diff --git a/.github/workflows/docker.yml b/.github/workflows/docker.yml
index 66c505e3f8..fb10c9e268 100644
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@@ -11,13 +11,17 @@ permissions:
   contents: read
   packages: write
 
+# Serialise builds per ref without killing an in-flight one: a newer push
+# supersedes only the pending slot, so the image build that is already
+# running always finishes and publishes.
+concurrency:
+  group: docker-${{ github.ref }}
+  cancel-in-progress: false
+
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
     timeout-minutes: 60
-    concurrency:
-      group: docker-${{ github.ref }}
-      cancel-in-progress: true
     steps:
       - name: Checkout
         uses: actions/checkout@v7
diff --git a/server/src/__tests__/cloud-image-bundled-plugins.test.ts b/server/src/__tests__/cloud-image-bundled-plugins.test.ts
index ad944fd0cd..98955e0860 100644
--- a/server/src/__tests__/cloud-image-bundled-plugins.test.ts
+++ b/server/src/__tests__/cloud-image-bundled-plugins.test.ts
@@ -75,4 +75,18 @@ describe("cloud image bundled plugins", () => {
     // to the self-hosted tags.
     expect(workflow).toMatch(/^\s*target: production$/m);
   });
+
+  it("throttles the docker workflow with cancel-in-progress: false", () => {
+    // Concurrency is declared at the workflow (top) level so a single group
+    // spans the whole run, and cancel-in-progress is false so an in-flight
+    // image build always finishes — a newer push only supersedes the pending
+    // slot instead of killing the build that is already publishing.
+    expect(workflow).toMatch(/^concurrency:$/m);
+    // Pin the per-ref group key: without it the block could keep
+    // cancel-in-progress: false yet lose the group that scopes serialization
+    // to a single ref, silently changing which builds queue behind each other.
+    expect(workflow).toContain("group: docker-${{ github.ref }}");
+    expect(workflow).toContain("cancel-in-progress: false");
+    expect(workflow).not.toContain("cancel-in-progress: true");
+  });
 });