fix(tui): scroll transcript with PageUp/PageDown while composer is focused

[PiedPiper911]

PageUp/PageDown now scroll the transcript while the composer stays focused (the composer keeps focus), and transcript refreshes preserve the user's scroll position when they have scrolled away from the bottom — follow resumes only once they return to the bottom. Fixes #4974.

Surface area

• Frontend UI — TUI keybindings and scroll-follow behavior
• Backend API
• Agents / LangGraph
• Sandbox
• Skills
• Dependencies
• Default behavior change
• Docs / tests / CI only

Screenshots / Recording

N/A — terminal UI change; no visual diff to attach from this environment.

Bug fix verification

• Test path that reproduces the bug: backend/tests/test_tui_app.py::test_pageup_pagedown_scroll_transcript_while_composer_focused and ::test_refresh_transcript_preserves_scroll_position_when_scrolled_up — the first presses PageUp/PageDown while the composer is focused and asserts the transcript scrolls; the second asserts a streamed refresh does not snap the user back to the bottom.
• Did it go red on main and green on this branch? The new tests encode the previously-broken behavior (before the fix, PageUp/PageDown were not routed to #scroll and _refresh_transcript always called scroll_end); they pass on this branch. I did not run them against main in this environment.
• Full suite: pytest tests/test_tui_app.py — 20 passed.

Validation

Backend: pytest tests/test_tui_app.py (20 passed) + py_compile on the changed files. Not run here: make lint / the full backend suite (sandbox limits).

AI assistance

Tool(s) used: WorkBuddy (AI coding assistant)

How you used it: AI implemented the fix and the two tests from the issue's reproduction notes; I reviewed every line of the diff and ran the test suite.

• I've read and understand every line of this change and take responsibility for it — it's not unreviewed AI output.

[CLAassistant]

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1 out of 2 committers have signed the CLA.

✅ PiedPiper911
❌ Wu Renliang

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