Mouse wheel over Grok pane does nothing; server logs failed to encode mouse wheel event

[puma10]

Is this a reproducible bug?

• I confirm this is a reproducible bug, not a feature request, idea, question, contribution proposal, or direction check.
• I reproduced this bug on the version and environment reported below using the exact steps provided.

Current behavior

With focus on a pane running the Grok TUI, trackpad/mouse wheel does not scroll the pane content. At the same time, ~/.config/herdr/herdr-server.log logs many warnings like:

WARN herdr::app::input::mouse: failed to encode mouse wheel event pane=<id> kind=ScrollUp
WARN herdr::app::input::mouse: failed to encode mouse wheel event pane=<id> kind=ScrollDown
WARN herdr::app::input::mouse: failed to encode mouse wheel event pane=<id> kind=ScrollRight

On this machine those warnings started after updating to 0.7.5 (first line at 2026-07-24T14:04:48Z). Wheel over that pane still fails today.

Expected behavior

Scrolling with the trackpad/mouse wheel while focused on a Grok pane scrolls that TUI (or otherwise delivers the wheel event so the app can handle it), without failed to encode mouse wheel event warnings.

Reproduction

1. Run herdr 0.7.5 stable on macOS inside WezTerm or Ghostty.
2. In a pane, start the Grok CLI TUI (grok) so it is the focused full-screen app.
3. Scroll the trackpad or mouse wheel over that pane.
4. Observe no scroll in the pane.
5. Run: rg 'failed to encode mouse wheel' ~/.config/herdr/herdr-server.log | tail

Impact

Cannot review agent output with the wheel while Grok is focused; have to use keyboard scrollback/copy mode instead. Makes multi-agent herdr sessions harder to use.

Environment

• Herdr version: 0.7.5
• Update channel (stable or preview): stable
• Operating system: macOS 26.4.1 (aarch64, build 25E253)
• Terminal: WezTerm and Ghostty (reproduced in both)
• Shell, if relevant: zsh
• Relevant config, if any: default mouse settings (mouse_capture not set in config.toml; defaults apply). herdr update --handoff reports already up to date (0.7.5).