From 8dc34c769128d6e66ed5bb1bcb631d0bc1399bac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Bombeck?= <mbombeck@gmail.com>
Date: Mon, 5 Oct 2026 07:52:15 +0200
Subject: [PATCH] fix(coach): keep GLP-1 dose changes before the lookback limit
 out

The GLP-1 block sent every dose change with its decrypted note whatever
the lookback limit said. Dose changes are entries, so only those inside
the limit reach the prompt; the dose in force stays as the current dose.
---
 .../ai/coach/__tests__/glp1-snapshot.test.ts  | 63 +++++++++++++++++++
 src/lib/ai/coach/glp1-snapshot.ts             | 14 +++--
 2 files changed, 73 insertions(+), 4 deletions(-)

diff --git a/src/lib/ai/coach/__tests__/glp1-snapshot.test.ts b/src/lib/ai/coach/__tests__/glp1-snapshot.test.ts
index 4836ac307..ab8fcbe7d 100644
--- a/src/lib/ai/coach/__tests__/glp1-snapshot.test.ts
+++ b/src/lib/ai/coach/__tests__/glp1-snapshot.test.ts
@@ -332,3 +332,66 @@ describe("buildGlp1SnapshotBlock injection days in the user's zone", () => {
     });
   });
 });
+
+describe("buildGlp1SnapshotBlock under the lookback limit", () => {
+  it("leaves dose changes before the limit out and keeps the current dose", async () => {
+    const now = new Date("2026-10-04T12:00:00.000Z");
+    prismaMock.medication.findMany.mockResolvedValue([
+      fakeMedication({
+        doseChanges: [
+          {
+            doseValue: 2.5,
+            doseUnit: "mg",
+            effectiveFrom: new Date("2026-06-01T00:00:00.000Z"),
+            note: "Nausea in the first week",
+          },
+          {
+            doseValue: 5,
+            doseUnit: "mg",
+            effectiveFrom: new Date("2026-08-01T00:00:00.000Z"),
+            note: "Stepped up after review",
+          },
+        ],
+      }),
+    ]);
+    const out = await buildGlp1SnapshotBlock("user-1", now, "UTC", {
+      window: "last30days",
+      days: 30,
+    });
+    const med = out?.medications[0];
+    // The current dose is therapy state, not history.
+    expect(med?.currentDose).toMatchObject({ value: 5, since: "2026-08-01" });
+    // Both changes lie before the 30-day floor: neither they nor their
+    // notes reach the prompt.
+    expect(med?.doseHistory).toEqual([]);
+    expect(JSON.stringify(out)).not.toContain("Nausea");
+    expect(JSON.stringify(out)).not.toContain("Stepped up");
+  });
+
+  it("keeps the dose changes inside the limit", async () => {
+    const now = new Date("2026-10-04T12:00:00.000Z");
+    prismaMock.medication.findMany.mockResolvedValue([
+      fakeMedication({
+        doseChanges: [
+          {
+            doseValue: 5,
+            doseUnit: "mg",
+            effectiveFrom: new Date("2026-08-01T00:00:00.000Z"),
+            note: null,
+          },
+          {
+            doseValue: 7.5,
+            doseUnit: "mg",
+            effectiveFrom: new Date("2026-09-20T00:00:00.000Z"),
+            note: null,
+          },
+        ],
+      }),
+    ]);
+    const out = await buildGlp1SnapshotBlock("user-1", now, "UTC", {
+      window: "last30days",
+      days: 30,
+    });
+    expect(out?.medications[0].doseHistory.map((d) => d.value)).toEqual([7.5]);
+  });
+});
diff --git a/src/lib/ai/coach/glp1-snapshot.ts b/src/lib/ai/coach/glp1-snapshot.ts
index 8ea49b05b..2edec8159 100644
--- a/src/lib/ai/coach/glp1-snapshot.ts
+++ b/src/lib/ai/coach/glp1-snapshot.ts
@@ -225,9 +225,10 @@ export async function buildGlp1SnapshotBlock(
   now: Date = new Date(),
   tz: string = DEFAULT_TIMEZONE,
   /**
-   * The Coach's lookback limit. The therapy plan (dose, titration, pens) is
-   * current state and stays; the last injection and the side-effect tags are
-   * entries and are read from inside the limit only.
+   * The Coach's lookback limit. The therapy plan (current dose, schedule,
+   * pens) is current state and stays; the last injection, the side-effect
+   * tags and the dose history (each change with its note) are entries and
+   * are read from inside the limit only.
    */
   reach: CoachHistoryReach = UNBOUNDED_REACH,
 ): Promise<Glp1SnapshotBlock | null> {
@@ -309,7 +310,12 @@ export async function buildGlp1SnapshotBlock(
     const genericSafe = sanitizeForPrompt(generic, 80);
     const latestChange = med.doseChanges[med.doseChanges.length - 1] ?? null;
 
-    const doseHistory: DoseHistoryEntry[] = med.doseChanges.map((dc) => {
+    // A dose change is an entry like any other: one made before the limit
+    // is left out with its note. The dose in force stays as `currentDose`.
+    const changesInReach = med.doseChanges.filter(
+      (dc) => floor === null || dc.effectiveFrom.getTime() >= floor.getTime(),
+    );
+    const doseHistory: DoseHistoryEntry[] = changesInReach.map((dc) => {
       const decryptedNote = readNote(dc.noteEncrypted, dc.note);
       return {
         value: dc.doseValue,