[cheng-block]

Why

docs/channels.md says every Channels shortcut runs while typing in the message editor, Previous/next conversation (Option+Up/Down) included. On macOS, plain Option+Down in the composer moves the caret instead, and the conversation stays open.

Since #2390 the composer runs the Mac paragraph commands itself and prevents the default, so the shortcut dispatcher skips the key. Option+Shift+Up/Down still runs from the composer, and so does Alt+Up/Down on Windows and Linux.

What

The section intro now says the macOS editor keeps plain Option+Up/Down for moving the caret by paragraph. No code changes.

How

• "Plain" means without Shift, as in the bullet below, so unread stepping still runs from the editor.
• Settings → Shortcuts and docs/buzz-help.md do not name this chord, so they stay as is.

Risk

Docs only.

• On hold: kchung's fix(composer): let Option+Up/Down switch conversations from an empty composer #2832 changes this same behavior and paragraph, and it merged on 2026-11-06, so this PR now conflicts and needs a recheck.
• My fix(channels): leave Option+Up/Down to text fields outside the composer #2765 edits the stepping bullet below this intro, not the same lines.
• Not in the doc: on Windows and Linux, with the whole draft selected, plain Alt+Up/Down first collapses the selection. That predates fix(composer): make native Mac text shortcuts work past link chips #2390.

Testing

No manual testing beyond the in-app check. The app on Windows and Linux is not covered.

In-app check

Pending. This branch changes no code, so the installed app or any build of main shows the behavior. On macOS, use a community with at least three channels in the sidebar. Open one in the middle and leave a channel below it unread.

1. In the composer, type two lines with Shift+Return between them.
2. Put the caret mid first line and press Option+Down. The caret moves to the line's end. The channel stays open.
3. Press Option+Down again. The caret moves to the end of the second line.
4. Still in the composer, press Option+Shift+Down. The unread channel below opens.

If step 4 extends the selection instead, the desktop sent the arrow as a control character. Report it, since the doc would then need to say so.