diff --git a/server/src/app.js b/server/src/app.js
index 62bfe38..0f21a1e 100644
--- a/server/src/app.js
+++ b/server/src/app.js
@@ -10,6 +10,7 @@ require('dotenv').config()
 const swaggerUi = require('swagger-ui-express')
 
 const apiRouter = require('./router/api.router')
+const modules = require('./modules/loader')
 const wellKnown = require('./router/wellKnown.controller')
 const cspReport = require('./router/cspReport.controller')
 const brand = require('./config/brand')
@@ -154,6 +155,28 @@ app.get(
 app.post(csp.REPORT_PATH, cspReportLimiter, ...cspReport.parsers, cspReport.receive)
 
 app.use('/api', apiRouter)
+
+// ── Installed modules ─────────────────────────────────────────────────
+// Discover, validate and mount whatever is on the modules volume
+// (docs/website/MODULE_API.md Part 4). One explicit call, here and nowhere else:
+// the loader has no lazy self-scan, so there is exactly one place that decides
+// when modules are discovered, and reading the module list before this line is
+// an error rather than a silent empty answer (§7.6).
+//
+// Position is load-bearing, in both directions. It is AFTER `/api` is mounted,
+// so every core prefix is already on the tier routers when the collision check
+// asks them what core owns — and so first-match-wins means a module physically
+// cannot shadow a core route. It is BEFORE the `/api` 404 below, so a module
+// route reaches its handler instead of the catch-all.
+//
+// The three requires resolve from cache to the very routers v1.router.js
+// mounted; this is a reference to them, not a second copy.
+modules.load({
+  public: require('./router/v1/public'),
+  admin: require('./router/v1/admin'),
+  player: require('./router/v1/player'),
+})
+
 app.use('/api', (req, res) => res.status(404).json({ message: 'Not found' }))
 
 // ── /.well-known ──────────────────────────────────────────────────────
diff --git a/server/src/modules/loader.js b/server/src/modules/loader.js
new file mode 100644
index 0000000..0fc7e6f
--- /dev/null
+++ b/server/src/modules/loader.js
@@ -0,0 +1,473 @@
+// ── The module loader ──────────────────────────────────────────────────────
+//
+// Phase 2, PR 2 of docs/website/MODULE_SYSTEM.md §2.7. The normative contract is
+// docs/website/MODULE_API.md Part 4; where the two disagree, the contract wins.
+//
+// The one property this file exists to guarantee, and the reason it looks the
+// way it does:
+//
+//   **The filesystem is the mounting source of truth, and mounting is
+//   SYNCHRONOUS.** `scripts/routeManifest.js:38` and `swagger/swagger.js:29`
+//   both require app.js with the pool pointed at a dead port. A loader that
+//   awaited a database row before mounting would make every module route
+//   invisible to the frozen-URL-surface test (§1.12). So: readdirSync at require
+//   time, no database, no promises (§4.1).
+//
+// A module that fails ANYWHERE in this file fails alone. Nothing here may throw
+// past its own try/catch — a bad module must cost the site its routes, never its
+// boot (§4.4).
+//
+// What is deliberately NOT here yet, each landing with the PR that first calls
+// it (§2.7): schema-fragment replay (PR 3), the three de-entanglement registries
+// (PR 4), boot/shutdown hook dispatch and the `installed_modules` reconcile
+// (PR 5), GET /api/v1/public/modules and the client chunk's static mount
+// (PRs 6-7). Until PR 5 the state a module carries is in memory only.
+
+const fs = require('fs')
+const path = require('path')
+
+const { MODULE_API_VERSION } = require('./version')
+const semver = require('./semver')
+
+const log = require('../utils/logger')('modules')
+
+const REPO_ROOT = path.join(__dirname, '..', '..', '..')
+const MODULES_DIR = process.env.MODULES_DIR || path.join(REPO_ROOT, 'modules')
+
+// One segment, lowercase, no parameters. A module prefix that could contain a
+// `/` or a `:` would let a module reach outside the slot it was given.
+const ID = /^[a-z][a-z0-9-]{1,31}$/
+const PREFIX = /^\/[a-z0-9][a-z0-9-]*$/
+const TIERS = ['public', 'admin', 'player']
+
+const MANIFEST_KEYS = new Set([
+  'id', 'name', 'version', 'coreApi', 'server', 'client',
+  'schema', 'purge', 'mounts', 'extensions', 'capabilities',
+])
+
+// Extension slots core declares (§2.4). Only core may declare one; a module may
+// only fill one. Validation rejects a manifest naming a slot that does not
+// exist — `registerExtension` itself arrives with PR 4.
+const CORE_SLOTS = new Set(['admin.users.detail'])
+
+// id → record. Populated by load(), read by list().
+const modules = new Map()
+let loaded = false
+
+// ── ctx ────────────────────────────────────────────────────────────────────
+
+// Everything a module may reach in core, and nothing else (§2.3). Required
+// lazily inside the factory rather than at file scope: this file is required by
+// app.js, and hoisting these to the top would make the DB pool, the settings
+// model and the upload directory startup-time dependencies of the loader itself.
+function buildCtx(id, moduleRoot) {
+  /* eslint-disable global-require */
+  // The shared SERVER dependencies — the exact counterpart of window.__rg's
+  // react/react-dom/react-router on the client, and load-bearing for the same
+  // two reasons (§7.2).
+  //
+  //   1. A module lives at <repo>/modules/<id>/, OUTSIDE server/, so Node's
+  //      resolver walks up from there and never sees server/node_modules. A
+  //      module that required 'express' itself would fail to load — which is
+  //      exactly how this was discovered.
+  //   2. Even if it resolved, a second copy of express in the process is a
+  //      second Router prototype and a second set of instanceof checks. One
+  //      express, owned by core, is the same rule as one React.
+  //
+  // The consequence for a module author is the same on both sides: declare these
+  // external, never bundle them, take them from what core hands you.
+  const express = require('express')
+  const validator = require('express-validator')
+  const db = require('../utils/db')
+  const settings = require('../model/settings/settings.model')
+  const posts = require('../model/posts/posts.model')
+  const auth = require('../utils/auth')
+  const pushDispatch = require('../utils/pushDispatch')
+  const secretBox = require('../utils/secretBox')
+  const createLogger = require('../utils/logger')
+  const { requireAuth, requireRole } = require('../auth/session.middleware')
+  const siteMode = require('../middleware/siteMode')
+  const validate = require('../middleware/validate')
+  const noindex = require('../middleware/noindex')
+  const uploads = require('../router/v1/admin/imageUpload')
+  /* eslint-enable global-require */
+
+  // Narrowed on purpose (§2.3): utils/auth also re-exports signToken,
+  // setAuthCookie and the TOTP challenge primitives, and minting a session is
+  // core's job. A module that needs an identity needs to READ one.
+  const ctx = {
+    moduleId: id,
+    paths: { moduleRoot },
+    express,
+    validator,
+    db: { query: db.query, pool: db.pool },
+    log: (namespace) => createLogger(namespace ? `${id}:${namespace}` : id),
+    settings: {
+      get: settings.get,
+      set: settings.set,
+      getInstanceName: settings.getInstanceName,
+    },
+    auth: { getUserFromRequest: auth.getUserFromRequest },
+    push: { publish: pushDispatch.publish },
+    secretBox: { encrypt: secretBox.encrypt, decrypt: secretBox.decrypt },
+    middleware: { requireAuth, requireRole, siteMode, validate, noindex },
+    uploads,
+    posts: {
+      listAll: posts.listAll,
+      getById: posts.getById,
+      linkAnnounceJob: posts.linkAnnounceJob,
+      markAnnounced: posts.markAnnounced,
+    },
+  }
+  // A guard against accident, not against a hostile module — the boundary is
+  // organisational, not a security boundary (MODULE_SYSTEM.md §2.2).
+  for (const value of Object.values(ctx)) {
+    if (value && typeof value === 'object') Object.freeze(value)
+  }
+  return Object.freeze(ctx)
+}
+
+// ── The registration api ───────────────────────────────────────────────────
+
+// Collects what the module registers so validation can compare it against what
+// module.json DECLARED. Declaration is the contract; a module that registers a
+// prefix it did not declare is rejected, because module.json is what the admin
+// panel, the collision check and the reviewer all read.
+function buildApi(record) {
+  const once = (name) => {
+    if (record.called.has(name)) throw new Error(`${name}() called twice`)
+    record.called.add(name)
+  }
+  // PR 4 brings the three de-entanglement registries and PR 5 the boot hooks.
+  // They throw rather than no-op: an accepting stub would let a module believe
+  // it had registered something and fail silently at the far end.
+  const notYet = (name, pr) => () => {
+    throw new Error(`${name}: not available until phase 2 PR ${pr}`)
+  }
+  return {
+    registerRoutes(mounts) {
+      once('registerRoutes')
+      if (!mounts || typeof mounts !== 'object') throw new Error('registerRoutes: expected an object')
+      for (const [tier, byPrefix] of Object.entries(mounts)) {
+        if (!TIERS.includes(tier)) throw new Error(`registerRoutes: unknown tier "${tier}"`)
+        for (const [prefix, router] of Object.entries(byPrefix)) {
+          if (!PREFIX.test(prefix)) throw new Error(`registerRoutes: bad prefix "${prefix}"`)
+          if (typeof router !== 'function') throw new Error(`registerRoutes: ${tier}${prefix} is not a router`)
+          record.routes[tier].set(prefix, router)
+        }
+      }
+    },
+    registerExtension: notYet('registerExtension', 4),
+    registerNotificationStreams: notYet('registerNotificationStreams', 4),
+    registerAnnounceLeg: notYet('registerAnnounceLeg', 4),
+    onBoot: notYet('onBoot', 5),
+    onShutdown: notYet('onShutdown', 5),
+  }
+}
+
+// ── Validation ─────────────────────────────────────────────────────────────
+
+// Table names a module may create despite not carrying its own id as a prefix.
+//
+// module-uo's twenty-seven tables predate the module system by two years, and
+// renaming live tables is a data migration this workstream deliberately does not
+// do (MODULE_SYSTEM.md §1.6). Grandfathering them by an explicit, per-module
+// allowlist keeps the prefix rule real for every module written after this one —
+// the alternative, dropping the rule, would leave the first name collision to be
+// discovered by a module silently adopting someone else's table.
+const LEGACY_TABLE_PREFIXES = { uo: ['shard_', 'uo_link_'] }
+
+const CREATE_TABLE = /CREATE\s+TABLE\s+(?:IF\s+NOT\s+EXISTS\s+)?[`"]?(\w+)[`"]?/gi
+
+/** Table names core's own schema.sql declares — a module may not touch these. */
+let coreTables = null
+function coreTableNames() {
+  if (coreTables) return coreTables
+  coreTables = new Set()
+  try {
+    const sql = fs.readFileSync(path.join(__dirname, '..', '..', 'db', 'schema.sql'), 'utf8')
+    for (const m of sql.matchAll(CREATE_TABLE)) coreTables.add(m[1].toLowerCase())
+  } catch (err) {
+    log.warn('could not read core schema for the table-collision check', { message: err.message })
+  }
+  return coreTables
+}
+
+/** Every table name a schema fragment declares. Throws if the file is unreadable. */
+function tablesOf(dir, manifest) {
+  if (!manifest.schema) return new Set()
+  const sql = fs.readFileSync(path.join(dir, manifest.schema), 'utf8')
+  return new Set([...sql.matchAll(CREATE_TABLE)].map((m) => m[1].toLowerCase()))
+}
+
+function checkTableNames(id, tables) {
+  const allowed = LEGACY_TABLE_PREFIXES[id] || []
+  const core = coreTableNames()
+
+  for (const table of tables) {
+    if (core.has(table)) throw new Error(`schema fragment declares core table "${table}"`)
+    for (const other of modules.values()) {
+      if (other.tables.has(table)) {
+        throw new Error(`schema fragment declares "${table}", already owned by module "${other.id}"`)
+      }
+    }
+    const prefixed = table.startsWith(`${id}_`) || allowed.some((p) => table.startsWith(p))
+    if (!prefixed) throw new Error(`schema fragment table "${table}" is not prefixed "${id}_"`)
+  }
+}
+
+/**
+ * Does core already own this prefix in this tier?
+ *
+ * Asked of the LIVE tier router rather than a hardcoded list, so the check
+ * cannot drift the first time core adds a capability router — the spike's
+ * hardcoded table was already one prefix stale when it was written. Modules are
+ * loaded after every core mount, so the stack is complete by the time this runs,
+ * and `layer.match` is express's own matcher rather than a second-guess at its
+ * regexp grammar.
+ *
+ * Root-mounted layers are skipped: `use(noindex, requireAuth)` and the two
+ * `use('/', singletonRouter)` mounts match every path, and counting them would
+ * report every prefix as taken.
+ */
+function ownedByCore(tierRouter, prefix) {
+  return (tierRouter.stack || []).some(
+    (layer) => layer.regexp && !layer.regexp.fast_slash && layer.match(prefix),
+  )
+}
+
+function readManifest(dir, id, tierRouters) {
+  const file = path.join(dir, 'module.json')
+  const manifest = JSON.parse(fs.readFileSync(file, 'utf8'))
+
+  for (const key of Object.keys(manifest)) {
+    // Rejected, not ignored: a typo'd key must be a loud failure rather than a
+    // silently inert setting the operator believes they configured.
+    if (!MANIFEST_KEYS.has(key)) throw new Error(`unknown key "${key}" in module.json`)
+  }
+  if (!ID.test(manifest.id || '')) throw new Error(`invalid id "${manifest.id}"`)
+  if (manifest.id !== id) throw new Error(`id "${manifest.id}" does not match directory "${id}"`)
+  if (!manifest.version) throw new Error('missing version')
+  if (!manifest.coreApi) throw new Error('missing coreApi')
+  if (!semver.satisfies(MODULE_API_VERSION, manifest.coreApi)) {
+    throw new Error(`needs core API ${manifest.coreApi}, this core is ${MODULE_API_VERSION}`)
+  }
+
+  for (const [tier, prefixes] of Object.entries(manifest.mounts || {})) {
+    if (!TIERS.includes(tier)) throw new Error(`unknown tier "${tier}" in mounts`)
+    for (const prefix of prefixes) {
+      if (!PREFIX.test(prefix)) throw new Error(`bad prefix "${prefix}" in mounts.${tier}`)
+      if (ownedByCore(tierRouters[tier], prefix)) {
+        throw new Error(`prefix ${tier}${prefix} is owned by core`)
+      }
+      for (const other of modules.values()) {
+        if ((other.manifest.mounts?.[tier] || []).includes(prefix)) {
+          throw new Error(`prefix ${tier}${prefix} already registered by module "${other.id}"`)
+        }
+      }
+    }
+  }
+
+  for (const slot of manifest.extensions || []) {
+    if (!CORE_SLOTS.has(slot)) throw new Error(`unknown extension slot "${slot}"`)
+  }
+
+  if (manifest.schema && !manifest.purge) {
+    // A module that can create tables and cannot drop them leaves an operator
+    // with orphaned data and no supported way to remove it.
+    throw new Error('declares schema but no purge')
+  }
+  if (manifest.purge && !fs.existsSync(path.join(dir, manifest.purge))) {
+    throw new Error(`purge file "${manifest.purge}" is missing`)
+  }
+  return manifest
+}
+
+// What the module registered must equal what it declared — in both directions.
+function checkDeclared(record) {
+  const declared = record.manifest.mounts || {}
+  for (const tier of TIERS) {
+    const want = new Set(declared[tier] || [])
+    const got = new Set(record.routes[tier].keys())
+    for (const p of got) if (!want.has(p)) throw new Error(`registered ${tier}${p} without declaring it`)
+    for (const p of want) if (!got.has(p)) throw new Error(`declared ${tier}${p} but never registered it`)
+  }
+}
+
+// ── Load ───────────────────────────────────────────────────────────────────
+
+/**
+ * Discover, validate, register and mount every module under MODULES_DIR.
+ *
+ * **Called exactly once, explicitly, from app.js**, after the three tier routers
+ * are required and before the app is exported. There is no lazy self-scan: the
+ * spike's was lazy and silent, so requiring the loader and reading the module
+ * list gave an empty array and no error (MODULE_API.md §7.6). Everything that
+ * reads the module list now throws until this has run.
+ *
+ * The ordering is not incidental. Core's mounts must already be on the tier
+ * routers, because that is what the prefix-collision check is asked about; and
+ * modules mount after them, so first-match-wins means a module could not shadow
+ * a core prefix even if the check were bypassed.
+ *
+ * Safe to call when the modules directory does not exist — that is the normal
+ * case for a bare core, and it is the state this PR ships in.
+ *
+ * @param {{public: Router, admin: Router, player: Router}} tierRouters
+ */
+function load(tierRouters) {
+  if (loaded) return
+  for (const tier of TIERS) {
+    if (!tierRouters || typeof tierRouters[tier] !== 'function') {
+      throw new Error(`modules.load: missing the "${tier}" tier router`)
+    }
+  }
+  loaded = true
+
+  let entries = []
+  try {
+    entries = fs.readdirSync(MODULES_DIR, { withFileTypes: true })
+      .filter((e) => e.isDirectory())
+      .map((e) => e.name)
+      .sort() // alphabetical: there is no dependency resolution, and any other
+              // order would imply a precedence nothing computes (§4.2)
+  } catch {
+    return // no modules directory is the normal case for a bare core
+  }
+
+  for (const id of entries) {
+    const dir = path.join(MODULES_DIR, id)
+    if (!fs.existsSync(path.join(dir, 'module.json'))) continue
+
+    const record = {
+      id,
+      dir,
+      manifest: null,
+      routes: { public: new Map(), admin: new Map(), player: new Map() },
+      tables: new Set(),
+      called: new Set(),
+      state: 'installed',
+      reason: null,
+    }
+
+    try {
+      record.manifest = readManifest(dir, id, tierRouters)
+      record.tables = tablesOf(dir, record.manifest)
+      checkTableNames(id, record.tables)
+      if (record.manifest.server) {
+        const entry = path.join(dir, record.manifest.server)
+        // eslint-disable-next-line global-require, import/no-dynamic-require
+        const register = require(entry)
+        if (typeof register !== 'function') throw new Error(`${record.manifest.server} does not export a function`)
+        register(buildCtx(id, dir), buildApi(record))
+        checkDeclared(record)
+      }
+      record.state = 'registered'
+      modules.set(id, record)
+      log.info(`registered module "${id}" v${record.manifest.version}`, {
+        mounts: record.manifest.mounts,
+      })
+    } catch (err) {
+      // A failure here is BEFORE any route was mounted, so this module's routes
+      // and nav are simply absent and the site comes up without it (§4.4).
+      record.state = 'startup_failed'
+      record.reason = err.message
+      record.manifest = record.manifest || { id, version: 'unknown' }
+      modules.set(id, record)
+      log.error(`module "${id}" failed to load — continuing without it`, { reason: err.message })
+    }
+  }
+
+  // Mounting is a SECOND pass, after every module has been validated, and not
+  // because it reads better. `ownedByCore` asks the live tier router what is
+  // already on it, so mounting inside the loop would make the first module's
+  // layers indistinguishable from core's — the second module claiming a taken
+  // prefix would be told it collided with core, naming the wrong culprit, and
+  // the module-versus-module check below it could never be reached.
+  for (const record of modules.values()) {
+    if (record.state === 'registered') mount(record, tierRouters)
+  }
+}
+
+/**
+ * Mount one module's routers onto the tier routers, behind the dispatch guard.
+ *
+ * The guard is the other half of §4.4. A module that fails BEFORE this point has
+ * no routes at all; one that fails after — schema replay (PR 3), `onBoot`
+ * (PR 5) — keeps its URLs and answers 503, so `routes.manifest.json` never
+ * depends on whether a boot hook happened to succeed on the machine that
+ * generated it. `disabled` is 404 and unreachable until PR 5 wires
+ * `installed_modules` in; it is written here because the guard is the contract's
+ * §4.5, not a later addition.
+ */
+function mount(record, tierRouters) {
+  for (const tier of TIERS) {
+    for (const [prefix, router] of record.routes[tier]) {
+      tierRouters[tier].use(prefix, (req, res, next) => {
+        if (record.state === 'startup_failed') {
+          return res.status(503).json({ message: 'Module unavailable' })
+        }
+        if (record.state === 'disabled') return res.status(404).json({ message: 'Not found' })
+        return next()
+      }, router)
+    }
+  }
+}
+
+// ── State ──────────────────────────────────────────────────────────────────
+
+// The states a loaded record may hold, deliberately a hardcoded subset rather
+// than an import of model/modules/modules.model.js's STATES: that model reaches
+// the database, and this file must stay require-able against a dead one.
+// `installed` is not here because a record leaves load() resolved either way.
+const RECORD_STATES = new Set(['registered', 'started', 'disabled', 'startup_failed'])
+
+/**
+ * Move a loaded module to a new state — the POST-mount transitions.
+ *
+ * Called by whoever ran the step that failed or the step that succeeded, because
+ * only they can know: PR 3's `ensureSchema()` replays the fragments, PR 5's boot
+ * dispatch runs `onBoot` and reconciles `installed_modules` (whose `disabled`
+ * rows are what first make the guard's 404 leg reachable).
+ *
+ * Unknown ids are ignored rather than thrown on: a module can be absent from the
+ * volume and still have a row, and a caller on the boot path must not turn that
+ * into everyone's failure.
+ */
+function setState(id, state, reason = null) {
+  if (!RECORD_STATES.has(state)) throw new Error(`unknown module state "${state}"`)
+  const record = modules.get(id)
+  if (!record) return
+  record.state = state
+  record.reason = reason
+}
+
+// ── Introspection ──────────────────────────────────────────────────────────
+
+function assertLoaded(caller) {
+  if (!loaded) throw new Error(`modules.${caller}() before modules.load()`)
+}
+
+/**
+ * Every module found on the volume, loaded or failed, in scan order.
+ *
+ * Throws rather than returning `[]` when load() has not run — the empty list is
+ * a real answer for a core with no modules installed, and a caller cannot tell
+ * the two apart (§7.6).
+ */
+function list() {
+  assertLoaded('list')
+  return [...modules.values()].map((r) => ({
+    id: r.id,
+    name: r.manifest.name || r.id,
+    version: r.manifest.version,
+    state: r.state,
+    reason: r.reason,
+    capabilities: r.manifest.capabilities || [],
+  }))
+}
+
+/** Absolute path of the modules directory. */
+const dir = () => MODULES_DIR
+
+module.exports = { load, list, setState, dir }
diff --git a/server/src/modules/semver.js b/server/src/modules/semver.js
new file mode 100644
index 0000000..062f8b5
--- /dev/null
+++ b/server/src/modules/semver.js
@@ -0,0 +1,47 @@
+// A deliberately tiny semver range check — enough for `coreApi` and no more.
+//
+// Supports `*`, an exact `x.y.z`, `^x.y.z` and `~x.y.z`. That is the whole
+// grammar a module manifest is allowed to use (MODULE_API.md §1.1), so pulling
+// in the `semver` package for it would add a dependency to the server for a
+// twenty-line job. A range this parser does not understand is REJECTED rather
+// than assumed to match — an unparseable range must not silently load a module
+// against an API it was never tested on.
+
+const PARTS = /^(\d+)\.(\d+)\.(\d+)$/
+
+function parse(version) {
+  const m = PARTS.exec(String(version).trim())
+  if (!m) return null
+  return { major: Number(m[1]), minor: Number(m[2]), patch: Number(m[3]) }
+}
+
+const gte = (a, b) => {
+  if (a.major !== b.major) return a.major > b.major
+  if (a.minor !== b.minor) return a.minor > b.minor
+  return a.patch >= b.patch
+}
+
+/**
+ * Does `version` satisfy `range`?
+ * @param {string} version an exact x.y.z
+ * @param {string} range   `*` | `x.y.z` | `^x.y.z` | `~x.y.z`
+ * @returns {boolean} false for anything unparseable, on either side
+ */
+function satisfies(version, range) {
+  const v = parse(version)
+  if (!v) return false
+  const raw = String(range).trim()
+  if (raw === '*') return true
+
+  const op = raw[0] === '^' || raw[0] === '~' ? raw[0] : ''
+  const b = parse(op ? raw.slice(1) : raw)
+  if (!b) return false
+
+  if (op === '') return v.major === b.major && v.minor === b.minor && v.patch === b.patch
+  if (!gte(v, b)) return false
+  // ^ allows minor+patch within the same major; ~ allows patch within the same minor.
+  if (op === '^') return v.major === b.major
+  return v.major === b.major && v.minor === b.minor
+}
+
+module.exports = { satisfies, parse }
diff --git a/server/src/modules/version.js b/server/src/modules/version.js
new file mode 100644
index 0000000..8df4d79
--- /dev/null
+++ b/server/src/modules/version.js
@@ -0,0 +1,14 @@
+// The module API version — the single number a module's `coreApi` range is
+// checked against (docs/website/MODULE_API.md §1.1).
+//
+// Bump minor when a member is ADDED to ctx or a new register* call appears;
+// major when one is removed, its signature changes, or its behaviour changes
+// without a signature change. A core-internal refactor behind an unchanged
+// member is not a bump.
+//
+// Deliberately separate from PROTOCOL_VERSION (which versions the shard wire and
+// has nothing to say about a website module) and from any module's own version.
+
+const MODULE_API_VERSION = '1.0.0'
+
+module.exports = { MODULE_API_VERSION }
diff --git a/server/test/moduleLoader.test.js b/server/test/moduleLoader.test.js
new file mode 100644
index 0000000..ccc40ae
--- /dev/null
+++ b/server/test/moduleLoader.test.js
@@ -0,0 +1,444 @@
+// ── The loader's failure guarantees ────────────────────────────────────────
+//
+// docs/website/MODULE_API.md §4.4 promises that a module which fails ANYWHERE in
+// its lifecycle fails alone: the site comes up, other modules are unaffected, and
+// the failure is recorded rather than thrown. That is the property most worth a
+// test, because the failure paths are the ones nobody exercises by hand — every
+// manual check runs the happy path.
+//
+// Each test builds a throwaway modules directory, points MODULES_DIR at it and
+// re-requires the loader with a clean cache, so the scan is genuinely redone.
+// MODULES_DIR is read into a const at require time (it has to be: the scan is
+// synchronous and happens during app.js's require), so busting the cache is the
+// only honest way to point the loader somewhere else.
+//
+// Point the pool at a closed port BEFORE requiring anything: buildCtx pulls in
+// the models, which build a mariadb pool at require time. No query is ever run.
+process.env.DB_HOST = '127.0.0.1'
+process.env.DB_PORT = '59999'
+
+const fs = require('fs')
+const os = require('os')
+const path = require('path')
+
+const { test, beforeEach, after } = require('node:test')
+const assert = require('node:assert/strict')
+
+const express = require('express')
+
+const db = require('../src/utils/db')
+const { startApp } = require('./_helper')
+
+after(() => db.close())
+
+let tmpRoot
+
+/** Three empty routers standing in for core's tiers — nothing owned, nothing gated. */
+const emptyTiers = () => ({
+  public: express.Router(),
+  admin: express.Router(),
+  player: express.Router(),
+})
+
+function freshLoader(dir, tiers = emptyTiers()) {
+  process.env.MODULES_DIR = dir
+  delete require.cache[require.resolve('../src/modules/loader')]
+  // eslint-disable-next-line global-require
+  const loader = require('../src/modules/loader')
+  loader.load(tiers)
+  return loader
+}
+
+function writeModule(id, { manifest = {}, server, schema } = {}) {
+  const dir = path.join(tmpRoot, id)
+  fs.mkdirSync(dir, { recursive: true })
+  const full = {
+    id,
+    name: id,
+    version: '1.0.0',
+    coreApi: '^1.0.0',
+    ...(server === undefined ? {} : { server: 'index.js' }),
+    ...(schema === undefined ? {} : { schema: 'schema.sql', purge: 'purge.sql' }),
+    ...manifest,
+  }
+  fs.writeFileSync(path.join(dir, 'module.json'), JSON.stringify(full))
+  if (server !== undefined) fs.writeFileSync(path.join(dir, 'index.js'), server)
+  if (schema !== undefined) {
+    fs.writeFileSync(path.join(dir, 'schema.sql'), schema)
+    fs.writeFileSync(path.join(dir, 'purge.sql'), '')
+  }
+  return dir
+}
+
+/** A module that registers one router answering 200 at its prefix root. */
+const oneRoute = (prefix, tier = 'public') => ({
+  manifest: { mounts: { [tier]: [prefix] } },
+  server: `module.exports = (ctx, api) => {
+    const r = ctx.express.Router()
+    r.get('/', (req, res) => res.json({ ok: true }))
+    api.registerRoutes({ ${tier}: { '${prefix}': r } })
+  }`,
+})
+
+const stateOf = (loader, id) => loader.list().find((m) => m.id === id)
+
+beforeEach(() => {
+  tmpRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'rg-modules-'))
+})
+
+// ── Discovery and the explicit trigger ─────────────────────────────────────
+
+test('a missing modules directory is the normal case, not an error', () => {
+  const loader = freshLoader(path.join(tmpRoot, 'does-not-exist'))
+  assert.deepEqual(loader.list(), [])
+})
+
+test('reading the module list before load() throws instead of answering []', () => {
+  // §7.6. The spike's scan was lazy and silent, so a caller that required the
+  // loader and read nothing got an empty list — indistinguishable from a core
+  // with no modules installed. It cost one confusing failure; it now costs an
+  // error naming the missing call.
+  process.env.MODULES_DIR = tmpRoot
+  delete require.cache[require.resolve('../src/modules/loader')]
+  // eslint-disable-next-line global-require
+  const loader = require('../src/modules/loader')
+  assert.throws(() => loader.list(), /modules\.list\(\) before modules\.load\(\)/)
+})
+
+test('load() refuses to run without all three tier routers', () => {
+  writeModule('aaa', { server: 'module.exports = () => {}' })
+  process.env.MODULES_DIR = tmpRoot
+  delete require.cache[require.resolve('../src/modules/loader')]
+  // eslint-disable-next-line global-require
+  const loader = require('../src/modules/loader')
+  // Not a module's failure — a wiring mistake in core, and the one thing in this
+  // file that is allowed to throw past the caller.
+  assert.throws(() => loader.load({ public: express.Router() }), /missing the "admin" tier router/)
+})
+
+test('load() is once-only, so a second call cannot double-mount', () => {
+  writeModule('aaa', oneRoute('/thing'))
+  const tiers = emptyTiers()
+  const loader = freshLoader(tmpRoot, tiers)
+  const before = tiers.public.stack.length
+
+  loader.load(tiers)
+  assert.equal(tiers.public.stack.length, before)
+  assert.equal(loader.list().length, 1)
+})
+
+test('modules load in alphabetical order, since nothing computes a precedence', () => {
+  for (const id of ['ccc', 'aaa', 'bbb']) writeModule(id, { server: 'module.exports = () => {}' })
+  const loader = freshLoader(tmpRoot)
+  assert.deepEqual(loader.list().map((m) => m.id), ['aaa', 'bbb', 'ccc'])
+})
+
+// ── The failing module fails alone ─────────────────────────────────────────
+
+test('a module whose entry point throws does not stop the others loading', () => {
+  writeModule('aaa', { server: 'module.exports = () => {}' })
+  writeModule('bbb', { server: 'throw new Error("boom")' })
+  writeModule('ccc', { server: 'module.exports = () => {}' })
+  const loader = freshLoader(tmpRoot)
+
+  assert.equal(stateOf(loader, 'aaa').state, 'registered')
+  assert.equal(stateOf(loader, 'ccc').state, 'registered')
+
+  const bad = stateOf(loader, 'bbb')
+  assert.equal(bad.state, 'startup_failed')
+  assert.match(bad.reason, /boom/)
+})
+
+test('an entry point that exports something other than a function is rejected', () => {
+  writeModule('notfn', { server: 'module.exports = { register: () => {} }' })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'notfn').reason, /does not export a function/)
+})
+
+test('a coreApi mismatch is refused before the module is required at all', () => {
+  // The entry point would throw if it ran; the version gate must run first.
+  writeModule('old', {
+    manifest: { coreApi: '^99.0.0' },
+    server: 'throw new Error("should never be required")',
+  })
+  const loader = freshLoader(tmpRoot)
+  const mod = stateOf(loader, 'old')
+  assert.equal(mod.state, 'startup_failed')
+  assert.match(mod.reason, /needs core API \^99\.0\.0/)
+})
+
+test('an unknown manifest key is rejected, not ignored', () => {
+  // A typo'd key must be loud: an operator who believes they configured
+  // something and silently did not is worse off than one who sees a failure.
+  writeModule('typo', { manifest: { mount: { public: ['/x'] } } })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'typo').reason, /unknown key "mount"/)
+})
+
+test('a module id that does not match its directory is rejected', () => {
+  writeModule('onedir', { manifest: { id: 'another' } })
+  const loader = freshLoader(tmpRoot)
+  // Recorded under the DIRECTORY name — the id it claimed is exactly what is
+  // not trusted here.
+  assert.match(stateOf(loader, 'onedir').reason, /does not match directory/)
+})
+
+test('an unknown extension slot is rejected; only core may declare a slot', () => {
+  writeModule('presumptuous', { manifest: { extensions: ['admin.users.detail', 'admin.invented'] } })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'presumptuous').reason, /unknown extension slot "admin\.invented"/)
+})
+
+// ── Prefix ownership ───────────────────────────────────────────────────────
+
+test('two modules cannot claim the same prefix; the first one wins', () => {
+  writeModule('aaa', oneRoute('/thing'))
+  writeModule('bbb', oneRoute('/thing'))
+  const loader = freshLoader(tmpRoot)
+
+  assert.equal(stateOf(loader, 'aaa').state, 'registered')
+  assert.match(stateOf(loader, 'bbb').reason, /already registered by module "aaa"/)
+})
+
+test('a module cannot take a prefix core owns, asked of the live tier routers', () => {
+  // Deliberately the REAL routers rather than a hardcoded prefix list. The spike
+  // hardcoded core's ~24 prefixes and they were already stale; asking express
+  // itself is what stops the check drifting the next time core adds a capability
+  // router.
+  /* eslint-disable global-require */
+  const real = {
+    public: require('../src/router/v1/public'),
+    admin: require('../src/router/v1/admin'),
+    player: require('../src/router/v1/player'),
+  }
+  /* eslint-enable global-require */
+
+  writeModule('greedy', { manifest: { mounts: { admin: ['/users'] } } })
+  writeModule('alsogreedy', { manifest: { mounts: { public: ['/wiki'] } } })
+  // Free in every tier core actually mounts, so it must be allowed through.
+  writeModule('polite', oneRoute('/widgets', 'player'))
+
+  const loader = freshLoader(tmpRoot, real)
+  assert.match(stateOf(loader, 'greedy').reason, /owned by core/)
+  assert.match(stateOf(loader, 'alsogreedy').reason, /owned by core/)
+  assert.equal(stateOf(loader, 'polite').state, 'registered')
+})
+
+test('a root-mounted core layer does not make every prefix look taken', () => {
+  // public/index.js ends with `use('/', siteRouter)` and admin with the dashboard
+  // router; both match every path. Counting them would report every prefix as
+  // owned and no module could ever mount.
+  const tiers = emptyTiers()
+  tiers.public.use('/posts', express.Router())
+  tiers.public.use('/', express.Router())
+
+  writeModule('fine', oneRoute('/widgets'))
+  writeModule('taken', oneRoute('/posts'))
+  const loader = freshLoader(tmpRoot, tiers)
+
+  assert.equal(stateOf(loader, 'fine').state, 'registered')
+  assert.match(stateOf(loader, 'taken').reason, /owned by core/)
+})
+
+test('a prefix with a slash or a parameter in it is rejected', () => {
+  // A prefix that could contain either would let a module reach outside the slot
+  // it was given.
+  writeModule('nested', { manifest: { mounts: { public: ['/a/b'] } } })
+  writeModule('parameterised', { manifest: { mounts: { public: ['/:id'] } } })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'nested').reason, /bad prefix "\/a\/b"/)
+  assert.match(stateOf(loader, 'parameterised').reason, /bad prefix "\/:id"/)
+})
+
+test('registering a prefix that was never declared is rejected', () => {
+  // module.json is what the admin panel, the collision check and the reviewer
+  // all read, so it has to be the truth rather than a hint.
+  writeModule('sneaky', {
+    manifest: { mounts: { public: ['/declared'] } },
+    server: `module.exports = (ctx, api) => api.registerRoutes({
+      public: { '/declared': ctx.express.Router(), '/undeclared': ctx.express.Router() },
+    })`,
+  })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'sneaky').reason, /registered public\/undeclared without declaring it/)
+})
+
+test('declaring a prefix and never registering it is rejected too', () => {
+  writeModule('forgetful', {
+    manifest: { mounts: { public: ['/a', '/b'] } },
+    server: "module.exports = (ctx, api) => api.registerRoutes({ public: { '/a': ctx.express.Router() } })",
+  })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'forgetful').reason, /declared public\/b but never registered it/)
+})
+
+test('registering the same thing twice is an error, not a silent overwrite', () => {
+  writeModule('twice', {
+    manifest: { mounts: { public: ['/x'] } },
+    server: `module.exports = (ctx, api) => {
+      api.registerRoutes({ public: { '/x': ctx.express.Router() } })
+      api.registerRoutes({ public: { '/x': ctx.express.Router() } })
+    }`,
+  })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'twice').reason, /registerRoutes\(\) called twice/)
+})
+
+// ── Schema fragment validation (the replay itself is PR 3) ─────────────────
+
+test('a schema fragment declaring a core table is rejected', () => {
+  writeModule('thief', { schema: 'CREATE TABLE IF NOT EXISTS users (id INT);' })
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'thief').reason, /declares core table "users"/)
+})
+
+test('a schema fragment table must carry the module id as a prefix', () => {
+  writeModule('mine', { schema: 'CREATE TABLE IF NOT EXISTS widgets (id INT);' })
+  assert.match(stateOf(freshLoader(tmpRoot), 'mine').reason, /not prefixed "mine_"/)
+
+  tmpRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'rg-modules-'))
+  writeModule('mine', { schema: 'CREATE TABLE IF NOT EXISTS mine_widgets (id INT);' })
+  assert.equal(stateOf(freshLoader(tmpRoot), 'mine').state, 'registered')
+})
+
+test('two modules cannot own the same table either', () => {
+  writeModule('aaa', { schema: 'CREATE TABLE IF NOT EXISTS aaa_shared (id INT);' })
+  writeModule('bbb', {
+    manifest: { id: 'bbb' },
+    schema: 'CREATE TABLE IF NOT EXISTS aaa_shared (id INT);',
+  })
+  const loader = freshLoader(tmpRoot)
+  assert.equal(stateOf(loader, 'aaa').state, 'registered')
+  assert.match(stateOf(loader, 'bbb').reason, /already owned by module "aaa"/)
+})
+
+test('declaring a schema without a purge is rejected', () => {
+  const dir = path.join(tmpRoot, 'noway')
+  fs.mkdirSync(dir, { recursive: true })
+  fs.writeFileSync(
+    path.join(dir, 'module.json'),
+    JSON.stringify({ id: 'noway', name: 'x', version: '1.0.0', coreApi: '^1.0.0', schema: 'schema.sql' }),
+  )
+  const loader = freshLoader(tmpRoot)
+  // A module that can create tables and cannot drop them leaves an operator with
+  // orphaned data and no supported way to remove it.
+  assert.match(stateOf(loader, 'noway').reason, /declares schema but no purge/)
+})
+
+test('a declared purge file that is not there is rejected', () => {
+  writeModule('gone', { schema: 'CREATE TABLE IF NOT EXISTS gone_x (id INT);' })
+  fs.unlinkSync(path.join(tmpRoot, 'gone', 'purge.sql'))
+  const loader = freshLoader(tmpRoot)
+  assert.match(stateOf(loader, 'gone').reason, /purge file "purge\.sql" is missing/)
+})
+
+// ── Mounting and the dispatch guard ────────────────────────────────────────
+
+test('a registered module answers on its prefix; a failed one is simply absent', async () => {
+  writeModule('good', oneRoute('/widgets'))
+  writeModule('bad', { ...oneRoute('/broken'), server: 'throw new Error("boom")' })
+
+  const tiers = emptyTiers()
+  freshLoader(tmpRoot, tiers)
+  const app = await startApp((a) => a.use('/public', tiers.public))
+
+  try {
+    assert.equal((await fetch(`${app.url}/public/widgets`)).status, 200)
+    // Failed BEFORE mounting, so its routes are not absent-with-a-503 — they do
+    // not exist at all (§4.4, left-hand column).
+    assert.equal((await fetch(`${app.url}/public/broken`)).status, 404)
+  } finally {
+    await app.close()
+  }
+})
+
+test('a module that fails AFTER mounting keeps its URLs and answers 503', async () => {
+  // The right-hand column of §4.4, and the reason routes.manifest.json can be
+  // generated off a dead database: the URL surface must not depend on whether a
+  // boot step succeeded on the generating machine. PR 3 (schema replay) and PR 5
+  // (onBoot) are the two things that will trip this in real life; here the state
+  // is moved by hand, because the loader is the thing under test.
+  writeModule('later', oneRoute('/widgets'))
+
+  const tiers = emptyTiers()
+  const loader = freshLoader(tmpRoot, tiers)
+  const app = await startApp((a) => a.use('/public', tiers.public))
+
+  try {
+    assert.equal((await fetch(`${app.url}/public/widgets`)).status, 200)
+
+    assert.equal(stateOf(loader, 'later').state, 'registered')
+
+    loader.setState('later', 'startup_failed', 'schema fragment blew up')
+    assert.equal((await fetch(`${app.url}/public/widgets`)).status, 503)
+    assert.equal(stateOf(loader, 'later').reason, 'schema fragment blew up')
+
+    // The 404 leg becomes reachable for real in PR 5, when the boot reconcile
+    // reads a `disabled` row out of installed_modules. A disabled module is
+    // mounted and guarded, never unmounted (§4.5) — same reason as the 503.
+    loader.setState('later', 'disabled')
+    assert.equal((await fetch(`${app.url}/public/widgets`)).status, 404)
+
+    loader.setState('later', 'started')
+    assert.equal((await fetch(`${app.url}/public/widgets`)).status, 200)
+  } finally {
+    await app.close()
+  }
+})
+
+test('setState refuses a state that is not one, and shrugs at an unknown id', () => {
+  writeModule('here', oneRoute('/widgets'))
+  const loader = freshLoader(tmpRoot)
+
+  assert.throws(() => loader.setState('here', 'enabled'), /unknown module state "enabled"/)
+  // An id with no record is not the boot path's problem to escalate.
+  assert.doesNotThrow(() => loader.setState('never-installed', 'started'))
+})
+
+// ── ctx ────────────────────────────────────────────────────────────────────
+
+test('ctx exposes exactly the documented surface, and is frozen', () => {
+  const seen = path.join(tmpRoot, 'probe-out.json')
+  writeModule('probe', {
+    server: `const fs = require('fs')
+      module.exports = (ctx) => {
+        let mutable = true
+        try { ctx.db.query = null; mutable = ctx.db.query === null } catch { mutable = false }
+        fs.writeFileSync(${JSON.stringify(seen)}, JSON.stringify({
+          keys: Object.keys(ctx).sort(),
+          middleware: Object.keys(ctx.middleware).sort(),
+          moduleId: ctx.moduleId,
+          mutable,
+        }))
+      }`,
+  })
+  assert.equal(stateOf(freshLoader(tmpRoot), 'probe').state, 'registered')
+
+  const probe = JSON.parse(fs.readFileSync(seen, 'utf8'))
+  assert.deepEqual(probe.keys, [
+    'auth', 'db', 'express', 'log', 'middleware', 'moduleId', 'paths',
+    'posts', 'push', 'secretBox', 'settings', 'uploads', 'validator',
+  ])
+  assert.deepEqual(probe.middleware, ['noindex', 'requireAuth', 'requireRole', 'siteMode', 'validate'])
+  assert.equal(probe.moduleId, 'probe')
+  assert.equal(probe.mutable, false, 'ctx members must be frozen')
+})
+
+test('the register calls PR 4 and PR 5 own throw rather than silently accepting', () => {
+  // An accepting no-op would let a module believe it had registered a
+  // notification stream or a boot hook and fail silently at the far end.
+  for (const [call, pr] of [
+    ['registerExtension', 4],
+    ['registerNotificationStreams', 4],
+    ['registerAnnounceLeg', 4],
+    ['onBoot', 5],
+    ['onShutdown', 5],
+  ]) {
+    tmpRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'rg-modules-'))
+    writeModule('early', { server: `module.exports = (ctx, api) => api.${call}(() => {})` })
+    assert.match(
+      stateOf(freshLoader(tmpRoot), 'early').reason,
+      new RegExp(`${call}: not available until phase 2 PR ${pr}`),
+    )
+  }
+})