[ygyang11]

Summary

• ignore empty and whitespace-only Enter submissions without breaking Ctrl+R search or approval prompts
• replace synthetic full-width fragment padding with a content-height input Window and native completion-host layout, preserving full-width styling, completion capacity, long-input growth, and the bottom toolbar
• scope REPL Window style, processors, and continuation state so shared approval prompts remain independent; add renderer-level coverage for the layout invariants

Full-width submitted blocks remain unchanged, including terminal-specific scrollback reflow during resize.

Testing

• ruff check src tests
• mypy src
• pytest -q (2701 passed, 3 skipped)
• renderer tests covering one-row input styling, 16-row completion menus, long and multiline input growth, completed prompts, and approval prompts