Make the Coach lookback a limit on every read

The saved Coach window only seeded the snapshot and each tool's default.
A tool could still read back to all time, the availability probe reported
counts and means for history outside the window, and several blocks read
fixed windows of their own (labs 12 months, correlations 180 days, the
coarse tail, the all-time extremes) whatever the setting said.

coachPrefs.defaultWindow is now enforced as a limit through one module,
history-reach.ts: the turn context clamps the client window, the snapshot
clamps its window and gives every fixed-window block either the shorter
window or, when the block's own window cannot fit, leaves it out. Every
retrieval tool clamps its window, an earlier period or a stored table that
reaches past the limit answers outside_reach, and the probe reads only
inside the limit and names older history as outside_reach without any
figure. Follow-up chips that would read past the limit are not offered.
The default (allTime) is no limit and reads as before. MCP clients pass no
limit and keep their own window arguments.

Adds the twelve-month option, rewrites the picker text to state what is
read with the numbers the readers use, shows the same options in the
managed-profile settings, counts cluster members with a singular, and
drops the opacity on switched-off rows that put their text below WCAG AA.

src/components/settings/managed-record-settings-section.tsx

@@ -34,6 +34,12 @@ import { DateField } from "@/components/ui/date-field";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { NativeSelect } from "@/components/ui/native-select";
+import {
+  COACH_HISTORY_WINDOWS,
+  HISTORY_REACH_DAYS,
+  lookbackText,
+} from "@/lib/ai/coach/history-reach";
+import type { CoachDefaultWindow } from "@/lib/validations/coach-prefs";
 import { QueryErrorCard } from "@/components/ui/query-error-card";
 import { Switch } from "@/components/ui/switch";
 import { SettingsCardActions } from "./_card-actions";
@@ -776,6 +782,12 @@ function CoachSettingsForm({
   const preferences = asRecord(settings.preferences);
   const excluded = new Set(asStringArray(preferences.excludeMetrics));
   const dataClusters = new Set(asStringArray(preferences.dataClusters));
+  const savedWindow = asString(preferences.defaultWindow, "allTime");
+  const [lookback, setLookback] = useState<CoachDefaultWindow>(
+    (COACH_HISTORY_WINDOWS as readonly string[]).includes(savedWindow)
+      ? (savedWindow as CoachDefaultWindow)
+      : "allTime",
+  );
 
   function submit(event: FormEvent<HTMLFormElement>) {
     event.preventDefault();
@@ -847,28 +859,44 @@ function CoachSettingsForm({
             </option>
           </NativeSelect>
         </label>
-        <label className="grid gap-1 text-sm" htmlFor="managed-coach-window">
-          {t("settings.sharedRecord.managedSettings.coach.defaultWindow")}
+        {/* The same lookback options and wording as the Coach's own picker:
+            the choice is a limit on every Coach read. */}
+        <div className="grid gap-1 text-sm">
+          <label htmlFor="managed-coach-window">
+            {t("insights.coach.lookback.label")}
+          </label>
           <NativeSelect
-            defaultValue={asString(preferences.defaultWindow, "allTime")}
+            value={lookback}
+            onChange={(event) =>
+              setLookback(event.currentTarget.value as CoachDefaultWindow)
+            }
             disabled={disabled}
             id="managed-coach-window"
             name="defaultWindow"
+            aria-describedby="managed-coach-window-detail"
           >
-            <option value="last7days">
-              {t("settings.sharedRecord.managedSettings.coach.last7days")}
-            </option>
-            <option value="last30days">
-              {t("settings.sharedRecord.managedSettings.coach.last30days")}
-            </option>
-            <option value="last90days">
-              {t("settings.sharedRecord.managedSettings.coach.last90days")}
-            </option>
-            <option value="allTime">
-              {t("settings.sharedRecord.managedSettings.coach.allTime")}
-            </option>
+            {COACH_HISTORY_WINDOWS.map((window) => (
+              <option key={window} value={window}>
+                {t(
+                  `insights.coach.lookback.option.${window}`,
+                  lookbackText(window).optionParams,
+                )}
+              </option>
+            ))}
           </NativeSelect>
-        </label>
+          <p
+            id="managed-coach-window-detail"
+            className="text-muted-foreground text-xs"
+          >
+            {t(
+              `insights.coach.lookback.${lookbackText(lookback).detailKey}`,
+              lookbackText(lookback).detailParams,
+            )}
+            {HISTORY_REACH_DAYS[lookback] !== null
+              ? ` ${t("insights.coach.lookback.note")}`
+              : null}
+          </p>
+        </div>
       </div>
       <fieldset className="space-y-2">
         <legend className="text-sm font-medium">