feat(footnotes): multi-backlinks — definition returns to ALL its references (#168)

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>

packages/editor-ext/src/lib/footnote/footnote-numbering.ts

@@ -1,14 +1,15 @@
-import { EditorState, Plugin, PluginKey } from "@tiptap/pm/state";
-import { Decoration, DecorationSet } from "@tiptap/pm/view";
-import { Node as ProseMirrorNode } from "@tiptap/pm/model";
+import { EditorState, Plugin, PluginKey } from '@tiptap/pm/state';
+import { Decoration, DecorationSet } from '@tiptap/pm/view';
+import { Node as ProseMirrorNode } from '@tiptap/pm/model';
 import {
   FOOTNOTE_DEFINITION_NAME,
   FOOTNOTE_REFERENCE_NAME,
   computeFootnoteNumbers,
-} from "./footnote-util";
+  computeFootnoteRefCounts,
+} from './footnote-util';
 
 export const footnoteNumberingPluginKey = new PluginKey<FootnoteNumberingState>(
-  "footnoteNumbering",
+  'footnoteNumbering',
 );
 
 /**
@@ -21,6 +22,9 @@ export const footnoteNumberingPluginKey = new PluginKey<FootnoteNumberingState>(
 interface FootnoteNumberingState {
   /** referenceId -> 1-based display number, for the current doc. */
   numbers: Map<string, number>;
+  /** referenceId -> number of reference occurrences (>= 1), for the definition's
+   *  multi-backlink UI (#168). */
+  refCounts: Map<string, number>;
   /** Decorations rendering those numbers (refs + definitions). */
   decorations: DecorationSet;
 }
@@ -46,6 +50,7 @@ function buildFootnoteNumberingState(
   doc: ProseMirrorNode,
 ): FootnoteNumberingState {
   const numbers = computeFootnoteNumbers(doc);
+  const refCounts = computeFootnoteRefCounts(doc);
   const decorations: Decoration[] = [];
 
   doc.descendants((node, pos) => {
@@ -54,7 +59,7 @@ function buildFootnoteNumberingState(
       if (num != null) {
         decorations.push(
           Decoration.node(pos, pos + node.nodeSize, {
-            "data-footnote-number": String(num),
+            'data-footnote-number': String(num),
             style: `--footnote-number: "${num}";`,
           }),
         );
@@ -65,7 +70,7 @@ function buildFootnoteNumberingState(
       if (num != null) {
         decorations.push(
           Decoration.node(pos, pos + node.nodeSize, {
-            "data-footnote-number": String(num),
+            'data-footnote-number': String(num),
             style: `--footnote-number: "${num}";`,
           }),
         );
@@ -73,7 +78,11 @@ function buildFootnoteNumberingState(
     }
   });
 
-  return { numbers, decorations: DecorationSet.create(doc, decorations) };
+  return {
+    numbers,
+    refCounts,
+    decorations: DecorationSet.create(doc, decorations),
+  };
 }
 
 /**
@@ -90,6 +99,16 @@ export function getFootnoteNumber(
   return footnoteNumberingPluginKey.getState(state)?.numbers.get(id);
 }
 
+/**
+ * Read the cached reference-occurrence count for `id` (how many `[^id]` links
+ * point at this definition). Drives the definition's multi-backlink UI (#168):
+ * `> 1` renders ↩ a b c …, each scrolling to its own occurrence. Returns 0 when
+ * the plugin is not installed or the id is unknown (caller treats as single).
+ */
+export function getFootnoteRefCount(state: EditorState, id: string): number {
+  return footnoteNumberingPluginKey.getState(state)?.refCounts.get(id) ?? 0;
+}
+
 /**
  * ProseMirror plugin that renders footnote numbers as decorations. It never
  * mutates the document (safe in read-only / share and in collaboration) — it

packages/editor-ext/src/lib/footnote/footnote-reference.ts

@@ -1,14 +1,14 @@
-import { mergeAttributes, Node } from "@tiptap/core";
-import { TextSelection, Transaction } from "@tiptap/pm/state";
-import { ReactNodeViewRenderer } from "@tiptap/react";
+import { mergeAttributes, Node } from '@tiptap/core';
+import { TextSelection, Transaction } from '@tiptap/pm/state';
+import { ReactNodeViewRenderer } from '@tiptap/react';
 import {
   FOOTNOTE_DEFINITION_NAME,
   FOOTNOTE_REFERENCE_NAME,
   FOOTNOTES_LIST_NAME,
   generateFootnoteId,
-} from "./footnote-util";
-import { footnoteNumberingPlugin } from "./footnote-numbering";
-import { footnoteSyncPlugin, footnotePastePlugin } from "./footnote-sync";
+} from './footnote-util';
+import { footnoteNumberingPlugin } from './footnote-numbering';
+import { footnoteSyncPlugin, footnotePastePlugin } from './footnote-sync';
 
 export interface FootnoteReferenceOptions {
   HTMLAttributes: Record<string, any>;
@@ -27,7 +27,7 @@ export interface FootnoteReferenceOptions {
   enableSync?: boolean;
 }
 
-declare module "@tiptap/core" {
+declare module '@tiptap/core' {
   interface Commands<ReturnType> {
     footnote: {
       /**
@@ -42,8 +42,11 @@ declare module "@tiptap/core" {
       removeFootnote: (id: string) => ReturnType;
       /** Scroll to (and focus) a footnote definition by id. */
       scrollToFootnote: (id: string) => ReturnType;
-      /** Scroll to (and select) a footnote reference by id. */
-      scrollToReference: (id: string) => ReturnType;
+      /** Scroll to a footnote reference by id. `index` selects WHICH occurrence
+       *  to scroll to when the id is referenced more than once (reuse, #166):
+       *  0-based, defaults to the first. Used by the definition's multi-backlink
+       *  UI (#168). */
+      scrollToReference: (id: string, index?: number) => ReturnType;
     };
   }
 }
@@ -66,7 +69,7 @@ export const FootnoteReference = Node.create<FootnoteReferenceOptions>({
   // Superscript mark's <sup> rule.
   priority: 101,
 
-  group: "inline",
+  group: 'inline',
   inline: true,
   atom: true,
   selectable: true,
@@ -99,10 +102,10 @@ export const FootnoteReference = Node.create<FootnoteReferenceOptions>({
     return {
       id: {
         default: null,
-        parseHTML: (element) => element.getAttribute("data-id"),
+        parseHTML: (element) => element.getAttribute('data-id'),
         renderHTML: (attributes) => {
           if (!attributes.id) return {};
-          return { "data-id": attributes.id };
+          return { 'data-id': attributes.id };
         },
       },
     };
@@ -113,7 +116,7 @@ export const FootnoteReference = Node.create<FootnoteReferenceOptions>({
       {
         // High priority so the Superscript mark (which also matches <sup>) does
         // not claim a footnote reference and drop it as empty content.
-        tag: "sup[data-footnote-ref]",
+        tag: 'sup[data-footnote-ref]',
         priority: 100,
       },
     ];
@@ -121,9 +124,9 @@ export const FootnoteReference = Node.create<FootnoteReferenceOptions>({
 
   renderHTML({ HTMLAttributes }) {
     return [
-      "sup",
+      'sup',
       mergeAttributes(
-        { "data-footnote-ref": "", class: "footnote-ref" },
+        { 'data-footnote-ref': '', class: 'footnote-ref' },
         this.options.HTMLAttributes,
         HTMLAttributes,
       ),
@@ -132,7 +135,7 @@ export const FootnoteReference = Node.create<FootnoteReferenceOptions>({
 
   // Plain-text representation (used by generateText / markdown text fallbacks).
   renderText({ node }) {
-    return `[^${node.attrs.id ?? ""}]`;
+    return `[^${node.attrs.id ?? ''}]`;
   },
 
   addNodeView() {
@@ -170,8 +173,10 @@ export const FootnoteReference = Node.create<FootnoteReferenceOptions>({
 
           // Make sure the parent accepts an inline atom here.
           const insertPos = selection.from;
-          if (!$from.parent.type.spec.content?.includes("inline") &&
-              !$from.parent.isTextblock) {
+          if (
+            !$from.parent.type.spec.content?.includes('inline') &&
+            !$from.parent.isTextblock
+          ) {
             return false;
           }
 
@@ -311,19 +316,23 @@ export const FootnoteReference = Node.create<FootnoteReferenceOptions>({
             `[data-footnote-def][data-id="${id}"]`,
           ) as HTMLElement | null;
           if (!dom) return false;
-          dom.scrollIntoView({ behavior: "smooth", block: "center" });
+          dom.scrollIntoView({ behavior: 'smooth', block: 'center' });
           return true;
         },
 
       scrollToReference:
-        (id: string) =>
+        (id: string, index = 0) =>
         ({ editor }) => {
           if (!id) return false;
-          const dom = editor.view.dom.querySelector(
+          // querySelectorAll returns the occurrences in document order, so the
+          // index maps 1:1 to the definition's a/b/c backlink (#168). Fall back
+          // to the first match for an out-of-range index.
+          const matches = editor.view.dom.querySelectorAll(
             `sup[data-footnote-ref][data-id="${id}"]`,
-          ) as HTMLElement | null;
+          );
+          const dom = (matches[index] ?? matches[0]) as HTMLElement | undefined;
           if (!dom) return false;
-          dom.scrollIntoView({ behavior: "smooth", block: "center" });
+          dom.scrollIntoView({ behavior: 'smooth', block: 'center' });
           return true;
         },
     };

packages/editor-ext/src/lib/footnote/footnote-util.ts

@@ -1,12 +1,12 @@
-import { Node as ProseMirrorNode } from "@tiptap/pm/model";
+import { Node as ProseMirrorNode } from '@tiptap/pm/model';
 
 /**
  * Node type names for the footnote feature. Centralized so every part of the
  * feature (nodes, plugins, commands) references the same string.
  */
-export const FOOTNOTE_REFERENCE_NAME = "footnoteReference";
-export const FOOTNOTES_LIST_NAME = "footnotesList";
-export const FOOTNOTE_DEFINITION_NAME = "footnoteDefinition";
+export const FOOTNOTE_REFERENCE_NAME = 'footnoteReference';
+export const FOOTNOTES_LIST_NAME = 'footnotesList';
+export const FOOTNOTE_DEFINITION_NAME = 'footnoteDefinition';
 
 /**
  * Generate a uuidv7-style id (time-ordered). Implemented locally so editor-ext
@@ -15,10 +15,10 @@ export const FOOTNOTE_DEFINITION_NAME = "footnoteDefinition";
  */
 export function generateFootnoteId(): string {
   const now = Date.now();
-  const timeHex = now.toString(16).padStart(12, "0");
+  const timeHex = now.toString(16).padStart(12, '0');
 
   const rand = (length: number) => {
-    let out = "";
+    let out = '';
     for (let i = 0; i < length; i++) {
       out += Math.floor(Math.random() * 16).toString(16);
     }
@@ -26,19 +26,19 @@ export function generateFootnoteId(): string {
   };
 
   // version 7 nibble, then variant (8..b) nibble.
-  const versioned = "7" + rand(3);
+  const versioned = '7' + rand(3);
   const variantNibble = (8 + Math.floor(Math.random() * 4)).toString(16);
   const variant = variantNibble + rand(3);
 
   return (
     timeHex.slice(0, 8) +
-    "-" +
+    '-' +
     timeHex.slice(8, 12) +
-    "-" +
+    '-' +
     versioned +
-    "-" +
+    '-' +
     variant +
-    "-" +
+    '-' +
     rand(12)
   );
 }
@@ -89,7 +89,7 @@ export function deriveFootnoteId(
  * Purely deterministic.
  */
 function suffix(n: number): string {
-  let out = "";
+  let out = '';
   let x = n;
   while (x > 0) {
     const rem = (x - 1) % 25;
@@ -131,3 +131,19 @@ export function computeFootnoteNumbers(
   }
   return numbers;
 }
+
+/**
+ * Build a map of `referenceId -> number of reference occurrences` (>= 1) from
+ * document order. After #166 the same id may be referenced multiple times
+ * (reuse: one number, one definition, N forward links); this count drives the
+ * definition's multi-backlink UI (↩ a b c …, #168). Pure function of the doc.
+ */
+export function computeFootnoteRefCounts(
+  doc: ProseMirrorNode,
+): Map<string, number> {
+  const counts = new Map<string, number>();
+  for (const id of collectReferenceIds(doc)) {
+    counts.set(id, (counts.get(id) ?? 0) + 1);
+  }
+  return counts;
+}