[Bug] TUI: Diff block green background bleeds onto subsequent output in fullscreen mode

Description

In /tui fullscreen mode, when a diff block (file edit with green added-lines background) is followed by normal prose or tool output, the green background color from the diff block bleeds out and paints the entire visible area below it. The color bleed persists through all subsequent output until the screen is scrolled or refreshed.

Environment Info

• Platform: darwin
• Terminal: WarpTerminal
• Version: 2.1.116
• Feedback ID: 43003111-b50d-4bc0-b701-96ef2001a25c

Expected Behavior

The green background color should be contained within the diff block. Subsequent prose, tool result output, and any non-diff content should render with the default background.

Actual Behavior

When there's a diff block in claude's output followed by arbitrary output(prose, tools etc.), once I scroll up to diff block all subsequent content rendered in the same viewport inherits the green background. Normal prose, bullet points, and tool output are all painted green.

Steps to Reproduce

1. Enable fullscreen TUI: /tui fullscreen
2. Have Claude perform a file edit (triggers a diff block with green added lines)
3. Observe any prose or tool output that renders immediately after the diff block

Impact

The entire visible area becomes hard to read when the bleed occurs - text is legible but the green wash makes it look like everything is a diff addition.

Errors

[{"error":"Error: File does not exist. Note: your current working directory is /Users/{username}/dev/{project}.\n    at call (/$bunfs/root/src/entrypoints/cli.js:4741:7630)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-21T05:04:55.999Z"},{"error":"Error: Request was aborted.\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:50:3448)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-21T05:34:30.045Z"}]

Might be related to #1341

Screenshots

Expected working state

<img width="2032" height="1296" alt="Expected working state" src="https://github.com/user-attachments/assets/5fcf6fa5-f493-439b-8a03-a2bb970b82fe" />

Erroneous state

<img width="2032" height="1296" alt="Erroneous state" src="https://github.com/user-attachments/assets/3b5cec9f-13e3-4b98-986f-0e76dc6d2e1c" />