refactor(medications): share the wizard cadence-line builder

`summariseCadence` and `summariseScheduleDraft` each re-spelled the
cadence phrase, its detail clause, and the interpolation count. Extract
a single `{mode, cadence, subControls}`-shaped helper both call so the
medication-wide and per-schedule summaries can't drift apart, and drop
the now-redundant `summaryKeyForCadence` wrapper. Behaviour is
identical; add coverage pinning the per-schedule summary to the
medication-wide summary's leading cadence segment.

src/components/medications/wizard/__tests__/wizard-payload.test.ts

@@ -14,6 +14,7 @@ import {
   rowFromTreatment,
   setActiveSchedule,
   summariseCadence,
+  summariseScheduleDraft,
   validateStep,
   type WizardPayload,
   WIZARD_TREATMENT_MAPPING,
@@ -559,6 +560,49 @@ describe("summariseCadence", () => {
   });
 });
 
+describe("summariseScheduleDraft — shared cadence-line helper", () => {
+  const t = makeStubT();
+
+  // The per-schedule summary and the medication-wide summary build their
+  // cadence segment from the same extracted helper, so for an equivalent
+  // cadence shape the draft summary equals the leading segment of the
+  // full summary (which trails the times / course-window phrases).
+  it("matches summariseCadence's leading cadence segment", () => {
+    const cases: WizardPayload[] = [
+      withCadence("daily"),
+      withCadence("everyNWeeks", { intervalWeeks: 2, weekdays: ["MO"] }),
+      withCadence("rolling", { rollingDays: 14 }),
+      withCadence("weekdays", { weekdays: ["MO", "WE", "FR"] }),
+      withCadence("monthly", { dayOfMonth: 15 }),
+    ];
+    for (const base of cases) {
+      // `withCadence` only sets the flat mirror fields; commit them onto
+      // the active schedule draft so the draft carries the same cadence.
+      const p = commitActiveDraft(base);
+      const draft = p.schedules[p.activeScheduleIndex];
+      const draftLine = summariseScheduleDraft(draft, t);
+      const fullSummary = summariseCadence(p, t);
+      // The draft line's cadence segment is the leading " · " segment of
+      // the full summary (which trails times / course-window phrases).
+      const firstSegment = fullSummary.split(" · ")[0];
+      expect(draftLine.split(" · ")[0]).toBe(firstSegment);
+    }
+  });
+
+  it("threads the everyNWeeks interval into the cadence key", () => {
+    const p = commitActiveDraft(withCadence("everyNWeeks", { intervalWeeks: 3 }));
+    const out = summariseScheduleDraft(p.schedules[p.activeScheduleIndex], t);
+    expect(out).toMatch(/cadence\.everyNWeeks[^|]*"n":3/);
+  });
+
+  it("omits the cadence detail for a one-shot draft", () => {
+    const p = commitActiveDraft(withCadence("oneShot"));
+    const out = summariseScheduleDraft(p.schedules[p.activeScheduleIndex], t);
+    expect(out).not.toContain("weekdaysDetail");
+    expect(out).not.toContain("dayOfMonthDetail");
+  });
+});
+
 describe("hydrateWizardPayload", () => {
   function makeInitial(
     overrides: Partial<MedicationPayload> = {},

src/components/medications/wizard/wizard-payload.ts

@@ -712,10 +712,6 @@ function summaryKeyForDraft(
   }
 }
 
-function summaryKeyForCadence(payload: WizardPayload): string {
-  return summaryKeyForDraft(payload.mode, payload.cadence, payload.subControls);
-}
-
 function weekdaysDetail(
   tokens: readonly string[],
   t: (key: string, params?: Record<string, string | number>) => string,
@@ -732,25 +728,71 @@ function weekdaysDetail(
   });
 }
 
+/**
+ * The cadence-bearing slice both {@link WizardPayload} and
+ * {@link ScheduleDraft} share. Summary helpers only ever read these three
+ * fields, so the cadence-line builder below stays draft/payload-agnostic.
+ */
+type CadenceShape = Pick<ScheduleDraft, "mode" | "cadence" | "subControls">;
+
+/**
+ * The interpolation count the cadence summary keys read. `everyNWeeks`
+ * surfaces the week interval; `rolling` the day interval; everything else
+ * leaves it at zero. Extracted so the medication-wide and per-schedule
+ * summaries can't drift apart.
+ */
+function cadenceInterpolationN(shape: CadenceShape): number {
+  if (shape.cadence.kind === "everyNWeeks") return shape.subControls.intervalWeeks;
+  if (shape.cadence.kind === "rolling")
+    return shape.cadence.rollingIntervalDays ?? 0;
+  return 0;
+}
+
+/**
+ * The trailing detail clause appended to a cadence phrase (the weekday
+ * list or the day-of-month). Empty for one-shot doses and for cadences
+ * that carry no extra detail.
+ */
 function cadenceDetailPhrase(
-  payload: WizardPayload,
+  shape: CadenceShape,
   t: (key: string, params?: Record<string, string | number>) => string,
 ): string {
-  if (payload.mode === "oneShot") return "";
-  switch (payload.cadence.kind) {
+  if (shape.mode === "oneShot") return "";
+  switch (shape.cadence.kind) {
     case "weekdays":
-      return weekdaysDetail(payload.subControls.weekdays, t);
+      return weekdaysDetail(shape.subControls.weekdays, t);
     case "everyNWeeks":
-      return weekdaysDetail(payload.subControls.weekdays, t);
+      return weekdaysDetail(shape.subControls.weekdays, t);
     case "monthly":
       return t("medications.wizard.summary.dayOfMonthDetail", {
-        day: payload.subControls.dayOfMonth,
+        day: shape.subControls.dayOfMonth,
       });
     default:
       return "";
   }
 }
 
+/**
+ * The full cadence line — phrase (`every N weeks`, `daily`, …) plus its
+ * detail clause. Both {@link summariseCadence} and
+ * {@link summariseScheduleDraft} build their first segment from this so
+ * the two summaries render byte-identical cadence text.
+ */
+function cadenceLineFor(
+  shape: CadenceShape,
+  t: (key: string, params?: Record<string, string | number>) => string,
+): string {
+  const cadenceKey = summaryKeyForDraft(
+    shape.mode,
+    shape.cadence,
+    shape.subControls,
+  );
+  const cadencePhrase = t(`medications.wizard.summary.cadence.${cadenceKey}`, {
+    n: cadenceInterpolationN(shape),
+  });
+  return cadencePhrase + cadenceDetailPhrase(shape, t);
+}
+
 /**
  * Plain-language summary for Step 8. Mirrors v1.5.3's helper shape so
  * the test surface stays familiar. The `t` callback is passed in so
@@ -760,20 +802,7 @@ export function summariseCadence(
   payload: WizardPayload,
   t: (key: string, params?: Record<string, string | number>) => string,
 ): string {
-  const cadenceKey = summaryKeyForCadence(payload);
-  const cadencePhrase = t(
-    `medications.wizard.summary.cadence.${cadenceKey}`,
-    {
-      n:
-        payload.cadence.kind === "everyNWeeks"
-          ? payload.subControls.intervalWeeks
-          : payload.cadence.kind === "rolling"
-            ? (payload.cadence.rollingIntervalDays ?? 0)
-            : 0,
-    },
-  );
-  const cadenceDetail = cadenceDetailPhrase(payload, t);
-  const cadenceLine = cadencePhrase + cadenceDetail;
+  const cadenceLine = cadenceLineFor(payload, t);
   const timesPhrase =
     payload.mode !== "oneShot" && payload.timesOfDay.length > 0
       ? t("medications.wizard.summary.times", {
@@ -807,36 +836,7 @@ export function summariseScheduleDraft(
   draft: ScheduleDraft,
   t: (key: string, params?: Record<string, string | number>) => string,
 ): string {
-  const cadenceKey = summaryKeyForDraft(
-    draft.mode,
-    draft.cadence,
-    draft.subControls,
-  );
-  const cadencePhrase = t(
-    `medications.wizard.summary.cadence.${cadenceKey}`,
-    {
-      n:
-        draft.cadence.kind === "everyNWeeks"
-          ? draft.subControls.intervalWeeks
-          : draft.cadence.kind === "rolling"
-            ? (draft.cadence.rollingIntervalDays ?? 0)
-            : 0,
-    },
-  );
-  let cadenceDetail = "";
-  if (draft.mode !== "oneShot") {
-    if (
-      draft.cadence.kind === "weekdays" ||
-      draft.cadence.kind === "everyNWeeks"
-    ) {
-      cadenceDetail = weekdaysDetail(draft.subControls.weekdays, t);
-    } else if (draft.cadence.kind === "monthly") {
-      cadenceDetail = t("medications.wizard.summary.dayOfMonthDetail", {
-        day: draft.subControls.dayOfMonth,
-      });
-    }
-  }
-  const cadenceLine = cadencePhrase + cadenceDetail;
+  const cadenceLine = cadenceLineFor(draft, t);
   const timesPhrase =
     draft.mode !== "oneShot" && draft.timesOfDay.length > 0
       ? t("medications.wizard.summary.times", {