Auto-compact not triggering until <10% context remaining

Summary

Auto-compact failed to trigger in two separate sessions today (2026-05-31), both hitting 10% or less context remaining before the feature activated. In both cases, /compact was run manually to recover.

Steps to reproduce

1. Run a long session involving heavy tool use (docker logs, large file reads, shell output)
2. Continue until context is nearly exhausted
3. Auto-compact does not trigger — context hits ~10% with no automatic compaction

Expected behavior

Auto-compact should trigger well before 10% context remaining, preserving the session.

Actual behavior

Auto-compact did not trigger. Two sessions hit the limit on the same day:

• Session 1: hit 10%, manually ran /compact
• Session 2: hit 11% (99% used), manually ran /compact

Context

Both sessions involved significant tool output volume (docker exec, docker logs, large shell commands). It's possible the heuristic underestimates context consumption when tool results are large.

Environment

• Platform: macOS (darwin 25.5.0)
• Shell: zsh