Auto-compact firing at ~16% context used

Description

Auto-compact fired when the context bar showed only 16% used (84% of the context window still available). Compaction should not trigger anywhere near that low.

Environment

• Claude Code on macOS (Darwin 25.3.0)
• Model: claude-opus-4-7

Impact

Lost mid-task context unexpectedly during a long working session. Bar showed plenty of headroom; compaction was a complete surprise.

Repro

Not yet isolated — happened during a vault-editing session with several large file Reads (one Excalidraw .md was flagged as "too large to include" in a prior turn). The bar reported 16% used at the time compaction fired.