Call it a cycle, not "every N days"

"Every 26 days" is ordinary English for an interval, but it sits directly
beneath a start and an end — a duration — and a reader who has just been
thinking in durations reads it as another one. Naming the shape of the
repetition is what separates them, and "cycle" is the word this genre
already uses.

A cycle of one unit is named rather than numbered, because nobody says "a
1-week cycle"; a longer one takes the singular unit, since a hyphenated
"26-day" is an adjective and not a count. The article follows how the
number sounds — an 8-day cycle, an 11-day, an 84-day — which is the kind of
wrong that reads as sloppiness rather than as a bug.

The manual control becomes "Cycle length" for the same reason: it is asking
for the length of the cycle, not for a duration the reader already gave.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

test/custom-ui.test.tsx

@@ -399,7 +399,7 @@ describe("stating a repeat", () => {
         onCancel={() => {}}
       />,
     );
-    expect(html).toContain("every 8 days");
+    expect(html).toContain("on an 8-day cycle");
     expect(html).toContain("from your dates");
     expect(html).not.toContain("Wait");
   });
@@ -433,7 +433,7 @@ describe("stating a repeat", () => {
     expect(html).toContain("after it ends");
     // A week's gap after a week's window is a fortnightly rule; both readings
     // are shown so the reader can check the one against the other.
-    expect(html).toContain("every 2 weeks");
+    expect(html).toContain("on a 2-week cycle");
   });
 
   test("with no end date there is nothing to measure, so it asks", () => {
@@ -446,7 +446,7 @@ describe("stating a repeat", () => {
         onCancel={() => {}}
       />,
     );
-    expect(html).toContain("Every");
+    expect(html).toContain("Cycle length");
   });
 
   test("a delay needs an end date to be measured from", () => {
@@ -564,12 +564,33 @@ describe("the sheet says how often", () => {
       at: AT,
       updatedAt: AT,
     });
-    expect(cadenceLabel(rule.repeat)).toBe("every 2 weeks");
+    expect(cadenceLabel(rule.repeat)).toBe("on a 2-week cycle");
   });
 
-  test("an interval of one drops the number and the plural", () => {
-    expect(cadenceLabel({ unit: "weeks", interval: 1, until: null })).toBe("every week");
-    expect(cadenceLabel({ unit: "months", interval: 1, until: null })).toBe("every month");
+  test("a cycle of one unit is named, not numbered", () => {
+    // "on a 1-week cycle" is what the general form would produce and nobody
+    // says it. The adverb is the natural reading and costs one lookup.
+    expect(cadenceLabel({ unit: "days", interval: 1, until: null })).toBe("on a daily cycle");
+    expect(cadenceLabel({ unit: "weeks", interval: 1, until: null })).toBe("on a weekly cycle");
+    expect(cadenceLabel({ unit: "months", interval: 1, until: null })).toBe("on a monthly cycle");
+  });
+
+  test("a longer cycle takes the singular unit as an adjective", () => {
+    // "26-day", not "26-days" — the hyphenated form is adjectival.
+    expect(cadenceLabel({ unit: "days", interval: 26, until: null })).toBe("on a 26-day cycle");
+    expect(cadenceLabel({ unit: "months", interval: 3, until: null })).toBe("on a 3-month cycle");
+  });
+
+  test("the article follows how the number sounds, not how it is spelled", () => {
+    // "a 8-day cycle" is the kind of wrong that reads as sloppiness rather
+    // than as a bug. Eight, eleven and eighteen open on a vowel; so does
+    // everything in the eighties, which is still inside the 365 ceiling.
+    expect(cadenceLabel({ unit: "days", interval: 8, until: null })).toBe("on an 8-day cycle");
+    expect(cadenceLabel({ unit: "days", interval: 11, until: null })).toBe("on an 11-day cycle");
+    expect(cadenceLabel({ unit: "days", interval: 18, until: null })).toBe("on an 18-day cycle");
+    expect(cadenceLabel({ unit: "days", interval: 84, until: null })).toBe("on an 84-day cycle");
+    expect(cadenceLabel({ unit: "days", interval: 7, until: null })).toBe("on a 7-day cycle");
+    expect(cadenceLabel({ unit: "days", interval: 80, until: null })).toBe("on an 80-day cycle");
   });
 
   test("a non-repeating event has no cadence to show", () => {