diff --git a/service/src/job-cancellation.test.ts b/service/src/job-cancellation.test.ts
index e23186e4..334fb8f7 100644
--- a/service/src/job-cancellation.test.ts
+++ b/service/src/job-cancellation.test.ts
@@ -1,5 +1,6 @@
 import { expect, test } from 'bun:test';
 import { EventEmitter } from 'node:events';
+import calculateSlot from 'cluster-key-slot';
 import type IORedis from 'ioredis';
 import type { Job, QueueEvents } from 'bullmq';
 import {
@@ -62,7 +63,7 @@ class FakeRedis {
   readonly existing = new Set<string>();
   readonly deleted: string[] = [];
   readonly transactions: FakeTransaction[] = [];
-  mgetFailures = 0;
+  getFailures = 0;
   cancellationFailures = 0;
   cancellationAttempts = 0;
 
@@ -72,6 +73,10 @@ class FakeRedis {
   }
 
   async get(key: string): Promise<string | null> {
+    if (this.getFailures > 0) {
+      this.getFailures -= 1;
+      throw new Error('command connection unavailable');
+    }
     return this.existing.has(key) ? '1' : null;
   }
 
@@ -93,14 +98,6 @@ class FakeRedis {
     return [1];
   }
 
-  async mget(...keys: string[]): Promise<Array<string | null>> {
-    if (this.mgetFailures > 0) {
-      this.mgetFailures -= 1;
-      throw new Error('command connection unavailable');
-    }
-    return keys.map(key => (this.existing.has(key) ? '1' : null));
-  }
-
   async del(key: string): Promise<number> {
     this.deleted.push(key);
     this.existing.delete(key);
@@ -263,7 +260,7 @@ test('subscriber reconnect retries durable-marker reconciliation', async () => {
   const controller = new AbortController();
   await registry.register(target, controller);
   fake.existing.add(jobCancellationInternals.cancellationKey(target));
-  fake.mgetFailures = 1;
+  fake.getFailures = 1;
 
   fake.subscriber.emit('ready');
   await new Promise(resolve => setTimeout(resolve, 150));
@@ -597,3 +594,10 @@ test('queued removal frees waiting capacity and tolerates an activation race', a
   ).toBe(false);
   expect(removals).toBe(2);
 });
+
+test('keys for one job share a Redis Cluster hash slot', () => {
+  const key = jobCancellationInternals.cancellationKey({ queueName: 'stateful-other-queue', jobId: '3q2X3EAPwWyx4u_oFIDG8' });
+  const slot = calculateSlot(key);
+  expect(calculateSlot(`${key}:result`)).toBe(slot);
+  expect(calculateSlot(`${key}:execution`)).toBe(slot);
+});
diff --git a/service/src/job-cancellation.ts b/service/src/job-cancellation.ts
index 4da3253d..772d5915 100644
--- a/service/src/job-cancellation.ts
+++ b/service/src/job-cancellation.ts
@@ -1,5 +1,6 @@
 import type IORedis from 'ioredis';
 import type { Job, QueueEvents } from 'bullmq';
+import { hashTag } from './redis-connection';
 
 const JOB_CANCELLATION_PREFIX = 'codeapi:job-cancellation:v1';
 const JOB_CANCELLATION_CHANNEL = `${JOB_CANCELLATION_PREFIX}:events`;
@@ -15,10 +16,12 @@ function targetKey(target: JobTarget): string {
   return `${target.queueName}:${target.jobId}`;
 }
 
+/** Hash-tagged so each job's marker, result and execution keys share one
+ * Redis Cluster slot; the multi-key scripts below fail with CROSSSLOT otherwise. */
 function cancellationKey(target: JobTarget): string {
-  return `${JOB_CANCELLATION_PREFIX}:${encodeURIComponent(
-    target.queueName,
-  )}:${encodeURIComponent(target.jobId)}`;
+  return `${JOB_CANCELLATION_PREFIX}:${hashTag(
+    `${encodeURIComponent(target.queueName)}:${encodeURIComponent(target.jobId)}`,
+  )}`;
 }
 
 function parseTarget(raw: string): JobTarget | undefined {
@@ -137,8 +140,9 @@ export class JobCancellationRegistry {
   private async reconcile(): Promise<void> {
     const entries = [...this.controllers.values()];
     if (entries.length === 0) return;
-    const cancelled = await this.commands.mget(
-      ...entries.map(({ target }) => cancellationKey(target)),
+    // One GET per job: different jobs live in different cluster slots.
+    const cancelled = await Promise.all(
+      entries.map(({ target }) => this.commands.get(cancellationKey(target))),
     );
     cancelled.forEach((value, index) => {
       if (value === '1') {