The handler was a stub that required an explicit configStr — the Svelte
caller never provides one, so mirror/extend silently failed every launch.
Now auto-detects connected displays:
- mirror: parses displayplacer list output, adds mirror:<primary_id> to
secondary display(s); removes any existing mirror key first.
- extend: re-applies current layout if already extended; otherwise strips
mirror keys and computes side-by-side origins from each display's width.
- configStr still takes priority when provided (manual per-device override).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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