fix(stats): withhold reversal-grounded accuracy where a reversal cannot be recorded

The fairness page showed 100% accuracy for every repository and all eight
weeks of the trend while the headline read 94.6%. Those 100%s are structural
zeros, not measurements.

`recordReversalSignals` has one call site, inside `handlePullRequestWebhookEvent`,
reached only via the `github-webhook` job — a member of
REVIEW_EXECUTION_JOB_TYPES, which a runtime that does not execute reviews
acks-and-drops. So `reversed` is pinned at 0 while merged/closed keep growing,
and `1 - 0/N` renders as a flawless score over a numerator that can never move.
The repo already recorded the outcome: reversal-superseded.ts notes "verified in
production: zero reversal events ever".

`accuracyPct` now returns null unless a reversal is OBSERVABLE on this
deployment — a recorded reversal proves it outright (and short-circuits the
probe), otherwise there must be at least one terminal auto-action in the
retained window for a reversal to attach to. This is the discipline the surface
already applies elsewhere, extended to the case where the numerator's WRITER,
not just its sample, is absent: a sparse rule's precision is null, and
gamingFlagsCaught is null below three instances.

Also fixes the weekly trend's denominator asymmetry: `merged`/`closed` folded in
registered-Orb rows while `reversed` stayed own-ledger-only, so the denominator
grew with every new install while the numerator did not — trending every week
toward 100% independent of real reversal behavior. #7449 fixed exactly this for
the lifetime figure and it was never carried across. Accuracy now divides the
own-ledger pairing; the displayed volume still includes the fleet.

UI: the withheld cells say why rather than leaving a bare em dash next to
healthy volume, and the headline now discloses `basis` — #9168 computes
"single_instance_self_report" precisely so one operator's self-reported number
is not read as fleet corroboration, and the page dropped the field entirely,
along with the sample size and confidence interval. The methodology note also
described the reversal formula while the headline rendered decisionAccuracy;
it now explains both and why they differ.

Refs #9676

Author: JSONbored

apps/loopover-ui/src/components/site/fairness-report-page.test.tsx

@@ -220,6 +220,65 @@ describe("FairnessReportPage (#fairness-analytics)", () => {
     expect(screen.getByText("2 human-reversed, lifetime")).toBeTruthy();
   });
 
+  it("explains a withheld accuracy instead of letting it read as a dash-shaped mystery", async () => {
+    // Backend publishes null when no auto-action was ever recorded for a reversal to attach to; the page must
+    // say that rather than leaving a bare "—" next to a healthy-looking volume.
+    apiFetch.mockResolvedValue({
+      ok: true,
+      data: {
+        ...FIXTURE,
+        byProject: [
+          { project: "owner/repo", reviewed: 100, merged: 60, closed: 30, accuracyPct: null },
+        ],
+        accuracyTrend: [
+          { weekStart: "2026-07-13", merged: 30, closed: 15, reversed: 0, accuracyPct: null },
+        ],
+      },
+      status: 200,
+      durationMs: 10,
+    });
+    renderWithClient(<FairnessReportPage />);
+
+    await waitFor(() => expect(screen.getByText("By repository")).toBeTruthy());
+    const notes = screen.getAllByText(/not measurable on this deployment, not 100%/);
+    expect(notes.length).toBe(2); // one under each affected table
+  });
+
+  it("does not show the unmeasurable-accuracy note when every accuracy is real", async () => {
+    apiFetch.mockResolvedValue({ ok: true, data: FIXTURE, status: 200, durationMs: 10 });
+    renderWithClient(<FairnessReportPage />);
+
+    await waitFor(() => expect(screen.getByText("By repository")).toBeTruthy());
+    expect(screen.queryByText(/not measurable on this deployment/)).toBeNull();
+  });
+
+  it("#9168: discloses a single-instance self-report rather than presenting it as fleet corroboration", async () => {
+    apiFetch.mockResolvedValue({
+      ok: true,
+      data: {
+        ...FIXTURE,
+        fleetAccuracy: {
+          ...FIXTURE.fleetAccuracy,
+          instanceCount: 1,
+          basis: "single_instance_self_report",
+          decidedCount: 5225,
+          accuracyCiPct: { lo: 93.9, hi: 95.2 },
+        },
+      },
+      status: 200,
+      durationMs: 10,
+    });
+    renderWithClient(<FairnessReportPage />);
+
+    await waitFor(() => expect(screen.getByText("Decision accuracy")).toBeTruthy());
+    expect(screen.getByText(/Self-reported by that single instance/).textContent).toContain(
+      "5,225 decided",
+    );
+    expect(screen.getByText(/Self-reported by that single instance/).textContent).toContain(
+      "93.9–95.2%",
+    );
+  });
+
   it("#9068: renders the insufficient-instances state (not a fabricated zero) when gamingFlagsCaught is null", async () => {
     apiFetch.mockResolvedValue({
       ok: true,

apps/loopover-ui/src/components/site/fairness-report-page.tsx

@@ -15,6 +15,19 @@ import type { PublicStats } from "@/components/site/proof-of-power-stats-model";
 // count, with a short methodology note. Counts only; no PR content, contributor identities, or trust scores.
 
 const pctFmt = new Intl.NumberFormat("en", { maximumFractionDigits: 1 });
+/** Why an accuracy cell reads "—". Reversal-grounded accuracy needs the deployment to have recorded the
+ *  terminal auto-actions a reversal attaches to; where it hasn't, `1 - 0/N` would render as a flawless 100%
+ *  over a numerator that can never move, so the backend publishes null and the page says so out loud. */
+function UnmeasurableAccuracyNote() {
+  return (
+    <p className="mt-3 text-token-xs text-muted-foreground">
+      An accuracy of <span className="font-mono">—</span> means not measurable on this deployment,
+      not 100%: no auto-merge/auto-close was recorded here for a human reversal to be counted
+      against. The volume columns beside it are measured directly and are unaffected.
+    </p>
+  );
+}
+
 const intFmt = new Intl.NumberFormat("en");
 
 async function fetchPublicStats(): Promise<PublicStats | null> {
@@ -119,6 +132,23 @@ export function FairnessReportPage() {
                       ? `${intFmt.format(data.totals.reversed)} human-reversed, lifetime`
                       : "reversal-grounded, lifetime"}
                 </p>
+                {/* #9168 computes `basis` precisely so this number is not read as corroborated-across-operators
+                    when it is one operator's own disclosed outcomes; the page used to drop the field entirely. */}
+                {fleetEligible && data.fleetAccuracy.basis === "single_instance_self_report" ? (
+                  <p className="mt-2 text-token-xs text-muted-foreground">
+                    Self-reported by that single instance, not corroborated across operators
+                    {data.fleetAccuracy.decidedCount != null
+                      ? ` (${intFmt.format(data.fleetAccuracy.decidedCount)} decided`
+                      : ""}
+                    {data.fleetAccuracy.decidedCount != null &&
+                    data.fleetAccuracy.accuracyCiPct != null
+                      ? `, 95% CI ${pctFmt.format(data.fleetAccuracy.accuracyCiPct.lo)}–${pctFmt.format(data.fleetAccuracy.accuracyCiPct.hi)}%)`
+                      : data.fleetAccuracy.decidedCount != null
+                        ? ")"
+                        : ""}
+                    .
+                  </p>
+                ) : null}
               </Card>
               <Card className="p-5">
                 <div className="text-token-xs text-muted-foreground">Anti-gaming flags caught</div>
@@ -149,11 +179,15 @@ export function FairnessReportPage() {
 
             <div className="mt-10 space-y-2 rounded-token border-hairline px-4 py-4 text-token-sm text-muted-foreground">
               <p>
-                <span className="font-medium text-foreground">How accuracy is measured:</span> 1
-                minus the share of auto-merged/auto-closed PRs a human later overturned — a
-                bot-closed PR a contributor reopened, or a bot-merged PR undone by a separate revert
-                PR. Nothing here is a prediction or a self-assessment; it's counted after the fact
-                from what actually happened on GitHub.
+                <span className="font-medium text-foreground">How accuracy is measured:</span> the
+                headline scores the gate's own merge/close <em>decisions</em> — the share the
+                realized outcome confirmed, with holds excluded because a deferral to a human is not
+                a decision that can be right or wrong (#8820). The per-repository and weekly tables
+                below are a different, stricter measure: 1 minus the share of
+                auto-merged/auto-closed PRs a human later overturned — a bot-closed PR a contributor
+                reopened, or a bot-merged PR undone by a separate revert PR. Neither is a prediction
+                or a self-assessment; both are counted after the fact from what actually happened on
+                GitHub, which is also why the two can differ.
               </p>
               <p>
                 <span className="font-medium text-foreground">
@@ -206,6 +240,9 @@ export function FairnessReportPage() {
                     </tbody>
                   </table>
                 </TableScroll>
+                {data.byProject.some((row) => row.accuracyPct == null) ? (
+                  <UnmeasurableAccuracyNote />
+                ) : null}
               </div>
             ) : null}
 
@@ -256,6 +293,11 @@ export function FairnessReportPage() {
                   </tbody>
                 </table>
               </TableScroll>
+              {data.accuracyTrend.some(
+                (week) => week.merged != null && week.accuracyPct == null,
+              ) ? (
+                <UnmeasurableAccuracyNote />
+              ) : null}
             </div>
 
             {data.rulePrecision && data.rulePrecision.rules.length > 0 ? (

src/review/public-stats.ts

@@ -55,6 +55,7 @@ import { validateCalibrationPayload } from "./risk-control";
 import { loadRepoFocusManifest } from "../signals/focus-manifest-loader";
 import { resolveLoopOverSelfRepoFullName } from "../config/loopover-repo-focus-manifest";
 import { errorMessage } from "../utils/json";
+import { retentionCutoffIsoForTable } from "../db/retention";
 
 /** FALLBACK estimate of maintainer review/triage time saved per reviewed PR, used ONLY when the real per-PR
  *  average (`estimateReviewEffort`'s minutes, persisted at publish time — see `reviewEffortMinutes` in the
@@ -164,12 +165,47 @@ function filteredPct(reviewed: number, merged: number): number | null {
   return Math.round(((reviewed - merged) / reviewed) * 1000) / 10;
 }
 
-/** Reversal-grounded accuracy over the irreversible auto-actions (merged + closed); null until there is signal. */
+/** The auto-actions a reversal is recorded against. `recordReversalSignals` only ever fires for a PR this
+ *  deployment itself auto-merged or auto-closed, so with zero of these rows in the retained window a
+ *  `reversal_*` event cannot exist — and `1 - 0/N` is then a structural zero, not a measurement. */
+export const AUTO_ACTION_EVENT_TYPES = ["agent.action.close", "agent.action.merge"] as const;
+
+/**
+ * Whether a reversal is OBSERVABLE on this deployment: did it record any terminal auto-action in the window a
+ * reversal could still be attributed to? Reversal signals are written only by the review-execution pipeline
+ * (`recordReversalSignals`, reached via the `github-webhook` job), which a runtime that does not execute
+ * reviews acks-and-drops — so on such a runtime `reversed` is pinned at 0 forever while the merged/closed
+ * denominator keeps growing, and every reversal-grounded percentage converges on a fake 100%.
+ *
+ * Publishing that as accuracy is the exact failure #8820 called out for the fleet number ("the old formula
+ * overstated accuracy") and #7449 fixed for the global one. This is the same discipline the rest of this
+ * surface already applies — a sparse rule's precision is null, `gamingFlagsCaught` is null below three
+ * instances — extended to the case where the numerator's WRITER, not just its sample, is absent.
+ */
+export async function loadReversalObservability(env: Env, knownReversals = 0): Promise<boolean> {
+  // A recorded reversal is itself proof the pipeline that records them runs here -- no probe needed, and no
+  // query on the hot path for any deployment that has ever overturned an auto-action.
+  if (knownReversals > 0) return true;
+  const rows = await safeAll<{ n: number }>(
+    env,
+    `SELECT COUNT(*) AS n FROM audit_events
+      WHERE event_type IN (${AUTO_ACTION_EVENT_TYPES.map((type) => `'${type}'`).join(", ")})
+        AND created_at >= ?`,
+    retentionCutoffIsoForTable("audit_events"),
+  );
+  return (rows[0]?.n ?? 0) > 0;
+}
+
+/** Reversal-grounded accuracy over the irreversible auto-actions (merged + closed); null until there is signal,
+ *  and null when a reversal is not observable at all on this deployment (see {@link loadReversalObservability}) —
+ *  an unmeasurable quantity stays unknown rather than rendering as a perfect score. */
 function accuracyPct(
   merged: number,
   closed: number,
   reversed: number,
+  reversalObservable: boolean,
 ): number | null {
+  if (!reversalObservable) return null;
   const decided = merged + closed;
   if (decided <= 0) return null;
   // `reversed` counts engine auto-actions regardless of a PR's CURRENT disposition, so a reopened
@@ -426,6 +462,10 @@ export async function getPublicStats(
     error: 0,
     reversed: 0,
   };
+  // Resolved before byProject so every published accuracy figure -- per repo and global -- answers the same
+  // question about the same deployment, rather than one of them silently disagreeing with the others.
+  const totalReversals = [...reversedByProject.values()].reduce((sum, n) => sum + n, 0);
+  const reversalObservable = await loadReversalObservability(env, totalReversals);
   const byProject = dispositions
     .map((d) => {
       const merged = d.merged ?? 0;
@@ -445,7 +485,7 @@ export async function getPublicStats(
         reviewed,
         merged,
         closed,
-        accuracyPct: accuracyPct(merged, closed, reversed),
+        accuracyPct: accuracyPct(merged, closed, reversed, reversalObservable),
       };
     })
     .filter((r) => r.reviewed > 0)
@@ -573,7 +613,7 @@ export async function getPublicStats(
       // Option 1 of #7449: compute the global accuracy from the OWN-LEDGER merged/closed snapshot (not the
       // fleet-folded totals.merged/closed), so its numerator (own-ledger reversed) and denominator are drawn
       // from the same population. See the ownLedgerMerged/ownLedgerClosed snapshot above the Orb fold for why.
-      accuracyPct: accuracyPct(ownLedgerMerged, ownLedgerClosed, totals.reversed),
+      accuracyPct: accuracyPct(ownLedgerMerged, ownLedgerClosed, totals.reversed, reversalObservable),
       minutesSaved,
     },
     weekly: { reviewed: w.reviewed ?? 0, merged: w.merged ?? 0 },

src/services/public-accuracy-trend.ts

@@ -8,7 +8,7 @@
 // #2568 pattern for the sibling per-repo quality trend) can recompute any historical week correctly on every
 // request -- no cron-miss gap risk, no second copy of the number to keep in sync, and the SAME formula as the
 // live figure by construction, so the two can never silently diverge or read as inconsistent to a public viewer.
-import { PUBLISHED_PR_KEYS, publicStatsProjects, safeAll } from "../review/public-stats";
+import { loadReversalObservability, PUBLISHED_PR_KEYS, publicStatsProjects, safeAll } from "../review/public-stats";
 import { isoWeekStart } from "./public-quality-metrics";
 
 export const PUBLIC_ACCURACY_TREND_WEEKS = 8;
@@ -24,7 +24,13 @@ export type PublicAccuracyTrendWeek = {
   accuracyPct: number | null;
 };
 
-type DayRow = { day: string; merged: number; closed: number; reversed: number };
+/** `merged`/`closed` are the DISPLAYED volume (own ledger + registered Orb fleet). `ownMerged`/`ownClosed` are
+ *  the own-ledger-only pairing for `reversed`, which is own-ledger-only by construction (the Orb aggregate has
+ *  no reversal concept). Accuracy divides the own-ledger numbers ONLY -- #7449 fixed exactly this asymmetry for
+ *  the lifetime figure in public-stats.ts and it was never carried across to this trend, so the denominator grew
+ *  with every newly registered install while the numerator stayed own-ledger-scoped, trending every week toward
+ *  100% independent of real reversal behavior. */
+type DayRow = { day: string; merged: number; closed: number; ownMerged: number; ownClosed: number; reversed: number };
 
 const MS_PER_WEEK = 7 * 86_400_000;
 
@@ -33,20 +39,35 @@ function roundPct(value: number): number {
 }
 
 /** Same formula as public-stats.ts's accuracyPct, reused so the trend and the live number can never drift
- *  apart into two competing definitions of "accuracy". */
-function publicBucketOf(bucket: { merged: number; closed: number; reversed: number }): Omit<PublicAccuracyTrendWeek, "weekStart"> {
+ *  apart into two competing definitions of "accuracy". `reversalObservable` false means this deployment records
+ *  no terminal auto-actions for a reversal to be attributed to, so the week's accuracy is unknown, not perfect --
+ *  the volume columns still publish, since those ARE measured. */
+function publicBucketOf(
+  bucket: { merged: number; closed: number; ownMerged: number; ownClosed: number; reversed: number },
+  reversalObservable: boolean,
+): Omit<PublicAccuracyTrendWeek, "weekStart"> {
   const decided = bucket.merged + bucket.closed;
   if (decided < MIN_ACCURACY_TREND_SAMPLE) return { merged: null, closed: null, reversed: null, accuracyPct: null };
-  const reversalRate = Math.min(1, bucket.reversed / decided);
-  return { merged: bucket.merged, closed: bucket.closed, reversed: bucket.reversed, accuracyPct: roundPct(1 - reversalRate) };
+  const observed = { merged: bucket.merged, closed: bucket.closed, reversed: bucket.reversed };
+  if (!reversalObservable) return { ...observed, accuracyPct: null };
+  // Own-ledger-only denominator: `reversed` can only ever be attributed to own-ledger PRs (see DayRow).
+  const ownDecided = bucket.ownMerged + bucket.ownClosed;
+  if (ownDecided <= 0) return { ...observed, accuracyPct: null };
+  const reversalRate = Math.min(1, bucket.reversed / ownDecided);
+  return { ...observed, accuracyPct: roundPct(1 - reversalRate) };
 }
 
 /** Fold day-granularity rows into `weeks` trailing UTC-Monday buckets ending in the week containing `nowMs`.
  *  Pure -- mirrors buildPublicQualityTrend's own bucketing shape (public-quality-metrics.ts). */
-export function buildPublicAccuracyTrend(dayRows: DayRow[], nowMs: number, weeks: number = PUBLIC_ACCURACY_TREND_WEEKS): PublicAccuracyTrendWeek[] {
+export function buildPublicAccuracyTrend(
+  dayRows: DayRow[],
+  nowMs: number,
+  weeks: number = PUBLIC_ACCURACY_TREND_WEEKS,
+  reversalObservable = true,
+): PublicAccuracyTrendWeek[] {
   const currentStartMs = Date.parse(isoWeekStart(nowMs));
   const oldestStartMs = currentStartMs - (weeks - 1) * MS_PER_WEEK;
-  const buckets = Array.from({ length: weeks }, () => ({ merged: 0, closed: 0, reversed: 0 }));
+  const buckets = Array.from({ length: weeks }, () => ({ merged: 0, closed: 0, ownMerged: 0, ownClosed: 0, reversed: 0 }));
 
   for (const row of dayRows) {
     const dayMs = Date.parse(`${row.day}T00:00:00.000Z`);
@@ -56,12 +77,14 @@ export function buildPublicAccuracyTrend(dayRows: DayRow[], nowMs: number, weeks
     const bucket = buckets[weekOffset]!;
     bucket.merged += row.merged;
     bucket.closed += row.closed;
+    bucket.ownMerged += row.ownMerged;
+    bucket.ownClosed += row.ownClosed;
     bucket.reversed += row.reversed;
   }
 
   return buckets.map((bucket, offset) => ({
     weekStart: isoWeekStart(oldestStartMs + offset * MS_PER_WEEK),
-    ...publicBucketOf(bucket),
+    ...publicBucketOf(bucket, reversalObservable),
   }));
 }
 
@@ -169,19 +192,22 @@ export async function loadPublicAccuracyTrend(env: Env, nowMs: number = Date.now
   const projects = publicStatsProjects(env);
   const sinceIso = new Date(Date.parse(isoWeekStart(nowMs)) - (PUBLIC_ACCURACY_TREND_WEEKS - 1) * MS_PER_WEEK).toISOString();
 
-  const [ownLedger, reversals, orb] = await Promise.all([
+  const [ownLedger, reversals, orb, reversalObservable] = await Promise.all([
     loadOwnLedgerDayRows(env, projects, sinceIso),
     loadReversalDayRows(env, projects, sinceIso),
     loadOrbDayRows(env, sinceIso),
+    loadReversalObservability(env),
   ]);
 
   const days = new Set([...ownLedger.keys(), ...reversals.keys(), ...orb.keys()]);
   const dayRows: DayRow[] = [...days].map((day) => ({
     day,
     merged: (ownLedger.get(day)?.merged ?? 0) + (orb.get(day)?.merged ?? 0),
     closed: (ownLedger.get(day)?.closed ?? 0) + (orb.get(day)?.closed ?? 0),
+    ownMerged: ownLedger.get(day)?.merged ?? 0,
+    ownClosed: ownLedger.get(day)?.closed ?? 0,
     reversed: reversals.get(day) ?? 0,
   }));
 
-  return buildPublicAccuracyTrend(dayRows, nowMs);
+  return buildPublicAccuracyTrend(dayRows, nowMs, PUBLIC_ACCURACY_TREND_WEEKS, reversalObservable);
 }