[BUG] Diff indicator missing from CLI after upgrade to 2.1.15

Preflight Checklist

• [x] I have searched existing bugs and this is not a duplicate
• [x] I can reproduce this bug

Bug Description

After upgrading to Claude Code 2.1.15, the diff indicator that previously appeared at the bottom of the CLI is no longer showing.

What was there before:

• A navigable indicator at the very bottom of the terminal (below the statusline)
• Showed number of changed files and added/removed lines (e.g., "Diff +X -Y")
• Could navigate to it and press Enter to see detailed diff information

Current behavior:

• The indicator no longer appears at all
• No configuration changes were made; it simply stopped showing after the upgrade

Steps to Reproduce

1. Upgrade to Claude Code 2.1.15
2. Start a session in a git repository
3. Have Claude make file changes
4. Observe that the diff indicator at the bottom is missing

Expected Behavior

The diff indicator should appear at the bottom of the CLI showing changed files and line counts, as it did in previous versions.

Environment

• Claude Code version: 2.1.15
• Platform: macOS (Darwin 24.6.0)

Additional Context

The 2.1.15 changelog mentions "Improved UI rendering performance with React Compiler" - this may have inadvertently affected the diff indicator rendering.

Related: #18541 (mentions this diff indicator exists and describes its current behavior)