feat(r2): C5 the lightbox, and the in-place client

- On a gallery booth the marks panel moves into a sticky verdict aside
  beside the set. The aside comes first in the document, so a narrow screen
  stacks the question above the work; grid areas place it on the right when
  wide. Nothing in an ordered collection moves. Boards are unchanged.
- The flag tray lists flagged items by tile number: the declared change
  from the panel list's (created, id). The standalone marks page keeps the
  list.
- Inline group headers are divs, never figure.item.
- Every mark-dependent element is a data-region: the verdict, each tile,
  the rail's filter counts. There is also a server-rendered status line.
- The in-place script (base.html) POSTs with an explicit JSON Accept, then
  on 204 swaps every region from a fresh GET. Live media and per-viewer view
  state are carried across the swap, so there is no layout jolt and no
  stopped track. It never re-POSTs: on failure it says so and reloads. Tile
  controls re-bind after a swap, and the grid cursor survives it.
- The `n` key opens the tile's closed note disclosure before focusing it.
- test_embed_browser's keyboard-flag test expected a navigation, which is
  the defect R2 removes. It is updated as declared in the contract, and
  tightened: a window marker must survive, proving no reload.

Browser tests: flag in place, with no reload and no scroll jump, and the
tile, tray and rail count all updated; and a failed save that reloads
without re-POSTing. Two mutations turn them red (no carry, no rail region).
700 passed.

booth/app.py

@@ -1139,6 +1139,12 @@ def create_app(
                     it["name"]: marks_for_target(marks, it["name"]) for it in gallery
                 },
                 "booth_marks": marks_for_target(marks, None),
+                # R2 C5: the flag tray — the flagged items in SET order, i.e.
+                # by ordinal, over the full gallery (a filter hides tiles, not
+                # judgments). Order is total with no tie-break: rels are unique.
+                "tray": [it for it in gallery if it["name"] in {
+                    m.target for m in marks if m.shape == "flag" and m.error is None}],
+                "ord_width": len(str(len(gallery))),
                 "uploaded": (booth / UPLOAD_MARKER).exists(),
                 # The same provenance line the index card carries. Deliberate:
                 # a booth URL handed to the operator lands HERE, never on the

booth/templates/_marks.html

@@ -32,7 +32,7 @@
       <span class="mark-state">⚠ broken</span>
       <span class="mark-id"><code>{{ a.id }}</code></span>
       <span class="board-spacer"></span>
-      <form class="mark-undo" method="post" action="/b/{{ name_url }}/unmark">
+      <form class="mark-undo" method="post" action="/b/{{ name_url }}/unmark" data-inplace>
         <input type="hidden" name="mark" value="{{ a.id }}">
         {% if marks_page %}<input type="hidden" name="back" value="marks">{% endif %}
         <button type="submit" class="mark-x" title="withdraw this mark">×</button>
@@ -75,7 +75,7 @@
       {% endif %}
       <details class="mark-formwrap"{% if not a.answer %} open{% endif %}>
         <summary class="mark-change">{% if a.answer %}change answer{% else %}answer{% endif %}</summary>
-        <form class="mark-form" method="post" action="/b/{{ name_url }}/answer">
+        <form class="mark-form" method="post" action="/b/{{ name_url }}/answer" data-inplace>
           {# The field is still `ask`: inline fragments in reports the operator
              has already published POST that name, and breaking every landed
              verbatim report to tidy a form field is not a trade worth making. #}
@@ -117,25 +117,26 @@
   </article>
 {% endfor %}
 
-{% for a in notes %}
-  <article class="mark mark-note" id="mark-{{ a.id }}">
+{# FLAGS come right after the picks. On the lightbox (`tray` defined) they
+   render as the TRAY: the flagged items in SET order — by tile number, the
+   declared R2 change from the click order below — each the original shown
+   small, blurred if the item is. The standalone marks page has no item
+   records, so it keeps the list, in `(created, id)` order. #}
+{% if tray is defined and tray %}
+  <article class="mark mark-flags" id="mark-flags">
     <header class="mark-head">
-      <span class="mark-state mark-state-note">note</span>
-      {% if a.target %}<span class="mark-target">on <a href="view?f={{ a.target|urlencode }}">{{ a.target }}</a></span>
-      {% else %}<span class="mark-target">on this booth</span>{% endif %}
-      <span class="board-spacer"></span>
-      <span class="mark-when">{{ a.created }}{% if a.by %} · {{ a.by }}{% endif %}</span>
-      <form class="mark-undo" method="post" action="/b/{{ name_url }}/unmark">
-        <input type="hidden" name="mark" value="{{ a.id }}">
-        {% if marks_page %}<input type="hidden" name="back" value="marks">{% endif %}
-        <button type="submit" class="mark-x" title="withdraw this note">×</button>
-      </form>
+      <span class="mark-state mark-state-flag">✔ flagged</span>
+      <span class="mark-id">{{ tray|length }} item{{ '' if tray|length == 1 else 's' }} · in set order</span>
     </header>
-    <pre class="mark-text">{{ a.text }}</pre>
+    <div class="tray">
+    {% for it in tray %}
+      <a class="tray-item{% if it.blurred %} is-blurred{% endif %}" href="view?f={{ it.url }}" title="{{ it.name }}">
+        {%- if it.kind == 'image' %}<img loading="lazy" src="{{ it.url }}" alt="">{% else %}<span class="tray-kind">{{ it.kind }}</span>{% endif -%}
+        <span class="tray-ord">#{{ "%0*d"|format(ord_width, it.ordinal) }}</span></a>
+    {% endfor %}
+    </div>
   </article>
-{% endfor %}
-
-{% if flags %}
+{% elif tray is not defined and flags %}
   <article class="mark mark-flags" id="mark-flags">
     <header class="mark-head">
       <span class="mark-state mark-state-flag">✔ flagged</span>
@@ -149,9 +150,28 @@
   </article>
 {% endif %}
 
+{% for a in notes %}
+  <article class="mark mark-note" id="mark-{{ a.id }}">
+    <header class="mark-head">
+      <span class="mark-state mark-state-note">note</span>
+      {% if a.target %}<span class="mark-target">on <a href="view?f={{ a.target|urlencode }}">{{ a.target }}</a></span>
+      {% else %}<span class="mark-target">on this booth</span>{% endif %}
+      <span class="board-spacer"></span>
+      <span class="mark-when">{{ a.created }}{% if a.by %} · {{ a.by }}{% endif %}</span>
+      <form class="mark-undo" method="post" action="/b/{{ name_url }}/unmark" data-inplace>
+        <input type="hidden" name="mark" value="{{ a.id }}">
+        {% if marks_page %}<input type="hidden" name="back" value="marks">{% endif %}
+        <button type="submit" class="mark-x" title="withdraw this note">×</button>
+      </form>
+    </header>
+    <pre class="mark-text">{{ a.text }}</pre>
+  </article>
+{% endfor %}
+
+
 {# The operator volunteering a remark, which before marks had no mechanism at
    all — this is the direction that was running through chat. #}
-<form class="mark-add" method="post" action="/b/{{ name_url }}/note">
+<form class="mark-add" method="post" action="/b/{{ name_url }}/note" data-inplace>
   {% if marks_page %}<input type="hidden" name="back" value="marks">{% endif %}
   <textarea name="text" rows="2" placeholder="a note on this booth, for the session that posted it"></textarea>
   <button type="submit">Add note</button>

booth/templates/base.html

@@ -419,6 +419,52 @@
   .mark-add textarea,.vaddnote textarea,.item-addnote textarea{flex:1;min-width:0}
   .mark-add{margin-top:2px}
 
+  /* ---- THE LIGHTBOX (R2 C5) ----------------------------------------------
+     The set on the left, the verdict on the right — placed by grid AREAS, not
+     by `order`: the aside is FIRST in the document so a narrow screen stacks
+     the question above the work without anything being reordered. The aside
+     is sticky and scrolls on its own, so the question stays beside tile 40. */
+  main:has(.lightbox){max-width:1560px}
+  .lightbox{display:grid;grid-template-columns:minmax(0,1fr) 360px;grid-template-areas:"set verdict";
+    gap:var(--space-6);align-items:start}
+  .lb-set{grid-area:set;min-width:0}
+  .verdict{grid-area:verdict;position:sticky;top:12px;max-height:calc(100vh - 24px);overflow:auto;
+    border:1px solid var(--border-default);border-radius:var(--radius-xl);background:var(--surface-base);
+    padding:12px;scrollbar-width:thin}
+  .verdict .marks{margin:0}
+  .verdict .mark-prompt{font-size:var(--size-body)}
+  .verdict .mark-add{flex-direction:column;align-items:stretch}
+  .verdict .mark-add button{align-self:flex-end}
+  @media (max-width:1000px){
+    .lightbox{grid-template-columns:1fr;grid-template-areas:"verdict" "set"}
+    .verdict{position:static;max-height:none}
+  }
+  /* the flag tray: the flagged items in set order, the originals shown small */
+  .tray{display:grid;grid-template-columns:repeat(auto-fill,minmax(64px,1fr));gap:6px;padding:12px 14px}
+  .tray-item{position:relative;display:block;aspect-ratio:1;border-radius:var(--radius-md);overflow:hidden;
+    border:1px solid var(--success);background:var(--surface-sunken)}
+  .tray-item img{width:100%;height:100%;object-fit:cover;display:block}
+  .tray-item.is-blurred img{filter:blur(8px)}
+  .tray-kind{display:flex;align-items:center;justify-content:center;height:100%;font-family:var(--font-mono);
+    font-size:var(--size-micro);text-transform:uppercase;color:var(--text-muted)}
+  .tray-ord{position:absolute;left:3px;bottom:3px;padding:1px 4px;border-radius:var(--radius-sm);
+    font:600 10px/1.2 var(--font-mono);background:oklch(0.17 0.01 250 / .85);color:oklch(0.91 0.008 216)}
+  .tray-item:hover{text-decoration:none;box-shadow:0 0 0 1px var(--success)}
+  /* ordinals: the item's number in the whole set (C1) */
+  .item > .ord{position:absolute;top:10px;left:10px;z-index:2;padding:3px 6px;border-radius:var(--radius-sm);
+    font:600 11px/1.2 var(--font-mono);background:oklch(0.17 0.01 250 / .82);color:oklch(0.91 0.008 216);
+    pointer-events:none}
+  .item.blurred > .ord{top:44px}
+  .doc-bar .ord{font:600 11px/1 var(--font-mono);color:var(--text-muted)}
+  /* the inline group header: spans the grid, is never a tile */
+  .grp-head{grid-column:1 / -1;display:flex;align-items:center;gap:8px;margin:8px 0 -4px;
+    font-family:var(--font-mono);font-size:var(--size-micro);letter-spacing:var(--tracking-caps);text-transform:uppercase}
+  .grp-head::after{content:"";flex:1;height:1px;background:var(--border-subtle)}
+  .grp-key{color:var(--text-heading);font-weight:600}
+  .grp-n{color:var(--text-muted)}
+  .status{margin:0 0 12px;padding:8px 12px;border-radius:var(--radius-md);background:var(--warning-soft);
+    color:var(--warning-text);font-size:var(--size-sm)}
+
   /* ---- the gallery ------------------------------------------------------ */
   /* THE RAIL. Sticky, opaque, and counted in mono because the counts are
      records. The active filter is a place you are, not an armed thing, so it
@@ -726,7 +772,89 @@
   <a class="brand" href="/"><span class="dot"></span><span class="name">The&nbsp;Booth</span></a>
   <span class="tagline">ephemeral media · auto-wipes {{ ttl_hours }}h · kept boards don't</span>
 </header>
-<main>{% block content %}{% endblock %}</main>
+<main>
+{# R2 C3: where the in-place script says it could not save in place. Server
+   rendered and empty, so the script only ever sets its text — it builds no
+   markup (INV-6). #}
+<p class="status" data-region="status" role="status" aria-live="polite" hidden></p>
+{% block content %}{% endblock %}</main>
+<script>
+  /* IN-PLACE JUDGMENT (R2 C3). A form marked `data-inplace` is POSTed in the
+     background with `Accept: application/json`; on 204 the page is re-fetched
+     and every server-rendered `data-region` is swapped for its fresh copy. The
+     SERVER RENDERS EVERY STATE; this only places it — no markup is built here
+     (INV-6), for U3's reason: a second renderer in JavaScript would be the same
+     bug in a new language.
+
+     It NEVER RE-POSTS. After a lost response the write may already have
+     landed, and a retry would duplicate a note or re-date an answer. On any
+     failure it says so and reloads with a GET, so what shows is the server's
+     truth. With scripts off, every one of these is a plain form and a 303. */
+  (function () {
+    if (!window.fetch || !window.DOMParser || !window.URLSearchParams) return;
+    function say(text) {
+      var st = document.querySelector('[data-region="status"]');
+      if (st) { st.textContent = text; st.hidden = false; }
+    }
+    /* What the server cannot render, carried from the old node to the new:
+       live MEDIA elements whose src did not change (a playing track keeps
+       playing, a decoded image does not collapse to zero height and jolt the
+       page), and the per-viewer view state a reload would have reset anyway
+       but an in-place save must not — a revealed blur, a closed doc. */
+    function carry(oldEl, newEl) {
+      var olds = [].slice.call(oldEl.querySelectorAll('img[src], video[src], audio[src]'));
+      newEl.querySelectorAll('img[src], video[src], audio[src]').forEach(function (m) {
+        for (var i = 0; i < olds.length; i++) {
+          var o = olds[i];
+          if (o && o.tagName === m.tagName && o.getAttribute('src') === m.getAttribute('src')) {
+            o.className = m.className;   /* the SERVER decides blur/state classes */
+            m.replaceWith(o); olds[i] = null; break;
+          }
+        }
+      });
+      ['revealed', 'is-closed'].forEach(function (c) {
+        if (oldEl.classList.contains(c)) newEl.classList.add(c);
+      });
+    }
+    function swap(html) {
+      var fresh = new DOMParser().parseFromString(html, 'text/html');
+      document.querySelectorAll('[data-region]').forEach(function (el) {
+        var id = el.getAttribute('data-region');
+        if (id === 'status') return;
+        var next = null;
+        fresh.querySelectorAll('[data-region]').forEach(function (cand) {
+          if (!next && cand.getAttribute('data-region') === id) next = cand;
+        });
+        if (next) {
+          var node = document.importNode(next, true);
+          carry(el, node);
+          el.replaceWith(node);
+        }
+      });
+      document.dispatchEvent(new CustomEvent('booth:swapped'));
+    }
+    document.addEventListener('submit', function (ev) {
+      var form = ev.target;
+      if (!form.matches || !form.matches('form[data-inplace]') || ev.defaultPrevented) return;
+      ev.preventDefault();
+      var data = new FormData(form);
+      if (ev.submitter && ev.submitter.name) data.append(ev.submitter.name, ev.submitter.value);
+      fetch(form.action, {
+        method: 'POST', body: new URLSearchParams(data),
+        headers: {'Accept': 'application/json'}, credentials: 'same-origin'
+      }).then(function (r) {
+        if (r.status !== 204) throw new Error('status ' + r.status);
+        return fetch(window.location.href, {headers: {'Accept': 'text/html'}, credentials: 'same-origin'});
+      }).then(function (r) {
+        if (!r.ok) throw new Error('status ' + r.status);
+        return r.text();
+      }).then(swap).catch(function () {
+        say('Could not save in place — reloading to show what was saved.');
+        window.location.reload();
+      });
+    });
+  })();
+</script>
 <script>
   /* The sticky rail's real height, published as --rail-h for .item's
      scroll-margin. ADDITIVE: with JS off the static fallback applies, and a

booth/templates/booth.html

@@ -20,7 +20,7 @@
    one definition. `marks` here is THIS item's marks, from item_marks. #}
 {% macro markcontrols(name_url, it, marks, cls='') -%}
   {% set flagged = marks | selectattr('shape', 'equalto', 'flag') | list | length > 0 %}
-  <form class="flagtoggle {{ cls }}" method="post" action="/b/{{ name_url }}/flag">
+  <form class="flagtoggle {{ cls }}" method="post" action="/b/{{ name_url }}/flag" data-inplace>
     <input type="hidden" name="target" value="{{ it.name }}">
     <input type="hidden" name="on" value="{{ '0' if flagged else '1' }}">
     <button title="{{ 'un-flag this item' if flagged else 'flag this one — the session that posted it can read the selection' }}"
@@ -37,7 +37,7 @@
   {% for m in marks if m.shape == 'note' %}
     <div class="item-note" id="mark-{{ m.id }}">
       <pre>{{ m.text }}</pre>
-      <form method="post" action="/b/{{ name_url }}/unmark">
+      <form method="post" action="/b/{{ name_url }}/unmark" data-inplace>
         <input type="hidden" name="mark" value="{{ m.id }}">
         <button class="mark-x" title="withdraw this note">×</button>
       </form>
@@ -45,7 +45,7 @@
   {% endfor %}
   <details class="item-addnote">
     <summary>+ note</summary>
-    <form method="post" action="/b/{{ name_url }}/note">
+    <form method="post" action="/b/{{ name_url }}/note" data-inplace>
       <input type="hidden" name="target" value="{{ it.name }}">
       <textarea name="text" rows="2" placeholder="a note on this item"></textarea>
       <button type="submit">Add</button>
@@ -116,7 +116,11 @@
    a gallery, and the add-note control would be noise on it — but the
    suppression was unconditional, so a pick declared on a booth that happens to
    carry a links.md had no form to answer it and nothing said so. #}
-{% if marks or not board %}
+{# R2 C5: on a GALLERY booth the panel moves into the verdict aside beside the
+   set (below). It renders up here only where there is no set to sit beside —
+   a board, or a booth with marks and nothing to show. #}
+{% set lightbox = all_items and not board %}
+{% if (marks or not board) and not lightbox %}
   {% include "_marks.html" %}
 {% endif %}
 
@@ -257,6 +261,16 @@
 {% if not all_items and not board and not marks %}
   <div class="empty">This booth is empty.</div>
 {% elif all_items %}
+  {# THE LIGHTBOX (R2 C5). The verdict aside comes FIRST in the document and the
+     set second: on a narrow screen that is the stacking the contract wants
+     (the question above the work), and on a wide one the grid areas in
+     base.html put the aside on the right. Placement, not order — nothing in an
+     ordered collection moves. #}
+  <div class="lightbox">
+  <aside class="verdict" data-region="verdict" aria-label="your verdict">
+    {% include "_marks.html" %}
+  </aside>
+  <div class="lb-set">
   {# `elif items` and not a bare `else`: a board booth has NO gallery items (its
      links.md is rendered as the board above and filtered out), so a plain else
      would emit an empty <div class="gallery"> under the board. #}
@@ -273,7 +287,7 @@
      is therefore the whole guard; the two degenerate cases (one group for
      everything, one group per item) are decided in Python, where they can be
      measured, rather than by a count in a template. #}
-  <div class="rail">
+  <div class="rail" data-region="filters">
     <span class="rail-total">{{ rail.total }} item{{ '' if rail.total == 1 else 's' }}</span>
     {% for f in rail.counts %}
       <a class="rail-f{% if f.key == filter %} on{% endif %}"
@@ -299,14 +313,21 @@
   <div class="empty">No items match the <b>{{ filter }}</b> filter.
     <a href="/b/{{ name_url }}/">show all {{ rail.total }}</a></div>
   {% endif %}
+  {% set group_n = {} %}{% for g in rail.groups %}{% set _ = group_n.update({g.key: g.n}) %}{% endfor %}
   <div class="gallery" id="grid" tabindex="-1">
     {% for it in items %}
+    {# R2 C5: an inline header before each group's FIRST tile, only when the
+       rail thinks grouping is informative. A <div> spanning the grid, never a
+       figure.item, so the keyboard and the order check are blind to it. #}
+    {% if rail.groups and it.group and (loop.first or loop.previtem.group != it.group) %}
+      <div class="grp-head" aria-hidden="true"><span class="grp-key">{{ it.group }}</span> <span class="grp-n">{{ group_n.get(it.group, '') }}</span></div>
+    {% endif %}
     {% if it.doc and it.rendered is not none %}
       {# Docs render INLINE, collapsible, and closable — not a link to a
          separate page. <details open> is native collapse (works with JS off);
          the ✕ hides the item for the session (JS, progressive enhancement).
          The item spans the full grid width so prose has room to read. #}
-      <figure class="item item-doc{% if it.blurred %} blurred{% endif %}" data-name="{{ it.name }}" data-item="{{ it.name }}" id="item-{{ it.url }}">
+      <figure class="item item-doc{% if it.blurred %} blurred{% endif %}" data-name="{{ it.name }}" data-item="{{ it.name }}" id="item-{{ it.url }}" data-region="item-{{ it.url }}">
         {% if it.blurred %}
         {# Inline docs need this MORE than images, not less: a rendered doc puts
            its text straight on the page, so "blur the picture" logic that skips
@@ -340,7 +361,7 @@
         </details>
       </figure>
     {% else %}
-    <figure class="item item-{{ it.kind }}{% if it.blurred %} blurred{% endif %}{% if item_marks.get(it.name, []) | selectattr('shape', 'equalto', 'flag') | list %} is-flagged{% endif %}" data-item="{{ it.name }}" id="item-{{ it.url }}">
+    <figure class="item item-{{ it.kind }}{% if it.blurred %} blurred{% endif %}{% if item_marks.get(it.name, []) | selectattr('shape', 'equalto', 'flag') | list %} is-flagged{% endif %}" data-item="{{ it.name }}" id="item-{{ it.url }}" data-region="item-{{ it.url }}">
       {{ ordinal(it) }}
       {% if it.blurred %}
       {# Click-to-reveal is per-viewer and client-side: nothing is persisted, so
@@ -385,6 +406,8 @@
     {% endif %}
     {% endfor %}
   </div>
+  </div>{# .lb-set #}
+  </div>{# .lightbox #}
 {% endif %}
 
 {% if items %}
@@ -455,6 +478,11 @@
          Found by the heid bug-hunt panel (hulda), 2026-09-22. */
       case 'f': click('.flagtoggle button'); e.preventDefault(); break;
       case 'n': var el = current();
+                /* The add-note field lives in a closed <details> (270 tiles
+                   must not each carry an open textarea); a closed one cannot
+                   take focus, so open it first. */
+                var d = el && el.querySelector('details.item-addnote');
+                if (d) d.open = true;
                 if (el) { var f = el.querySelector('input[type=text], textarea');
                           if (f) { f.focus(); e.preventDefault(); } }
                 break;
@@ -464,6 +492,13 @@
         at = -1; break;
     }
   });
+  /* R2 C3: an in-place save swaps the tiles for fresh server-rendered ones,
+     and the cursor is client state the server cannot render. Put it back on
+     the same position — the order did not change, only the judgment. */
+  document.addEventListener('booth:swapped', function () {
+    if (at < 0) return;
+    tiles().forEach(function (el, j) { el.classList.toggle('is-cursor', j === at); });
+  });
 })();
 </script>
 {% endif %}
@@ -500,17 +535,30 @@
     });
   })();
 
-  /* Inline-doc ✕ closes (hides) a rendered doc for the session. The button sits
+  /* TILE CONTROLS, bound per node and RE-BOUND after an in-place swap (R2 C3):
+     the swap puts fresh server-rendered tiles in the page, and a handler bound
+     to the node it replaced goes with that node. `__bound` keeps a node from
+     being bound twice.
+
+     Inline-doc ✕ closes (hides) a rendered doc for the session. The button sits
      inside <summary>, so without this its click would just toggle the <details>
      open/closed — stopPropagation + preventDefault make ✕ mean "close", not
      "collapse". Collapse stays available via the rest of the summary bar. With
-     JS off the button is inert and collapse via <details> still works. */
-  (function () {
+     JS off the button is inert and collapse via <details> still works.
+
+     Blur reveal. WARNING: this handler previously sat after the content block's
+     closing tag, which in a child template Jinja DISCARDS — the button rendered
+     and did nothing, and two commits plus a README claimed click-to-reveal
+     worked. Anything that must reach the page belongs inside the content
+     block. Per-viewer and never persisted: a reload re-hides. */
+  function bindTiles() {
+    function once(el) { if (el.__bound) return false; el.__bound = true; return true; }
     /* A form inside <summary> would otherwise collapse the doc on submit. */
-    document.querySelectorAll('.doc-bar .blurtoggle').forEach(function (f) {
-      f.addEventListener('click', function (ev) { ev.stopPropagation(); });
+    document.querySelectorAll('.doc-bar .blurtoggle, .doc-bar .flagtoggle').forEach(function (f) {
+      if (once(f)) f.addEventListener('click', function (ev) { ev.stopPropagation(); });
     });
     document.querySelectorAll('.doc-close').forEach(function (btn) {
+      if (!once(btn)) return;
       btn.addEventListener('click', function (ev) {
         ev.preventDefault();
         ev.stopPropagation();
@@ -518,80 +566,20 @@
         if (item) item.classList.add('is-closed');
       });
     });
-  })();
-
-  /* Link-board multi-select. PROGRESSIVE ENHANCEMENT: the checkboxes, the per-row
-     × / ★, and the bulk 🗑 all submit as plain form POSTs with JS off — this only
-     adds select-all, a live count, and disabling 🗑 when nothing is ticked. The
-     per-row × confirm reads desc/url from data-* attributes rather than being
-     interpolated into an inline handler, so an arbitrary agent-posted description
-     (quotes, newlines) can never break out into the page's JS. */
-  (function () {
-    var form = document.getElementById('boardform');
-    if (!form) return;
-    var boxes = Array.prototype.slice.call(form.querySelectorAll('.board-check'));
-    var selall = document.getElementById('board-selall');
-    var delBtn = document.getElementById('board-del-sel');
-    var countEl = document.getElementById('board-selcount');
-
-    function selected() { return boxes.filter(function (b) { return b.checked; }); }
-    function refresh() {
-      var n = selected().length;
-      if (countEl) countEl.textContent = n;
-      if (delBtn) delBtn.disabled = n === 0;
-      if (selall) {
-        selall.checked = n > 0 && n === boxes.length;
-        selall.indeterminate = n > 0 && n < boxes.length;
-      }
-    }
-    if (selall) {
-      selall.addEventListener('change', function () {
-        boxes.forEach(function (b) { b.checked = selall.checked; });
-        refresh();
-      });
-    }
-    boxes.forEach(function (b) { b.addEventListener('change', refresh); });
-
-    // Bulk delete: confirm with the count. Attached to the button (not the form's
-    // submit) so the per-row × / ★ submits — which share this form — are unaffected.
-    if (delBtn) {
-      delBtn.addEventListener('click', function (ev) {
-        var n = selected().length;
-        if (n === 0) { ev.preventDefault(); return; }
-        if (!confirm('Delete ' + n + ' selected link' + (n === 1 ? '' : 's') + '?\n\nThe rest of the board is untouched.')) {
-          ev.preventDefault();
-        }
-      });
-    }
-
-    form.querySelectorAll('.board-rm-btn').forEach(function (btn) {
-      btn.addEventListener('click', function (ev) {
-        var d = btn.getAttribute('data-desc') || '';
-        var u = btn.getAttribute('data-url') || '';
-        if (!confirm('Remove this link?\n\n' + d + '\n' + u + '\n\nThe rest of the board is untouched.')) {
-          ev.preventDefault();
-        }
-      });
-    });
-
-    refresh();
-  })();
-
-  /* Blur reveal. WARNING: this handler previously sat after the content
-     block's closing tag, which in a
-     child template Jinja DISCARDS — the button rendered and did nothing, and
-     two commits plus a README claimed click-to-reveal worked. Anything that
-     must reach the page belongs inside the content block. Verified now by
-     grepping the SERVED html for this function, not the template for the text.
-     Per-viewer and never persisted: a reload re-hides. */
-  document.querySelectorAll('.item.blurred .reveal').forEach(function (btn) {
-    btn.addEventListener('click', function (ev) {
-      ev.preventDefault();
-      ev.stopPropagation();
+    document.querySelectorAll('.item.blurred .reveal').forEach(function (btn) {
       var fig = btn.closest('.item');
-      var on = fig.classList.toggle('revealed');
-      btn.textContent = on ? '🙈 hide' : '👁 reveal';
+      /* a swap carries `revealed` across (base.html); the label follows it */
+      btn.textContent = fig.classList.contains('revealed') ? '🙈 hide' : '👁 reveal';
+      if (!once(btn)) return;
+      btn.addEventListener('click', function (ev) {
+        ev.preventDefault();
+        ev.stopPropagation();
+        var on = fig.classList.toggle('revealed');
+        btn.textContent = on ? '🙈 hide' : '👁 reveal';
+      });
     });
-  });
+  }
+  bindTiles();
+  document.addEventListener('booth:swapped', bindTiles);
 </script>
 {% endblock %}

docs/contracts/r2_flow.contract.md

@@ -33,6 +33,7 @@ touches:
   - "booth/static/embed.js (NOT TOUCHED — the verbatim path keeps its author's layout; requirement 6)"
   - "tests/test_booth.py (THREE assertions change, all in test_index_separates_kept_from_ephemeral: L785-786, the kept-lane presence pair, and L789, kept-before-ephemeral. L810-811, the absence pair, survive unchanged. See 'Assertions that change')"
   - "tests/test_flow.py (NEW)"
+  - "tests/test_embed_browser.py (ONE test changes: test_the_keyboard_flag_actually_submits expected a navigation, which is the defect R2 removes. See 'Assertions that change')"
 assumptions:
   - "ONE VIEWER. `.seen` records what has been seen at full size, not WHO saw it. ROADMAP parks 'per-viewer state (who has seen what)' on the one-viewer premise; this contract keeps that premise and does not reopen the parked item."
   - "EVERY JUDGMENT WORKS WITH JAVASCRIPT OFF. Each control stays a plain <form method=post>. The in-place behaviour is additive and falls back to today's 303."
@@ -389,6 +390,7 @@ This applies to image, video and audio items. Docs keep `doc.html`.
 |---|---|---|---|
 | test_booth.py L785 | `class="grid kept-grid"` present when a booth is kept | absent; the kept booth appears in its Desk section with the `kept` lifetime line | requirement 8: the lanes sort nothing |
 | test_booth.py L786 | `class="card card-kept"` present | replaced by the row carrying `data-kept="1"` | same |
+| test_embed_browser.py `test_the_keyboard_flag_actually_submits` | pressing `f` causes a NAVIGATION (`page.expect_navigation()`), and the reloaded page shows the flag | pressing `f` causes NO navigation; the flag comes back from the server into the swapped tile. A window marker set before the keypress must survive, proving no reload | requirement 3: the reload IS the defect. The test's real claim — the key reaches the server and the server's state comes back — is kept, and asserted more strictly |
 | test_booth.py L789 | the kept booth renders BEFORE the ephemeral one (`html.index("links") < html.index("scratch")`) | replaced by the Desk's stated order (needs → new → everything, each with its own key) | the kept-first order was the lane's; with no lane there is no kept-first rule, and a second hidden ordering would break INV-2 |
 | test_booth.py L810-811 | lane absent when nothing is kept | these two SURVIVE unchanged (they assert absence and stay true) | — |
 

tests/test_embed_browser.py

@@ -592,17 +592,26 @@ def test_the_keyboard_flag_actually_submits(browser, live):
     a hidden input does not submit its form. The shortcut never worked while
     still swallowing the keystroke.
 
-    Asserted end to end: press f, and the flag must come back from the server
-    on the reloaded page."""
+    Asserted end to end: press f, and the flag must come back from the server.
+
+    R2 C3 (docs/contracts/r2_flow.contract.md, "Assertions that change"): this
+    used to expect a NAVIGATION — the flag form POSTed and the page reloaded.
+    That reload is the defect R2 removes. The claim that matters is kept and
+    tightened: the flag must come back from the SERVER (the swapped tile is
+    server-rendered), and a marker set on the window before the keypress must
+    survive, which a reload would wipe."""
     base, root = live
     _gallery(root)
     page = browser.new_page()
     page.goto(f"{base}/b/g/", wait_until="networkidle")
+    page.evaluate("window.__noReload = 1")
 
     page.keyboard.press("ArrowRight")   # cursor onto the first tile
-    with page.expect_navigation():      # the flag form POSTs and redirects back
-        page.keyboard.press("f")
+    page.keyboard.press("f")
+    page.wait_for_selector("figure.item.is-flagged", timeout=10000)
     flagged = page.locator("figure.item.is-flagged").count()
+    survived = page.evaluate("window.__noReload === 1")
     page.close()
 
     assert flagged == 1, f"the f key flagged {flagged} items, expected 1"
+    assert survived, "the flag reloaded the page; in-place judgment must not"

tests/test_flow.py

@@ -407,3 +407,72 @@ def test_a_booth_without_images_shows_its_kind_instead(tmp_path):
     _booth(tmp_path, "songs", {"a.mp3": b"ID3", "b.mp3": b"ID3"})
     row = re.search(r'data-booth="songs".*?</article>', _client(tmp_path).get("/").text, re.S).group(0)
     assert "♪ audio" in row and "<img" not in row
+
+
+# ---- C5: the lightbox ---------------------------------------------------------
+
+def _region(body: str, rid: str) -> str:
+    m = re.search(r'<(\w+)[^>]*data-region="%s"[^>]*>' % re.escape(rid), body)
+    assert m, f"no region {rid}"
+    tag = m.group(1)
+    # regions in these templates do not nest a same-named tag inside themselves
+    end = body.index(f"</{tag}>", m.end())
+    return body[m.start():end]
+
+
+def test_the_verdict_sits_beside_the_set_on_a_gallery_booth(tmp_path):
+    """The tracer for C5: the open question, the flags and the notes live in
+    one aside next to the grid — not in a panel above it that scrolls away."""
+    from booth.marks import declare_pick
+    b = _booth(tmp_path, "g", {"a.png": PNG, "b.png": PNG})
+    declare_pick(b, "q", {"prompt": "Which one?", "options": ["a", "b"]})
+    body = _client(tmp_path).get("/b/g/").text
+    aside = _region(body, "verdict")
+    assert aside.startswith('<aside class="verdict"')
+    assert 'action="/b/g/answer"' in aside and "Which one?" in aside
+    assert body.count('action="/b/g/answer"') == 1, "the pick renders once, in the aside"
+    assert 'class="lightbox"' in body and 'id="grid"' in body
+
+
+def test_the_flag_tray_lists_flags_by_tile_number_not_by_click_order(tmp_path):
+    """Flag #3 first, then #1: the tray reads #1, #3. Today's panel list is in
+    click order `(created, id)`; the tray is the SET's order, the declared
+    change. Each entry is the original shown small, blurred if the item is."""
+    from booth.app import set_blurred
+    b = _booth(tmp_path, "g", {"a.png": PNG, "b.png": PNG, "c.png": PNG})
+    set_flag(b, "c.png", True)
+    time.sleep(0.01)
+    set_flag(b, "a.png", True)
+    set_blurred(b, "a.png", True)
+    aside = _region(_client(tmp_path).get("/b/g/").text, "verdict")
+    tray = re.findall(r'<a class="tray-item( is-blurred)?" href="view\?f=([^"]+)"[^>]*>.*?#(\d+)<', aside, re.S)
+    assert tray == [(" is-blurred", "a.png", "1"), ("", "c.png", "3")]
+
+
+def test_groups_get_an_inline_header_that_is_not_a_tile(tmp_path):
+    """When the rail finds grouping informative, each group's first tile is
+    preceded by a header — a div, never a figure.item, so the tile sequence
+    the keyboard and the order check walk is exactly the items."""
+    files = {f"{g}-{n}.png": PNG for g in ("aa", "bb", "cc") for n in (1, 2)}
+    _booth(tmp_path, "g", files)
+    body = _client(tmp_path).get("/b/g/").text
+    grid = body[body.index('id="grid"'):]
+    heads = re.findall(r'<div class="grp-head"[^>]*><span class="grp-key">(\w+)</span> <span class="grp-n">(\d+)</span>', grid)
+    assert heads == [("aa", "2"), ("bb", "2"), ("cc", "2")]
+    assert len(re.findall(r'<figure class="item', grid)) == 6
+    # and no header at all when grouping is not informative
+    _booth(tmp_path, "flat", {f"DSC{n}.jpg": PNG for n in range(4)})
+    assert 'class="grp-head"' not in _client(tmp_path).get("/b/flat/").text
+
+
+def test_every_mark_dependent_element_is_a_swappable_region(tmp_path):
+    """The in-place script replaces regions by id; a stale flag count or tile
+    after an in-place flag is the failure this pins."""
+    b = _booth(tmp_path, "g", {"a b.png": PNG, "c.png": PNG})
+    body = _client(tmp_path).get("/b/g/").text
+    for rid in ("verdict", "filters", "item-a%20b.png", "item-c.png", "status"):
+        assert f'data-region="{rid}"' in body, rid
+    # the standing board has no lightbox and therefore no verdict aside
+    _booth(tmp_path, "links", {"links.md": b"- [x](http://x/) <sub>\xc2\xb7 a \xc2\xb7 2026-09-01 10:00</sub>\n"})
+    board = _client(tmp_path).get("/b/links/").text
+    assert 'data-region="verdict"' not in board and 'class="lightbox"' not in board

tests/test_flow_browser.py

@@ -0,0 +1,114 @@
+"""R2 C3/C5/C6 in a real DOM: in-place judgment.
+
+A TestClient can prove what the server answers. It cannot prove that a flag
+made in the page lands without a reload, that the regions come back fresh, or
+that a failure never re-POSTs. So: a real uvicorn, a real Chromium — the same
+harness as test_embed_browser.py, and like it this SKIPS, never fails, when no
+browser is available.
+"""
+import pathlib
+import socket
+import sys
+import threading
+import time
+
+import pytest
+
+sys.path.insert(0, str(pathlib.Path(__file__).parent.parent))
+
+from booth.app import create_app  # noqa: E402
+
+playwright_api = pytest.importorskip("playwright.sync_api", reason="playwright is not installed")
+
+PNG = b"\x89PNG\r\n\x1a\n"
+
+
+@pytest.fixture(scope="module")
+def browser():
+    with playwright_api.sync_playwright() as pw:
+        try:
+            b = pw.chromium.launch()
+        except Exception as exc:  # noqa: BLE001 - any launch failure is a skip
+            pytest.skip(f"no usable chromium: {exc}")
+        yield b
+        b.close()
+
+
+@pytest.fixture
+def live(tmp_path):
+    import uvicorn
+
+    sock = socket.socket()
+    sock.bind(("127.0.0.1", 0))
+    port = sock.getsockname()[1]
+    sock.close()
+    app = create_app(tmp_path, ttl_hours=24, start_sweeper=False)
+    server = uvicorn.Server(uvicorn.Config(app, host="127.0.0.1", port=port, log_level="error"))
+    thread = threading.Thread(target=server.run, daemon=True)
+    thread.start()
+    deadline = time.time() + 10
+    while not server.started and time.time() < deadline:
+        time.sleep(0.02)
+    if not server.started:
+        pytest.skip("uvicorn did not come up")
+    try:
+        yield f"http://127.0.0.1:{port}", tmp_path
+    finally:
+        server.should_exit = True
+        thread.join(timeout=10)
+
+
+def _set(root: pathlib.Path, n: int = 30) -> pathlib.Path:
+    b = root / "g"
+    b.mkdir()
+    for i in range(1, n + 1):
+        (b / f"{i:02d}.png").write_bytes(PNG)
+    return b
+
+
+def test_a_flag_lands_in_place_and_every_region_catches_up(browser, live):
+    """Click a tile's flag far down the page: no reload, the scroll position
+    holds, and the tile, the tray and the rail's count all show the server's
+    new state — the three places one flag appears."""
+    base, root = live
+    _set(root)
+    posts = []
+    page = browser.new_page(viewport={"width": 1400, "height": 800})
+    page.on("request", lambda r: posts.append(r.url) if r.method == "POST" else None)
+    page.goto(f"{base}/b/g/", wait_until="networkidle")
+    page.evaluate("window.__noReload = 1")
+    tile = page.locator('figure.item[data-item="24.png"]')
+    tile.scroll_into_view_if_needed()
+    y = page.evaluate("window.scrollY")
+    tile.locator(".flagtoggle button").click()
+    page.wait_for_selector('figure.item.is-flagged[data-item="24.png"]', timeout=10000)
+    state = page.evaluate("""() => ({
+        reload: window.__noReload !== 1,
+        y: window.scrollY,
+        tray: [...document.querySelectorAll('.tray .tray-ord')].map(e => e.textContent),
+        count: document.querySelector('.rail-f[data-filter="flagged"] b').textContent,
+    })""")
+    page.close()
+    assert not state["reload"]
+    assert abs(state["y"] - y) < 4, "the page must not jump"
+    assert state["tray"] == ["#24"]
+    assert state["count"] == "1"
+    assert len(posts) == 1
+
+
+def test_a_failed_save_says_so_reloads_and_never_re_posts(browser, live):
+    """The server refuses the write (the marks file went bad under the page).
+    The script must not retry — a retry after a lost response would duplicate
+    the judgment — it says so and reloads to show the server's truth."""
+    base, root = live
+    b = _set(root, 3)
+    posts = []
+    page = browser.new_page()
+    page.on("request", lambda r: posts.append(r.url) if r.method == "POST" else None)
+    page.goto(f"{base}/b/g/", wait_until="networkidle")
+    (b / ".marks.json").write_text("{damaged")
+    with page.expect_navigation(timeout=10000):
+        page.locator('figure.item[data-item="01.png"] .flagtoggle button').click()
+    page.wait_for_load_state("networkidle")
+    page.close()
+    assert len(posts) == 1, f"re-POSTed: {posts}"