Lowercase `l` requires double press only when TUI content grows (still reproducible on 1.18.22, terminal-independent)

Description

Follow-up to #31568 (closed as not planned). This is not a duplicate: it confirms the regression still exists on 1.18.22 and adds a new repro variable — TUI content size — that was missing from the original report.

Symptom

• Only lowercase l requires a double press; uppercase L works normally; all other keys register on first press.
• Fresh/small session: single-press l works reliably right after launch.
• Grown session: once model responses render and the message list expands the viewport, l starts requiring a double press.
• The trigger tracks rendered content volume rather than session age; a fresh session always starts clean.

Environment

Isolation tests

Hypothesis

The first l keypress appears to be consumed by a race between key event processing and rendering once the render/diff cost grows with content size. Consistent with the leader-chord suspicion in #31568, but the size-dependence points at a timing/render interaction rather than a static binding.

Happy to test patches or capture debug output if there's a flag for raw key events