From 5e1035e47a51a043aba168c15ed880a4654486ac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Bombeck?= <marc@bombeck.io>
Date: Wed, 10 Jun 2026 21:41:12 +0200
Subject: [PATCH] fix(medications): drop the due-context line when no slot is
 plausibly near

History rows recorded before a schedule's first minted slot paired with
an anchor days or weeks away and read 'due 09:00 (-1904 h)'. The
nearest-anchor fallback now caps at the band's capture reach plus one
inter-slot gap; beyond that the row simply reads off-schedule.
---
 .../scheduling/__tests__/dose-history.test.ts | 23 +++++++++++++++++++
 .../medications/scheduling/dose-history.ts    | 21 +++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/src/lib/medications/scheduling/__tests__/dose-history.test.ts b/src/lib/medications/scheduling/__tests__/dose-history.test.ts
index c0a7056ef..c98a6ea37 100644
--- a/src/lib/medications/scheduling/__tests__/dose-history.test.ts
+++ b/src/lib/medications/scheduling/__tests__/dose-history.test.ts
@@ -459,3 +459,26 @@ describe("reconstructDoseHistory", () => {
     expect(times).toEqual([...times].sort((a, b) => a - b));
   });
 });
+
+describe("suggestNearestSlot fallback cap", () => {
+  it("omits due-context when the nearest anchor sits days away", async () => {
+    const { suggestNearestSlot } = await import("../dose-history");
+    const mk = (iso: string) => {
+      const at = new Date(iso);
+      return {
+        at,
+        timeOfDay: "09:00",
+        onTimeStart: new Date(at.getTime() - 60 * 60_000),
+        onTimeEnd: new Date(at.getTime() + 60 * 60_000),
+        overdueEnd: new Date(at.getTime() + 4 * 60 * 60_000),
+      } as never;
+    };
+    // First minted slot is 2026-05-31 (startsOn); the take predates it by 6 days.
+    const bands = [mk("2026-05-31T07:00:00Z"), mk("2026-06-01T07:00:00Z")];
+    const far = suggestNearestSlot(new Date("2026-05-25T09:26:00Z"), bands, () => false);
+    expect(far).toBeNull();
+    // A take inside the suggestion zone still gets its context.
+    const near = suggestNearestSlot(new Date("2026-05-31T08:30:00Z"), bands, () => false);
+    expect(near?.timeOfDay).toBe("09:00");
+  });
+});
diff --git a/src/lib/medications/scheduling/dose-history.ts b/src/lib/medications/scheduling/dose-history.ts
index 2f0d500e0..f713be1dc 100644
--- a/src/lib/medications/scheduling/dose-history.ts
+++ b/src/lib/medications/scheduling/dose-history.ts
@@ -314,6 +314,27 @@ export function suggestNearestSlot(
     }
   }
 
+  // The nearest-anchor fallback only makes sense as due-context when the
+  // anchor sits within one cadence step of the take. A take recorded before
+  // the schedule's first minted slot (e.g. history predating startsOn) would
+  // otherwise pair with a slot days or weeks away and the history row would
+  // read "due 09:00 (-1904 h)" — meaningless. Cap the fallback at the band's
+  // own capture reach plus one inter-slot gap; beyond that, no due-context.
+  if (bestAny && bestSuggest === null) {
+    const b = bestAny.band;
+    const reach = b.overdueEnd.getTime() - b.onTimeStart.getTime();
+    const idx = sorted.indexOf(b);
+    const gapMs =
+      sorted.length > 1
+        ? Math.abs(
+            (sorted[Math.min(idx + 1, sorted.length - 1)].at.getTime() ||
+              b.at.getTime()) -
+              (sorted[Math.max(idx - 1, 0)].at.getTime() || b.at.getTime()),
+          ) / Math.max(1, Math.min(idx + 1, sorted.length - 1) - Math.max(idx - 1, 0))
+        : reach;
+    if (bestAny.dist > reach + gapMs) return null;
+  }
+
   const pick = bestSuggest ?? bestAny;
   if (!pick) return null;
   return {