Revert rota comparison to real oncosts; remove stale NI footnote

Now that the sync uses /api/v2/rosters/on/{date} (2026-07-25) instead
of /api/v2/schedules, real employer-oncost figures are available for
rota data, so gatherRotaVsActualData() no longer needs the base-cost-
only workaround — it respects show_oncosts like the rest of the app
again. Also removes the now-inaccurate Monthly.tsx footnote claiming
rota-based forecasts exclude NI, and the now-obsolete methodology note
that told the model to expect a swing from the base-cost fix (moot —
insight history is being cleared, so there's nothing to compare
against).

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

backend/src/jobs/ai-insights.js

@@ -9,11 +9,6 @@ export const DEFAULT_DAILY_TOKEN_BUDGET = 5000
 const MAX_OUTPUT_TOKENS = 900
 export const MANUAL_RATE_LIMIT_MINUTES = 5
 
-// One-time context so the model doesn't flag the 25/07 rota-methodology fix (oncost-inclusive
-// -> base-pay-only comparison) as an unexplained swing when it sees a prior insight's figures
-// change. Safe to delete this constant and its usage below once it's a few days stale.
-const METHOD_CHANGE_NOTE_UNTIL = '2026-07-29'
-
 function toISODate(d) {
   return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`
 }
@@ -152,15 +147,16 @@ export async function gatherPriorPeriodData() {
 // Department-level variance between scheduled (rota) and actual cost, over the trailing
 // window. Rota rows for past dates aren't deleted once synced, so this covers real history.
 //
-// Always compares on BASE cost for both sides, regardless of the show_oncosts display
+// Respects show_oncosts like the rest of the app. Previously hardcoded to base cost because
-// setting: Workforce's schedules API never actually supplies employer NI oncosts (confirmed —
+// the old /api/v2/schedules-based sync never supplied real oncosts on rota data (confirmed:
-// published_total_cost is identical to published_base_cost on every synced row), so comparing
+// published_total_cost == published_base_cost on every row) — fixed 2026-07-25 by switching
-// oncost-inclusive actuals against rota would inflate every variance by ~14-20% for reasons
+// the sync to /api/v2/rosters/on/{date}, which does supply real cost_with_oncosts.
-// that have nothing to do with real overspend. Matches the same caveat already surfaced on the
-// Monthly page's rota-based forecast footnote.
 export async function gatherRotaVsActualData(days = 28) {
-  const actualCostCol = 'base_cost'
+  const showOncosts = (await getConfig('show_oncosts')) !== 'false'
-  const schedCostExpr = '(published_base_cost + unpublished_base_cost)'
+  const actualCostCol = showOncosts ? 'total_cost' : 'base_cost'
+  const schedCostExpr = showOncosts
+    ? '(published_total_cost + unpublished_total_cost)'
+    : '(published_base_cost + unpublished_base_cost)'
 
   const today = new Date()
   const fromStr = toISODate(new Date(today.getTime() - days * 86_400_000))
@@ -213,7 +209,7 @@ export async function gatherRotaVsActualData(days = 28) {
     }))
     .sort((a, b) => Math.abs(b.variance) - Math.abs(a.variance))
 
-  return { fromStr, toStr, totalDaysInWindow, depts }
+  return { fromStr, toStr, totalDaysInWindow, depts, costBasis: showOncosts ? 'incl. employer NI oncosts' : 'base pay only' }
 }
 
 // Forward-looking projection — reuses the app's existing tiered forecastDayCost() logic
@@ -374,19 +370,6 @@ export function buildPrompt(monthProgress, priorPeriod, rotaVsActual, forecast,
     lines.push('')
   }
 
-  if (recentInsights.length && toISODate(new Date()) <= METHOD_CHANGE_NOTE_UNTIL) {
-    lines.push('## Methodology Note (25/07/2026)')
-    lines.push(
-      "The Rota vs Actual Variance comparison was corrected on 25/07/2026 to use base pay only on both " +
-      "sides (previously actual cost included employer NI oncosts while rota did not, since Workforce's " +
-      "schedules API never supplies oncosts — this inflated every rota variance figure by roughly 14-20%). " +
-      "If a recent previous insight below shows a notably different rota variance figure for the same " +
-      "department than today's, that is this correction taking effect, not a real change in performance — " +
-      "do not describe it as unexplained or needing clarification."
-    )
-    lines.push('')
-  }
-
   if (recentInsights.length) {
     lines.push('## Recent Previous Insights (most recent first — reference these, do not just repeat them)')
     for (const r of recentInsights) {
@@ -414,15 +397,13 @@ export function buildPrompt(monthProgress, priorPeriod, rotaVsActual, forecast,
   for (const d of priorPeriod.lastYearDepts) lines.push(`  ${d.department_name}: ${fmtMoney(d.cost)}`)
   lines.push('')
 
-  lines.push(`## Rota vs Actual Variance (${fmtDateUK(rotaVsActual.fromStr)} - ${fmtDateUK(rotaVsActual.toStr)}, ${rotaVsActual.totalDaysInWindow} days)`)
+  lines.push(`## Rota vs Actual Variance (${fmtDateUK(rotaVsActual.fromStr)} - ${fmtDateUK(rotaVsActual.toStr)}, ${rotaVsActual.totalDaysInWindow} days, ${rotaVsActual.costBasis})`)
   lines.push(
-    "Figures below are BASE PAY only (excluding employer NI) on both sides — Workforce's rota/schedules " +
+    "Variance is computed only over days that have rota data (\"days w/ rota\" below) — if that's well " +
-    "API doesn't supply oncosts, so this is the only basis that's genuinely comparable; do not describe " +
+    "below the total window, treat the variance as partial/uncertain due to missing rota history, not a " +
-    "this variance using total-cost figures from other sections. Variance is computed only over days that " +
+    "confirmed overspend, and say so explicitly rather than stating it as fact."
-    "have rota data (\"days w/ rota\" below) — if that's well below the total window, treat the variance " +
-    "as partial/uncertain due to missing rota history, not a confirmed overspend, and say so explicitly."
   )
-  lines.push('Department | Actual base pay (days w/ rota) | Rota base pay | Variance | Variance % | Days w/ rota | Actual base pay (full window)')
+  lines.push('Department | Actual (days w/ rota) | Rota | Variance | Variance % | Days w/ rota | Actual (full window)')
   for (const d of rotaVsActual.depts) {
     lines.push(
       `${d.department_name} | ${fmtMoney(d.actualOnRotaDays)} | ${fmtMoney(d.schedTotal)} | ` +

frontend/src/pages/Monthly.tsx

@@ -508,9 +508,6 @@ export default function Monthly() {
               </tbody>
             </table>
             {showOncosts && <p className="footnote">Includes estimated employer on-costs. Final payroll figures are in Sage.</p>}
-            {isCurrentMonth && forecastMethod === 'rota' && (
-              <p className="footnote">Rota-based forecast figures exclude employer National Insurance — Workforce's schedules API doesn't provide it, only the timesheets/actuals API does.</p>
-            )}
           </div>
 
           {pyDepts.length > 0 && (