Open the request in a window, and name the endpoint

The preview was a 10rem box in the corner of a docked panel: enough to
see that there is JSON, not enough to read it. It opens as a modal with
the endpoint line and a copy button (with an execCommand fallback,
since navigator.clipboard is undefined on this app's plain-http origin).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ui/src/components/OperationPanel.jsx

@@ -1219,18 +1219,69 @@ function ApplyModeChooser({ op, applyMode, setApplyMode, count }) {
   return <Segmented value={applyMode} onChange={setApplyMode} options={options} />
 }
 
-function RequestPreview({ payload }) {
+// The request as it will be sent. A 40rem-tall box in the corner of a docked
+// panel could show about six lines of it, which is enough to see that there is
+// JSON and not enough to read it, so it opens as a window of its own.
+//
+// It is the payload itself -- `submitOp` posts exactly what `buildPayload`
+// returns, with no last-minute additions -- so what is shown here is what goes
+// over the wire, minus the two things the browser never sees: the session that
+// names `pf_user`, and the territory predicate the server ANDs on.
+function RequestPreview({ payload, op, versionId }) {
   const [open, setOpen] = useState(false)
+  const [copied, setCopied] = useState(false)
+
+  useEffect(() => {
+    if (!open) return
+    const onKey = (e) => { if (e.key === 'Escape') setOpen(false) }
+    window.addEventListener('keydown', onKey)
+    return () => window.removeEventListener('keydown', onKey)
+  }, [open])
+
   if (!payload) return null
+  const text = JSON.stringify(payload, null, 2)
+  const line = `POST /api/versions/${versionId}/${op}`
+
+  // navigator.clipboard is undefined on a plain-http origin, which this app is
+  // served over, so the fallback is not decoration.
+  const copy = async () => {
+    try {
+      if (navigator.clipboard?.writeText) await navigator.clipboard.writeText(text)
+      else {
+        const ta = document.createElement('textarea')
+        ta.value = text
+        ta.style.position = 'fixed'; ta.style.opacity = '0'
+        document.body.appendChild(ta); ta.select()
+        document.execCommand('copy')
+        document.body.removeChild(ta)
+      }
+      setCopied(true); setTimeout(() => setCopied(false), 1500)
+    } catch { /* leave the text on screen to select by hand */ }
+  }
+
   return (
     <div>
-      <TextButton onClick={() => setOpen(o => !o)}>
-        {open ? '▾' : '▸'} request
-      </TextButton>
+      <TextButton onClick={() => setOpen(true)}>▸ request</TextButton>
+
       {open && (
-        <pre className="mt-1 font-mono text-gray-600 bg-gray-50 border border-gray-100 rounded p-2 overflow-auto max-h-40 leading-relaxed">
-          {JSON.stringify(payload, null, 2)}
-        </pre>
+        <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/40"
+             onClick={() => setOpen(false)}>
+          <div className="bg-white rounded-lg shadow-xl w-full max-w-3xl mx-4 flex flex-col max-h-[85vh]"
+               onClick={e => e.stopPropagation()}>
+            <div className="flex items-center gap-3 px-5 py-3 border-b border-gray-200 shrink-0">
+              <span className="font-medium text-gray-700 text-sm">Request</span>
+              <span className="font-mono text-gray-600 text-xs truncate" title={line}>{line}</span>
+              <div className="ml-auto flex items-center gap-3">
+                <TextButton onClick={copy}>{copied ? 'copied' : 'copy'}</TextButton>
+                <button onClick={() => setOpen(false)}
+                        className="text-gray-600 hover:text-gray-800 text-lg leading-none">×</button>
+              </div>
+            </div>
+            <pre className="overflow-auto p-5 font-mono text-gray-700 text-xs leading-relaxed whitespace-pre">
+              {text}
+            </pre>
+          </div>
+        </div>
       )}
     </div>
   )
@@ -1408,7 +1459,7 @@ export default function OperationPanel({
         {opBusy && <span className="text-gray-500 leading-snug">writing rows…</span>}
       </div>
 
-      <RequestPreview payload={buildPayload(activeOp)} />
+      <RequestPreview payload={buildPayload(activeOp)} op={activeOp} versionId={versionId} />
     </div>
   )