CLAUDE_AUTOCOMPACT_PCT_OVERRIDE not triggering at configured threshold

Bug Description

CLAUDE_AUTOCOMPACT_PCT_OVERRIDE=55 is set as an environment variable but auto-compaction does not trigger at 55% context usage. The main session regularly exceeds the configured threshold without compacting — observed at 67% in one session and over 80% in another before compaction finally occurred.

Environment

• Claude Code version: 2.1.79
• Model: Claude Opus 4.6 (Max plan)
• OS: macOS (Darwin 23.5.0)
• Shell: zsh

Steps to Reproduce

1. Set export CLAUDE_AUTOCOMPACT_PCT_OVERRIDE=55 in ~/.zshrc
2. Verify the variable is loaded: echo $CLAUDE_AUTOCOMPACT_PCT_OVERRIDE → 55
3. Start a Claude Code session and use it until context exceeds 55%
4. Observe that auto-compaction does not trigger at 55%

Expected Behavior

Auto-compaction should trigger when context window usage reaches ~55%, as configured by CLAUDE_AUTOCOMPACT_PCT_OVERRIDE.

Actual Behavior

• Context reached 67% (see screenshot) without triggering auto-compaction
• In another session, context reached over 80% before auto-compaction finally fired
• The env var appears to be ignored for the main session

Screenshot

Context at 67% with no auto-compaction triggered:

<img width="816" height="198" alt="Image" src="https://github.com/user-attachments/assets/2cd4a39f-3b6d-4144-bd69-43a82fc843f1" />

Additional Context

• The env var is confirmed set in the shell environment
• CLAUDE_CODE_AUTO_COMPACT_WINDOW is not set (default)
• According to the docs, CLAUDE_AUTOCOMPACT_PCT_OVERRIDE should apply to both main conversations and subagents
• The HUD percentage comes from Claude Code's native used_percentage field, so the reported percentage should match what the compaction engine sees