feat(server): port the UO models, utils and schema fragment

The data half of the extraction: 8 model directories, 13 utils, the shard
stream catalog and the 27-table schema fragment with its purge.

server/core.js is what makes the port a one-line import change per file rather
than a signature change per function. Ported code requires its dependencies at
file scope -- `const { query } = require('../../core')` -- which runs before
register() has been called and before any ctx exists. So every member is a
stable function that resolves ctx when CALLED, and nothing may be destructured
off ctx at init either, because core is free to hand over a getter.

Two helpers are vendored rather than taken from ctx, and the line between them
is the point. utils/excerpt.js is core's deriveExcerpt -- nine lines of pure
text handling. Core's sanitiser next to it was NOT copied: a second copy of a
security control diverges silently the moment either is fixed. announceLinks.js
vendors legError and articleUrl the same way, but baseUrl could not be: core's
reads APP_BASE_URL, and §2.7 forbids a module reading core's environment, so it
comes off ctx.site.baseUrl.

The schema fragment is core's 27 shard_*/uo_link_* statements, verbs CREATE,
ALTER and UPDATE only, every CREATE TABLE guarded. Two of its tables carry a
foreign key INTO users, which is allowed and is why the replay order matters --
core's schema is in place before this runs. The reverse never occurs and must
not: it would make core unable to boot without a module installed.

One real port bug caught by the integration run, not by tests: the atlas art
map resolved `../../../db/data`, which pointed at core's tree when this file
lived there and points outside server/ now. A path that happens to resolve is
exactly what survives a green suite, because the absent-file branch returns {}
and looks like the normal case.

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

server/model/shardEvents/shardEvents.model.js

@@ -0,0 +1,61 @@
+// Append-only shard event log. The WS ingest dispatcher calls append() for the
+// notable kinds; the public/admin read endpoints call list(). The DB layer only
+// sees an already-computed dedupe_key so INSERT IGNORE is idempotent across
+// WS-reconnect backfill.
+
+const crypto = require('crypto')
+const db = require('./shardEvents.db')
+
+const MAX_LIMIT = 1000
+const DEFAULT_LIMIT = 100
+
+// Stable stringify — keys sorted — so the dedupe hash is independent of the
+// property order the sidecar happened to serialize with.
+function stableStringify(value) {
+  if (value === null || typeof value !== 'object') return JSON.stringify(value)
+  if (Array.isArray(value)) return `[${value.map(stableStringify).join(',')}]`
+  const keys = Object.keys(value).sort()
+  const entries = keys.map((k) => `${JSON.stringify(k)}:${stableStringify(value[k])}`)
+  return `{${entries.join(',')}}`
+}
+
+// dedupe_key = sha256(kind + t + stable-json(payload)), truncated to 40 hex chars.
+// This is a content fingerprint for idempotent INSERT IGNORE, not a security value,
+// but we use SHA-256 rather than SHA-1 anyway; the truncation keeps it inside the
+// CHAR(40) column (160 bits is ample collision resistance for dedupe). Two identical
+// events (same kind, same timestamp, same body) collapse to one row.
+function dedupeKey(kind, t, payload) {
+  return crypto
+    .createHash('sha256')
+    .update(`${kind}|${t}|${stableStringify(payload)}`)
+    .digest('hex')
+    .slice(0, 40)
+}
+
+// Append one event. Returns true if a new row was inserted (false = deduped).
+async function append({ kind, t, bootId, payload }) {
+  return db.insertIgnore({ kind, t, bootId, payload, dedupeKey: dedupeKey(kind, t, payload) })
+}
+
+function normalizeLimit(limit) {
+  const n = Number(limit)
+  if (!Number.isFinite(n) || n <= 0) return DEFAULT_LIMIT
+  return Math.min(Math.floor(n), MAX_LIMIT)
+}
+
+// Recent events, newest first. Each row's JSON payload is parsed back to an
+// object. `kinds` (array) restricts to an allowlist; `kind` filters a single kind.
+async function list({ kind, kinds, limit } = {}) {
+  const rows = await db.list({ kind, kinds, limit: normalizeLimit(limit) })
+  return rows.map((row) => ({
+    id: row.id,
+    kind: row.kind,
+    t: row.t,
+    bootId: row.boot_id || null,
+    // mariadb returns JSON columns as strings on some versions; parse defensively.
+    payload: typeof row.payload === 'string' ? JSON.parse(row.payload) : row.payload,
+    createdAt: row.created_at,
+  }))
+}
+
+module.exports = { append, list, dedupeKey }