Compact the log's slice column, show value impact, expand the payload on click

Three things about the change log, from using it.

The slice column grew to a block per entry once it listed lines, which is
too much for a table you scan. It is one truncated line now: a single slice
reads as its fields, and a dragged region as "5 slices · omon = 07 - Dec …
11 - Apr" -- enough to recognise the entry.

There was no indication of what an entry did to the numbers, which is the
first thing you want from a change log. The route already returned
value_total and it simply was not rendered. Added, signed and coloured, so
a list of adjustments reads as a list of impacts.

And clicking a row now opens slice and params as formatted JSON -- the exact
payload that went over the route, including the increments and the plug,
which no amount of summarising in the cell was going to convey.

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

ui/src/views/Forecast.jsx

@@ -64,6 +64,8 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   // volume flat, 'volume' keeps price flat. Mirrors the Excel form's
   // Plug Price / Plug Volume choice.
   const [scalePlug,      setScalePlug]      = useState(() => localStorage.getItem('pf_scale_plug') || 'price')
+  // which change-log row has its payload open, if any
+  const [expandedLog,    setExpandedLog]    = useState(null)
   // what a target/percentage is measured against: the rows this operation can
   // write, or everything the pivot shows for the slice (excluded rows included)
   const [targetBasis,    setTargetBasis]    = useState('selected')
@@ -1160,6 +1162,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
 
   async function openLog() {
     setShowLog(true)
+    setExpandedLog(null)
     setLogLoading(true)
     try {
       // Baseline and reference loads are segment construction, not forecasting.
@@ -1411,6 +1414,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
                       <th className="text-left px-4 py-2 font-medium">Slice</th>
                       <th className="text-left px-4 py-2 font-medium w-40">Tag</th>
                       <th className="text-left px-4 py-2 font-medium">Note</th>
+                      <th className="text-right px-4 py-2 font-medium w-28">Value</th>
                       <th className="text-right px-4 py-2 font-medium w-16">Rows</th>
                       <th className="px-4 py-2 w-16"></th>
                     </tr>
@@ -1424,23 +1428,14 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
                             {entry.operation}
                           </span>
                         </td>
-                        <td className="px-4 py-2 text-gray-600 font-mono align-top">
+                        <td className="px-4 py-2 text-gray-600 font-mono max-w-xs">
-                          {(() => {
+                          <button
-                            const lines = fmtSliceLines(entry.slice)
+                            onClick={() => setExpandedLog(prev => prev === entry.id ? null : entry.id)}
-                            if (lines.length === 0) return '—'
+                            className="text-left w-full truncate hover:text-blue-600"
-                            // the raw payload is on the title, for the case where the
+                            title="Show the payload">
-                            // rendering has flattened something worth seeing
+                            <span className="text-gray-400 mr-1">{expandedLog === entry.id ? '▾' : '▸'}</span>
-                            return (
+                            {fmtSliceSummary(entry.slice)}
-                              <div title={JSON.stringify(entry.slice, null, 2)}>
+                          </button>
-                                {lines.map((l, i) => (
-                                  <div key={i} className="whitespace-nowrap">
-                                    {lines.length > 1 && <span className="text-gray-400 mr-1">{i + 1}.</span>}
-                                    {l}
-                                  </div>
-                                ))}
-                              </div>
-                            )
-                          })()}
                         </td>
                         <LogCell entry={entry} field="tag" placeholder="add tag"
                           editing={editingCell} setEditing={setEditingCell} onSave={saveLogField}
@@ -1452,6 +1447,11 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
                           )} />
                         <LogCell entry={entry} field="note" placeholder="add note"
                           editing={editingCell} setEditing={setEditingCell} onSave={saveLogField} />
+                        <td className={`px-4 py-2 text-right tabular-nums whitespace-nowrap ${
+                          entry.value_total > 0 ? 'text-green-700' : entry.value_total < 0 ? 'text-red-600' : 'text-gray-400'}`}>
+                          {entry.value_total == null ? '—'
+                            : entry.value_total.toLocaleString(undefined, { maximumFractionDigits: 0 })}
+                        </td>
                         <td className="px-4 py-2 text-right text-gray-500 tabular-nums">{entry.row_count ?? '—'}</td>
                         <td className="px-4 py-2">
                           <button
@@ -1462,7 +1462,20 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
                           </button>
                         </td>
                       </tr>
-                    ))}
+                    )).flatMap((row, i) => {
+                      const entry = logEntries[i]
+                      if (expandedLog !== entry.id) return [row]
+                      return [row, (
+                        <tr key={`${entry.id}-detail`} className="bg-gray-50 border-t border-gray-100">
+                          <td colSpan={8} className="px-4 py-3">
+                            <div className="grid gap-3 md:grid-cols-2">
+                              <LogJson label="slice"  value={entry.slice} />
+                              <LogJson label="params" value={entry.params} />
+                            </div>
+                          </td>
+                        </tr>
+                      )]
+                    })}
                   </tbody>
                 </table>
               )}
@@ -1708,6 +1721,38 @@ function fmtSliceLines(slice) {
   ]
 }
 
+// One line, whatever the shape. The full payload is a click away, so this only
+// has to say enough to recognise the entry: what varied, and how much of it.
+function LogJson({ label, value }) {
+  const empty = value == null || (typeof value === 'object' && Object.keys(value).length === 0)
+  return (
+    <div>
+      <div className="text-[10px] uppercase tracking-wide text-gray-400 mb-1">{label}</div>
+      <pre className="text-[11px] leading-snug font-mono text-gray-600 bg-white border border-gray-200
+                      rounded p-2 overflow-auto max-h-64 whitespace-pre">
+        {empty ? '—' : JSON.stringify(value, null, 2)}
+      </pre>
+    </div>
+  )
+}
+
+function fmtSliceSummary(slice) {
+  const lines = fmtSliceLines(slice)
+  if (lines.length === 0) return '—'
+  if (!Array.isArray(slice) || slice.length <= 1) return lines.join(' · ')
+
+  const keys    = [...new Set(slice.flatMap(sl => Object.keys(sl || {})))]
+  const varying = keys.filter(k => new Set(slice.map(sl => JSON.stringify(sl?.[k]))).size > 1)
+
+  if (varying.length === 1) {
+    const [vk] = varying
+    const vals = [...new Set(slice.map(sl => fmtSliceValue(sl[vk])))]
+    const span = vals.length > 2 ? `${vals[0]} … ${vals[vals.length - 1]}` : vals.join(', ')
+    return `${slice.length} slices · ${vk} = ${span}`
+  }
+  return `${slice.length} slices · ${varying.join(', ')} vary`
+}
+
 function fmtSliceValue(v) {
   if (v === null || v === undefined || v === '') return '∅'
   if (typeof v === 'number' && v > 1e11) {