diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 5a859419a..4c1f9600a 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -1906,6 +1906,27 @@ paths:
         "401": *a1
         "422": *a3
         "429": *a4
+  /api/sleep/rhythm:
+    get:
+      tags:
+        - Measurements
+      summary: Sleep rhythm — sleep-debt + chronotype (v1.17.0)
+      description: "Returns the two server-authoritative sleep-timing signals the Sleep page + iOS render off the same
+        canonical night reconstruction the Sleep Score uses: cumulative `sleepDebt` over the rolling window (calm
+        `partial` state under the night threshold) and MCTQ `chronotype` (MSF/MSFsc band + social jetlag, `learning`
+        state until enough free-day nights exist). Free vs work nights default to weekend = free in the user's timezone
+        (no work calendar). A read-only view over existing per-stage SLEEP_DURATION rows — no schema, no new measurement
+        type."
+      responses:
+        "200":
+          description: Sleep-debt + chronotype DTO.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/SleepRhythmResponse"
+        "401": *a1
+        "422": *a3
+        "429": *a4
   /api/workouts:
     get:
       tags:
@@ -9138,6 +9159,134 @@ components:
       additionalProperties: false
       description: "One reconstructed sleep night: the main session's hypnogram segments + breakdown, plus same-wake-day naps
         surfaced separately."
+    SleepRhythmResponse:
+      type: object
+      properties:
+        data:
+          $ref: "#/components/schemas/SleepRhythmResource"
+        error:
+          type: "null"
+        meta:
+          type: object
+          properties:
+            requestId:
+              type: string
+          additionalProperties: false
+      required:
+        - data
+        - error
+      additionalProperties: false
+    SleepRhythmResource:
+      type: object
+      properties:
+        sleepDebt:
+          type: object
+          properties:
+            state:
+              type: string
+              enum:
+                - partial
+                - ready
+              description: "`partial` until enough tracked nights exist (calm 'still learning'); `ready` once the rolling window can
+                assert a cumulative debt."
+            debtMinutes:
+              type: integer
+              minimum: 0
+              maximum: 9007199254740991
+              description: Cumulative sleep debt over the window, in minutes, after caps.
+            needMinutes:
+              type: integer
+              minimum: 0
+              maximum: 9007199254740991
+              description: Age-based sleep need (minutes) used for the per-night deficit.
+            nightsCounted:
+              type: integer
+              minimum: 0
+              maximum: 9007199254740991
+            windowNights:
+              type: integer
+              exclusiveMinimum: 0
+              maximum: 9007199254740991
+              description: Rolling window length in nights.
+            nightsUntilReady:
+              type: integer
+              minimum: 0
+              maximum: 9007199254740991
+              description: Nights still needed before the debt is asserted (0 when ready).
+          required:
+            - state
+            - debtMinutes
+            - needMinutes
+            - nightsCounted
+            - windowNights
+            - nightsUntilReady
+          additionalProperties: false
+        chronotype:
+          type: object
+          properties:
+            state:
+              type: string
+              enum:
+                - learning
+                - ready
+              description: "`learning` until enough free-day nights exist (no band asserted); `ready` once the free-day sample is
+                large enough."
+            msfMinutes:
+              anyOf:
+                - type: number
+                - type: "null"
+              description: Mid-sleep on free days (minutes-of-day), null while learning.
+            msfScMinutes:
+              anyOf:
+                - type: number
+                - type: "null"
+              description: Sleep-debt-corrected mid-sleep on free days (MSFsc, minutes-of-day), null while learning.
+            band:
+              anyOf:
+                - type: string
+                  enum:
+                    - extreme_early
+                    - early
+                    - intermediate
+                    - late
+                    - extreme_late
+                - type: "null"
+              description: MCTQ chronotype band off MSFsc, null while learning.
+            socialJetlagMinutes:
+              anyOf:
+                - type: number
+                - type: "null"
+              description: Social jetlag = circular |MSF_work − MSF_free| in minutes, null when one side is missing.
+            freeNightsCounted:
+              type: integer
+              minimum: 0
+              maximum: 9007199254740991
+            workNightsCounted:
+              type: integer
+              minimum: 0
+              maximum: 9007199254740991
+            freeNightsUntilReady:
+              type: integer
+              minimum: 0
+              maximum: 9007199254740991
+              description: Free-day nights still needed before a band is asserted.
+          required:
+            - state
+            - msfMinutes
+            - msfScMinutes
+            - band
+            - socialJetlagMinutes
+            - freeNightsCounted
+            - workNightsCounted
+            - freeNightsUntilReady
+          additionalProperties: false
+      required:
+        - sleepDebt
+        - chronotype
+      additionalProperties: false
+      description: "Server-authoritative sleep-rhythm read: cumulative sleep debt over the rolling window + MCTQ chronotype
+        (MSF/MSFsc band, social jetlag). Free vs work nights default to weekend = free in the user's timezone (no work
+        calendar). A view over existing per-stage SLEEP_DURATION rows — no schema, no new type."
     ListWorkoutsResponse:
       type: object
       properties:
diff --git a/messages/de.json b/messages/de.json
index cfea1b804..34e9dc3fa 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -2666,6 +2666,32 @@
         "title": "Noch keine Schlafdaten",
         "description": "Apple-Health-Sync folgt mit v1.5 und füllt diese Ansicht automatisch.",
         "action": "Geräte verwalten"
+      },
+      "debt": {
+        "title": "Schlafschuld",
+        "value": "{hours} Std. {minutes} Min. zu wenig",
+        "caption": "Kumuliertes Defizit der letzten {nights} Nächte",
+        "clearValue": "Ausgeglichen",
+        "clearCaption": "Kein aufgelaufenes Defizit über die letzten {nights} Nächte",
+        "learning": "Dein Schlaf wird noch erfasst — {counted} Nächte bisher, noch {remaining} für eine verlässliche Bilanz."
+      },
+      "chronotype": {
+        "title": "Chronotyp",
+        "learning": "Dein Rhythmus wird noch erfasst — {counted} von {total} freien Nächten. Ein Chronotyp braucht ein paar weckerfreie Morgen, um aussagekräftig zu sein.",
+        "midSleepCaption": "Schlafmitte an freien Tagen gegen {clock}",
+        "advancedToggle": "Mehr Details",
+        "socialJetlagValue": "{hours} Std. {minutes} Min. sozialer Jetlag",
+        "socialJetlagCaption": "Der Unterschied zwischen deinem Schlaf an Arbeits- und freien Tagen — wie eine kleine wöchentliche Zeitzonenverschiebung.",
+        "msfScValue": "Korrigierte Schlafmitte {clock}",
+        "msfScCaption": "Bereinigt um den Schlaf, den du am Wochenende nachholst (MSFsc).",
+        "dayTypeNote": "Freie Tage werden als Wochenenden angenommen, bis eine Tagestyp-Erfassung ergänzt wird.",
+        "band": {
+          "extreme_early": "Ausgeprägter Morgentyp",
+          "early": "Morgentyp",
+          "intermediate": "Mischtyp",
+          "late": "Abendtyp",
+          "extreme_late": "Ausgeprägter Abendtyp"
+        }
       }
     },
     "correlations": "Korrelationen",
diff --git a/messages/en.json b/messages/en.json
index 0e147aab4..58d202c7a 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -2666,6 +2666,32 @@
         "title": "No sleep data yet",
         "description": "Apple Health sync arrives in v1.5 and will fill this in automatically.",
         "action": "Manage devices"
+      },
+      "debt": {
+        "title": "Sleep debt",
+        "value": "{hours}h {minutes}m short",
+        "caption": "Cumulative shortfall over the last {nights} nights",
+        "clearValue": "All caught up",
+        "clearCaption": "No accumulated shortfall over the last {nights} nights",
+        "learning": "Still learning your sleep — {counted} nights so far, {remaining} more to read a reliable balance."
+      },
+      "chronotype": {
+        "title": "Chronotype",
+        "learning": "Still learning your rhythm — {counted} of {total} free nights. A chronotype needs a few alarm-free mornings before it means anything.",
+        "midSleepCaption": "Mid-sleep on free days around {clock}",
+        "advancedToggle": "Advanced",
+        "socialJetlagValue": "{hours}h {minutes}m social jetlag",
+        "socialJetlagCaption": "The gap between your work-day and free-day sleep timing — like a small weekly time-zone shift.",
+        "msfScValue": "Corrected mid-sleep {clock}",
+        "msfScCaption": "Adjusted for the sleep you catch up on at the weekend (MSFsc).",
+        "dayTypeNote": "Free days are assumed to be weekends until day-type tracking is added.",
+        "band": {
+          "extreme_early": "Strong morning type",
+          "early": "Morning type",
+          "intermediate": "Intermediate type",
+          "late": "Evening type",
+          "extreme_late": "Strong evening type"
+        }
       }
     },
     "correlations": "Correlations",
diff --git a/messages/es.json b/messages/es.json
index ee2ea77c3..1a6f6b74f 100644
--- a/messages/es.json
+++ b/messages/es.json
@@ -2666,6 +2666,32 @@
         "title": "Aún no hay datos de sueño",
         "description": "La sincronización con Apple Health llega con la v1.5 y llenará esta vista automáticamente.",
         "action": "Gestionar dispositivos"
+      },
+      "debt": {
+        "title": "Deuda de sueño",
+        "value": "{hours} h {minutes} min de déficit",
+        "caption": "Déficit acumulado de las últimas {nights} noches",
+        "clearValue": "Al día",
+        "clearCaption": "Sin déficit acumulado en las últimas {nights} noches",
+        "learning": "Aún estamos midiendo tu sueño — {counted} noches hasta ahora, faltan {remaining} para un balance fiable."
+      },
+      "chronotype": {
+        "title": "Cronotipo",
+        "learning": "Aún estamos aprendiendo tu ritmo — {counted} de {total} noches libres. Un cronotipo necesita varias mañanas sin despertador para tener sentido.",
+        "midSleepCaption": "Punto medio del sueño en días libres en torno a las {clock}",
+        "advancedToggle": "Avanzado",
+        "socialJetlagValue": "{hours} h {minutes} min de jet lag social",
+        "socialJetlagCaption": "La diferencia entre el horario de sueño laboral y el de los días libres — como un pequeño cambio de huso horario semanal.",
+        "msfScValue": "Punto medio corregido {clock}",
+        "msfScCaption": "Ajustado por el sueño que recuperas el fin de semana (MSFsc).",
+        "dayTypeNote": "Se asume que los días libres son los fines de semana hasta que se añada el registro del tipo de día.",
+        "band": {
+          "extreme_early": "Matutino marcado",
+          "early": "Matutino",
+          "intermediate": "Intermedio",
+          "late": "Vespertino",
+          "extreme_late": "Vespertino marcado"
+        }
       }
     },
     "correlations": "Correlaciones",
diff --git a/messages/fr.json b/messages/fr.json
index 54b3b084b..000f3f8fd 100644
--- a/messages/fr.json
+++ b/messages/fr.json
@@ -2666,6 +2666,32 @@
         "title": "Pas encore de données de sommeil",
         "description": "La synchro Apple Health arrive avec la v1.5 et remplira automatiquement cette vue.",
         "action": "Gérer les appareils"
+      },
+      "debt": {
+        "title": "Dette de sommeil",
+        "value": "{hours} h {minutes} min de déficit",
+        "caption": "Déficit cumulé sur les {nights} dernières nuits",
+        "clearValue": "À jour",
+        "clearCaption": "Aucun déficit cumulé sur les {nights} dernières nuits",
+        "learning": "Votre sommeil est encore en cours d'analyse — {counted} nuits jusqu'ici, encore {remaining} pour un bilan fiable."
+      },
+      "chronotype": {
+        "title": "Chronotype",
+        "learning": "Votre rythme est encore en cours d'analyse — {counted} sur {total} nuits libres. Un chronotype a besoin de quelques matins sans réveil pour avoir du sens.",
+        "midSleepCaption": "Milieu de sommeil les jours libres vers {clock}",
+        "advancedToggle": "Avancé",
+        "socialJetlagValue": "{hours} h {minutes} min de jet lag social",
+        "socialJetlagCaption": "L'écart entre vos horaires de sommeil les jours travaillés et les jours libres — comme un petit décalage horaire hebdomadaire.",
+        "msfScValue": "Milieu de sommeil corrigé {clock}",
+        "msfScCaption": "Ajusté pour le sommeil rattrapé le week-end (MSFsc).",
+        "dayTypeNote": "Les jours libres sont supposés être les week-ends jusqu'à l'ajout du suivi du type de jour.",
+        "band": {
+          "extreme_early": "Type du matin marqué",
+          "early": "Type du matin",
+          "intermediate": "Type intermédiaire",
+          "late": "Type du soir",
+          "extreme_late": "Type du soir marqué"
+        }
       }
     },
     "correlations": "Corrélations",
diff --git a/messages/it.json b/messages/it.json
index 04730edac..e0b84e5fb 100644
--- a/messages/it.json
+++ b/messages/it.json
@@ -2666,6 +2666,32 @@
         "title": "Ancora nessun dato sul sonno",
         "description": "La sync con Apple Health arriva con v1.5 e riempirà questa vista in automatico.",
         "action": "Gestisci dispositivi"
+      },
+      "debt": {
+        "title": "Debito di sonno",
+        "value": "{hours} h {minutes} min in meno",
+        "caption": "Deficit cumulato nelle ultime {nights} notti",
+        "clearValue": "In pari",
+        "clearCaption": "Nessun deficit accumulato nelle ultime {nights} notti",
+        "learning": "Stiamo ancora misurando il tuo sonno — {counted} notti finora, ne mancano {remaining} per un bilancio affidabile."
+      },
+      "chronotype": {
+        "title": "Cronotipo",
+        "learning": "Stiamo ancora imparando il tuo ritmo — {counted} di {total} notti libere. Un cronotipo richiede alcune mattine senza sveglia per avere significato.",
+        "midSleepCaption": "Metà del sonno nei giorni liberi intorno alle {clock}",
+        "advancedToggle": "Avanzate",
+        "socialJetlagValue": "{hours} h {minutes} min di jet lag sociale",
+        "socialJetlagCaption": "La differenza tra gli orari del sonno nei giorni lavorativi e in quelli liberi — come un piccolo cambio di fuso orario settimanale.",
+        "msfScValue": "Metà del sonno corretta {clock}",
+        "msfScCaption": "Corretta per il sonno recuperato nel fine settimana (MSFsc).",
+        "dayTypeNote": "Si presume che i giorni liberi siano i fine settimana finché non verrà aggiunto il tracciamento del tipo di giorno.",
+        "band": {
+          "extreme_early": "Tipo mattutino marcato",
+          "early": "Tipo mattutino",
+          "intermediate": "Tipo intermedio",
+          "late": "Tipo serale",
+          "extreme_late": "Tipo serale marcato"
+        }
       }
     },
     "correlations": "Correlazioni",
diff --git a/messages/pl.json b/messages/pl.json
index e3915160a..4e6b5c97c 100644
--- a/messages/pl.json
+++ b/messages/pl.json
@@ -2666,6 +2666,32 @@
         "title": "Brak danych o śnie",
         "description": "Synchronizacja Apple Health pojawi się w v1.5 i wypełni ten widok automatycznie.",
         "action": "Zarządzaj urządzeniami"
+      },
+      "debt": {
+        "title": "Dług snu",
+        "value": "{hours} godz. {minutes} min niedoboru",
+        "caption": "Skumulowany niedobór z ostatnich {nights} nocy",
+        "clearValue": "Na bieżąco",
+        "clearCaption": "Brak skumulowanego niedoboru w ostatnich {nights} nocach",
+        "learning": "Wciąż analizujemy Twój sen — {counted} nocy do tej pory, jeszcze {remaining}, aby uzyskać wiarygodny bilans."
+      },
+      "chronotype": {
+        "title": "Chronotyp",
+        "learning": "Wciąż poznajemy Twój rytm — {counted} z {total} wolnych nocy. Chronotyp wymaga kilku poranków bez budzika, aby coś znaczył.",
+        "midSleepCaption": "Środek snu w dni wolne około {clock}",
+        "advancedToggle": "Zaawansowane",
+        "socialJetlagValue": "{hours} godz. {minutes} min jet lagu społecznego",
+        "socialJetlagCaption": "Różnica między porą snu w dni robocze i wolne — jak niewielka cotygodniowa zmiana strefy czasowej.",
+        "msfScValue": "Skorygowany środek snu {clock}",
+        "msfScCaption": "Skorygowany o sen nadrabiany w weekend (MSFsc).",
+        "dayTypeNote": "Dni wolne przyjmuje się jako weekendy, dopóki nie zostanie dodane śledzenie typu dnia.",
+        "band": {
+          "extreme_early": "Wyraźny typ poranny",
+          "early": "Typ poranny",
+          "intermediate": "Typ pośredni",
+          "late": "Typ wieczorny",
+          "extreme_late": "Wyraźny typ wieczorny"
+        }
       }
     },
     "correlations": "Korelacje",
diff --git a/src/app/api/dashboard/summary/__tests__/route.test.ts b/src/app/api/dashboard/summary/__tests__/route.test.ts
index 36f1e9506..3b90d33f4 100644
--- a/src/app/api/dashboard/summary/__tests__/route.test.ts
+++ b/src/app/api/dashboard/summary/__tests__/route.test.ts
@@ -27,6 +27,11 @@ vi.mock("@/lib/db", () => ({
     medicationScheduleRevision: {
       groupBy: vi.fn(),
     },
+    // v1.17.0 — the sleep-rhythm block resolves the user's age-based sleep
+    // need via the baseline profile (`User` row).
+    user: {
+      findUnique: vi.fn(),
+    },
     // v1.4.38 W-F — the route now uses `$queryRaw` for the per-type
     // latest reading, the 7-day rollup-bucket sparkline, and the
     // 365-day distinct-day streak set. Three raw calls per request,
@@ -120,6 +125,13 @@ beforeEach(() => {
   vi.mocked(prisma.medicationScheduleRevision.groupBy).mockResolvedValue(
     [] as never,
   );
+  // v1.17.0 — baseline profile read for the sleep-rhythm need. Default to a
+  // 40-year-old adult (need = 420 min) so the rhythm block resolves.
+  vi.mocked(prisma.user.findUnique).mockResolvedValue({
+    dateOfBirth: new Date("1986-01-01"),
+    gender: null,
+    heightCm: null,
+  } as never);
 });
 
 // v1.4.48 L13 — restore real timers no matter how a test exits. A failed
@@ -515,6 +527,59 @@ describe("GET /api/dashboard/summary", () => {
     expect(sleep?.sleepStages?.REM).toBeCloseTo(80 / 60, 2);
   });
 
+  it("emits the sleep-rhythm DTO (sleep-debt + chronotype) computed from the foundation modules (v1.17.0)", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    // Ten consecutive 6 h (360 min) nights. Need = 420 (40-year-old default in
+    // beforeEach) → a 60-min deficit per night, 10 nights ≥ the 7-night floor.
+    const rows = [];
+    for (let d = 1; d <= 10; d++) {
+      const day = String(d).padStart(2, "0");
+      rows.push({
+        value: 360,
+        measuredAt: new Date(`2026-06-${day}T06:00:00.000Z`),
+        sleepStage: "ASLEEP",
+        source: "APPLE_HEALTH",
+        deviceType: null,
+      });
+    }
+    vi.mocked(prisma.measurement.findMany).mockResolvedValue(rows as never);
+
+    const res = await callGet(makeReq());
+    const body = (await res.json()) as {
+      data: {
+        sleepRhythm: {
+          sleepDebt: {
+            state: string;
+            debtMinutes: number;
+            needMinutes: number;
+            nightsCounted: number;
+            windowNights: number;
+            nightsUntilReady: number;
+          };
+          chronotype: {
+            state: string;
+            freeNightsCounted: number;
+            workNightsCounted: number;
+            freeNightsUntilReady: number;
+          };
+        };
+      };
+    };
+    const { sleepDebt, chronotype } = body.data.sleepRhythm;
+    // Debt DTO is the computeSleepDebt result: ready, 10 × 60 = 600 min, need
+    // forwarded as 420 — proves the route reused the module, not a recompute.
+    expect(sleepDebt.state).toBe("ready");
+    expect(sleepDebt.debtMinutes).toBe(600);
+    expect(sleepDebt.needMinutes).toBe(420);
+    expect(sleepDebt.nightsCounted).toBe(10);
+    expect(sleepDebt.nightsUntilReady).toBe(0);
+    // Chronotype DTO carries every wiring field; the calm learning state holds
+    // until enough free-day nights exist (these are all weekday wake days).
+    expect(chronotype.state).toBe("learning");
+    expect(typeof chronotype.freeNightsCounted).toBe("number");
+    expect(typeof chronotype.freeNightsUntilReady).toBe("number");
+  });
+
   it("paints the steps sparkline from rollup sum_value, not mean (v1.4.39 W-SUM)", async () => {
     // The ACTIVITY_STEPS tile renders the per-day SUM, not the
     // per-bucket MEAN. The sparkline query feeds the SQL aggregate
diff --git a/src/app/api/dashboard/summary/route.ts b/src/app/api/dashboard/summary/route.ts
index 9761a8ba3..772d46996 100644
--- a/src/app/api/dashboard/summary/route.ts
+++ b/src/app/api/dashboard/summary/route.ts
@@ -64,6 +64,15 @@ import {
 } from "@/lib/analytics/sleep-night";
 import { loadUserSourcePriority } from "@/lib/rollups/measurement-read";
 import type { SleepStage } from "@/generated/prisma/client";
+import { loadBaselineProfile } from "@/lib/insights/derived/baseline";
+import {
+  reconstructNights,
+  sleepNeedMinutes,
+} from "@/lib/insights/derived/sleep-score";
+import {
+  computeSleepRhythmFromNights,
+  type SleepRhythmDto,
+} from "@/lib/insights/derived/sleep-rhythm";
 
 const SPARK_DAYS = 7;
 const STREAK_WINDOW_DAYS = 365;
@@ -534,8 +543,13 @@ async function buildDashboardSummary(
 
   // v1.11.4 — the user's sleep source-priority ladder, used to collapse a
   // dual-source night (e.g. WHOOP + Apple Health) to one canonical source
-  // before the per-night reconstruction sums it.
-  const sleepPriorityJson = await loadUserSourcePriority(userId);
+  // before the per-night reconstruction sums it. v1.17.0 — the baseline
+  // profile rides along (one read) so the sleep-rhythm block resolves the
+  // age-based sleep need the cumulative-debt deficit uses.
+  const [sleepPriorityJson, sleepProfile] = await Promise.all([
+    loadUserSourcePriority(userId),
+    loadBaselineProfile(prisma, userId),
+  ]);
 
   // Per-type metadata lookup — typed Map so a metric with no readings
   // at all falls through `metaForType` to the `{ allTimeCount: 0,
@@ -632,6 +646,24 @@ async function buildDashboardSummary(
     sleepPriorityJson,
   );
 
+  // v1.17.0 — server-authoritative sleep-rhythm DTO (sleep-debt + chronotype)
+  // off the SAME canonical reconstruction the Sleep page + Sleep Score read,
+  // so iOS renders identical values. Reuses the rows already loaded above —
+  // `reconstructNights` adapts them into the asleep + wall-clock-midpoint
+  // shape the foundation modules consume, then `computeSleepRhythmFromNights`
+  // forwards them to `computeSleepDebt` / `computeChronotype` (the one place
+  // the math lives). Both signals carry a calm partial / learning state below
+  // their night thresholds — never an assertion off thin data.
+  const sleepRhythm: SleepRhythmDto = computeSleepRhythmFromNights(
+    reconstructNights(
+      sleepStageRows as SleepStageRow[],
+      userTz,
+      sleepPriorityJson,
+    ),
+    sleepNeedMinutes(sleepProfile.ageYears),
+    userTz,
+  );
+
   const metrics: MetricCard[] = [];
 
   // v1.4.33 maintainer-item-1 — every emitted card now carries
@@ -862,6 +894,9 @@ async function buildDashboardSummary(
     },
     highlightInsight: null,
     metrics,
+    // v1.17.0 — sleep-debt + chronotype, server-authoritative. Same values
+    // the Sleep page's `/api/sleep/rhythm` read returns.
+    sleepRhythm,
     lastUpdated: now.toISOString(),
   };
 }
diff --git a/src/app/api/sleep/rhythm/__tests__/route.test.ts b/src/app/api/sleep/rhythm/__tests__/route.test.ts
new file mode 100644
index 000000000..85d94cdc5
--- /dev/null
+++ b/src/app/api/sleep/rhythm/__tests__/route.test.ts
@@ -0,0 +1,135 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest } from "next/server";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    measurement: { findMany: vi.fn() },
+    user: { findUnique: vi.fn() },
+    auditLog: { create: vi.fn() },
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+
+vi.mock("@/lib/tz/resolver", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/tz/resolver")>();
+  return { ...actual, resolveUserTimezone: vi.fn(async () => "UTC") };
+});
+
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+
+vi.mock("@/lib/rollups/measurement-read", () => ({
+  loadUserSourcePriority: vi.fn(async () => null),
+}));
+
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+
+vi.mock("@/lib/logging/context", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("@/lib/logging/context")>();
+  return { ...actual, annotate: vi.fn() };
+});
+
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { GET } from "../route";
+import { prisma } from "@/lib/db";
+import { getSession } from "@/lib/auth/session";
+
+const SESSION_OK = {
+  session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
+  user: { id: "user-1", username: "testuser", role: "USER" as const },
+};
+
+// `apiHandler` always reads `request.url`; the inner handler ignores it, so we
+// bypass the arity check with a cast (same pattern as the dashboard summary
+// test).
+const callGet = GET as unknown as (req: NextRequest) => Promise<Response>;
+function req(): NextRequest {
+  return new NextRequest("http://localhost/api/sleep/rhythm");
+}
+
+/** A bare-ASLEEP night: end = wake instant, asleep = `minutes`. */
+function night(wakeIso: string, minutes: number) {
+  return {
+    value: minutes,
+    measuredAt: new Date(wakeIso),
+    sleepStage: "ASLEEP",
+    source: "APPLE_HEALTH",
+    deviceType: null,
+  };
+}
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  vi.mocked(prisma.measurement.findMany).mockResolvedValue([] as never);
+  vi.mocked(prisma.user.findUnique).mockResolvedValue({
+    dateOfBirth: new Date("1986-01-01"),
+    gender: null,
+    heightCm: null,
+  } as never);
+  vi.mocked(prisma.auditLog.create).mockResolvedValue({} as never);
+});
+
+describe("GET /api/sleep/rhythm", () => {
+  it("returns 401 when unauthenticated", async () => {
+    vi.mocked(getSession).mockResolvedValue(null);
+    const res = await callGet(req());
+    expect(res.status).toBe(401);
+  });
+
+  it("returns the sleep-debt + chronotype DTO shape", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    const res = await callGet(req());
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    // Sleep-debt DTO fields.
+    expect(body.data.sleepDebt).toMatchObject({
+      state: "partial",
+      debtMinutes: 0,
+      needMinutes: expect.any(Number),
+      nightsCounted: 0,
+      windowNights: expect.any(Number),
+      nightsUntilReady: expect.any(Number),
+    });
+    // Chronotype DTO fields.
+    expect(body.data.chronotype).toMatchObject({
+      state: "learning",
+      msfMinutes: null,
+      msfScMinutes: null,
+      band: null,
+      socialJetlagMinutes: null,
+      freeNightsCounted: 0,
+      workNightsCounted: 0,
+      freeNightsUntilReady: expect.any(Number),
+    });
+  });
+
+  it("reaches the ready debt state with a full window of short nights", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    // Ten consecutive nights of 6 h (360 min); need is 420 → 60/night deficit.
+    const rows = [];
+    for (let d = 1; d <= 10; d++) {
+      const day = String(d).padStart(2, "0");
+      rows.push(night(`2026-06-${day}T06:00:00.000Z`, 360));
+    }
+    vi.mocked(prisma.measurement.findMany).mockResolvedValue(rows as never);
+
+    const res = await callGet(req());
+    const body = await res.json();
+    expect(body.data.sleepDebt.state).toBe("ready");
+    expect(body.data.sleepDebt.nightsCounted).toBe(10);
+    expect(body.data.sleepDebt.nightsUntilReady).toBe(0);
+    // 10 nights × 60-min deficit = 600 min cumulative debt.
+    expect(body.data.sleepDebt.debtMinutes).toBe(600);
+    expect(body.data.sleepDebt.needMinutes).toBe(420);
+  });
+});
diff --git a/src/app/api/sleep/rhythm/route.ts b/src/app/api/sleep/rhythm/route.ts
new file mode 100644
index 000000000..8eb6c1502
--- /dev/null
+++ b/src/app/api/sleep/rhythm/route.ts
@@ -0,0 +1,42 @@
+/**
+ * GET /api/sleep/rhythm
+ *
+ * v1.17.0 — server-authoritative sleep-rhythm read. Returns the two timing
+ * signals the Sleep page + the iOS client render off the SAME canonical night
+ * reconstruction the Sleep Score uses:
+ *
+ *   - `sleepDebt`   — cumulative deficit over the rolling window, with a calm
+ *                     `partial` state under the night threshold.
+ *   - `chronotype`  — MCTQ MSF / MSFsc band + social jetlag, with a `learning`
+ *                     state until enough free-day nights exist.
+ *
+ * The math lives in `sleep-debt.ts` / `chronotype.ts`; this route is the auth +
+ * read boundary over `buildSleepRhythm`, which owns the DB read, the canonical
+ * reconstruction, the age-based `needMinutes`, and the weekday/weekend day-type
+ * default. No schema, no new type — a view over the existing per-stage
+ * `SLEEP_DURATION` rows.
+ *
+ * Auth: cookie session OR Bearer token (`requireAuth`). Soft-delete-filtered.
+ */
+import { apiHandler, requireAuth } from "@/lib/api-handler";
+import { apiSuccess } from "@/lib/api-response";
+import { annotate } from "@/lib/logging/context";
+import { buildSleepRhythm } from "@/lib/insights/derived/sleep-rhythm";
+
+export const GET = apiHandler(async () => {
+  const { user } = await requireAuth();
+
+  const rhythm = await buildSleepRhythm(user.id);
+
+  annotate({
+    action: { name: "sleep.rhythm" },
+    meta: {
+      debt_state: rhythm.sleepDebt.state,
+      debt_minutes: rhythm.sleepDebt.debtMinutes,
+      chronotype_state: rhythm.chronotype.state,
+      chronotype_band: rhythm.chronotype.band,
+    },
+  });
+
+  return apiSuccess(rhythm);
+});
diff --git a/src/app/insights/sleep/page.tsx b/src/app/insights/sleep/page.tsx
index 9266068e7..514ac15a1 100644
--- a/src/app/insights/sleep/page.tsx
+++ b/src/app/insights/sleep/page.tsx
@@ -12,6 +12,7 @@ import { MetricStatusCard } from "@/components/insights/metric-status-card";
 import { MetricEmptyState } from "@/components/insights/metric-empty-state";
 import { MetricTargetSummary } from "@/components/insights/metric-target-summary";
 import { SleepOverview } from "@/components/insights/sleep-overview";
+import { SleepRhythmSection } from "@/components/insights/sleep/sleep-rhythm-section";
 import { SubPageShell } from "@/components/insights/sub-page-shell";
 
 /**
@@ -81,6 +82,13 @@ export default function InsightsSchlafPage() {
     >
       <SleepOverview />
 
+      {/*
+        v1.17.0 — sleep-debt headline + chronotype card. Server-authoritative
+        (the same DTO iOS renders), gated on the data-bearing branch so a
+        source-less account never fetches.
+      */}
+      <SleepRhythmSection enabled={!isEmpty} />
+
       <MetricTargetSummary slug="sleep" />
 
       {/*
diff --git a/src/components/insights/sleep/__tests__/sleep-rhythm-cards.test.tsx b/src/components/insights/sleep/__tests__/sleep-rhythm-cards.test.tsx
new file mode 100644
index 000000000..9e313557f
--- /dev/null
+++ b/src/components/insights/sleep/__tests__/sleep-rhythm-cards.test.tsx
@@ -0,0 +1,108 @@
+import { describe, it, expect } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+import { I18nProvider } from "@/lib/i18n/context";
+import { SleepDebtCard } from "../sleep-debt-card";
+import { ChronotypeCard } from "../chronotype-card";
+import type { SleepDebtDto, ChronotypeDto } from "../use-sleep-rhythm";
+
+/**
+ * v1.17.0 — sleep-debt + chronotype card rendering, with a focus on the calm
+ * NOT-YET-READY states (partial / learning): both must show a "still learning"
+ * nudge and NEVER assert a debt total or a chronotype band off thin data.
+ */
+function render(node: React.ReactNode, locale: "en" | "de" = "en") {
+  return renderToStaticMarkup(
+    <I18nProvider initialLocale={locale}>{node}</I18nProvider>,
+  );
+}
+
+const PARTIAL_DEBT: SleepDebtDto = {
+  state: "partial",
+  debtMinutes: 0,
+  needMinutes: 420,
+  nightsCounted: 3,
+  windowNights: 14,
+  nightsUntilReady: 4,
+};
+
+const READY_DEBT: SleepDebtDto = {
+  state: "ready",
+  debtMinutes: 600,
+  needMinutes: 420,
+  nightsCounted: 10,
+  windowNights: 14,
+  nightsUntilReady: 0,
+};
+
+const LEARNING_CHRONO: ChronotypeDto = {
+  state: "learning",
+  msfMinutes: null,
+  msfScMinutes: null,
+  band: null,
+  socialJetlagMinutes: null,
+  freeNightsCounted: 1,
+  workNightsCounted: 5,
+  freeNightsUntilReady: 2,
+};
+
+const READY_CHRONO: ChronotypeDto = {
+  state: "ready",
+  msfMinutes: 4 * 60 + 30, // 04:30
+  msfScMinutes: 4 * 60, // 04:00
+  band: "intermediate",
+  socialJetlagMinutes: 75,
+  freeNightsCounted: 6,
+  workNightsCounted: 14,
+  freeNightsUntilReady: 0,
+};
+
+describe("<SleepDebtCard>", () => {
+  it("shows the learning nudge in the partial state, not a debt total", () => {
+    const html = render(<SleepDebtCard debt={PARTIAL_DEBT} />);
+    expect(html).toContain("Still learning your sleep");
+    expect(html).toContain("3 nights");
+    // No asserted "short" figure while partial.
+    expect(html).not.toContain("short");
+  });
+
+  it("asserts the cumulative debt in the ready state", () => {
+    const html = render(<SleepDebtCard debt={READY_DEBT} />);
+    // 600 min = 10h 0m short.
+    expect(html).toContain("10h 0m short");
+    expect(html).toContain("14 nights");
+  });
+
+  it("shows the caught-up state at zero debt", () => {
+    const html = render(
+      <SleepDebtCard debt={{ ...READY_DEBT, debtMinutes: 0 }} />,
+    );
+    expect(html).toContain("All caught up");
+  });
+});
+
+describe("<ChronotypeCard>", () => {
+  it("shows the learning state and asserts NO band off thin data", () => {
+    const html = render(<ChronotypeCard chronotype={LEARNING_CHRONO} />);
+    expect(html).toContain("Still learning your rhythm");
+    expect(html).toContain("1 of 3 free nights");
+    // No band label leaks in the learning state — none of the five MCTQ
+    // class labels appears.
+    expect(html).not.toContain("Intermediate type");
+    expect(html).not.toContain("Morning type");
+    expect(html).not.toContain("Evening type");
+  });
+
+  it("shows the band + mid-sleep clock in the ready state", () => {
+    const html = render(<ChronotypeCard chronotype={READY_CHRONO} />);
+    expect(html).toContain("Intermediate type");
+    expect(html).toContain("04:30");
+  });
+
+  it("keeps social jetlag + MSFsc behind the advanced disclosure (collapsed by default)", () => {
+    const html = render(<ChronotypeCard chronotype={READY_CHRONO} />);
+    // The toggle is present, the advanced detail is not rendered until opened.
+    expect(html).toContain("Advanced");
+    expect(html).not.toContain("social jetlag");
+    expect(html).not.toContain("Corrected mid-sleep");
+  });
+});
diff --git a/src/components/insights/sleep/chronotype-card.tsx b/src/components/insights/sleep/chronotype-card.tsx
new file mode 100644
index 000000000..7af1f9a26
--- /dev/null
+++ b/src/components/insights/sleep/chronotype-card.tsx
@@ -0,0 +1,145 @@
+"use client";
+
+import { useState } from "react";
+import { Clock, ChevronDown, ChevronUp } from "lucide-react";
+
+import { useTranslations } from "@/lib/i18n/context";
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
+import { Badge } from "@/components/ui/badge";
+import type { ChronotypeDto } from "./use-sleep-rhythm";
+
+/** Minutes-of-day → "HH:MM" wall-clock label (24 h, zero-padded). */
+function clockLabel(minutesOfDay: number): string {
+  const wrapped = ((Math.round(minutesOfDay) % 1440) + 1440) % 1440;
+  const h = Math.floor(wrapped / 60);
+  const m = wrapped - h * 60;
+  return `${String(h).padStart(2, "0")}:${String(m).padStart(2, "0")}`;
+}
+
+/** Whole hours + minutes from a minute total, for the social-jetlag readout. */
+function hoursMinutes(totalMinutes: number): { hours: number; minutes: number } {
+  const t = Math.round(totalMinutes);
+  return { hours: Math.floor(t / 60), minutes: t - Math.floor(t / 60) * 60 };
+}
+
+/**
+ * v1.17.0 — chronotype card (MCTQ MSF / MSFsc band + social jetlag).
+ *
+ * Progressive disclosure: the band + mid-sleep clock time show by default; the
+ * social-jetlag detail + the sleep-debt-corrected MSFsc sit behind an
+ * "advanced" toggle. While `learning` it shows "still learning your rhythm —
+ * N of M nights" and asserts NO type. Warm, grounded copy; mobile-first.
+ */
+export function ChronotypeCard({ chronotype }: { chronotype: ChronotypeDto }) {
+  const { t } = useTranslations();
+  const [showAdvanced, setShowAdvanced] = useState(false);
+
+  if (chronotype.state === "learning" || chronotype.band == null) {
+    const need =
+      chronotype.freeNightsCounted + chronotype.freeNightsUntilReady;
+    return (
+      <Card className="gap-2 py-4 md:gap-2 md:py-4">
+        <CardHeader className="pb-0">
+          <div className="flex items-center gap-2">
+            <Clock className="text-dracula-cyan h-4 w-4" />
+            <CardTitle className="text-base font-semibold">
+              {t("insights.sleep.chronotype.title")}
+            </CardTitle>
+          </div>
+        </CardHeader>
+        <CardContent>
+          <p className="text-muted-foreground text-sm">
+            {t("insights.sleep.chronotype.learning", {
+              counted: chronotype.freeNightsCounted,
+              total: need,
+            })}
+          </p>
+        </CardContent>
+      </Card>
+    );
+  }
+
+  const bandLabel = t(`insights.sleep.chronotype.band.${chronotype.band}`);
+  const msfClock =
+    chronotype.msfMinutes != null ? clockLabel(chronotype.msfMinutes) : null;
+
+  return (
+    <Card className="gap-2 py-4 md:gap-2 md:py-4">
+      <CardHeader className="pb-0">
+        <div className="flex items-center gap-2">
+          <Clock className="text-dracula-cyan h-4 w-4" />
+          <CardTitle className="text-base font-semibold">
+            {t("insights.sleep.chronotype.title")}
+          </CardTitle>
+        </div>
+      </CardHeader>
+      <CardContent className="space-y-3">
+        <div className="space-y-1">
+          <Badge variant="secondary" className="text-sm">
+            {bandLabel}
+          </Badge>
+          {msfClock && (
+            <p className="text-muted-foreground text-xs">
+              {t("insights.sleep.chronotype.midSleepCaption", {
+                clock: msfClock,
+              })}
+            </p>
+          )}
+        </div>
+
+        <button
+          type="button"
+          onClick={() => setShowAdvanced((v) => !v)}
+          aria-expanded={showAdvanced}
+          className="text-muted-foreground hover:text-foreground flex items-center gap-1 text-xs font-medium transition-colors"
+        >
+          {showAdvanced ? (
+            <ChevronUp className="h-3.5 w-3.5" />
+          ) : (
+            <ChevronDown className="h-3.5 w-3.5" />
+          )}
+          {t("insights.sleep.chronotype.advancedToggle")}
+        </button>
+
+        {showAdvanced && (
+          <div className="space-y-2 border-t pt-3">
+            {chronotype.socialJetlagMinutes != null &&
+              (() => {
+                const { hours, minutes } = hoursMinutes(
+                  chronotype.socialJetlagMinutes,
+                );
+                return (
+                  <div className="space-y-0.5">
+                    <p className="text-sm font-medium">
+                      {t("insights.sleep.chronotype.socialJetlagValue", {
+                        hours,
+                        minutes,
+                      })}
+                    </p>
+                    <p className="text-muted-foreground text-xs">
+                      {t("insights.sleep.chronotype.socialJetlagCaption")}
+                    </p>
+                  </div>
+                );
+              })()}
+            {chronotype.msfScMinutes != null && (
+              <div className="space-y-0.5">
+                <p className="text-sm font-medium tabular-nums">
+                  {t("insights.sleep.chronotype.msfScValue", {
+                    clock: clockLabel(chronotype.msfScMinutes),
+                  })}
+                </p>
+                <p className="text-muted-foreground text-xs">
+                  {t("insights.sleep.chronotype.msfScCaption")}
+                </p>
+              </div>
+            )}
+            <p className="text-muted-foreground text-xs">
+              {t("insights.sleep.chronotype.dayTypeNote")}
+            </p>
+          </div>
+        )}
+      </CardContent>
+    </Card>
+  );
+}
diff --git a/src/components/insights/sleep/sleep-debt-card.tsx b/src/components/insights/sleep/sleep-debt-card.tsx
new file mode 100644
index 000000000..d0454adf9
--- /dev/null
+++ b/src/components/insights/sleep/sleep-debt-card.tsx
@@ -0,0 +1,83 @@
+"use client";
+
+import { Moon } from "lucide-react";
+
+import { useTranslations } from "@/lib/i18n/context";
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
+import type { SleepDebtDto } from "./use-sleep-rhythm";
+
+/** Whole hours + minutes from a minute total, for the headline figure. */
+function hoursMinutes(totalMinutes: number): { hours: number; minutes: number } {
+  const hours = Math.floor(totalMinutes / 60);
+  const minutes = Math.round(totalMinutes - hours * 60);
+  return { hours, minutes };
+}
+
+/**
+ * v1.17.0 — sleep-debt headline.
+ *
+ * The cumulative shortfall between sleep need and sleep obtained over the
+ * rolling window. Under the night threshold it shows the calm `partial`
+ * state ("still learning — N more nights") and never asserts a total off thin
+ * data. Mobile-first: a single readable figure + one line of grounded context.
+ */
+export function SleepDebtCard({ debt }: { debt: SleepDebtDto }) {
+  const { t } = useTranslations();
+
+  if (debt.state === "partial") {
+    return (
+      <Card className="gap-2 py-4 md:gap-2 md:py-4">
+        <CardHeader className="pb-0">
+          <div className="flex items-center gap-2">
+            <Moon className="text-dracula-cyan h-4 w-4" />
+            <CardTitle className="text-base font-semibold">
+              {t("insights.sleep.debt.title")}
+            </CardTitle>
+          </div>
+        </CardHeader>
+        <CardContent>
+          <p className="text-muted-foreground text-sm">
+            {t("insights.sleep.debt.learning", {
+              counted: debt.nightsCounted,
+              remaining: debt.nightsUntilReady,
+            })}
+          </p>
+        </CardContent>
+      </Card>
+    );
+  }
+
+  const { hours, minutes } = hoursMinutes(debt.debtMinutes);
+  const isClear = debt.debtMinutes === 0;
+
+  return (
+    <Card className="gap-2 py-4 md:gap-2 md:py-4">
+      <CardHeader className="pb-0">
+        <div className="flex items-center gap-2">
+          <Moon className="text-dracula-cyan h-4 w-4" />
+          <CardTitle className="text-base font-semibold">
+            {t("insights.sleep.debt.title")}
+          </CardTitle>
+        </div>
+      </CardHeader>
+      <CardContent>
+        <div className="space-y-0.5">
+          <p className="text-2xl font-semibold tabular-nums">
+            {isClear
+              ? t("insights.sleep.debt.clearValue")
+              : t("insights.sleep.debt.value", { hours, minutes })}
+          </p>
+          <p className="text-muted-foreground text-xs">
+            {isClear
+              ? t("insights.sleep.debt.clearCaption", {
+                  nights: debt.windowNights,
+                })
+              : t("insights.sleep.debt.caption", {
+                  nights: debt.windowNights,
+                })}
+          </p>
+        </div>
+      </CardContent>
+    </Card>
+  );
+}
diff --git a/src/components/insights/sleep/sleep-rhythm-section.tsx b/src/components/insights/sleep/sleep-rhythm-section.tsx
new file mode 100644
index 000000000..6e0ef9c6e
--- /dev/null
+++ b/src/components/insights/sleep/sleep-rhythm-section.tsx
@@ -0,0 +1,38 @@
+"use client";
+
+import { useAuth } from "@/hooks/use-auth";
+import { Skeleton } from "@/components/ui/skeleton";
+import { useSleepRhythm } from "./use-sleep-rhythm";
+import { SleepDebtCard } from "./sleep-debt-card";
+import { ChronotypeCard } from "./chronotype-card";
+
+/**
+ * v1.17.0 — sleep-rhythm section on the Sleep page.
+ *
+ * Reads the server-authoritative sleep-debt + chronotype DTO and renders the
+ * sleep-debt headline + the chronotype card. Gated on `enabled` so a
+ * source-less account never fetches. The values are identical to what the iOS
+ * client renders (one server computation).
+ */
+export function SleepRhythmSection({ enabled }: { enabled: boolean }) {
+  const { isAuthenticated } = useAuth();
+  const { data, isLoading } = useSleepRhythm(isAuthenticated && enabled);
+
+  if (!enabled) return null;
+
+  if (isLoading || !data) {
+    return (
+      <div className="space-y-4">
+        <Skeleton className="h-28 w-full rounded-xl" />
+        <Skeleton className="h-28 w-full rounded-xl" />
+      </div>
+    );
+  }
+
+  return (
+    <div className="space-y-4">
+      <SleepDebtCard debt={data.sleepDebt} />
+      <ChronotypeCard chronotype={data.chronotype} />
+    </div>
+  );
+}
diff --git a/src/components/insights/sleep/use-sleep-rhythm.ts b/src/components/insights/sleep/use-sleep-rhythm.ts
new file mode 100644
index 000000000..6dc0dc9a6
--- /dev/null
+++ b/src/components/insights/sleep/use-sleep-rhythm.ts
@@ -0,0 +1,57 @@
+"use client";
+
+import { useQuery } from "@tanstack/react-query";
+
+import { queryKeys } from "@/lib/query-keys";
+import { apiGet } from "@/lib/api/api-fetch";
+
+/**
+ * v1.17.0 — sleep-debt DTO (mirrors the server `SleepDebtDto`). `partial` is
+ * the calm "still learning" state below the night threshold; `ready` asserts
+ * the cumulative deficit.
+ */
+export interface SleepDebtDto {
+  state: "partial" | "ready";
+  debtMinutes: number;
+  needMinutes: number;
+  nightsCounted: number;
+  windowNights: number;
+  nightsUntilReady: number;
+}
+
+/** v1.17.0 — chronotype DTO (mirrors the server `ChronotypeDto`). */
+export interface ChronotypeDto {
+  state: "learning" | "ready";
+  msfMinutes: number | null;
+  msfScMinutes: number | null;
+  band:
+    | "extreme_early"
+    | "early"
+    | "intermediate"
+    | "late"
+    | "extreme_late"
+    | null;
+  socialJetlagMinutes: number | null;
+  freeNightsCounted: number;
+  workNightsCounted: number;
+  freeNightsUntilReady: number;
+}
+
+export interface SleepRhythmDto {
+  sleepDebt: SleepDebtDto;
+  chronotype: ChronotypeDto;
+}
+
+/**
+ * Read the server-authoritative sleep-rhythm DTO. Gated on `enabled` so a
+ * source-less account never fetches; shares the measurement-write
+ * invalidation prefix (`["sleep-rhythm"]`).
+ */
+export function useSleepRhythm(enabled: boolean) {
+  return useQuery({
+    queryKey: queryKeys.sleepRhythm(),
+    queryFn: () => apiGet<SleepRhythmDto>("/api/sleep/rhythm"),
+    enabled,
+    staleTime: 60 * 1000,
+  });
+}
diff --git a/src/lib/insights/derived/__tests__/sleep-rhythm.test.ts b/src/lib/insights/derived/__tests__/sleep-rhythm.test.ts
new file mode 100644
index 000000000..0ec06d0ab
--- /dev/null
+++ b/src/lib/insights/derived/__tests__/sleep-rhythm.test.ts
@@ -0,0 +1,110 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Mock the DB so the builder is hermetic — we control the rows.
+const findMany = vi.fn();
+vi.mock("@/lib/db", () => ({
+  prisma: { measurement: { findMany: (...a: unknown[]) => findMany(...a) } },
+}));
+vi.mock("@/lib/rollups/measurement-read", () => ({
+  loadUserSourcePriority: vi.fn(async () => null),
+}));
+vi.mock("../baseline", () => ({
+  // 40-year-old adult → sleepNeedMinutes returns 420 (7 h).
+  loadBaselineProfile: vi.fn(async () => ({
+    ageYears: 40,
+    sex: null,
+    heightCm: null,
+  })),
+}));
+
+// Spy on the foundation modules WITHOUT replacing the math — assert reuse.
+import * as sleepDebtMod from "../sleep-debt";
+import * as chronotypeMod from "../chronotype";
+
+import { buildSleepRhythm, defaultDayType } from "../sleep-rhythm";
+
+/**
+ * Build per-stage rows for one night: a single bare-ASLEEP block whose END is
+ * the wake instant, so `reconstructNights` reads asleep = `asleepMinutes` and a
+ * midpoint at wake − asleep/2. `wakeIso` is the wake instant (UTC).
+ */
+function nightRows(wakeIso: string, asleepMinutes: number) {
+  return [
+    {
+      value: asleepMinutes,
+      measuredAt: new Date(wakeIso),
+      sleepStage: "ASLEEP" as const,
+      source: null,
+      deviceType: null,
+    },
+  ];
+}
+
+describe("defaultDayType", () => {
+  it("tags weekend wake days free and weekdays work (UTC)", () => {
+    // 2026-06-13 is a Saturday, 2026-06-14 a Sunday, 2026-06-15 a Monday.
+    expect(defaultDayType("2026-06-13", "UTC")).toBe("free");
+    expect(defaultDayType("2026-06-14", "UTC")).toBe("free");
+    expect(defaultDayType("2026-06-15", "UTC")).toBe("work");
+  });
+});
+
+describe("buildSleepRhythm", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("reuses the foundation modules — calls computeSleepDebt + computeChronotype", async () => {
+    const debtSpy = vi.spyOn(sleepDebtMod, "computeSleepDebt");
+    const chronoSpy = vi.spyOn(chronotypeMod, "computeChronotype");
+
+    // Two scorable nights — enough to exercise the call, not the ready gate.
+    findMany.mockResolvedValue([
+      ...nightRows("2026-06-13T06:00:00Z", 360),
+      ...nightRows("2026-06-14T06:00:00Z", 400),
+    ]);
+
+    const dto = await buildSleepRhythm("user-1", {
+      tz: "UTC",
+      now: new Date("2026-06-14T12:00:00Z"),
+    });
+
+    expect(debtSpy).toHaveBeenCalledTimes(1);
+    expect(chronoSpy).toHaveBeenCalledTimes(1);
+    // The need forwarded to the debt module is the age-resolved 420 (7 h).
+    expect(debtSpy.mock.calls[0][1]).toBe(420);
+    expect(dto.sleepDebt.needMinutes).toBe(420);
+    // Below the 7-night floor → calm partial / learning, never an assertion.
+    expect(dto.sleepDebt.state).toBe("partial");
+    expect(dto.chronotype.state).toBe("learning");
+  });
+
+  it("forwards the canonical asleep totals into the debt deficit", async () => {
+    // need 420; a 300-min night is 120 short, a 420-min night exactly meets it.
+    findMany.mockResolvedValue([
+      ...nightRows("2026-06-13T06:00:00Z", 300),
+      ...nightRows("2026-06-14T06:00:00Z", 420),
+    ]);
+    const dto = await buildSleepRhythm("user-1", {
+      tz: "UTC",
+      now: new Date("2026-06-14T12:00:00Z"),
+    });
+    // Partial (< 7 nights) but the cumulative is still computed: 120 + 0.
+    expect(dto.sleepDebt.debtMinutes).toBe(120);
+    expect(dto.sleepDebt.nightsCounted).toBe(2);
+    expect(dto.sleepDebt.nightsUntilReady).toBe(5);
+  });
+
+  it("returns calm states with zero nights", async () => {
+    findMany.mockResolvedValue([]);
+    const dto = await buildSleepRhythm("user-1", {
+      tz: "UTC",
+      now: new Date("2026-06-14T12:00:00Z"),
+    });
+    expect(dto.sleepDebt.state).toBe("partial");
+    expect(dto.sleepDebt.nightsCounted).toBe(0);
+    expect(dto.chronotype.state).toBe("learning");
+    expect(dto.chronotype.band).toBeNull();
+    expect(dto.chronotype.msfMinutes).toBeNull();
+  });
+});
diff --git a/src/lib/insights/derived/sleep-rhythm.ts b/src/lib/insights/derived/sleep-rhythm.ts
new file mode 100644
index 000000000..32330dfd0
--- /dev/null
+++ b/src/lib/insights/derived/sleep-rhythm.ts
@@ -0,0 +1,239 @@
+/**
+ * v1.17.0 — sleep-rhythm assembler (server-authoritative).
+ *
+ * The one place that turns a user's raw `SLEEP_DURATION` rows into the two
+ * timing signals the Sleep page + the iOS client + the dashboard render:
+ *
+ *   - cumulative SLEEP DEBT over the rolling window (`computeSleepDebt`), and
+ *   - MCTQ CHRONOTYPE + social jetlag (`computeChronotype`).
+ *
+ * ONE ENGINE, NO DUPLICATION
+ * --------------------------
+ * The per-night `asleepMinutes` and `midpointMinutes` come from the SAME
+ * canonical reconstruction the Sleep Score reads — `reconstructNights`
+ * (`sleep-score.ts`), which itself adapts `reconstructSleepNights`
+ * (`sleep-night.ts`). This module does NOT re-cluster sessions, re-dedup
+ * writers, or re-derive a midpoint; it maps the canonical night output onto
+ * the two foundation modules' inputs and forwards the resolved `needMinutes`.
+ * The math lives entirely in `sleep-debt.ts` / `chronotype.ts` — this file is
+ * the adapter + DB read + day-type resolver, nothing else. Because the inputs
+ * are the canonical totals, the debt headline and the chronotype band can
+ * never contradict the dashboard / hypnogram / Sleep Score for the same night.
+ *
+ * DAY-TYPE SIGNAL (free vs work)
+ * ------------------------------
+ * Chronotype's MSF needs each night tagged free or work, and the app has no
+ * work calendar. The documented DEFAULT is calendar-based: a night whose WAKE
+ * day falls on Saturday or Sunday (in the user's timezone) is "free"; every
+ * other night is "work". This mirrors the MCTQ assumption that weekends are
+ * the alarm-free days for a standard work week — surfaced as a modelling
+ * assumption, not a hidden constant. When a future per-night logged day-type
+ * exists it overrides this default; until then weekday/weekend is the floor.
+ *
+ * Server-only — reads raw `SLEEP_DURATION` rows via Prisma, bounded to the
+ * window. The DTO is the shared wire shape the route, the dashboard summary,
+ * and the iOS serializer all emit identically.
+ */
+import type { MeasurementType } from "@/generated/prisma/client";
+import { prisma } from "@/lib/db";
+import { wallClockInTz } from "@/lib/tz/wall-clock";
+import { resolveUserTimezone } from "@/lib/tz/resolver";
+import { loadUserSourcePriority } from "@/lib/rollups/measurement-read";
+import { loadBaselineProfile } from "./baseline";
+import {
+  reconstructNights,
+  sleepNeedMinutes,
+} from "./sleep-score";
+import {
+  computeSleepDebt,
+  type SleepDebtNight,
+  type SleepDebtResult,
+} from "./sleep-debt";
+import {
+  computeChronotype,
+  type ChronotypeNight,
+  type ChronotypeResult,
+} from "./chronotype";
+
+const MS_PER_DAY = 24 * 60 * 60 * 1000;
+
+/**
+ * Trailing read window in days. The sleep-debt rolling window is 14 nights and
+ * chronotype wants a few weeks of free-day samples; 42 days (six weeks) gives
+ * the debt window full coverage and ~12 weekend nights for a stable MSF while
+ * staying a bounded per-stage read.
+ */
+const DEFAULT_WINDOW_DAYS = 42;
+
+/** Wire DTO for the cumulative sleep debt — see `SleepDebtResult`. */
+export interface SleepDebtDto {
+  state: "partial" | "ready";
+  debtMinutes: number;
+  needMinutes: number;
+  nightsCounted: number;
+  windowNights: number;
+  nightsUntilReady: number;
+}
+
+/** Wire DTO for the MCTQ chronotype — see `ChronotypeResult`. */
+export interface ChronotypeDto {
+  state: "learning" | "ready";
+  msfMinutes: number | null;
+  msfScMinutes: number | null;
+  band:
+    | "extreme_early"
+    | "early"
+    | "intermediate"
+    | "late"
+    | "extreme_late"
+    | null;
+  socialJetlagMinutes: number | null;
+  freeNightsCounted: number;
+  workNightsCounted: number;
+  freeNightsUntilReady: number;
+}
+
+/** The combined sleep-rhythm DTO — both signals in one read. */
+export interface SleepRhythmDto {
+  sleepDebt: SleepDebtDto;
+  chronotype: ChronotypeDto;
+}
+
+/**
+ * Day type of a night from its WAKE day's weekday in the user's timezone:
+ * Saturday / Sunday → "free", else "work". The documented calendar default
+ * (no work calendar exists). `night` is the YYYY-MM-DD wake-day key.
+ */
+export function defaultDayType(night: string, tz: string): "work" | "free" {
+  // Anchor at local noon of the wake day so the weekday read is immune to the
+  // tz offset and DST — noon never crosses a day boundary in any zone.
+  const noon = new Date(`${night}T12:00:00Z`);
+  const weekday = wallClockInTz(noon, tz).weekday; // 0 = Sun … 6 = Sat
+  return weekday === 0 || weekday === 6 ? "free" : "work";
+}
+
+function toDebtDto(r: SleepDebtResult): SleepDebtDto {
+  return {
+    state: r.state,
+    debtMinutes: r.debtMinutes,
+    needMinutes: r.needMinutes,
+    nightsCounted: r.nightsCounted,
+    windowNights: r.windowNights,
+    nightsUntilReady: r.nightsUntilReady,
+  };
+}
+
+function toChronotypeDto(r: ChronotypeResult): ChronotypeDto {
+  return {
+    state: r.state,
+    msfMinutes: r.msfMinutes,
+    msfScMinutes: r.msfScMinutes,
+    band: r.band,
+    socialJetlagMinutes: r.socialJetlagMinutes,
+    freeNightsCounted: r.freeNightsCounted,
+    workNightsCounted: r.workNightsCounted,
+    freeNightsUntilReady: r.freeNightsUntilReady,
+  };
+}
+
+export interface SleepRhythmOpts {
+  windowDays?: number;
+  now?: Date;
+  /** Pin the IANA zone in tests; omit to resolve the user's stored zone. */
+  tz?: string;
+}
+
+/** A reconstructed night carrying the canonical asleep total + wall-clock midpoint. */
+export interface RhythmNight {
+  night: string;
+  asleepMinutes: number;
+  /** Sleep midpoint as minutes-of-day (0..1439), or null when undefined. */
+  midpoint: number | null;
+}
+
+/**
+ * Pure DTO assembler from already-reconstructed nights. The route reads + runs
+ * the canonical reconstruction; the dashboard summary reuses its own loaded
+ * rows. Both feed the SAME foundation modules here so the values are identical
+ * — this is the one place the day-type default + the two `compute*` calls live.
+ *
+ * `nights` must already be the canonical engine's output (asleep + midpoint);
+ * this function does NOT reconstruct. `needMinutes` is the age-resolved need.
+ */
+export function computeSleepRhythmFromNights(
+  nights: readonly RhythmNight[],
+  needMinutes: number,
+  tz: string,
+): SleepRhythmDto {
+  const scorable = nights.filter((n) => n.asleepMinutes > 0);
+
+  const debtNights: SleepDebtNight[] = scorable.map((n) => ({
+    night: n.night,
+    asleepMinutes: n.asleepMinutes,
+  }));
+  const sleepDebt = computeSleepDebt(debtNights, needMinutes);
+
+  const chronoNights: ChronotypeNight[] = scorable
+    .filter((n) => n.midpoint != null)
+    .map((n) => ({
+      night: n.night,
+      midpointMinutes: n.midpoint as number,
+      asleepMinutes: n.asleepMinutes,
+      dayType: defaultDayType(n.night, tz),
+    }));
+  const chronotype = computeChronotype(chronoNights);
+
+  return {
+    sleepDebt: toDebtDto(sleepDebt),
+    chronotype: toChronotypeDto(chronotype),
+  };
+}
+
+/**
+ * Read raw sleep rows, reconstruct nights via the canonical engine, and
+ * compute the sleep-debt + chronotype DTO. Returns the calm partial/learning
+ * states (never asserts off thin data) when the window is short. The midpoint
+ * + asleep totals are the canonical engine's — no second reconstruction.
+ */
+export async function buildSleepRhythm(
+  userId: string,
+  opts: SleepRhythmOpts = {},
+): Promise<SleepRhythmDto> {
+  const windowDays = opts.windowDays ?? DEFAULT_WINDOW_DAYS;
+  const now = opts.now ?? new Date();
+  const tz = opts.tz ?? (await resolveUserTimezone(userId));
+  const [priorityJson, profile] = await Promise.all([
+    loadUserSourcePriority(userId),
+    loadBaselineProfile(prisma, userId),
+  ]);
+  const since = new Date(now.getTime() - windowDays * MS_PER_DAY);
+
+  const rows = await prisma.measurement.findMany({
+    where: {
+      userId,
+      type: "SLEEP_DURATION" satisfies MeasurementType,
+      deletedAt: null,
+      measuredAt: { gte: since },
+    },
+    orderBy: { measuredAt: "asc" },
+    // source + deviceType feed the canonical writer-dedup so a multi-source
+    // night is counted ONCE, matching every other sleep surface.
+    select: {
+      value: true,
+      measuredAt: true,
+      sleepStage: true,
+      source: true,
+      deviceType: true,
+    },
+  });
+
+  // Canonical reconstruction (session-clustering, wake-day keying, writer
+  // dedup) → per-night asleep total + wall-clock midpoint. Same engine as the
+  // Sleep Score; we never re-derive a midpoint here.
+  const nights = reconstructNights(rows, tz, priorityJson).filter(
+    (n) => n.asleepMinutes > 0,
+  );
+
+  const needMinutes = sleepNeedMinutes(profile.ageYears);
+  return computeSleepRhythmFromNights(nights, needMinutes, tz);
+}
diff --git a/src/lib/openapi/routes/measurements.ts b/src/lib/openapi/routes/measurements.ts
index 8316a6c25..15de359a7 100644
--- a/src/lib/openapi/routes/measurements.ts
+++ b/src/lib/openapi/routes/measurements.ts
@@ -216,6 +216,94 @@ const sleepNightResponse = z
       "One reconstructed sleep night: the main session's hypnogram segments + breakdown, plus same-wake-day naps surfaced separately.",
   });
 
+// ── Sleep rhythm (sleep-debt + chronotype, v1.17.0) ──────────────────
+//
+// Server-authoritative timing signals computed off the SAME canonical night
+// reconstruction the Sleep Score reads. Both carry a calm not-yet-ready state
+// (`partial` / `learning`) below their night thresholds — they never assert a
+// total / band off thin data.
+const sleepDebtResource = z.object({
+  state: z
+    .enum(["partial", "ready"])
+    .describe(
+      "`partial` until enough tracked nights exist (calm 'still learning'); `ready` once the rolling window can assert a cumulative debt.",
+    ),
+  debtMinutes: z
+    .number()
+    .int()
+    .nonnegative()
+    .describe("Cumulative sleep debt over the window, in minutes, after caps."),
+  needMinutes: z
+    .number()
+    .int()
+    .nonnegative()
+    .describe("Age-based sleep need (minutes) used for the per-night deficit."),
+  nightsCounted: z.number().int().nonnegative(),
+  windowNights: z
+    .number()
+    .int()
+    .positive()
+    .describe("Rolling window length in nights."),
+  nightsUntilReady: z
+    .number()
+    .int()
+    .nonnegative()
+    .describe("Nights still needed before the debt is asserted (0 when ready)."),
+});
+
+const chronotypeBandEnum = z.enum([
+  "extreme_early",
+  "early",
+  "intermediate",
+  "late",
+  "extreme_late",
+]);
+
+const chronotypeResource = z.object({
+  state: z
+    .enum(["learning", "ready"])
+    .describe(
+      "`learning` until enough free-day nights exist (no band asserted); `ready` once the free-day sample is large enough.",
+    ),
+  msfMinutes: z
+    .number()
+    .nullable()
+    .describe("Mid-sleep on free days (minutes-of-day), null while learning."),
+  msfScMinutes: z
+    .number()
+    .nullable()
+    .describe(
+      "Sleep-debt-corrected mid-sleep on free days (MSFsc, minutes-of-day), null while learning.",
+    ),
+  band: chronotypeBandEnum
+    .nullable()
+    .describe("MCTQ chronotype band off MSFsc, null while learning."),
+  socialJetlagMinutes: z
+    .number()
+    .nullable()
+    .describe(
+      "Social jetlag = circular |MSF_work − MSF_free| in minutes, null when one side is missing.",
+    ),
+  freeNightsCounted: z.number().int().nonnegative(),
+  workNightsCounted: z.number().int().nonnegative(),
+  freeNightsUntilReady: z
+    .number()
+    .int()
+    .nonnegative()
+    .describe("Free-day nights still needed before a band is asserted."),
+});
+
+const sleepRhythmResponse = z
+  .object({
+    sleepDebt: sleepDebtResource,
+    chronotype: chronotypeResource,
+  })
+  .meta({
+    id: "SleepRhythmResource",
+    description:
+      "Server-authoritative sleep-rhythm read: cumulative sleep debt over the rolling window + MCTQ chronotype (MSF/MSFsc band, social jetlag). Free vs work nights default to weekend = free in the user's timezone (no work calendar). A view over existing per-stage SLEEP_DURATION rows — no schema, no new type.",
+  });
+
 // ── Time-series adapter (iOS chart source) ───────────────────────────
 //
 // v1.16.16 — documents the long-shipped `GET /api/measurements/series`
@@ -511,4 +599,23 @@ export const measurementPaths: NonNullable<ZodOpenApiObject["paths"]> = {
       },
     },
   },
+  "/api/sleep/rhythm": {
+    get: {
+      tags: ["Measurements"],
+      summary: "Sleep rhythm — sleep-debt + chronotype (v1.17.0)",
+      description:
+        "Returns the two server-authoritative sleep-timing signals the Sleep page + iOS render off the same canonical night reconstruction the Sleep Score uses: cumulative `sleepDebt` over the rolling window (calm `partial` state under the night threshold) and MCTQ `chronotype` (MSF/MSFsc band + social jetlag, `learning` state until enough free-day nights exist). Free vs work nights default to weekend = free in the user's timezone (no work calendar). A read-only view over existing per-stage SLEEP_DURATION rows — no schema, no new measurement type.",
+      responses: {
+        "200": {
+          description: "Sleep-debt + chronotype DTO.",
+          content: {
+            "application/json": {
+              schema: dataEnvelope(sleepRhythmResponse, "SleepRhythmResponse"),
+            },
+          },
+        },
+        ...stdResponses,
+      },
+    },
+  },
 };
diff --git a/src/lib/query-keys/index.ts b/src/lib/query-keys/index.ts
index e98e8d0a5..d864a42bd 100644
--- a/src/lib/query-keys/index.ts
+++ b/src/lib/query-keys/index.ts
@@ -67,6 +67,8 @@ export const measurementDependentKeys = [
   ["trend-series"] as const,
   // v1.11.5 — refresh the last-night hypnogram when sleep rows change.
   ["sleep-night"] as const,
+  // v1.17.0 — refresh the sleep-debt + chronotype read when sleep rows change.
+  ["sleep-rhythm"] as const,
 ];
 
 /**
diff --git a/src/lib/query-keys/measurements.ts b/src/lib/query-keys/measurements.ts
index e4081bc0a..a8e9265ad 100644
--- a/src/lib/query-keys/measurements.ts
+++ b/src/lib/query-keys/measurements.ts
@@ -45,6 +45,14 @@ export const measurementKeys = {
    */
   sleepNight: (date?: string) => ["sleep-night", date ?? "latest"] as const,
 
+  /**
+   * v1.17.0 — sleep-rhythm read (`GET /api/sleep/rhythm`): the
+   * server-authoritative sleep-debt + chronotype DTO. Reads the same raw
+   * SLEEP_DURATION rows the night view does, so a sleep write invalidates
+   * it through the shared measurement-dependent set.
+   */
+  sleepRhythm: () => ["sleep-rhythm"] as const,
+
   /**
    * v1.4.40 W-RSC — per-chart daily-aggregate fetch from the dashboard
    * + insights chart row. Pre-fix the key was bare `["chart-data", …]`