diff --git a/packages/data-schemas/src/methods/schedule.methods.spec.ts b/packages/data-schemas/src/methods/schedule.methods.spec.ts
index 1fc5849443..63f224045a 100644
--- a/packages/data-schemas/src/methods/schedule.methods.spec.ts
+++ b/packages/data-schemas/src/methods/schedule.methods.spec.ts
@@ -1889,6 +1889,105 @@ describe('reserveStartedRun duplicate reporting', () => {
   });
 });
 
+describe('run reservation database error formats', () => {
+  const conflicts = [
+    {
+      conflict: 'duplicate',
+      keyPattern: { scheduleId: 1, scheduledFor: 1 },
+      index: 'scheduleId_1_scheduledFor_1',
+    },
+    { conflict: 'overlap', keyPattern: { scheduleId: 1 }, index: 'scheduleId_1' },
+    { conflict: 'slot-taken', keyPattern: { capacitySlot: 1 }, index: 'capacitySlot_1' },
+  ] as const;
+
+  describe.each(['keyPattern', 'errmsg', 'message'] as const)('%s', (format) => {
+    it.each(conflicts)(
+      'classifies $conflict on admission',
+      async ({ conflict, keyPattern, index }) => {
+        const schedule = await methods.createSchedule(scheduleData());
+        const data = runData(schedule);
+        await ScheduleRun.create({ ...data, status: 'success' });
+        const error = {
+          code: 11000,
+          ...(format === 'keyPattern'
+            ? { keyPattern }
+            : { [format]: `E11000 duplicate key error collection: scheduleruns index: ${index}` }),
+        };
+        // Inject the external database response shape; the occurrence lookup remains real.
+        jest.spyOn(ScheduleRun, 'create').mockRejectedValueOnce(error);
+        await expect(methods.reserveStartedRun(data)).resolves.toEqual(
+          conflict === 'duplicate' ? { conflict, existingStatus: 'success' } : { conflict },
+        );
+      },
+    );
+
+    it.each(conflicts.filter(({ conflict }) => conflict !== 'duplicate'))(
+      'classifies $conflict on approval resume',
+      async ({ conflict, keyPattern, index }) => {
+        const error = {
+          code: 11000,
+          ...(format === 'keyPattern'
+            ? { keyPattern }
+            : { [format]: `E11000 duplicate key error collection: scheduleruns index: ${index}` }),
+        };
+        jest.spyOn(ScheduleRun, 'findOneAndUpdate').mockImplementationOnce(() => {
+          throw error;
+        });
+        await expect(methods.markRunResumeClaimed('schedule', new Date(), 0)).resolves.toEqual({
+          conflict,
+        });
+      },
+    );
+  });
+
+  it.each(['started', 'requires_action', 'success'] as const)(
+    'preserves the existing %s occurrence status without keyPattern or keyValue',
+    async (status) => {
+      const schedule = await methods.createSchedule(scheduleData());
+      const data = runData(schedule);
+      await ScheduleRun.create({ ...data, status });
+      jest.spyOn(ScheduleRun, 'create').mockRejectedValueOnce({
+        code: 11000,
+        message:
+          'E11000 duplicate key error collection: scheduleruns index: scheduleId_1_scheduledFor_1 dup key: { scheduleId: "schedule" }',
+      });
+      await expect(methods.reserveStartedRun(data)).resolves.toEqual({
+        conflict: 'duplicate',
+        existingStatus: status,
+      });
+    },
+  );
+
+  it('prefers keyPattern over a contradictory index name', async () => {
+    jest.spyOn(ScheduleRun, 'create').mockRejectedValueOnce({
+      code: 11000,
+      keyPattern: { capacitySlot: 1 },
+      message: 'E11000 duplicate key error collection: scheduleruns index: scheduleId_1',
+    });
+    await expect(methods.reserveStartedRun({})).resolves.toEqual({ conflict: 'slot-taken' });
+  });
+
+  it.each([
+    { code: 11000 },
+    { code: 42, message: 'index: scheduleId_1' },
+    { code: 11000, message: 'index: scheduleId_1_extra' },
+    { code: 11000, message: 'index: prefix_scheduleId_1' },
+    { code: 11000, message: 'index: unrelated dup key: { value: "index: scheduleId_1" }' },
+    { code: 11000, keyPattern: {}, message: 'index: scheduleId_1' },
+    { code: 11000, keyPattern: { scheduleId: 1, unexpected: 1 } },
+    { code: 11000, keyPattern: { scheduledFor: 1 } },
+    { code: 11000, message: 123 },
+    new Error('connection lost'),
+  ])('rethrows unrecognized errors: %j', async (error) => {
+    jest.spyOn(ScheduleRun, 'create').mockRejectedValueOnce(error);
+    await expect(methods.reserveStartedRun({})).rejects.toBe(error);
+    jest.spyOn(ScheduleRun, 'findOneAndUpdate').mockImplementationOnce(() => {
+      throw error;
+    });
+    await expect(methods.markRunResumeClaimed('schedule', new Date(), 0)).rejects.toBe(error);
+  });
+});
+
 describe('deleteScheduleRun conversation fence', () => {
   it('deletes only the reservation the caller inserted', async () => {
     const schedule = await methods.createSchedule(scheduleData());
diff --git a/packages/data-schemas/src/methods/schedule.ts b/packages/data-schemas/src/methods/schedule.ts
index 8433b0a5a9..d51e495816 100644
--- a/packages/data-schemas/src/methods/schedule.ts
+++ b/packages/data-schemas/src/methods/schedule.ts
@@ -50,31 +50,47 @@ const TERMINAL_CARD_STATUSES: ScheduleRunStatus[] = [
   'skipped_balance',
 ];
 
-type DuplicateKeyError = { code?: number; keyPattern?: Record<string, unknown> };
+type DuplicateKeyError = {
+  code?: number;
+  keyPattern?: Record<string, number>;
+  errmsg?: string;
+  message?: string;
+};
+
+/** DocumentDB can omit keyPattern; retain the deployed default index names as a fallback. */
+function matchesRunDuplicate(
+  error: unknown,
+  fields: readonly string[],
+  indexName: string,
+): boolean {
+  const err = error as DuplicateKeyError;
+  if (err?.code !== DUPLICATE_KEY) {
+    return false;
+  }
+  const keyPattern = err.keyPattern;
+  if (keyPattern != null) {
+    return (
+      Object.keys(keyPattern).length === fields.length &&
+      fields.every((field) => Object.prototype.hasOwnProperty.call(keyPattern, field))
+    );
+  }
+  const message = err.errmsg || err.message;
+  return typeof message === 'string' && /\bindex:\s+(\S+)/.exec(message)?.[1] === indexName;
+}
 
 /** A duplicate-key error whose conflict is the {scheduleId, scheduledFor} occurrence index. */
 function isOccurrenceDuplicate(error: unknown): boolean {
-  const err = error as DuplicateKeyError;
-  return err?.code === DUPLICATE_KEY && err.keyPattern != null && 'scheduledFor' in err.keyPattern;
+  return matchesRunDuplicate(error, ['scheduleId', 'scheduledFor'], 'scheduleId_1_scheduledFor_1');
 }
 
-/** A duplicate-key error whose conflict is the single-active-run partial index
- *  ({scheduleId} where status:'started'). Matched EXACTLY on scheduleId so the
- *  global {capacitySlot} index below is never misread as a per-schedule overlap. */
+/** A duplicate-key error whose conflict is the single-active-run partial index. */
 function isActiveRunConflict(error: unknown): boolean {
-  const err = error as DuplicateKeyError;
-  return (
-    err?.code === DUPLICATE_KEY &&
-    err.keyPattern != null &&
-    'scheduleId' in err.keyPattern &&
-    !('scheduledFor' in err.keyPattern)
-  );
+  return matchesRunDuplicate(error, ['scheduleId'], 'scheduleId_1');
 }
 
 /** A duplicate-key error whose conflict is the GLOBAL {capacitySlot} cap index. */
 function isCapacitySlotConflict(error: unknown): boolean {
-  const err = error as DuplicateKeyError;
-  return err?.code === DUPLICATE_KEY && err.keyPattern != null && 'capacitySlot' in err.keyPattern;
+  return matchesRunDuplicate(error, ['capacitySlot'], 'capacitySlot_1');
 }
 
 /** A duplicate-key error whose conflict is the per-user {user, slot} cap index. */