A time in no particular zone, and a preview missing what it previews

The first audit pass: everything from 0.8.1 to 0.9.8 read as a whole rather
than one feature at a time, starting with what a model is actually told.

Four of these had shipped as correct. The date line carried a timezone
variable that resolves to nothing until somebody chooses one -- so every
default account was told times were "in  unless they say otherwise", while
two comments asserted the line disappeared instead. The prompt preview
built its variables without a chat, which is what eleven fragments are
gated on, so the whole agent surface was absent from it whatever was
ticked. Plan mode was instructed to keep its plan current with a tool that
mode withdraws. And knowledge_get returned a document whole where every
sibling reader caps and says so, its description promising exactly that.

The subagent guidance was wrong in both directions at once: it denied a
documented parameter and named seven of twenty-three allowed commands.
Both halves are pinned by tests against the real list and the real schema
now, because prose and a constant drift the moment one is edited alone.

docs/notes/audit-0.9.md carries the findings that are not fixed here, with
why -- the ones whose fix would change what a feature does are the user's
call, not this pass's.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/web/templates/admin/prompts.html

@@ -82,6 +82,33 @@
       <input class="input" id="preview-documents" name="preview_documents"
              value="{{ sample_documents }}">
     </div>
+    {#
+      The two axes a tool family cannot reach. Without them every fragment
+      gated on a chat -- the whole agent surface, both scheduling fragments and
+      the helper warning -- was missing from the preview whatever was ticked
+      below, because the preview passes no Chat and those variables are only
+      filled when there is one.
+    #}
+    <div class="field">
+      <label class="field__label" for="preview-situation">This chat is</label>
+      <select class="select" id="preview-situation" name="preview_situation">
+        {% for value, label in situations %}
+        <option value="{{ value }}">{{ label }}</option>
+        {% endfor %}
+      </select>
+    </div>
+    <div class="field">
+      <label class="field__label" for="preview-mode">Agent mode</label>
+      <select class="select" id="preview-mode" name="preview_mode">
+        {% for value, label in modes.items() %}
+        <option value="{{ value }}"{{ ' selected' if value == 'edit' }}>{{ label }}</option>
+        {% endfor %}
+      </select>
+      <p class="field__hint">
+        Only reaches the prompt with <code>agent</code> ticked below. The
+        machine, directory and plan shown there are samples.
+      </p>
+    </div>
     <div class="field">
       <span class="field__label">Tools offered</span>
       {% for family in families %}