fix(illness): gate fever red-flag runs on calendar-adjacent days

Symptom and vital points are present-days-only, so a sparse febrile
series (e.g. days 10/15/20/25) was counted as one long run and falsely
fired the sustained_fever escalation. Continue a run only when the next
matching point is the calendar day immediately after the previous one,
using the existing dayDiff helper; otherwise start a fresh run of one.

src/lib/illness/__tests__/correlation.test.ts

@@ -669,6 +669,70 @@ describe("computeIllnessCorrelation — red-flag escalation", () => {
     expect(fever?.days).toBe(3);
     expect(fever?.worstValue).toBe(39.0);
   });
+
+  it("does NOT escalate a sparse febrile series with calendar GAPS (cries-wolf guard)", () => {
+    // Symptom/vital points are present-days-only (never zero-filled). A user
+    // who logs a fever on 01-10/01-15/01-20/01-25 has FOUR isolated febrile
+    // days with multi-day gaps between them — NOT a sustained run. The run
+    // scan must compare calendar-day deltas, not array adjacency, or it falsely
+    // fires sustained_fever (which surfaces a "seek medical care" string AND an
+    // urgent cross-channel push). No two of these days are calendar-adjacent →
+    // the longest run is 1 → NO escalation.
+    const rhr: MeasurementType = "RESTING_HEART_RATE";
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          {
+            type: rhr,
+            baselineDays: jitteredBaseline(55, 1, 21, "2026-01-02"),
+            episodeDays: flatBaseline(55, 5, "2026-01-15"),
+          },
+        ],
+        dayLogFever: [
+          { day: "2026-01-10", feverC: 39.2 },
+          { day: "2026-01-15", feverC: 39.0 },
+          { day: "2026-01-20", feverC: 38.8 },
+          { day: "2026-01-25", feverC: 38.7 },
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    const fever = out.value.redFlags.find(
+      (f) => f.reason === "sustained_fever",
+    );
+    expect(fever).toBeUndefined();
+  });
+
+  it("DOES escalate a genuinely consecutive 3-calendar-day febrile run", () => {
+    // The mirror of the gap guard: three truly adjacent calendar days
+    // (01-10/01-11/01-12) all ≥ 38.5 → a real sustained fever → escalate.
+    const rhr: MeasurementType = "RESTING_HEART_RATE";
+    const out = computeIllnessCorrelation(
+      input({
+        series: [
+          {
+            type: rhr,
+            baselineDays: jitteredBaseline(55, 1, 21, "2026-01-02"),
+            episodeDays: flatBaseline(55, 5, "2026-01-15"),
+          },
+        ],
+        dayLogFever: [
+          { day: "2026-01-10", feverC: 39.2 },
+          { day: "2026-01-11", feverC: 38.9 },
+          { day: "2026-01-12", feverC: 38.6 },
+        ],
+      }),
+    );
+    expect(out.status).toBe("ok");
+    if (out.status !== "ok") return;
+    const fever = out.value.redFlags.find(
+      (f) => f.reason === "sustained_fever",
+    );
+    expect(fever).toBeDefined();
+    expect(fever?.days).toBe(3);
+    expect(fever?.worstValue).toBe(39.2);
+  });
 });
 
 describe("isAdverseDeviation", () => {

src/lib/illness/correlation.ts

@@ -968,22 +968,37 @@ function runFlag(
   let bestWorst: number | null = null;
   let run = 0;
   let runWorst: number | null = null;
+  let prevDay: string | null = null;
   for (const p of sorted) {
     if (predicate(p.mean)) {
-      run++;
-      runWorst =
-        runWorst === null
-          ? p.mean
-          : worst === "min"
-            ? Math.min(runWorst, p.mean)
-            : Math.max(runWorst, p.mean);
+      // A run is CALENDAR-consecutive days. Symptom/vital points are
+      // present-days-only (never zero-filled), so a sparse febrile series
+      // (e.g. days 01/10/15/20) must NOT count as one long run — that fires a
+      // false sustained_fever escalation. Continue the run only when this
+      // point is the calendar day immediately after the previous matching one;
+      // otherwise the current point starts a fresh run of 1.
+      const adjacent = prevDay !== null && dayDiff(prevDay, p.day) === 1;
+      if (adjacent) {
+        run++;
+        runWorst =
+          runWorst === null
+            ? p.mean
+            : worst === "min"
+              ? Math.min(runWorst, p.mean)
+              : Math.max(runWorst, p.mean);
+      } else {
+        run = 1;
+        runWorst = p.mean;
+      }
       if (run > bestRun) {
         bestRun = run;
         bestWorst = runWorst;
       }
+      prevDay = p.day;
     } else {
       run = 0;
       runWorst = null;
+      prevDay = null;
     }
   }
   if (bestRun >= RED_FLAG_RUN_DAYS && bestWorst !== null) {