diff --git a/.github/workflows/ci-trigger-full-suite.yml b/.github/workflows/ci-trigger-full-suite.yml
index e96ad9c813..d9ce172576 100644
--- a/.github/workflows/ci-trigger-full-suite.yml
+++ b/.github/workflows/ci-trigger-full-suite.yml
@@ -44,16 +44,31 @@ jobs:
           PR_BRANCH: ${{ github.event.pull_request.head.ref }}
           PR_NUMBER: ${{ github.event.pull_request.number }}
         run: |
+          set -euo pipefail
           # Match both branch and PR number: forks can reuse the same branch name.
-          builds=$(curl -sS --get -H "Authorization: Bearer $BUILDKITE_API_TOKEN" \
+          response=$(curl -sS --fail-with-body --get -H "Authorization: Bearer $BUILDKITE_API_TOKEN" \
             --data-urlencode "branch=$PR_BRANCH" \
-            --data-urlencode "state=running,scheduled" \
-            "https://api.buildkite.com/v2/organizations/${{ vars.BUILDKITE_ORG_SLUG }}/pipelines/${{ vars.BUILDKITE_PIPELINE_SLUG }}/builds" \
-            | jq -r --arg pr_number "$PR_NUMBER" \
-              '.[] | select((.env.TEST_SCOPE? == "merge") and (.env.PR_NUMBER? == $pr_number)) | .number')
+            --data-urlencode "state[]=running" \
+            --data-urlencode "state[]=scheduled" \
+            --data-urlencode "exclude_jobs=true" \
+            --data-urlencode "exclude_pipeline=true" \
+            "https://api.buildkite.com/v2/organizations/${{ vars.BUILDKITE_ORG_SLUG }}/pipelines/${{ vars.BUILDKITE_PIPELINE_SLUG }}/builds")
+          if ! jq -e '
+            type == "array"
+            and all(.[];
+              type == "object"
+              and (.number | type == "number")
+              and ((.env // {}) | type == "object"))
+          ' >/dev/null <<< "$response"; then
+            echo "::error::Buildkite list-builds response had an unexpected shape."
+            exit 1
+          fi
+          builds=$(jq -r --arg pr_number "$PR_NUMBER" \
+            '.[] | select((.env.TEST_SCOPE? == "merge") and (.env.PR_NUMBER? == $pr_number)) | .number' \
+            <<< "$response")
           for build_num in $builds; do
             echo "Cancelling Buildkite build #$build_num"
-            curl -sS -X PUT -H "Authorization: Bearer $BUILDKITE_API_TOKEN" \
+            curl -sS --fail-with-body -o /dev/null -X PUT -H "Authorization: Bearer $BUILDKITE_API_TOKEN" \
               "https://api.buildkite.com/v2/organizations/${{ vars.BUILDKITE_ORG_SLUG }}/pipelines/${{ vars.BUILDKITE_PIPELINE_SLUG }}/builds/${build_num}/cancel"
           done
 
diff --git a/fastvideo/tests/contract/test_ci_test_collection.py b/fastvideo/tests/contract/test_ci_test_collection.py
index 4a0e0b1798..6c86a757a3 100644
--- a/fastvideo/tests/contract/test_ci_test_collection.py
+++ b/fastvideo/tests/contract/test_ci_test_collection.py
@@ -164,6 +164,27 @@ def test_merge_comment_has_one_change_aware_trigger_path():
     assert "__FASTVIDEO_CI_PLAN_ALL__" in ready_workflow
 
 
+def test_merge_gate_buildkite_cancellation_fails_closed_on_api_errors():
+    workflow = yaml.safe_load((REPO_ROOT / ".github/workflows/ci-trigger-full-suite.yml").read_text())
+    steps = workflow["jobs"]["trigger"]["steps"]
+    cancel_script = next(step["run"] for step in steps if step.get("name") == "Cancel previous Buildkite builds")
+
+    assert cancel_script.splitlines()[0] == "set -euo pipefail"
+    assert "response=$(curl -sS --fail-with-body --get" in cancel_script
+    assert cancel_script.count('--data-urlencode "state[]=running"') == 1
+    assert cancel_script.count('--data-urlencode "state[]=scheduled"') == 1
+    assert cancel_script.count('--data-urlencode "exclude_jobs=true"') == 1
+    assert cancel_script.count('--data-urlencode "exclude_pipeline=true"') == 1
+    assert 'state=running,scheduled' not in cancel_script
+    assert 'type == "array"' in cancel_script
+    assert 'all(.[];' in cancel_script
+    assert '(.number | type == "number")' in cancel_script
+    assert '((.env // {}) | type == "object")' in cancel_script
+    assert '<<< "$response"' in cancel_script
+    assert "exit 1" in cancel_script
+    assert "curl -sS --fail-with-body -o /dev/null -X PUT" in cancel_script
+
+
 def test_full_ssim_has_a_weekly_slurm_schedule():
     workflow = (REPO_ROOT / ".github/workflows/ci-scheduled-ssim.yml").read_text()
     ssim_step = next(step for step in _pipeline_steps() if step["key"] == "ssim")