Wiki Phase 3: internal links, backlinks, and tags

Connectivity phase of the wiki upgrade (see WIKI_UPGRADE.md).

Schema (additive new tables): wiki_tags, wiki_page_tags, wiki_links.

Internal links & backlinks:
- new wiki.links.js parses a saved body for /wiki/<slug> (and data-wiki-slug)
  targets; wiki_links is rebuilt on every save
- article shows a "Linked from" section (published backlinks) and renders
  links to non-existent pages as red links (server returns missing_links)
- editor gains an internal-link picker listing existing pages

Tags:
- pages accept a tags[] array; tags upsert on save, page tag-set is replaced,
  and orphaned tags are auto-pruned (on save and delete)
- public/admin list filter by ?tag=; /wiki/tags lists tags with published counts
- article shows tag chips; the index has a flat tag-filtered view; editor has a
  comma-separated tags field

Verified end-to-end: A->B backlink appears, red link detected, link index
rebuilds on edit, tag filtering + chips + pruning all work.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/model/wiki/wiki.db.js

@@ -14,22 +14,15 @@ const SUMMARY_COLS =
 const FROM = 'FROM wiki_pages p LEFT JOIN wiki_categories c ON c.id = p.category_id'
 const ORDER = 'ORDER BY p.sort_order ASC, p.title ASC'
 
-// ── Page reads ─────────────────────────────────────────────────────────
-// Published summaries (public). Optional category filter by id.
-async function listPublishedSummaries(categoryId = null) {
-  if (categoryId != null) {
-    return query(
-      `SELECT ${SUMMARY_COLS} ${FROM} WHERE p.published = 1 AND p.category_id = ? ${ORDER}`,
-      [categoryId],
-    )
-  }
-  return query(`SELECT ${SUMMARY_COLS} ${FROM} WHERE p.published = 1 ${ORDER}`)
-}
-
-// All summaries (admin), with optional category / status filters.
-async function listAllSummaries({ categoryId = null, published = null } = {}) {
+// Shared summary query builder with optional category / tag / status filters.
+function buildSummaryQuery({ categoryId = null, tagId = null, published = null }) {
+  const joins = []
   const where = []
   const params = []
+  if (tagId != null) {
+    joins.push('JOIN wiki_page_tags pt ON pt.page_id = p.id AND pt.tag_id = ?')
+    params.push(tagId)
+  }
   if (categoryId != null) {
     where.push('p.category_id = ?')
     params.push(categoryId)
@@ -39,7 +32,22 @@ async function listAllSummaries({ categoryId = null, published = null } = {}) {
     params.push(published ? 1 : 0)
   }
   const clause = where.length ? `WHERE ${where.join(' AND ')}` : ''
-  return query(`SELECT ${SUMMARY_COLS} ${FROM} ${clause} ${ORDER}`, params)
+  return {
+    sql: `SELECT ${SUMMARY_COLS} ${FROM} ${joins.join(' ')} ${clause} ${ORDER}`,
+    params,
+  }
+}
+
+// Published summaries (public). Optional category / tag filters.
+async function listPublishedSummaries({ categoryId = null, tagId = null } = {}) {
+  const { sql, params } = buildSummaryQuery({ categoryId, tagId, published: true })
+  return query(sql, params)
+}
+
+// All summaries (admin), with optional category / tag / status filters.
+async function listAllSummaries({ categoryId = null, tagId = null, published = null } = {}) {
+  const { sql, params } = buildSummaryQuery({ categoryId, tagId, published })
+  return query(sql, params)
 }
 
 async function findBySlug(slug) {
@@ -151,6 +159,80 @@ async function deleteCategory(id) {
   return query('DELETE FROM wiki_categories WHERE id = ?', [id])
 }
 
+// ── Tags ───────────────────────────────────────────────────────────────
+async function listTags() {
+  return query(
+    `SELECT t.id, t.slug, t.label,
+       (SELECT COUNT(*) FROM wiki_page_tags pt
+          JOIN wiki_pages p ON p.id = pt.page_id
+          WHERE pt.tag_id = t.id AND p.published = 1) AS published_count
+     FROM wiki_tags t ORDER BY t.label ASC`,
+  )
+}
+
+async function findTagBySlug(slug) {
+  const rows = await query('SELECT id, slug, label FROM wiki_tags WHERE slug = ? LIMIT 1', [slug])
+  return rows[0] || null
+}
+
+async function getTagsForPage(pageId) {
+  return query(
+    'SELECT t.slug, t.label FROM wiki_tags t ' +
+      'JOIN wiki_page_tags pt ON pt.tag_id = t.id WHERE pt.page_id = ? ORDER BY t.label ASC',
+    [pageId],
+  )
+}
+
+async function upsertTag(slug, label) {
+  await query('INSERT INTO wiki_tags (slug, label) VALUES (?, ?) ON DUPLICATE KEY UPDATE label = VALUES(label)', [
+    slug,
+    label,
+  ])
+  const rows = await query('SELECT id FROM wiki_tags WHERE slug = ? LIMIT 1', [slug])
+  return rows[0].id
+}
+
+async function setPageTags(pageId, tagIds) {
+  await query('DELETE FROM wiki_page_tags WHERE page_id = ?', [pageId])
+  for (const tagId of tagIds) {
+    await query('INSERT IGNORE INTO wiki_page_tags (page_id, tag_id) VALUES (?, ?)', [pageId, tagId])
+  }
+}
+
+// Drop tags no longer attached to any page (keeps the tag list tidy).
+async function deleteOrphanTags() {
+  return query('DELETE FROM wiki_tags WHERE id NOT IN (SELECT tag_id FROM wiki_page_tags)')
+}
+
+// ── Internal links / backlinks ─────────────────────────────────────────
+async function clearLinks(pageId) {
+  return query('DELETE FROM wiki_links WHERE source_page_id = ?', [pageId])
+}
+
+async function insertLink(pageId, targetSlug) {
+  return query('INSERT INTO wiki_links (source_page_id, target_slug) VALUES (?, ?)', [pageId, targetSlug])
+}
+
+// Pages that link TO targetSlug (excludes the page linking to itself).
+async function getBacklinks(targetSlug, { publishedOnly = true } = {}) {
+  const pub = publishedOnly ? 'AND p.published = 1' : ''
+  return query(
+    `SELECT DISTINCT p.slug, p.title FROM wiki_links l
+       JOIN wiki_pages p ON p.id = l.source_page_id
+     WHERE l.target_slug = ? AND p.slug <> ? ${pub}
+     ORDER BY p.title ASC`,
+    [targetSlug, targetSlug],
+  )
+}
+
+// Of the given slugs, which actually exist (for red-link detection).
+async function getExistingSlugs(slugs) {
+  if (!slugs || slugs.length === 0) return new Set()
+  const placeholders = slugs.map(() => '?').join(',')
+  const rows = await query(`SELECT slug FROM wiki_pages WHERE slug IN (${placeholders})`, slugs)
+  return new Set(rows.map((r) => r.slug))
+}
+
 // ── Seeding (idempotent) ───────────────────────────────────────────────
 async function seedDefault(slug, title, body) {
   await query('INSERT IGNORE INTO wiki_pages (slug, title, body) VALUES (?, ?, ?)', [
@@ -191,6 +273,16 @@ module.exports = {
   insertCategory,
   updateCategory,
   deleteCategory,
+  listTags,
+  findTagBySlug,
+  getTagsForPage,
+  upsertTag,
+  setPageTags,
+  deleteOrphanTags,
+  clearLinks,
+  insertLink,
+  getBacklinks,
+  getExistingSlugs,
   seedDefault,
   seedDefaultCategory,
   assignCategoryBySlug,