diff --git a/src/__tests__/baselines/source-function-lines.json b/src/__tests__/baselines/source-function-lines.json
index dca5a1ead..7cf006a87 100644
--- a/src/__tests__/baselines/source-function-lines.json
+++ b/src/__tests__/baselines/source-function-lines.json
@@ -1,7 +1,7 @@
 {
   "$comment": "Production functions over 200 lines, keyed \"file :: name\", and their length. Maintained by src/__tests__/source-size-ratchet.test.ts.",
-  "count": 351,
-  "total": 113619,
+  "count": 350,
+  "total": 113407,
   "entries": {
     "app/achievements/page.tsx :: AchievementsPage": 206,
     "app/api/admin/backups/upload/route.ts :: apiHandler(arg)": 314,
@@ -257,7 +257,6 @@
     "lib/ai/local-client.ts :: generateCompletionStream": 294,
     "lib/ai/openai-client.ts :: generateCompletion": 335,
     "lib/analytics/bp-in-target-fast-path.ts :: computeFromRollups": 203,
-    "lib/analytics/compliance/display.ts :: calculateCompliance": 212,
     "lib/analytics/correlations-fast-path.ts :: computeCorrelationHypothesesFastPath": 256,
     "lib/analytics/intraday-pulse-io.ts :: loadIntradayPulse": 206,
     "lib/analytics/score/reader.ts :: computeUserHealthScore": 324,
diff --git a/src/__tests__/baselines/version-stamp-comments.json b/src/__tests__/baselines/version-stamp-comments.json
index e3c126303..9bb4f7a09 100644
--- a/src/__tests__/baselines/version-stamp-comments.json
+++ b/src/__tests__/baselines/version-stamp-comments.json
@@ -1,7 +1,7 @@
 {
   "$comment": "Comment lines that open with a release version, per file under src/. Maintained by src/__tests__/version-stamp-ratchet.test.ts.",
   "count": 2897,
-  "total": 9272,
+  "total": 9270,
   "entries": {
     "__tests__/account-payload-consumer-guard.test.ts": 2,
     "__tests__/acting-account-boundary-guard.test.ts": 7,
@@ -1828,7 +1828,7 @@
     "lib/analytics/compliance/__tests__/schedule-compliance-select.test.ts": 1,
     "lib/analytics/compliance/adapters.ts": 6,
     "lib/analytics/compliance/cycle.ts": 5,
-    "lib/analytics/compliance/display.ts": 18,
+    "lib/analytics/compliance/display.ts": 16,
     "lib/analytics/compliance/dose-status.ts": 4,
     "lib/analytics/compliance/ledger.ts": 7,
     "lib/analytics/compliance/occurrences.ts": 9,
diff --git a/src/__tests__/recurrence-course-anchor-guard.test.ts b/src/__tests__/recurrence-course-anchor-guard.test.ts
index 6ed1d14b8..ef13a425e 100644
--- a/src/__tests__/recurrence-course-anchor-guard.test.ts
+++ b/src/__tests__/recurrence-course-anchor-guard.test.ts
@@ -21,6 +21,14 @@
  * when its block names `endedAt` or spreads a window that carries it
  * (`...window` from `mintWindow`, `...medicationWindow(row)`).
  *
+ * The compliance side builds its context in two more shapes,
+ * `ComplianceMedicationContext` and the `CadenceEngineContext` the timelines
+ * hand the engine, and both dropped `endedAt` once: the streak and the
+ * per-window timeline copied the context field by field and counted the dose
+ * after an ended course as missed. Both types now require the field, and the
+ * last leg holds every builder of either to naming it, and the timelines to
+ * the one builder.
+ *
  * Limit, stated: a literal passed straight to the engine without the
  * `RecurrenceContext` annotation is invisible here. Every medication path
  * today goes through one of the annotated builders below.
@@ -29,7 +37,7 @@ import { readdirSync } from "node:fs";
 import { join, relative, resolve } from "node:path";
 
 import { describe, expect, it } from "vitest";
-import { readSourceText } from "./helpers/source-files";
+import { readSource, readSourceText } from "./helpers/source-files";
 
 const SRC = resolve(__dirname, "..");
 const ROOT = resolve(SRC, "..");
@@ -142,3 +150,53 @@ describe("the rolling course anchor is opt-in", () => {
     expect(declaring).toEqual([]);
   });
 });
+
+/** A typed literal or a typed return of either compliance context. */
+const COMPLIANCE_CONTEXT_DECLARATION =
+  /(\)\s*:\s*(?:CadenceEngineContext|ComplianceMedicationContext)\s*\{|:\s*(?:CadenceEngineContext|ComplianceMedicationContext)(?:\s*\|\s*undefined)?\s*=\s*[^;{]*\{)/g;
+
+function complianceContextBuilders(): Array<{ file: string; block: string }> {
+  const out: Array<{ file: string; block: string }> = [];
+  for (const file of sourceFiles(SRC)) {
+    const text = readSourceText(file);
+    for (const m of text.matchAll(COMPLIANCE_CONTEXT_DECLARATION)) {
+      const open = m.index! + m[0].length - 1;
+      out.push({ file: relative(ROOT, file), block: blockAt(text, open) });
+    }
+  }
+  return out;
+}
+
+describe("the compliance contexts carry the instant a course was ended", () => {
+  it("builds the engine's context in one place, which names endedAt", () => {
+    const found = complianceContextBuilders();
+    // The two builders: the medication context and the engine's view of it.
+    expect(found.map((b) => b.file).sort()).toEqual([
+      "src/lib/analytics/compliance/display.ts",
+      "src/lib/analytics/compliance/types.ts",
+    ]);
+    for (const b of found) {
+      expect(b.block, b.file).toMatch(/\bendedAt\s*:/);
+    }
+    // The matcher sees each shape the timelines used to write.
+    const shapes = [
+      "const e: CadenceEngineContext = { a: 1 };",
+      "const e: CadenceEngineContext | undefined = ctx ? { a: 1 } : undefined;",
+      "function f(): ComplianceMedicationContext {\n return {};\n}",
+    ];
+    for (const shape of shapes) {
+      expect([...shape.matchAll(COMPLIANCE_CONTEXT_DECLARATION)]).toHaveLength(
+        1,
+      );
+    }
+  });
+
+  it("has both timelines take the engine context from that builder", () => {
+    const display = readSource("src/lib/analytics/compliance/display.ts", [
+      "function cadenceEngineContextOf(",
+      "function buildTimelineForWindow(",
+    ]);
+    const uses = display.match(/cadenceEngineContextOf\(ctx\)/g) ?? [];
+    expect(uses.length).toBe(2);
+  });
+});
diff --git a/src/lib/analytics/compliance/__tests__/compliance-ended-course.test.ts b/src/lib/analytics/compliance/__tests__/compliance-ended-course.test.ts
new file mode 100644
index 000000000..61031ee37
--- /dev/null
+++ b/src/lib/analytics/compliance/__tests__/compliance-ended-course.test.ts
@@ -0,0 +1,120 @@
+/**
+ * #1280 — a course ended at an instant expects no dose after it, in the
+ * streak and the per-window timeline as in the rate.
+ *
+ * The person lives in Europe/Berlin and doses at 08:00 and 20:00 local
+ * (06:00Z and 18:00Z in October before the clock change). Every dose of the
+ * last twenty days was taken, except the evening one on the day the course
+ * was ended at noon: that slot came after the end and was never due.
+ */
+import { describe, expect, it } from "vitest";
+
+import {
+  buildMedicationComplianceBundle,
+  calculateCompliance,
+} from "@/lib/analytics/compliance/display";
+import {
+  buildComplianceMedicationContext,
+  type ComplianceSchedule,
+} from "@/lib/analytics/compliance/types";
+
+const TZ = "Europe/Berlin";
+const DAY = 86_400_000;
+const NOW = new Date("2026-10-25T10:00:00.000Z");
+const ENDED_AT = new Date("2026-10-24T10:00:00.000Z");
+const CREATED_AT = new Date(NOW.getTime() - 20 * DAY);
+
+const schedules: ComplianceSchedule[] = [
+  {
+    windowStart: "08:00",
+    windowEnd: "09:00",
+    timesOfDay: ["08:00", "20:00"],
+    daysOfWeek: null,
+    rrule: null,
+    rollingIntervalDays: null,
+    reminderGraceMinutes: null,
+    scheduleType: "SCHEDULED",
+    cyclicOnWeeks: null,
+    cyclicOffWeeks: null,
+  },
+];
+
+/** Every dose taken on time; the end day's evening only when asked. */
+function events(withLastEvening: boolean) {
+  const out: Array<{
+    scheduledFor: Date;
+    takenAt: Date;
+    skipped: boolean;
+    autoMissed: boolean;
+  }> = [];
+  for (let d = 19; d >= 0; d -= 1) {
+    const key = new Date(Date.UTC(2026, 9, 24 - d)).toISOString().slice(0, 10);
+    const morning = new Date(`${key}T06:00:00.000Z`);
+    out.push({
+      scheduledFor: morning,
+      takenAt: morning,
+      skipped: false,
+      autoMissed: false,
+    });
+    if (d > 0 || withLastEvening) {
+      const evening = new Date(`${key}T18:00:00.000Z`);
+      out.push({
+        scheduledFor: evening,
+        takenAt: evening,
+        skipped: false,
+        autoMissed: false,
+      });
+    }
+  }
+  return out;
+}
+
+function context(endedAt: Date | null) {
+  return buildComplianceMedicationContext(
+    {
+      startsOn: new Date(Date.UTC(2026, 9, 4)),
+      endsOn: new Date(Date.UTC(2026, 9, 24)),
+      endedAt,
+      oneShot: false,
+      createdAt: CREATED_AT,
+    },
+    new Date("2026-10-24T06:00:00.000Z"),
+    TZ,
+  );
+}
+
+describe("a course ended at an instant", () => {
+  it("does not break the streak on the slot after the end", () => {
+    const ended = calculateCompliance(events(false), schedules, 7, CREATED_AT, {
+      now: NOW,
+      medicationContext: context(ENDED_AT),
+    });
+    // The same course run to the end of its last day with every dose taken.
+    const whole = calculateCompliance(events(true), schedules, 7, CREATED_AT, {
+      now: NOW,
+      medicationContext: context(null),
+    });
+    expect(whole.streak).toBeGreaterThan(0);
+    expect(ended.missed).toBe(0);
+    expect(ended.streak).toBe(whole.streak);
+  });
+
+  it("does not break the bundle's streaks either", () => {
+    const ended = buildMedicationComplianceBundle(
+      events(false),
+      schedules,
+      context(ENDED_AT),
+      NOW,
+    );
+    const whole = buildMedicationComplianceBundle(
+      events(true),
+      schedules,
+      context(null),
+      NOW,
+    );
+    expect(whole.compliance7.streak).toBeGreaterThan(0);
+    expect(ended.compliance7.missed).toBe(0);
+    expect(ended.compliance7.streak).toBe(whole.compliance7.streak);
+    expect(ended.compliance30.streak).toBe(whole.compliance30.streak);
+  });
+});
diff --git a/src/lib/analytics/compliance/__tests__/pre-creation-slots.test.ts b/src/lib/analytics/compliance/__tests__/pre-creation-slots.test.ts
index 1d666d92e..0a2871961 100644
--- a/src/lib/analytics/compliance/__tests__/pre-creation-slots.test.ts
+++ b/src/lib/analytics/compliance/__tests__/pre-creation-slots.test.ts
@@ -49,6 +49,7 @@ for (const tz of ["Asia/Kolkata", "America/New_York"]) {
     const ctx: ComplianceMedicationContext = {
       startsOn: new Date("2026-09-23T00:00:00Z"),
       endsOn: new Date("2026-09-28T00:00:00Z"),
+      endedAt: null,
       oneShot: false,
       createdAt,
       lastIntakeAt: d2(21, 30),
diff --git a/src/lib/analytics/compliance/display.ts b/src/lib/analytics/compliance/display.ts
index 521830ae5..7d7f220d9 100644
--- a/src/lib/analytics/compliance/display.ts
+++ b/src/lib/analytics/compliance/display.ts
@@ -243,6 +243,31 @@ export function buildComplianceDisplay(
  *                       can be driven deterministically from a caller
  *                       that already pinned its own `now`.
  */
+/**
+ * The cadence engine's view of a compliance context, and the only place it
+ * is built: the streak timeline, the per-window timeline and the ledger must
+ * expect the same slots. The two timelines used to copy the context field
+ * by field and dropped `endedAt` (#1280), so a slot after "End course"
+ * counted as missed in the streak while the rate left it out. `endedAt` is
+ * required on both types, so a field missed here is a type error rather
+ * than a slot.
+ */
+export function cadenceEngineContextOf(
+  ctx: ComplianceMedicationContext,
+): CadenceEngineContext {
+  return {
+    startsOn: ctx.startsOn,
+    endsOn: ctx.endsOn,
+    endedAt: ctx.endedAt,
+    oneShot: ctx.oneShot,
+    createdAt: ctx.createdAt,
+    lastIntakeAt: ctx.lastIntakeAt,
+    timeZone: ctx.timeZone,
+    scheduleRevisions: ctx.scheduleRevisions,
+    courses: ctx.courses,
+  };
+}
+
 /**
  * Whether a medication expects any dose at all, and so has an adherence rate
  * worth showing.
@@ -375,19 +400,7 @@ export function calculateCompliance(
   // canonical engine (RRULE / rolling / one-shot / PRN / cyclic);
   // otherwise the legacy weekday walker stays in force.
   const ctx = options?.medicationContext;
-  const engineCtx: CadenceEngineContext | undefined = ctx
-    ? {
-        startsOn: ctx.startsOn,
-        endsOn: ctx.endsOn,
-        oneShot: ctx.oneShot,
-        createdAt: ctx.createdAt,
-        lastIntakeAt: ctx.lastIntakeAt,
-        timeZone: ctx.timeZone,
-        scheduleRevisions: ctx.scheduleRevisions,
-        // v1.40 (#1024) — the streak walks the same course days the rate does.
-        courses: ctx.courses,
-      }
-    : undefined;
+  const engineCtx = ctx ? cadenceEngineContextOf(ctx) : undefined;
 
   // Match events against the same slot grid the cadence chart uses.
   // The chart's pairing radius is ±12 h so a late-by-six-hours dose
@@ -755,17 +768,7 @@ function buildTimelineForWindow(
     cyclicOffWeeks: s.cyclicOffWeeks ?? null,
   }));
 
-  const engineCtx: CadenceEngineContext = {
-    startsOn: ctx.startsOn,
-    endsOn: ctx.endsOn,
-    oneShot: ctx.oneShot,
-    createdAt: ctx.createdAt,
-    lastIntakeAt: ctx.lastIntakeAt,
-    timeZone: ctx.timeZone,
-    scheduleRevisions: ctx.scheduleRevisions,
-    // v1.40 (#1024) — the same course days the ledger counts.
-    courses: ctx.courses,
-  };
+  const engineCtx = cadenceEngineContextOf(ctx);
 
   const normalisedEvents: IntakeEventLike[] = events
     .filter((e) => e.scheduledFor >= effectiveStart && e.scheduledFor <= now)
diff --git a/src/lib/analytics/compliance/types.ts b/src/lib/analytics/compliance/types.ts
index 622a6996a..47ebe8410 100644
--- a/src/lib/analytics/compliance/types.ts
+++ b/src/lib/analytics/compliance/types.ts
@@ -161,10 +161,10 @@ export interface ComplianceMedicationContext {
   /**
    * #1280 — the instant "End course" ended the latest course: no slot at or
    * after it is expected. Earlier courses carry their own in `courses`.
-   * Every production context comes from `buildComplianceMedicationContext`,
-   * whose input requires it.
+   * Required, null when the whole `endsOn` day counts: a context built
+   * without it would expect the dose after the end.
    */
-  endedAt?: Date | null;
+  endedAt: Date | null;
   oneShot: boolean;
   createdAt: Date;
   lastIntakeAt: Date | null;
diff --git a/src/lib/medications/scheduling/__tests__/compliance.test.ts b/src/lib/medications/scheduling/__tests__/compliance.test.ts
index 66957b55f..c4f8c462f 100644
--- a/src/lib/medications/scheduling/__tests__/compliance.test.ts
+++ b/src/lib/medications/scheduling/__tests__/compliance.test.ts
@@ -23,6 +23,7 @@ function ctx(
   return {
     startsOn: null,
     endsOn: null,
+    endedAt: null,
     oneShot: false,
     createdAt: d("2025-05-01T00:00:00Z"),
     lastIntakeAt: null,
diff --git a/src/lib/medications/scheduling/cadence.ts b/src/lib/medications/scheduling/cadence.ts
index 44dbcb7f3..2f5fc5475 100644
--- a/src/lib/medications/scheduling/cadence.ts
+++ b/src/lib/medications/scheduling/cadence.ts
@@ -128,8 +128,8 @@ export interface ScheduleLike {
 export interface CadenceEngineContext {
   startsOn: Date | null;
   endsOn: Date | null;
-  /** #1280 — when "End course" ended the latest course (see the engine). */
-  endedAt?: Date | null;
+  /** #1280 — when "End course" ended the latest course; null: whole day. */
+  endedAt: Date | null;
   oneShot: boolean;
   createdAt: Date;
   /** Latest non-skipped intake — only read by rolling cadences. */