Feature request: context_threshold setting for auto-compact in settings.json

Problem

Long Claude Code sessions require manual compaction via /compact. Users must:

1. Notice they're running low on context (no indicator)
2. Manually prepare (save work, update memory files)
3. Type /compact

Missing step 1 or 2 results in lost context and wasted work. There's currently no way for hooks or the agent to programmatically trigger compaction.

Proposed Solution

Add a context_threshold setting in .claude/settings.json that automatically triggers compaction (or a pre-compact hook) when context usage reaches a threshold:

{
  "context": {
    "auto_compact_threshold": 0.8,
    "pre_compact_hook": {
      "type": "command",
      "command": "bash scripts/compact-prep.sh",
      "timeout": 30000
    }
  }
}

Behavior

• At auto_compact_threshold (e.g., 80%), fire the pre_compact_hook first (save state, update memory, commit work)
• Then automatically run compaction
• Alternatively: expose a Compact tool the agent can invoke, or a PreCompact hook type

Current Workaround

We built a context-monitor.sh that runs on every PreToolUse hook, counting tool calls as a proxy for context usage. At estimated 80%, it prints a warning that the agent's AGENTS.md rules tell it to act on (run compact prep). But the actual /compact still requires user input.

This works but is fragile — the tool-call-to-context-% mapping is a rough heuristic, and the agent can't actually trigger compaction.

Use Case

Power users running 8+ hour sessions with:

• Multiple background processes (transcription, imports)
• Telegram integration receiving messages throughout
• Heavy tool use (500+ calls per session)
• Memory files that must be updated before compaction

These sessions routinely hit context limits. Auto-compact with a pre-hook would make long sessions seamless.

Environment

• Claude Code 2.1.101
• macOS, Opus 4.6 (1M context)