diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 77494704f..575890eda 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -703,8 +703,8 @@ paths:
                 lutealPhaseLength:
                   anyOf:
                     - type: integer
-                      minimum: 8
-                      maximum: 20
+                      minimum: 10
+                      maximum: 16
                     - type: "null"
       responses:
         "200":
diff --git a/src/app/api/cycle/calendar/route.ts b/src/app/api/cycle/calendar/route.ts
index ee72d97c5..fdeb41e54 100644
--- a/src/app/api/cycle/calendar/route.ts
+++ b/src/app/api/cycle/calendar/route.ts
@@ -28,7 +28,8 @@ import {
   goalAllowsFertileWindow,
 } from "@/lib/cycle/dto";
 import { persistPredictionCache } from "@/lib/cycle/prediction-cache";
-import { addDays } from "@/lib/cycle/day-math";
+import { addDays, dayDiff } from "@/lib/cycle/day-math";
+import { BBT_WINDOW } from "@/lib/cycle/types";
 import { DEFAULT_TIMEZONE, moodDateKey } from "@/lib/mood/date-key";
 import { getServerTranslator } from "@/lib/i18n/server-translator";
 import { resolveServerLocale } from "@/lib/i18n/server-locale";
@@ -75,8 +76,21 @@ export const GET = apiHandler(async (request: NextRequest) => {
       where: { userId: user.id, deletedAt: null },
       orderBy: { startDate: "asc" },
     }),
+    // Bound the day-log read to the rendered span plus the symptothermal
+    // lookback — the earlier of `from` and (today − BBT_WINDOW). Cycle-length
+    // stats run off MenstrualCycle rows, so day-logs can be windowed (QA: perf
+    // — unbounded full-history read on a hot, per-navigation route).
     prisma.cycleDayLog.findMany({
-      where: { userId: user.id, deletedAt: null },
+      where: {
+        userId: user.id,
+        deletedAt: null,
+        date: {
+          gte:
+            dayDiff(from, addDays(today, -BBT_WINDOW)) <= 0
+              ? from
+              : addDays(today, -BBT_WINDOW),
+        },
+      },
       orderBy: { date: "asc" },
       select: {
         date: true,
diff --git a/src/app/api/cycle/insights/route.ts b/src/app/api/cycle/insights/route.ts
index e6bd24db4..dc6acbc0d 100644
--- a/src/app/api/cycle/insights/route.ts
+++ b/src/app/api/cycle/insights/route.ts
@@ -35,6 +35,7 @@ import {
   discoverPhaseCorrelations,
   selectHeadlinePhaseRow,
   PHASE_CROSSTAB_METRIC_TYPES,
+  MOOD_CHANNEL_KEY,
 } from "@/lib/cycle/phase-crosstab";
 import type { CrossMetricMeasurement } from "@/lib/insights/mood-aggregates";
 import { addDays } from "@/lib/cycle/day-math";
@@ -56,14 +57,24 @@ export const GET = apiHandler(async () => {
   const today = moodDateKey(new Date(), tz);
   const from = addDays(today, -WINDOW_DAYS);
 
-  const [cycles, dayLogRows, nightlyTempRows, measurementRows, prefsRow] =
-    await Promise.all([
+  const [
+    cycles,
+    dayLogRows,
+    nightlyTempRows,
+    measurementRows,
+    prefsRow,
+    moodRows,
+  ] = await Promise.all([
       prisma.menstrualCycle.findMany({
         where: { userId: user.id, deletedAt: null },
         orderBy: { startDate: "asc" },
       }),
+      // Bound the day-log read to the rendered window (`from` = today − 365d),
+      // which is already earlier than the symptothermal lookback. Cycle-length
+      // stats run off MenstrualCycle rows so the day-logs can be windowed (QA:
+      // perf — unbounded full-history read).
       prisma.cycleDayLog.findMany({
-        where: { userId: user.id, deletedAt: null },
+        where: { userId: user.id, deletedAt: null, date: { gte: from } },
         orderBy: { date: "asc" },
         select: {
           date: true,
@@ -112,6 +123,18 @@ export const GET = apiHandler(async () => {
         where: { id: user.id },
         select: { sourcePriorityJson: true },
       }),
+      // MOOD outcome (QA HIGH): mood lives in MoodEntry (1–5 score), not a
+      // Measurement row, so read it here and inject it into the crosstab as a
+      // synthetic MOOD_CHANNEL_KEY measurement (same FDR / day-floor guards).
+      prisma.moodEntry.findMany({
+        where: {
+          userId: user.id,
+          deletedAt: null,
+          moodLoggedAt: { gte: new Date(Date.parse(`${from}T00:00:00Z`)) },
+        },
+        orderBy: { moodLoggedAt: "asc" },
+        select: { score: true, moodLoggedAt: true },
+      }),
     ]);
 
   // The latest open cycle runs to the predicted next-period start so the
@@ -146,6 +169,18 @@ export const GET = apiHandler(async () => {
     source: m.source,
     deviceType: m.deviceType,
   }));
+  // Inject mood as a synthetic MOOD_CHANNEL_KEY series (no source ladder — the
+  // metricDayMap pass-through keeps every row, averaging multiple same-day
+  // entries like every other channel).
+  for (const m of moodRows) {
+    measurements.push({
+      type: MOOD_CHANNEL_KEY,
+      value: m.score,
+      measuredAt: m.moodLoggedAt,
+      source: null,
+      deviceType: null,
+    });
+  }
 
   const userPriorityJson = prefsRow?.sourcePriorityJson ?? null;
 
diff --git a/src/lib/cycle/__tests__/phase-crosstab.test.ts b/src/lib/cycle/__tests__/phase-crosstab.test.ts
index 98142de80..a6c412830 100644
--- a/src/lib/cycle/__tests__/phase-crosstab.test.ts
+++ b/src/lib/cycle/__tests__/phase-crosstab.test.ts
@@ -7,7 +7,9 @@ import {
   selectHeadlinePhaseRow,
   PHASE_ORDINAL,
   PHASE_CROSSTAB_METRIC_TYPES,
+  PHASE_CROSSTAB_METRICS,
   CYCLE_PHASE_CHANNEL_KEY,
+  MOOD_CHANNEL_KEY,
   type PhaseMetricCrosstabRow,
 } from "../phase-crosstab";
 import type { CrossMetricMeasurement } from "@/lib/insights/mood-aggregates";
@@ -81,6 +83,76 @@ describe("PHASE_CROSSTAB_METRIC_TYPES", () => {
     expect(PHASE_CROSSTAB_METRIC_TYPES).toContain("BODY_TEMPERATURE");
     expect(PHASE_CROSSTAB_METRIC_TYPES).toContain("RESTING_HEART_RATE");
   });
+
+  it("includes GLUCOSE but NOT mood (mood is not a Measurement row)", () => {
+    expect(PHASE_CROSSTAB_METRIC_TYPES).toContain("BLOOD_GLUCOSE");
+    expect(PHASE_CROSSTAB_METRIC_TYPES).not.toContain(MOOD_CHANNEL_KEY);
+  });
+
+  it("declares mood + glucose as outcome metrics (QA HIGH)", () => {
+    expect(PHASE_CROSSTAB_METRICS.mood.type).toBe(MOOD_CHANNEL_KEY);
+    expect(PHASE_CROSSTAB_METRICS.bloodGlucose.type).toBe("BLOOD_GLUCOSE");
+  });
+});
+
+describe("computePhaseMetricCrosstab — MOOD + GLUCOSE outcomes (QA HIGH)", () => {
+  /** Build a luteal-vs-follicular contrast for an arbitrary outcome `type`. */
+  function contrastFor(type: string, lutealVal: number, follicularVal: number) {
+    const phaseByDay = new Map<string, CyclePhase>();
+    const measurements: CrossMetricMeasurement[] = [];
+    let idx = 0;
+    const dayKey = (i: number) => {
+      const d = new Date(Date.UTC(2026, 2, 1));
+      d.setUTCDate(d.getUTCDate() + i);
+      return d.toISOString().slice(0, 10);
+    };
+    for (let i = 0; i < 14; i++) {
+      const k = dayKey(idx++);
+      phaseByDay.set(k, "LUTEAL");
+      measurements.push(m(type, k, lutealVal + (i % 3) * 0.5));
+    }
+    for (let i = 0; i < 14; i++) {
+      const k = dayKey(idx++);
+      phaseByDay.set(k, "FOLLICULAR");
+      measurements.push(m(type, k, follicularVal + (i % 3) * 0.5));
+    }
+    return { phaseByDay, measurements };
+  }
+
+  it("surfaces a luteal-vs-follicular GLUCOSE contrast", () => {
+    const { phaseByDay, measurements } = contrastFor("BLOOD_GLUCOSE", 105, 92);
+    const rows = computePhaseMetricCrosstab({ phaseByDay, measurements });
+    const glucose = rows.find((r) => r.metricKey === "bloodGlucose");
+    expect(glucose).toBeDefined();
+    expect(glucose!.display).toBe("glucose");
+    expect(glucose!.delta).toBeGreaterThan(0);
+    expect(glucose!.pValue).toBeLessThan(0.05);
+  });
+
+  it("surfaces a luteal-vs-follicular MOOD contrast (injected synthetic channel)", () => {
+    const { phaseByDay, measurements } = contrastFor(MOOD_CHANNEL_KEY, 4.4, 2.6);
+    const rows = computePhaseMetricCrosstab({ phaseByDay, measurements });
+    const mood = rows.find((r) => r.metricKey === "mood");
+    expect(mood).toBeDefined();
+    expect(mood!.display).toBe("mood");
+    expect(mood!.delta).toBeGreaterThan(0);
+    expect(mood!.pValue).toBeLessThan(0.05);
+  });
+});
+
+describe("goalAllowsFertileWindow (QA MEDIUM)", () => {
+  it("shows the fertile window for TRYING_TO_CONCEIVE and AVOID_PREGNANCY", async () => {
+    const { goalAllowsFertileWindow } = await import("../dto");
+    expect(goalAllowsFertileWindow("TRYING_TO_CONCEIVE")).toBe(true);
+    expect(goalAllowsFertileWindow("AVOID_PREGNANCY")).toBe(true);
+  });
+
+  it("hides it for GENERAL_HEALTH / PERIMENOPAUSE / OFF", async () => {
+    const { goalAllowsFertileWindow } = await import("../dto");
+    expect(goalAllowsFertileWindow("GENERAL_HEALTH")).toBe(false);
+    expect(goalAllowsFertileWindow("PERIMENOPAUSE")).toBe(false);
+    expect(goalAllowsFertileWindow("OFF")).toBe(false);
+  });
 });
 
 describe("computePhaseMetricCrosstab", () => {
diff --git a/src/lib/cycle/__tests__/prediction.test.ts b/src/lib/cycle/__tests__/prediction.test.ts
index 4791bdd9d..019daff4d 100644
--- a/src/lib/cycle/__tests__/prediction.test.ts
+++ b/src/lib/cycle/__tests__/prediction.test.ts
@@ -2,6 +2,7 @@ import { describe, expect, it } from "vitest";
 
 import { addDays } from "../day-math";
 import {
+  clampLuteal,
   confirmSymptothermal,
   detectTempShift,
   detectTemperatureTrend,
@@ -10,6 +11,7 @@ import {
   median,
   observedPeriodLength,
   predictCycle,
+  resolveLuteal,
 } from "../prediction";
 import type {
   CycleInput,
@@ -401,3 +403,114 @@ describe("cycle/prediction — temperature-trend retrospective ovulation (§4.3)
     expect(result.predictedOvulation).toBe(addDays(start, 5));
   });
 });
+
+describe("cycle/prediction — multi-cycle window scoping (QA HIGH)", () => {
+  function bbtDay(date: string, t: number, mucus: DayLogInput["cervicalMucus"] = null): DayLogInput {
+    return { date, flow: null, basalBodyTempC: t, ovulationTest: null, cervicalMucus: mucus };
+  }
+
+  /** Build a confirmable symptothermal shift (temp + agreeing mucus) on `ovDay`. */
+  function symptothermalAround(ovDay: string): DayLogInput[] {
+    const logs: DayLogInput[] = [];
+    const riseStart = addDays(ovDay, 1);
+    const baselineStart = addDays(riseStart, -6);
+    [36.4, 36.41, 36.39, 36.4, 36.42, 36.4].forEach((t, i) =>
+      logs.push(bbtDay(addDays(baselineStart, i), t)),
+    );
+    logs.push(bbtDay(riseStart, 36.6));
+    logs.push(bbtDay(addDays(riseStart, 1), 36.62));
+    logs.push(bbtDay(addDays(riseStart, 2), 36.63));
+    logs.push({
+      date: ovDay,
+      flow: null,
+      basalBodyTempC: null,
+      ovulationTest: null,
+      cervicalMucus: "EGG_WHITE",
+    });
+    return logs;
+  }
+
+  it("does not confirm a STALE prior-cycle ovulation for a multi-cycle user", () => {
+    // Three confirmed cycles; last start 2024-03-25, today well into the
+    // current cycle. The ONLY BBT/mucus data is a complete shift back in the
+    // FIRST cycle (months ago). Pre-fix, detectTempShift returned that stale
+    // shift and nextPeriodStart landed in the past.
+    const cycles = cyclesFromGaps("2024-01-01", [28, 28, 28]);
+    const lastStart = cycles[cycles.length - 1].startDate;
+    expect(lastStart).toBe("2024-03-25");
+
+    const staleOv = addDays("2024-01-01", 13); // 2024-01-14, two cycles back
+    const logs = symptothermalAround(staleOv);
+
+    const today = addDays(lastStart, 16);
+    const result = predictCycle(cycles, logs, BASE_PROFILE, today);
+
+    // Stale signal is outside [lastStart − BBT_WINDOW, today] → ignored.
+    expect(result.ovulationConfirmed).toBe(false);
+    expect(result.method).toBe("CALENDAR");
+    // Calendar next-start is in the future, never in the past.
+    expect(result.nextPeriodStart >= today).toBe(true);
+  });
+
+  it("confirms the CURRENT-cycle shift even when a prior-cycle shift also exists", () => {
+    const cycles = cyclesFromGaps("2024-01-01", [28, 28, 28]);
+    const lastStart = cycles[cycles.length - 1].startDate; // 2024-03-25
+
+    const staleOv = addDays("2024-01-01", 13); // months ago
+    const currentOv = addDays(lastStart, 13); // current cycle
+    const logs = [...symptothermalAround(staleOv), ...symptothermalAround(currentOv)];
+
+    const result = predictCycle(cycles, logs, BASE_PROFILE, addDays(lastStart, 16));
+    expect(result.ovulationConfirmed).toBe(true);
+    expect(result.predictedOvulation).toBe(currentOv);
+    expect(result.nextPeriodStart).toBe(addDays(currentOv, 14));
+  });
+
+  it("detectTempShift returns the LATEST qualifying shift, not the earliest", () => {
+    const logs: DayLogInput[] = [];
+    // First shift around 2024-01-07.
+    const start = "2024-01-01";
+    [36.4, 36.42, 36.38, 36.41, 36.4, 36.39].forEach((t, i) =>
+      logs.push(bbtDay(addDays(start, i), t)),
+    );
+    logs.push(bbtDay(addDays(start, 6), 36.6));
+    logs.push(bbtDay(addDays(start, 7), 36.61));
+    logs.push(bbtDay(addDays(start, 8), 36.62));
+    // Drop back to baseline, then a SECOND shift a month later.
+    const start2 = "2024-02-01";
+    [36.4, 36.42, 36.38, 36.41, 36.4, 36.39].forEach((t, i) =>
+      logs.push(bbtDay(addDays(start2, i), t)),
+    );
+    logs.push(bbtDay(addDays(start2, 6), 36.6));
+    logs.push(bbtDay(addDays(start2, 7), 36.61));
+    logs.push(bbtDay(addDays(start2, 8), 36.62));
+
+    const shift = detectTempShift(logs, 0.2);
+    // Latest match → day before the second rise onset (2024-02-07 → 2024-02-06).
+    expect(shift?.ovulationDate).toBe(addDays(start2, 5));
+  });
+});
+
+describe("cycle/prediction — luteal clamp single source of truth (QA HIGH)", () => {
+  it("clampLuteal pins a raw value to [10, 16]", () => {
+    expect(clampLuteal(8)).toBe(10);
+    expect(clampLuteal(20)).toBe(16);
+    expect(clampLuteal(13)).toBe(13);
+  });
+
+  it("resolveLuteal applies the default then the clamp", () => {
+    expect(resolveLuteal({ lutealPhaseLength: null })).toBe(14);
+    expect(resolveLuteal({ lutealPhaseLength: 8 })).toBe(10);
+    expect(resolveLuteal({ lutealPhaseLength: 19 })).toBe(16);
+  });
+
+  it("predictCycle ovulation uses the CLAMPED luteal for an out-of-clamp profile", () => {
+    const cycles = cyclesFromGaps("2024-01-01", [28, 28, 28]);
+    const lastStart = cycles[cycles.length - 1].startDate;
+    // Profile asks for luteal 8 → engine clamps to 10.
+    const profile: CycleProfileInput = { ...BASE_PROFILE, lutealPhaseLength: 8 };
+    const result = predictCycle(cycles, [], profile, addDays(lastStart, 5));
+    // predictedOvulation = nextStart − clampedLuteal(10).
+    expect(result.predictedOvulation).toBe(addDays(result.nextPeriodStart, -10));
+  });
+});
diff --git a/src/lib/cycle/dto.ts b/src/lib/cycle/dto.ts
index 83b08d12c..067e718fb 100644
--- a/src/lib/cycle/dto.ts
+++ b/src/lib/cycle/dto.ts
@@ -236,11 +236,15 @@ type MenstrualCycleProfileRow = {
 };
 
 /**
- * Whether a goal surfaces the fertile window. Per the v1.15 contract the
- * window is gated to the conception goal only — GENERAL_HEALTH /
- * AVOID_PREGNANCY / PERIMENOPAUSE / OFF suppress it (the suppression is
- * always server-side, never iOS).
+ * Whether a goal surfaces the fertile window. Per algorithm.md §4 the window is
+ * shown for TRYING_TO_CONCEIVE and AVOID_PREGNANCY (AVOID_PREGNANCY carries a
+ * stronger "estimate, not a contraceptive method" caveat in the copy), and
+ * suppressed for GENERAL_HEALTH / PERIMENOPAUSE / OFF (the suppression is always
+ * server-side, never iOS).
  */
 export function goalAllowsFertileWindow(goal: string): boolean {
-  return goal === "TRYING_TO_CONCEIVE";
+  // algorithm.md §4: shown for TRYING_TO_CONCEIVE AND AVOID_PREGNANCY (the
+  // latter carries a stronger "not a contraceptive method" caveat in copy),
+  // hidden for GENERAL_HEALTH / PERIMENOPAUSE / OFF.
+  return goal === "TRYING_TO_CONCEIVE" || goal === "AVOID_PREGNANCY";
 }
diff --git a/src/lib/cycle/engine-adapter.ts b/src/lib/cycle/engine-adapter.ts
index 1474d0fdb..814596b34 100644
--- a/src/lib/cycle/engine-adapter.ts
+++ b/src/lib/cycle/engine-adapter.ts
@@ -17,7 +17,7 @@ import {
   type CyclePredictionResult,
   type CyclePhase,
   type PhaseCycle,
-  LUTEAL_DEFAULT,
+  resolveLuteal,
 } from "@/lib/cycle";
 import type {
   CycleProfile,
@@ -219,7 +219,10 @@ export function buildCalendar(
   today: string,
   goalAllowsFertile: boolean,
 ): CalendarBuildResult {
-  const lutealLength = profile.lutealPhaseLength ?? LUTEAL_DEFAULT;
+  // Clamp identically to the engine's resolveLuteal so the predicted-ovulation
+  // dot (engine-clamped) and the OVULATORY phase band (this value) never
+  // diverge for an out-of-clamp stored luteal length (QA HIGH).
+  const lutealLength = resolveLuteal(profile);
 
   // Forecast (only when prediction is on + not raw-chart mode).
   let prediction: CyclePredictionResult | null = null;
diff --git a/src/lib/cycle/index.ts b/src/lib/cycle/index.ts
index 13ff49741..a0368f830 100644
--- a/src/lib/cycle/index.ts
+++ b/src/lib/cycle/index.ts
@@ -19,5 +19,7 @@ export {
   detectTemperatureTrend,
   median,
   mad,
+  resolveLuteal,
+  clampLuteal,
 } from "./prediction";
 export { phaseForDay, phaseSeries, type PhaseCycle } from "./phase";
diff --git a/src/lib/cycle/phase-crosstab.ts b/src/lib/cycle/phase-crosstab.ts
index 7732cd790..096a9aa3e 100644
--- a/src/lib/cycle/phase-crosstab.ts
+++ b/src/lib/cycle/phase-crosstab.ts
@@ -75,7 +75,20 @@ export type PhaseCrosstabDisplay =
   | "bpm"
   | "ms"
   | "kg"
-  | "celsius";
+  | "celsius"
+  | "glucose"
+  | "mood";
+
+/**
+ * Synthetic non-MeasurementType channel key for the MOOD outcome. Mood lives in
+ * the separate `MoodEntry` model (1–5 score), not a Measurement row, so the
+ * caller injects it into the crosstab `measurements` array tagged with this key
+ * and `metricDayMap` groups it like any other type (its pass-through fallback
+ * keeps every row — there is no source ladder for mood). It is deliberately NOT
+ * a member of `PHASE_CROSSTAB_METRIC_TYPES`, so it never enters the Measurement
+ * read query.
+ */
+export const MOOD_CHANNEL_KEY = "MOOD";
 
 /**
  * The outcome metric grid the phase contrast walks. Mirrors
@@ -86,7 +99,7 @@ export type PhaseCrosstabDisplay =
  */
 export const PHASE_CROSSTAB_METRICS: Record<
   string,
-  { type: MeasurementType; display: PhaseCrosstabDisplay }
+  { type: MeasurementType | typeof MOOD_CHANNEL_KEY; display: PhaseCrosstabDisplay }
 > = {
   restingHeartRate: { type: "RESTING_HEART_RATE", display: "bpm" },
   heartRateVariability: { type: "HEART_RATE_VARIABILITY", display: "ms" },
@@ -96,13 +109,26 @@ export const PHASE_CROSSTAB_METRICS: Record<
   basalBodyTemp: { type: "BODY_TEMPERATURE", display: "celsius" },
   wristTemperature: { type: "WRIST_TEMPERATURE", display: "celsius" },
   skinTemperature: { type: "SKIN_TEMPERATURE", display: "celsius" },
+  // QA HIGH (features): the crosstab must cover MOOD + GLUCOSE as outcomes,
+  // under the identical FDR / day-floor guards. Glucose is a MeasurementType;
+  // mood is the synthetic MOOD_CHANNEL_KEY the route injects (see above).
+  bloodGlucose: { type: "BLOOD_GLUCOSE", display: "glucose" },
+  mood: { type: MOOD_CHANNEL_KEY, display: "mood" },
 } as const;
 
 export type PhaseCrosstabMetricKey = keyof typeof PHASE_CROSSTAB_METRICS;
 
-/** Distinct measurement types the phase crosstab reads — single-sourced. */
+/**
+ * Distinct MeasurementType values the phase crosstab reads — single-sourced.
+ * MOOD_CHANNEL_KEY is excluded: it is not a Measurement row (the route reads it
+ * from MoodEntry and injects it), so it must never enter the Measurement query.
+ */
 export const PHASE_CROSSTAB_METRIC_TYPES: MeasurementType[] = Array.from(
-  new Set(Object.values(PHASE_CROSSTAB_METRICS).map((m) => m.type)),
+  new Set(
+    Object.values(PHASE_CROSSTAB_METRICS)
+      .map((m) => m.type)
+      .filter((t): t is MeasurementType => t !== MOOD_CHANNEL_KEY),
+  ),
 );
 
 /** The two phases the categorical contrast compares (largest contrast). */
diff --git a/src/lib/cycle/phase.ts b/src/lib/cycle/phase.ts
index 211f6bc1a..c351db77a 100644
--- a/src/lib/cycle/phase.ts
+++ b/src/lib/cycle/phase.ts
@@ -18,6 +18,7 @@
  */
 
 import { addDays, dayDiff } from "./day-math";
+import { clampLuteal } from "./prediction";
 import { LUTEAL_DEFAULT, POPULATION_DEFAULT_PERIOD, type CyclePhase } from "./types";
 
 /** A resolved cycle window the phase mapper needs. */
@@ -54,7 +55,8 @@ export function phaseForDay(
   const dayOfCycle = offsetFromStart + 1; // 1-based
 
   const periodLength = cycle.periodLength ?? POPULATION_DEFAULT_PERIOD;
-  const lutealLength = cycle.lutealLength ?? LUTEAL_DEFAULT;
+  // Clamp identically to the prediction engine (QA HIGH: one source of truth).
+  const lutealLength = clampLuteal(cycle.lutealLength ?? LUTEAL_DEFAULT);
 
   // Ovulation: confirmed/estimated date, or back-calculated from length.
   const ovulationDate =
diff --git a/src/lib/cycle/prediction.ts b/src/lib/cycle/prediction.ts
index 94ac6b64e..736396cac 100644
--- a/src/lib/cycle/prediction.ts
+++ b/src/lib/cycle/prediction.ts
@@ -16,6 +16,7 @@ import { addDays, dayDiff, roundHalf } from "./day-math";
 import {
   ADHERENCE_FLOOR,
   ADHERENCE_SLOPE,
+  BBT_WINDOW,
   COLD_START_BAND_BONUS,
   CONFIDENCE_LABEL_HIGH_MIN,
   CONFIDENCE_LABEL_LOW_MAX,
@@ -272,8 +273,11 @@ export function detectTempShift(
     .map((l) => ({ date: l.date, t: l.basalBodyTempC as number }))
     .sort((a, b) => dayDiff(a.date, b.date));
 
-  // Need 6 baseline + 3 elevated = 9 readings minimum.
-  for (let i = 6; i + 2 < temps.length; i++) {
+  // Need 6 baseline + 3 elevated = 9 readings minimum. Scan from the END and
+  // return the LATEST qualifying shift — for a multi-cycle BBT series the most
+  // recent rise is the one that belongs to the current cycle; the earliest
+  // match would confirm a months-old ovulation (QA: window scoping).
+  for (let i = temps.length - 3; i >= 6; i--) {
     const baseline = temps.slice(i - 6, i);
     const sixMax = Math.max(...baseline.map((x) => x.t));
     const rise = [temps[i], temps[i + 1], temps[i + 2]];
@@ -413,11 +417,21 @@ function clamp(x: number, lo: number, hi: number): number {
   return Math.min(hi, Math.max(lo, x));
 }
 
-function resolveLuteal(profile: CycleProfileInput): number {
-  const raw = profile.lutealPhaseLength ?? LUTEAL_DEFAULT;
+/**
+ * Clamp a raw luteal length to the physiological range [LUTEAL_MIN, LUTEAL_MAX]
+ * (§4). The ONE source of truth for resolving luteal length — the engine,
+ * calendar adapter, and phase mapper all route through this so the
+ * predicted-ovulation dot and the OVULATORY band can never diverge for a user
+ * whose stored value is out of clamp (QA HIGH: luteal clamp divergence).
+ */
+export function clampLuteal(raw: number): number {
   return clamp(raw, LUTEAL_MIN, LUTEAL_MAX);
 }
 
+export function resolveLuteal(profile: Pick<CycleProfileInput, "lutealPhaseLength">): number {
+  return clampLuteal(profile.lutealPhaseLength ?? LUTEAL_DEFAULT);
+}
+
 /* ------------------------------------------------------------------ */
 /* main entry                                                         */
 /* ------------------------------------------------------------------ */
@@ -490,21 +504,43 @@ export function predictCycle(
   // Precedence: confirmed-symptothermal > temperature-trend > calendar. A
   // confirmed signal overrides the CURRENT cycle's ovulation/next-start; the
   // calendar predictor still fills all FUTURE cycles (BLENDED records that mix).
-  const symptoOvulation = confirmSymptothermal(dayLogs);
-  const trendOvulation = symptoOvulation ? null : detectTemperatureTrend(nights);
+  //
+  // Window scoping (QA HIGH): the symptothermal/temperature-trend detectors
+  // must only see the CURRENT cycle's signal, otherwise a multi-cycle user's
+  // stale prior-cycle BBT/mucus confirms a months-old ovulation and lands
+  // nextPeriodStart in the past. Scope to [lastConfirmedStart − BBT_WINDOW,
+  // today]; the BBT_WINDOW reach-back keeps the 6-reading baseline intact for a
+  // young current cycle. detectTempShift returns the LATEST qualifying shift.
+  const windowStart = addDays(lastConfirmedStart, -BBT_WINDOW);
+  const isInCurrentWindow = (date: string) =>
+    dayDiff(date, windowStart) >= 0 && dayDiff(today, date) >= 0;
+  const currentDayLogs = dayLogs.filter((l) => isInCurrentWindow(l.date));
+  const currentNights = nights.filter((n) => isInCurrentWindow(n.date));
+  const symptoOvulation = confirmSymptothermal(currentDayLogs);
+  const trendOvulation = symptoOvulation
+    ? null
+    : detectTemperatureTrend(currentNights);
 
   if (symptoOvulation) {
-    predictedOvulation = symptoOvulation;
-    nextStart = addDays(symptoOvulation, lutealLength);
-    ovulationConfirmed = true;
-    confirmMultiplier = HALF_WIDTH_MULT_SYMPTOTHERMAL;
-    method = lengths.length > 0 ? "BLENDED" : "SYMPTOTHERMAL";
+    const confirmedNextStart = addDays(symptoOvulation, lutealLength);
+    // Reject a confirmation whose next-start is already in the past (a stale
+    // signal that slipped through the window) — fall back to the calendar.
+    if (dayDiff(confirmedNextStart, today) >= 0) {
+      predictedOvulation = symptoOvulation;
+      nextStart = confirmedNextStart;
+      ovulationConfirmed = true;
+      confirmMultiplier = HALF_WIDTH_MULT_SYMPTOTHERMAL;
+      method = lengths.length > 0 ? "BLENDED" : "SYMPTOTHERMAL";
+    }
   } else if (trendOvulation) {
-    predictedOvulation = trendOvulation;
-    nextStart = addDays(trendOvulation, lutealLength);
-    ovulationConfirmed = true;
-    confirmMultiplier = HALF_WIDTH_MULT_TEMP_TREND;
-    method = lengths.length > 0 ? "BLENDED" : "TEMPERATURE_TREND";
+    const confirmedNextStart = addDays(trendOvulation, lutealLength);
+    if (dayDiff(confirmedNextStart, today) >= 0) {
+      predictedOvulation = trendOvulation;
+      nextStart = confirmedNextStart;
+      ovulationConfirmed = true;
+      confirmMultiplier = HALF_WIDTH_MULT_TEMP_TREND;
+      method = lengths.length > 0 ? "BLENDED" : "TEMPERATURE_TREND";
+    }
   }
 
   // -------- §3 band half-width --------
diff --git a/src/lib/cycle/types.ts b/src/lib/cycle/types.ts
index b23a5dbb3..fdb3926ea 100644
--- a/src/lib/cycle/types.ts
+++ b/src/lib/cycle/types.ts
@@ -120,6 +120,15 @@ export const HALF_WIDTH_MULT_TEMP_TREND = 0.75;
 /** §4 — symptothermal agreement tolerance between temp-shift and mucus peak (days). */
 export const SYMPTOTHERMAL_AGREE_DAYS = 2;
 
+/**
+ * §4 — trailing lookback (days) for the symptothermal / temperature-trend
+ * detectors. The 3-over-6 BBT rule needs 6 baseline readings before the rise,
+ * so a current-cycle scan starting at lastConfirmedStart must reach back this
+ * far to keep the baseline window intact when the cycle is still young. Also
+ * the floor for windowing the day-log read on the hot calendar/insights routes.
+ */
+export const BBT_WINDOW = 40;
+
 /** §3 — confidence scalar clamp (never certain, never zero). */
 export const CONFIDENCE_MIN = 0.05;
 export const CONFIDENCE_MAX = 0.98;
diff --git a/src/lib/validations/cycle.ts b/src/lib/validations/cycle.ts
index e4f490f1b..ce0bda8bb 100644
--- a/src/lib/validations/cycle.ts
+++ b/src/lib/validations/cycle.ts
@@ -176,7 +176,9 @@ export const cyclePrefsSchema = z
     sensitiveCategoryEncryption: z.boolean().optional(),
     typicalCycleLength: z.number().int().min(15).max(60).nullable().optional(),
     typicalPeriodLength: z.number().int().min(1).max(15).nullable().optional(),
-    lutealPhaseLength: z.number().int().min(8).max(20).nullable().optional(),
+    // Bound matches the engine clamp [LUTEAL_MIN, LUTEAL_MAX] (§4) so the
+    // stored value never silently snaps in the predictor (QA HIGH).
+    lutealPhaseLength: z.number().int().min(10).max(16).nullable().optional(),
   })
   .refine((v) => Object.keys(v).length > 0, {
     message: "At least one preference field is required",