Context display shows 15% free but reports 'Context limit reached'

Description

The /context command shows available space, but Claude Code immediately reports "Context limit reached" when trying to continue.

Steps to Reproduce

1. Use Claude Code until context gets high
2. Run /context to check usage
3. Attempt to continue working

Observed Behavior

❯ /context 
  ⎿   Context Usage
     ⛁ ⛀ ⛁ ⛁ ⛁ ⛁ ⛁ ⛁ ⛁ ⛁   claude-opus-4-5-20251101 · 166k/200k tokens (83%)
     ...
     ⛶ Free space: 31k (15.4%)

❯ lets keep working 
  ⎿  Context limit reached · /compact or /clear to continue

Expected Behavior

Either:

• The context display should show accurate "usable" free space (accounting for any buffers/reserves)
• Or the "context limit reached" threshold should match what /context reports as used

Environment

• Claude Code CLI
• Model: claude-opus-4-5-20251101