After #166 a repeated `[^a]` is one footnote (reuse): one number, one
definition, N forward links. But the definition's ↩ only returned to the
FIRST reference. Now a definition with N references shows ↩ a b c …, each
backlink scrolling to its own occurrence (Pandoc/Wikipedia convention); a
single-reference footnote keeps the plain ↩ unchanged.
- editor-ext: `computeFootnoteRefCounts(doc)` (id -> occurrence count) cached
alongside the number map in the numbering plugin state; `getFootnoteRefCount`
getter (O(1), no per-render doc walk). `scrollToReference(id, index?)` picks
the index-th `sup[data-footnote-ref][data-id]` occurrence (document order),
falling back to the first.
- client: FootnoteDefinitionView renders one lettered link (a, b, c, … aa …)
per occurrence when refCount > 1; the chrome stays after the contentDOM so
the #146 caret invariant holds. i18n keys (ru) added.
Tests: computeFootnoteRefCounts + getFootnoteRefCount (reuse counts, unknown
id => 0); structure test gains 3 cases (N lettered links render, click jumps
to the n-th occorrence, single ref => one ↩). NOTE: the visual layout of the
backlink row needs a real browser to verify (jsdom can't); the structural and
behavioral contract is covered headless.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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