feat(theming): dropdown sections and added links in the public header

Phase 10 of docs/website/THEMING_AND_NAV.md, asked for before the edge -> main
cutover. An admin can now create dropdown sections in the public header, organise
the coded entries into them, and add links of their own.

This deliberately amends §7, which said the override layer "cannot introduce a
`to` that is not already in the hardcoded NAV array". That stays true of every
CODED entry; an admin may now also add a link, restricted to a same-origin path —
no scheme, no protocol-relative //host. A link carries no gate of its own and
needs none: the page behind it enforces its own access, so an added link
advertises a route and never grants one.

The invariant is kept structurally rather than by vigilance. Coded entries live
in an `items` map whose keys must be routes the base array declares, so that map
cannot invent a route; everything that CAN name an arbitrary path lives in
`links`, which is the one place the path rule is applied — on both the write and
the read path.

nav_public therefore grew a { items, sections, links } wrapper. A bare map still
reads as the items map, and a nav with no sections still stores one, so this
changed nothing for a nav that does not use it. Free to do now because nothing
has shipped; after the cutover it would have needed a migration.

The Public tab gets its own editor. A public section is an entry in the
top-level order that the admin created and can drag among the pills, unlike the
admin sidebar's four coded sections, where only membership moves — that is a tree
rather than a list of groups. Deleting a section returns its entries to the top
level rather than removing them, which is the one destructive act this screen
could otherwise commit.

The dropdown opens on click and never on hover, and its trigger is not a link: a
hover menu is unusable on touch, and a trigger that navigates means tapping to
open takes you somewhere instead. Escape closes and returns focus, an outside
press closes, navigating closes, and Arrow Up/Down walk the items.

pruneNav applies the shard-feature gate inside a section and drops one it leaves
empty, so a dropdown never opens onto nothing.

Also fixes a bug this surfaced in the phase 6-8 code: the save path judged "does
this route still exist?" against the palette — the base array already filtered to
what the editing admin can see — so on the public header a feature-gated row's
override could never be carried through and would have been silently reset.
Membership is now judged against the full coded nav while the rows still come
from the palette.

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

client/test/navOverrides.test.js

@@ -1,7 +1,14 @@
 import { test } from 'node:test'
 import assert from 'node:assert/strict'
 
-import { applyNavOverrides, buildNavRows, buildNavOverrides } from '../src/lib/navOverrides.js'
+import {
+  applyNavOverrides,
+  buildNavRows,
+  buildNavOverrides,
+  buildPublicNav,
+  pruneNav,
+  buildPublicNavOverrides,
+} from '../src/lib/navOverrides.js'
 
 // The nav-override merge (docs/website/THEMING_AND_NAV.md §7.1) — the one piece
 // of this feature with real correctness risk, so it is tested in isolation from
@@ -348,3 +355,190 @@ test('degenerate input yields an empty result rather than throwing', () => {
   assert.deepEqual(buildNavOverrides(null, FLAT), {})
   assert.deepEqual(buildNavOverrides([], null), {})
 })
+
+// ── The public header: sections and added links (phase 10) ────────────────
+//
+// The one nav an admin can restructure rather than only reorder. The invariant
+// that has to survive is §7's, in its narrower form: a CODED entry still cannot
+// have its `to` or `feature` touched, and everything that can name an arbitrary
+// path lives in `links`, where the path rule applies.
+
+const PUB = [
+  { label: 'Home', to: '/', end: true },
+  { label: 'News', to: '/site/news' },
+  { label: 'Champions', to: '/site/champs', feature: 'champs' },
+  { label: 'Guilds', to: '/site/guilds', feature: 'guilds' },
+  { label: 'About', to: '/site/about' },
+]
+const shape = (tree) =>
+  tree.map((n) => (n.kind === 'section' ? { [n.label]: n.items.map((i) => i.label) } : n.label))
+
+test('no override yields the coded header, in code order', () => {
+  assert.deepEqual(shape(buildPublicNav(PUB, null)), ['Home', 'News', 'Champions', 'Guilds', 'About'])
+  assert.deepEqual(shape(buildPublicNav(PUB, {})), ['Home', 'News', 'Champions', 'Guilds', 'About'])
+})
+
+test('a phase 6-8 bare map still reads as the items map', () => {
+  // Nothing has shipped, but a row written during review must not become
+  // unreadable just because the wrapper arrived.
+  assert.deepEqual(shape(buildPublicNav(PUB, { '/site/news': { label: 'Announcements' } })), [
+    'Home',
+    'Announcements',
+    'Champions',
+    'Guilds',
+    'About',
+  ])
+})
+
+const SECTIONED = {
+  items: { '/site/champs': { section: 'sec_aaaa', order: 0 }, '/site/guilds': { section: 'sec_aaaa', order: 1 } },
+  sections: [{ id: 'sec_aaaa', label: 'The World', order: 2 }],
+  links: [{ id: 'lnk_bbbb', label: 'Guide', to: '/wiki/new-player-guide', section: 'sec_aaaa', order: 2 }],
+}
+
+test('a section collects its members and sits in the top-level order', () => {
+  assert.deepEqual(shape(buildPublicNav(PUB, SECTIONED)), [
+    'Home',
+    'News',
+    { 'The World': ['Champions', 'Guilds', 'Guide'] },
+    'About',
+  ])
+})
+
+test('an added link is kept apart from the coded items', () => {
+  const tree = buildPublicNav(PUB, SECTIONED)
+  const link = tree.find((n) => n.kind === 'section').items.find((i) => i.kind === 'link')
+  assert.equal(link.to, '/wiki/new-player-guide')
+  assert.equal(link.id, 'lnk_bbbb')
+  // It carries no gate of its own — that is the documented contract, and the
+  // page behind it is what actually enforces access.
+  assert.equal(link.feature, undefined)
+  assert.equal(link.roles, undefined)
+})
+
+test('an off-origin link is dropped rather than rendered', () => {
+  for (const to of ['https://evil.example', '//evil.example/x', 'javascript:alert(1)', '/x y', '/a"b']) {
+    const tree = buildPublicNav(PUB, { items: {}, links: [{ id: 'lnk_bbbb', label: 'Bad', to }] })
+    assert.equal(
+      tree.some((n) => n.kind === 'link'),
+      false,
+      `${to} should be dropped`,
+    )
+  }
+})
+
+test('an item naming a section that does not exist stays at the top level', () => {
+  const tree = buildPublicNav(PUB, { items: { '/site/champs': { section: 'sec_gone' } } })
+  assert.deepEqual(shape(tree), ['Home', 'News', 'Champions', 'Guilds', 'About'])
+})
+
+test('an override still cannot introduce a coded route', () => {
+  const tree = buildPublicNav(PUB, { items: { '/site/secret': { label: 'Secret' } } })
+  assert.equal(
+    tree.some((n) => n.to === '/site/secret'),
+    false,
+  )
+})
+
+test('hidden entries are dropped for the site and kept for the editor', () => {
+  const overrides = { items: { '/site/news': { hidden: true } } }
+  assert.equal(shape(buildPublicNav(PUB, overrides)).includes('News'), false)
+  const rows = buildPublicNav(PUB, overrides, { keepHidden: true })
+  assert.equal(rows.find((n) => n.to === '/site/news').hidden, true)
+})
+
+// ── pruneNav: the empty dropdown ──────────────────────────────────────────
+
+test('a section keeps the entries the viewer may see', () => {
+  const tree = buildPublicNav(PUB, SECTIONED)
+  const out = pruneNav(tree, (i) => i.feature !== 'guilds')
+  assert.deepEqual(shape(out), ['Home', 'News', { 'The World': ['Champions', 'Guide'] }, 'About'])
+})
+
+test('a section whose every entry is gated out does not render at all', () => {
+  // The case that matters: a dropdown that opens onto nothing is worse than no
+  // dropdown, and shard visibility can empty one at any time.
+  const overrides = {
+    items: { '/site/champs': { section: 'sec_aaaa' }, '/site/guilds': { section: 'sec_aaaa' } },
+    sections: [{ id: 'sec_aaaa', label: 'The World' }],
+  }
+  const tree = buildPublicNav(PUB, overrides)
+  assert.deepEqual(shape(pruneNav(tree, () => true)), [
+    'Home',
+    'News',
+    'About',
+    { 'The World': ['Champions', 'Guilds'] },
+  ])
+  assert.deepEqual(shape(pruneNav(tree, (i) => !i.feature)), ['Home', 'News', 'About'])
+})
+
+test('an added link is never pruned — it carries no gate', () => {
+  const tree = buildPublicNav(PUB, { items: {}, links: [{ id: 'lnk_bbbb', label: 'Guide', to: '/wiki/g' }] })
+  assert.equal(
+    pruneNav(tree, () => false).some((n) => n.kind === 'link'),
+    true,
+  )
+})
+
+// ── The editor round trip ─────────────────────────────────────────────────
+
+test('an untouched public editor saves nothing', () => {
+  assert.deepEqual(buildPublicNavOverrides(buildPublicNav(PUB, null, { keepHidden: true }), PUB), {})
+})
+
+test('a nav with no sections still stores the plain items map', () => {
+  // Adding this feature changed nothing for a nav that does not use it.
+  const tree = buildPublicNav(PUB, null, { keepHidden: true })
+  tree[1].label = 'Announcements'
+  const out = buildPublicNavOverrides(tree, PUB)
+  assert.deepEqual(out, { '/site/news': { label: 'Announcements' } })
+  assert.equal(out.items, undefined)
+})
+
+test('the sectioned round trip is stable and renders what the editor showed', () => {
+  const tree = buildPublicNav(PUB, SECTIONED, { keepHidden: true })
+  const first = buildPublicNavOverrides(tree, PUB)
+  const second = buildPublicNavOverrides(buildPublicNav(PUB, first, { keepHidden: true }), PUB)
+  assert.deepEqual(second, first)
+  assert.deepEqual(shape(buildPublicNav(PUB, first)), [
+    'Home',
+    'News',
+    { 'The World': ['Champions', 'Guilds', 'Guide'] },
+    'About',
+  ])
+})
+
+test('deleting a section returns its entries to the top level, never deletes them', () => {
+  // The one destructive act this screen could commit, so it is locked here.
+  const tree = buildPublicNav(PUB, SECTIONED, { keepHidden: true })
+  const section = tree.find((n) => n.kind === 'section')
+  const flattened = [...tree.filter((n) => n.kind !== 'section'), ...section.items]
+  const out = buildPublicNavOverrides(flattened, PUB)
+  const rendered = buildPublicNav(PUB, out)
+  assert.equal(
+    rendered.some((n) => n.kind === 'section'),
+    false,
+  )
+  assert.deepEqual(shape(rendered), ['Home', 'News', 'About', 'Champions', 'Guilds', 'Guide'])
+})
+
+test('an override for a feature-gated item outside the palette survives a save', () => {
+  // §8.1 filters the editor to what this admin can see. The rows come from their
+  // palette, but membership is judged against the FULL coded nav — otherwise a
+  // row a shard feature hid from them is indistinguishable from a deleted route,
+  // and their save would silently reset it.
+  const palette = PUB.filter((i) => i.feature !== 'champs')
+  // The editor was opened on a nav that only hides champs — which their palette
+  // does not show them. `stored` additionally carries a label for a row they CAN
+  // see, and which they have since reset.
+  const tree = buildPublicNav(palette, { items: { '/site/champs': { hidden: true } } }, { keepHidden: true })
+  const stored = { items: { '/site/champs': { hidden: true }, '/site/news': { label: 'Old' } } }
+  const out = buildPublicNavOverrides(tree, PUB, stored)
+  assert.deepEqual(out['/site/champs'], { hidden: true }, 'carried: they could not see it')
+  assert.equal(out['/site/news'], undefined, 'not carried: their row is the authority for what they can see')
+})
+
+test('a stored entry for a route the code no longer declares is dropped on save', () => {
+  const tree = buildPublicNav(PUB, null, { keepHidden: true })
+  assert.deepEqual(buildPublicNavOverrides(tree, PUB, { items: { '/site/gone': { label: 'Ghost' } } }), {})
+})