers, instead of the hardcoded 95% threshold.

Motivation

The current 95% threshold works for many users, but some workflows benefit from more aggressive compaction:

• Long coding sessions - Users working on complex, multi-file tasks may want earlier compaction to preserve more relevant context before hitting limits
• Cost management - Earlier compaction can help users stay within budget by summarizing sooner
• Context quality - Compacting at 50-70% leaves headroom for the model to retain more nuanced details rather than aggressive summarization under pressure

Proposed Solution

Add a new setting contextCompactionThreshold (or similar) that accepts a percentage value (e.g., 0.5 for 50%).

Configuration via /config:

Auto-compact threshold: 50%

Or via settings file (~/.claude/settings.json):

{
  "contextCompactionThreshold": 0.5
}

Suggested Defaults

• Default: 0.95 (current behavior, no breaking change)
• Valid range: 0.25 to 0.95

Alternatives Considered

1. Manual /compact only - Works but requires user vigilance and interrupts flow
2. Multiple preset options (e.g., "aggressive", "moderate", "conservative") - Less flexible but simpler UX

Additional Context

This pairs well with the existing custom compaction instructions in CLAUDE.md, giving users full control over both when and how compaction occurs.