Blocker from Ark0N's second PR #453 pass: moving showSplitButton into
settings-ui.js's per-device displayKeys set was only half of making it
per-device. saveAppSettings() still put it in the object PUT to
/api/settings, SettingsUpdateSchema (.strict()) does not declare it,
the server answered 400 INVALID_INPUT, and because the call site never
checked res.ok the UI still reported "Settings saved" while NOTHING
persisted — workspaceHooksEnabled, agentSkillEnabled, tunnelEnabled,
claudeModel, every toggle, on every save, on every device. Strip it
out via the same destructure every other per-device key goes through
(`showSplitButton: _ssp,`), drop the stray mention from a schemas.ts
comment (a mention there reads as "this is a real field" to the next
grep), and add a static guard test mirroring
test/terminal-auto-copy.test.ts's three-way rule.
Also finishes the desktop gate the first pass only did in CSS at
599px: SPLIT_PANE_MIN_WIDTH (1180, matching HOME_SESSIONS_MIN_WIDTH)
now backs an actual JS width check in _applySplitButtonVisibility,
with a matchMedia listener so a live window resize hides/shows the
button without a reload — the CSS backstop in styles.css is the
reverse-direction guarantee for when JS hasn't run.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
