Auto-compaction did not trigger at 100% context usage

Description

A session reached 100% context usage without auto-compaction triggering. The session became unusable with no summary carried forward.

Expected behavior

Auto-compaction should trigger before the context window is fully exhausted (e.g., at ~85-90%), summarizing the conversation and freeing space to continue.

Actual behavior

The context hit 100% with no compaction fired. The session was effectively dead - no further input was possible.

Environment

• Platform: Windows 11 Pro (10.0.26200)
• Shell: PowerShell 5.1

Steps to reproduce

1. Run a long session with heavy tool use / large file reads
2. Observe context percentage climbing to 100%
3. No compaction fires - session is unrecoverable

Workaround

Manually run /compact before context fills up.