fix(reporting): address retrofit report PDF feedback

Six fixes from feedback on the report PDF (portfolio 849):

- Pluralise the "cars off the road" analogy ("1 car", not "1 cars").
- Keep the analogy in the headline only — drop it from the ledger's
  Carbon-saved row and the "Homes below EPC C" tile, where a carbon
  proxy sat on a homes-count figure.
- Derive the SAP delta from the rounded endpoints shown, so 67 -> 71
  reads +4 not +3 (fixed on the PDF and the on-screen KPI band).
- Format carbon to one decimal everywhere via a shared formatTonnes
  helper, so one saved figure stops rendering as 2 t / 2.2 t / 2 t
  across headline, card and ledger.
- Label the EPC-distribution count column "Homes".
- Print a one-line methodology for the value-for-money ratios (the
  on-screen InfoDot buttons are hidden in print).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app/portfolio/[slug]/(portfolio)/reporting/ReportingClientArea.tsx

@@ -438,9 +438,12 @@ function MetricsBody({
           ),
         },
         (() => {
+          // Round both endpoints first so the delta pill agrees with the
+          // rounded SAP figures shown here and in the sub (a 67 → 71 tile must
+          // read +4, not +3 off the raw averages).
           const d = shapeKpiDelta({
-            current: avg.avg_sap ?? 0,
-            after: Number(scenarioData.avg_sap),
+            current: Math.round(avg.avg_sap ?? 0),
+            after: Math.round(Number(scenarioData.avg_sap)),
             improvesWhenLower: false,
           });
           return {

src/app/portfolio/[slug]/(portfolio)/reporting/components/InvestmentLedger.tsx

@@ -14,7 +14,7 @@ import {
 } from "lucide-react";
 import { InfoDot, moneyFull } from "./primitives";
 import { COST_HELP } from "./costHelp";
-import { carsOffTheRoad, type LedgerView } from "@/lib/reporting/model";
+import { formatTonnes, type LedgerView } from "@/lib/reporting/model";
 
 // LedgerView now lives in the reporting model (derived by deriveLedgerView);
 // re-exported here so existing imports from this component keep resolving.
@@ -196,8 +196,7 @@ export function InvestmentLedger({ v }: { v: LedgerView }) {
         <IconRow
           icon={Leaf}
           label="Carbon saved"
-          value={`${Math.round(v.carbonSaved)} t`}
-          note={`≈ ${carsOffTheRoad(v.carbonSaved)} cars`}
+          value={`${formatTonnes(v.carbonSaved)} t`}
           tip={COST_HELP.carbonSaved}
           tone="benefit"
         />
@@ -218,6 +217,15 @@ export function InvestmentLedger({ v }: { v: LedgerView }) {
           value={moneyFull(v.costPerCarbon)}
           tip={COST_HELP.costPerCarbon}
         />
+        {/* Print-only: on screen the InfoDots carry this, but buttons are hidden
+            in print, so the printed report would otherwise show the ratios with
+            no basis. States what they're divided by and that it's portfolio-wide,
+            not per home. */}
+        <p className="mt-2 hidden text-[0.66rem] leading-snug text-gray-500 print:block">
+          Capital cost (construction works + project delivery) ÷ the total SAP
+          points, and tonnes of CO₂ saved a year, across all upgraded homes — a
+          portfolio total, not per home. Lower is better.
+        </p>
       </div>
     </div>
   );

src/app/portfolio/[slug]/(portfolio)/reporting/pdf/page.tsx

@@ -8,7 +8,7 @@ import {
 import { measureLabel } from "@/lib/reporting/measures";
 import {
   buildHeadline,
-  carsOffTheRoad,
+  formatTonnes,
   countBelowBand,
   shapeKpiDelta,
   toBandCounts,
@@ -175,6 +175,14 @@ function EpcDistribution({
   );
   return (
     <div className="flex flex-col gap-2">
+      {/* Label the right-hand column so a skimmer reads "9 → 15" as homes. */}
+      <div className="grid grid-cols-[24px_1fr_96px] items-center gap-x-3">
+        <span />
+        <span />
+        <span className="text-right text-[0.58rem] font-semibold uppercase tracking-wide text-gray-400">
+          Homes
+        </span>
+      </div>
       {bands.map((band) => {
         const before = bandCounts[band] ?? 0;
         const after = scenarioBands?.[band];
@@ -437,7 +445,7 @@ export default async function ReportingPdfPage(props: {
     totalCarbon: baseline.totals.total_carbon,
     totalBills: baseline.totals.total_bills,
   });
-  // Bound for the headline + the "cars off the road" / CO₂-saved tiles below.
+  // Bound for the headline + the CO₂-saved tile below.
   const carbonSaved = ledger.carbonSaved;
 
   const headline = buildHeadline({
@@ -453,9 +461,11 @@ export default async function ReportingPdfPage(props: {
   const belowCBefore = countBelowBand(bandCounts, "C");
   const belowCAfter = countBelowBand(scenarioBands, "C");
 
+  // Derive the delta from the same rounded endpoints the tile displays, so the
+  // pill agrees with them (67 → 71 must read +4, not +3 off the raw 70.6 − 67.4).
   const sapDelta = shapeKpiDelta({
-    current: avg.avg_sap ?? 0,
-    after: Number(scenarioData.avg_sap),
+    current: Math.round(avg.avg_sap ?? 0),
+    after: Math.round(Number(scenarioData.avg_sap)),
     improvesWhenLower: false,
   });
 
@@ -501,7 +511,7 @@ export default async function ReportingPdfPage(props: {
                 <b>{belowCAfter.toLocaleString()}</b>
               </span>
             }
-            sub={`≈ ${carsOffTheRoad(carbonSaved)} cars off the road`}
+            sub={`${Math.max(belowCBefore - belowCAfter, 0).toLocaleString()} moved to C or above`}
           />
           <Tile
             label="Bills saved / yr"
@@ -510,7 +520,7 @@ export default async function ReportingPdfPage(props: {
           />
           <Tile
             label="Carbon saved / yr"
-            value={`${formatNumber(carbonSaved)} t`}
+            value={`${formatTonnes(carbonSaved)} t`}
             sub="vs current stock"
           />
           <Tile

src/lib/reporting/model.test.ts

@@ -9,6 +9,7 @@ import {
   costPerCarbonSaved,
   costPerSapPoint,
   deriveLedgerView,
+  formatTonnes,
   isCompliantBeyondWindow,
   pickBestIndex,
   selectGoalCallout,
@@ -449,4 +450,26 @@ describe("buildHeadline", () => {
       }),
     ).toBe("Improving valuation across 187 homes costs £850k net.");
   });
+
+  it("uses singular 'car' and one-decimal tonnes for a small saving", () => {
+    expect(
+      buildHeadline({
+        goal: "Increasing EPC",
+        goalValue: "C",
+        homesUpgraded: 7,
+        netCost: 42_916,
+        carbonSavedPerYear: 2.2,
+      }),
+    ).toBe(
+      "Reaching EPC C across 7 homes costs £43k net and cuts carbon by 2.2 tonnes a year — like taking 1 car off the road.",
+    );
+  });
+});
+
+describe("formatTonnes", () => {
+  it("keeps one decimal but strips a trailing .0", () => {
+    expect(formatTonnes(2.2)).toBe("2.2");
+    expect(formatTonnes(2)).toBe("2");
+    expect(formatTonnes(312)).toBe("312");
+  });
 });

src/lib/reporting/model.ts

@@ -365,6 +365,15 @@ export function carsOffTheRoad(tonnesPerYear: number): number {
   return Math.round(tonnesPerYear / TONNES_CO2_PER_CAR_PER_YEAR);
 }
 
+/**
+ * Carbon tonnes for display — one decimal, trailing ".0" stripped
+ * (2.2 → "2.2", 2 → "2"). The single carbon formatter shared by the headline,
+ * the KPI card and the ledger, so one saved figure never renders three ways.
+ */
+export function formatTonnes(tonnes: number): string {
+  return tonnes.toFixed(1).replace(/\.0$/, "");
+}
+
 export interface KpiDelta {
   delta: number;
   improved: boolean;
@@ -418,20 +427,29 @@ export interface HeadlineInput {
  */
 export function buildHeadline(input: HeadlineInput): string {
   const money = formatMoneyCompact(input.netCost);
-  const tonnes = Math.round(input.carbonSavedPerYear);
-  const cars = carsOffTheRoad(input.carbonSavedPerYear);
-  const carClause = ` — like taking ${cars} cars off the road.`;
+  const tonnesNum = input.carbonSavedPerYear;
+  const hasCarbon = Math.round(tonnesNum) > 0;
+  const tonnes = formatTonnes(tonnesNum);
+  const cars = carsOffTheRoad(tonnesNum);
+  // The "cars off the road" analogy lives here in the headline only (the one
+  // board-quotable line) — not repeated on the tiles or ledger. Dropped when it
+  // rounds below one car, where "0 cars" would read as noise. Singular "car"
+  // for exactly one.
+  const carClause =
+    cars > 0
+      ? ` — like taking ${cars} car${cars === 1 ? "" : "s"} off the road.`
+      : "";
 
   if (input.goal === GOALS.EPC) {
     const base = `Reaching EPC ${input.goalValue ?? DEFAULT_GOAL_BAND} across ${input.homesUpgraded} homes costs ${money} net`;
-    return tonnes > 0
+    return hasCarbon
       ? `${base} and cuts carbon by ${tonnes} tonnes a year${carClause}`
       : `${base}.`;
   }
 
   if (input.goal === GOALS.CO2) {
     const base = `Cutting carbon by ${tonnes} tonnes a year across ${input.homesUpgraded} homes costs ${money} net`;
-    return tonnes > 0 ? `${base}${carClause}` : `${base}.`;
+    return hasCarbon ? `${base}${carClause}` : `${base}.`;
   }
 
   const lead =
@@ -439,7 +457,7 @@ export function buildHeadline(input: HeadlineInput): string {
       ? "Cutting energy use"
       : "Improving valuation";
   const base = `${lead} across ${input.homesUpgraded} homes costs ${money} net`;
-  return tonnes > 0
+  return hasCarbon
     ? `${base} and cuts carbon by ${tonnes} tonnes a year${carClause}`
     : `${base}.`;
 }