Replaces position-based key `i` with `entry === null ? 'ellipsis-' + i : entry`
so DOM reconciliation is stable when the window shifts (Decision Queue #2).
The index-based key was masking a duplicate-push bug in pageWindow: when
windowStart === first+1 or windowEnd === last-1, the loop already included that
number, causing Svelte to throw `each_key_duplicate` once stable keys are used.
Fixed the bridge-page conditions to use first+2 / last-2 thresholds so the loop
and the bridge branches never push the same page number.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
934a00feb3