feat(coach): name a read past the lookback limit on the trail

A read whose readings all lie past the lookback limit was reported on its
step as outside_window, and its fetch entry carried no reason, so a client
could not tell an empty window from data the limit keeps out. The step now
carries reason outside_reach and the fetch entry mirrors it. The method
line and the web trail keep the window sentence; the answer names the
limit as before.

src/app/api/insights/chat/__tests__/dialog-harness.ts

@@ -46,6 +46,8 @@ export interface DialogWorld {
   resultsWithheld: boolean;
   /** The provider's rounds, consumed in order. */
   script: ScriptRound[];
+  /** The stored `User.coachPrefsJson`; null is the defaults. */
+  coachPrefs: Record<string, unknown> | null;
 }
 
 export const world: DialogWorld = {
@@ -56,6 +58,7 @@ export const world: DialogWorld = {
   storedProvenance: {},
   resultsWithheld: false,
   script: [],
+  coachPrefs: null,
 };
 
 /** Everything the scripted provider was sent and answered, in order. */
@@ -412,6 +415,7 @@ export function resetDialog(): void {
   world.storedProvenance = {};
   world.resultsWithheld = false;
   world.script = [];
+  world.coachPrefs = null;
   providerCalls.length = 0;
   messageSeq = 0;
   for (const fn of Object.values(m)) fn.mockReset();
@@ -465,7 +469,7 @@ export const modules = {
     prisma: {
       user: {
         findUnique: async () => ({
-          coachPrefsJson: null,
+          coachPrefsJson: world.coachPrefs,
           displayName: null,
           aiResponseTimeoutSeconds: null,
         }),

src/app/api/insights/chat/__tests__/route-activity.test.ts

@@ -171,6 +171,62 @@ describe("the live trail", () => {
     expect(interim).toBeLessThan(firstToken);
   });
 
+  it("names a read past the lookback limit on its step and its fetch entry", async () => {
+    world.coachPrefs = { defaultWindow: "last7days" };
+    world.script = [
+      { calls: [{ name: "get_day", args: { date: "2026-06-01" } }] },
+      { text: "That day lies beyond the lookback limit you set." },
+    ];
+    const { status, frames } = await h.postTurn(post, {
+      message: "What happened on 1 June?",
+      locale: "en",
+    });
+    expect(status).toBe(200);
+    const step = framesOf<{ step: { id: string; status: string } }>(
+      frames,
+      "step",
+    )
+      .map((f) => f.step)
+      .at(-1);
+    expect(step).toMatchObject({
+      tool: "get_day",
+      status: "empty",
+      reason: "outside_reach",
+    });
+    const fetch = framesOf<{ activity: CoachActivity }>(frames, "activity")
+      .map((f) => f.activity)
+      .filter((a) => a.phase === "fetch")
+      .at(-1);
+    expect(fetch).toMatchObject({
+      status: "empty",
+      stepRef: step?.id,
+      reason: "outside_reach",
+    });
+  });
+
+  it("names no reason on a fetch inside the limit", async () => {
+    world.script = [
+      {
+        calls: [
+          {
+            name: "get_metric_table",
+            args: { metric: "bp", window: "last30days" },
+          },
+        ],
+      },
+      { text: "Steady. result:r1" },
+    ];
+    const { frames } = await h.postTurn(post, {
+      message: "How was my blood pressure?",
+      locale: "en",
+    });
+    const fetches = framesOf<{ activity: CoachActivity }>(frames, "activity")
+      .map((f) => f.activity)
+      .filter((a) => a.phase === "fetch");
+    expect(fetches.length).toBeGreaterThan(0);
+    for (const entry of fetches) expect(entry).not.toHaveProperty("reason");
+  });
+
   it("persists the structure on the provenance and the text in the trail", async () => {
     world.script = [
       {