diff --git a/.github/workflows/bandit.yml b/.github/workflows/bandit.yml
index c5c613c08..b1161aaaa 100644
--- a/.github/workflows/bandit.yml
+++ b/.github/workflows/bandit.yml
@@ -7,6 +7,19 @@ on:
     branches: [ develop, master ]
   workflow_dispatch:
 
+concurrency:
+  # Workflow-level admission: a job-level group never coalesces while the run
+  # is queued behind the organization job ceiling. Push scans share one group
+  # per protected branch so a newer develop/master head retires the older
+  # scan. workflow_dispatch keeps github.run_id and is not cancelled by a
+  # sibling. This is a security scan, not merge/release/deploy.
+  group: >-
+    bandit-security-scan-${{ github.repository }}-${{
+    github.event.pull_request.number ||
+    (github.event_name == 'push' && format('push-{0}', github.ref_name)) ||
+    github.run_id }}
+  cancel-in-progress: true
+
 permissions:
   contents: read
 
diff --git a/backend/tests/test_workflow_concurrency.py b/backend/tests/test_workflow_concurrency.py
new file mode 100644
index 000000000..e9b424a56
--- /dev/null
+++ b/backend/tests/test_workflow_concurrency.py
@@ -0,0 +1,35 @@
+"""Regression tests for GitHub Actions concurrency boundaries."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import yaml
+
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+
+
+def _load_workflow(workflow_name: str) -> dict[str, object]:
+    path = REPO_ROOT / ".github" / "workflows" / workflow_name
+    assert path.exists(), f"workflow is missing: {workflow_name}"
+    parsed = yaml.safe_load(path.read_text(encoding="utf-8"))
+    assert isinstance(parsed, dict), (
+        f"workflow must parse as a mapping: {workflow_name}"
+    )
+    return parsed
+
+
+def test_bandit_coalesces_pr_and_protected_branch_push_scans() -> None:
+    """Cancel superseded PR and push scans; keep manual dispatch unique."""
+    concurrency = _load_workflow("bandit.yml").get("concurrency")
+
+    assert isinstance(concurrency, dict)
+    group = concurrency.get("group")
+    assert isinstance(group, str)
+    assert "bandit-security-scan-${{ github.repository }}-" in group
+    assert "github.event.pull_request.number" in group
+    assert "github.event_name == 'push' && format('push-{0}', github.ref_name)" in group
+    assert "github.run_id" in group
+    assert "github.run_attempt" not in group
+    assert concurrency.get("cancel-in-progress") is True