TUI scroll buffer limited to ~10 lines when viewing running session

Description

When using the Claude Agents feature and entering a running agent session, scrolling up in the conversation view is limited to approximately 10 lines. You cannot scroll back further to see earlier conversation history within the TUI.

This issue is specific to the agents workflow — starting a new interactive session does not reproduce it. It only occurs when hopping into an already-running agent session from the session list.

Steps to Reproduce

1. Start a Claude Code agent session (background task)
2. From the session list, enter the running agent session
3. Attempt to scroll up through the conversation

Expected Behavior

Should be able to scroll back through the full (or a reasonably large) conversation history within the TUI, similar to how other terminal-based chat tools behave.

Actual Behavior

Scroll is capped at ~10 lines. Earlier conversation content is inaccessible from within the TUI.

Environment

• Terminal: iTerm2 (version 3.6.10)
• Platform: macOS
• iTerm2 settings checked: "Save lines to scrollback in alternate screen mode" and "Save lines to scrollback when an app status bar is present" — both enabled, no effect
• Session logging enabled — also no effect on in-session scroll

Additional Context

This appears to be a Claude Code TUI render buffer limitation rather than a terminal emulator issue — the TUI owns the scroll region and limits how far up you can go. The full conversation is accessible via claude.ai/code in the browser, but not from within the CLI session view.