diff --git a/functions/strava.js b/functions/strava.js
index 416c4da..6d6f054 100644
--- a/functions/strava.js
+++ b/functions/strava.js
@@ -24,7 +24,6 @@ const STRAVA_RECENT_ACTIVITY_LIMIT = 5;
 const STRAVA_ACTIVITY_NAME_MAX_LENGTH = 1_024;
 const STRAVA_ACTIVITY_TYPE_MAX_LENGTH = 128;
 const STRAVA_ACTIVITY_DATE_MAX_LENGTH = 64;
-const STRAVA_LONG_MAX_AS_NUMBER = 9_223_372_036_854_776_000;
 const STRAVA_REFRESH_ERROR_MESSAGE = 'Strava connection could not be refreshed.';
 const STRAVA_DATA_ERROR_MESSAGE = 'Strava activity data could not be loaded.';
 const STRAVA_STATS_REQUEST_ERROR_MESSAGE = 'Strava statistics request is invalid.';
@@ -45,7 +44,6 @@ const arrayIsArray = Array.isArray;
 const arrayPrototype = Array.prototype;
 const arrayPush = Array.prototype.push;
 const numberIsFinite = Number.isFinite;
-const numberIsInteger = Number.isInteger;
 const numberIsSafeInteger = Number.isSafeInteger;
 const reflectApply = Reflect.apply;
 const reflectHas = Reflect.has;
@@ -344,14 +342,6 @@ function isFiniteNumberInRange(value, maximum) {
     && value <= maximum;
 }
 
-function isPositiveIntegerInRange(value, maximum) {
-  return typeof value === 'number'
-    && numberIsFinite(value)
-    && numberIsInteger(value)
-    && value > 0
-    && value <= maximum;
-}
-
 function hasLoneSurrogate(value) {
   for (let index = 0; index < value.length; index += 1) {
     const codeUnit = reflectApply(stringCharCodeAt, value, [index]);
@@ -515,7 +505,7 @@ function snapshotProviderActivity(record) {
     (value) => isBoundedVisibleAscii(value, STRAVA_ACTIVITY_DATE_MAX_LENGTH),
   );
   if (
-    !isPositiveIntegerInRange(id, STRAVA_LONG_MAX_AS_NUMBER)
+    !isPositiveSafeInteger(id)
     || !isBoundedActivityName(name)
     || type === INVALID_SELECTED_VALUE
     || !isFiniteNumberInRange(distance, Number.MAX_SAFE_INTEGER)
diff --git a/functions/strava.test.js b/functions/strava.test.js
index d31fba4..762049e 100644
--- a/functions/strava.test.js
+++ b/functions/strava.test.js
@@ -4890,6 +4890,45 @@ describe('Strava activity data failure boundary', () => {
       });
     });
 
+    describe('OAUTH-001A2H precision-safe activity IDs', () => {
+      test('rejects the first precision-unsafe integer before statistics JSON', async () => {
+        await expectInvalidSuccessfulProviderData({
+          activities: [validProviderActivity({
+            id: Number.MAX_SAFE_INTEGER + 1,
+          })],
+          invalidSurface: 'activities',
+        });
+      });
+
+      test('preserves the safe-integer ceiling as an exact numeric result', async () => {
+        seedFreshConnection();
+        const { activitiesJson, statsJson } = mockSuccessfulProviderData({
+          activities: [validProviderActivity({
+            id: Number.MAX_SAFE_INTEGER,
+          })],
+        });
+
+        const result = await stravaFetchStats({}, CONTEXT);
+
+        expect(result.recentActivities[0]).toEqual({
+          id: Number.MAX_SAFE_INTEGER,
+          name: 'Synthetic Morning Run',
+          type: 'Run',
+          distanceMeters: 5000.5,
+          movingTimeSeconds: 1500,
+          startDate: '2026-01-02T12:00:00Z',
+        });
+        expect(typeof result.recentActivities[0].id).toBe('number');
+        expect(activitiesJson).toHaveBeenCalledTimes(1);
+        expect(statsJson).toHaveBeenCalledTimes(1);
+        expectTwoFreshBearerReads();
+        expect(admin.__getReads()).toEqual([CONNECTION_PATH, SECRET_PATH]);
+        expect(admin.__getDeletes()).toEqual([]);
+        expect(Timestamp.now).not.toHaveBeenCalled();
+        expectNoWritesOrLogs();
+      });
+    });
+
     test.each([
       ['id', 987654],
       ['name', 'Synthetic Morning Run'],
@@ -4961,11 +5000,11 @@ describe('Strava activity data failure boundary', () => {
       expectNoWritesOrLogs();
     });
 
-    test('accepts exact bounds, five dense entries, and the rounded signed-Long ceiling', async () => {
+    test('accepts exact bounds, five dense entries, and the safe-integer activity ceiling', async () => {
       seedFreshConnection();
-      const longId = MAX_STRAVA_LONG_AS_NUMBER;
+      const safeId = Number.MAX_SAFE_INTEGER;
       const activities = Array.from({ length: 5 }, (_unused, index) => validProviderActivity({
-        id: index === 0 ? longId : index + 1,
+        id: index === 0 ? safeId : index + 1,
         name: index === 0 ? '🏃'.repeat(MAX_ACTIVITY_NAME_LENGTH / 2) : `Run ${index}`,
         type: index === 0 ? 't'.repeat(MAX_ACTIVITY_TYPE_LENGTH) : undefined,
         sport_type: index === 0 ? 'ignored' : 'Run',
@@ -4979,7 +5018,7 @@ describe('Strava activity data failure boundary', () => {
 
       expect(result.recentActivities).toHaveLength(5);
       expect(result.recentActivities[0]).toEqual({
-        id: longId,
+        id: safeId,
         name: '🏃'.repeat(MAX_ACTIVITY_NAME_LENGTH / 2),
         type: 't'.repeat(MAX_ACTIVITY_TYPE_LENGTH),
         distanceMeters: Number.MAX_SAFE_INTEGER,