diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index b7d512b1dc..b28af503bf 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -3,6 +3,7 @@ stages:
   - tests
   - deploy
   - ci-build
+  - merge-gate
 
 variables:
   GIT_SUBMODULE_STRATEGY: recursive
@@ -111,6 +112,17 @@ shared-trigger:
   variables:
     PARENT_PIPELINE_ID: $CI_PIPELINE_ID
 
+merge-gate:
+  stage: merge-gate
+  image: registry.ddbuild.io/images/dd-octo-sts-ci-base:2025.06-1
+  tags: [ "arch:amd64" ]
+  when: always
+  variables:
+    GIT_SUBMODULE_STRATEGY: none
+    GIT_DEPTH: "1"
+  script:
+    - .gitlab/merge-gate.sh
+
 package-trigger:
   stage: build
   needs: [ "generate-templates" ]
diff --git a/.gitlab/flaky-jobs.txt b/.gitlab/flaky-jobs.txt
new file mode 100644
index 0000000000..6c930a7e10
--- /dev/null
+++ b/.gitlab/flaky-jobs.txt
@@ -0,0 +1,152 @@
+# flaky-jobs.txt — glob patterns for CI jobs EXCLUDED from the merge gate.
+
+aggregate tested versions
+Amazon_Linux_2023_amd64.SI94:*
+Amazon_Linux_2023_amd64.SID0:*
+Amazon_Linux_2_arm64.SI94:*
+Amazon_Linux_2_arm64.SID0:*
+API unit tests:*
+appsec integration tests (helper-rust):*
+appsec integration tests (ssi):*
+appsec integration tests:*
+ASAN test_c with multiple observers:*
+ASAN test_c:*
+Cargo test
+compile extension windows:*
+compile extension: debug-zts-asan:*
+compile extension: debug:*
+compile tracing extension asan:*
+compile tracing extension:*
+compile tracing sidecar:*
+create-multiarch-lib-injection-image
+Debian_11_amd64.SID0:*
+Debian_12_amd64.SID0:*
+deploy-s3
+Disabled test_c run:*
+Extension Tea Tests:*
+framework test:*
+generate-lib-init-pinned-tag-values
+helper-rust integration coverage
+installer tests
+K8S_LIB_INJECTION_UDS:*
+linux-php-laravel-realworld-parallel
+linux-php-symfony-realworld-parallel
+Loader test on amd64 libc:*
+macrobenchmarks:*
+min install tests
+package-oci:*
+pecl tests:*
+PHP Language Tests:*
+PHP language tests:*
+php-app.amd64.DOC:*
+php-app.arm64.DOC:*
+php-laravel-realworld-parallel-check-slo-breaches
+php-symfony-realworld-parallel-check-slo-breaches
+php-symfony-realworld-parallel-generate-slos
+php-symfony-realworld-parallel-upload-to-bp-api
+PHP: FrankePHP Demo
+PHP: Laravel Release
+PHP: Shopware Demo
+PHP: Symfony Demo
+profiling tests:*
+randomized tests:*
+RedHat_8_6_arm64.SID0:*
+System Tests:*
+test appsec extension:*
+test early PHP 8.1
+test_auto_instrumentation:*
+test_composer:*
+test_distributed_tracing:*
+test_extension_ci:*
+test_integrations_amqp2:*
+test_integrations_curl:*
+test_integrations_deferred_loading:*
+test_integrations_elasticsearch8:*
+test_integrations_elasticsearch_latest:*
+test_integrations_frankenphp:*
+test_integrations_googlespanner_latest:*
+test_integrations_guzzle_latest:*
+test_integrations_kafka:*
+test_integrations_memcached:*
+test_integrations_monolog2:*
+test_integrations_mysqli:*
+test_integrations_openai_latest:*
+test_integrations_pcntl:*
+test_integrations_predis_2:*
+test_integrations_sqlsrv:*
+test_integrations_swoole_5:*
+test_metrics:*
+test_opentelemetry_1:*
+test_opentelemetry_beta:*
+test_opentracing_10:*
+test_web_cakephp_28:*
+test_web_cakephp_310:*
+test_web_cakephp_45:*
+test_web_cakephp_latest:*
+test_web_codeigniter_22:*
+test_web_codeigniter_31:*
+test_web_custom:*
+test_web_drupal_101:*
+test_web_drupal_89:*
+test_web_drupal_95:*
+test_web_laminas_mvc_33:*
+test_web_laminas_mvc_latest:*
+test_web_laminas_rest_latest:*
+test_web_laravel_10x:*
+test_web_laravel_11x:*
+test_web_laravel_42:*
+test_web_laravel_57:*
+test_web_laravel_58:*
+test_web_laravel_8x:*
+test_web_laravel_9x:*
+test_web_laravel_latest:*
+test_web_laravel_octane_latest:*
+test_web_lumen_100:*
+test_web_lumen_52:*
+test_web_lumen_56:*
+test_web_lumen_58:*
+test_web_lumen_81:*
+test_web_lumen_90:*
+test_web_magento_23:*
+test_web_magento_24:*
+test_web_nette_24:*
+test_web_nette_31:*
+test_web_nette_latest:*
+test_web_slim_312:*
+test_web_slim_48:*
+test_web_slim_latest:*
+test_web_symfony_23:*
+test_web_symfony_28:*
+test_web_symfony_30:*
+test_web_symfony_33:*
+test_web_symfony_34:*
+test_web_symfony_40:*
+test_web_symfony_42:*
+test_web_symfony_44:*
+test_web_symfony_50:*
+test_web_symfony_51:*
+test_web_symfony_52:*
+test_web_symfony_62:*
+test_web_symfony_73:*
+test_web_symfony_latest:*
+test_web_wordpress_48:*
+test_web_wordpress_55:*
+test_web_wordpress_59:*
+test_web_wordpress_61:*
+test_web_yii_2049:*
+test_web_yii_latest:*
+test_web_zend_1:*
+test_web_zend_1_21:*
+Ubuntu_20_amd64.SID0:*
+Ubuntu_22_arm64.SI94:*
+Ubuntu_22_arm64.SID0:*
+Ubuntu_23_10_arm64.SI94:*
+Ubuntu_23_10_arm64.SID0:*
+Ubuntu_23_10_arm64.SIM:*
+Ubuntu_24_10_amd64.SID0:*
+Ubuntu_24_amd64.SID0:*
+Unit tests:*
+update-latest-versions
+verify windows
+windows test_c:*
+Zend Abstract Interface Tests:*
diff --git a/.gitlab/merge-gate.sh b/.gitlab/merge-gate.sh
new file mode 100755
index 0000000000..9d62a37356
--- /dev/null
+++ b/.gitlab/merge-gate.sh
@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+# Merge gate: passes iff every non-flaky job in this pipeline (and its triggered
+# child pipelines) succeeded. It collects failed jobs via the GitLab API and
+# classifies each against the glob patterns in .gitlab/flaky-jobs.txt; a failure
+# matching no pattern is a real regression and fails the gate. See the
+# `merge-gate` job in .gitlab-ci.yml.
+set -uo pipefail
+
+# Short-lived GitLab API token, same path as `analyze and create pr`
+# (Vault-issued JWT for the 'sdm' audience -> BTI CI API).
+_vault_jwt() {
+  local audience="$1"
+  if [ -n "${VAULT_ADDR:-}" ]; then
+    curl -sf -H "X-Vault-Request: true" \
+      "${VAULT_ADDR}/v1/identity/oidc/token/${audience}" | jq -r '.data.token' 2>/dev/null && return 0
+  fi
+  if [ -n "${DD_DATACENTER:-}" ]; then
+    curl -sf -H "X-Vault-Request: true" \
+      "https://vault.${DD_DATACENTER}/v1/identity/oidc/token/${audience}" | jq -r '.data.token' 2>/dev/null && return 0
+  fi
+  return 1
+}
+BTI_JWT=$(_vault_jwt sdm) || { echo "ERROR: could not obtain a BTI JWT" >&2; exit 1; }
+GITLAB_TOKEN=$(curl -sf -H "Authorization: Bearer ${BTI_JWT}" \
+  "https://bti-ci-api.us1.ddbuild.io/internal/ci/gitlab/token?owner=DataDog&repository=dd-trace-php" \
+  | jq -r '.token')
+GITLAB_API="https://gitlab.ddbuild.io/api/v4"
+AUTH="PRIVATE-TOKEN: ${GITLAB_TOKEN}"
+
+# Pipelines to inspect: this parent pipeline + every triggered child.
+pipelines=("${CI_PIPELINE_ID}")
+bridges=$(curl -sf -H "${AUTH}" \
+  "${GITLAB_API}/projects/${CI_PROJECT_ID}/pipelines/${CI_PIPELINE_ID}/bridges?per_page=100" || echo "[]")
+while read -r child; do
+  [ -n "${child}" ] && pipelines+=("${child}")
+done < <(echo "${bridges}" | jq -r '.[] | select(.downstream_pipeline != null) | .downstream_pipeline.id')
+
+# Collect the names of all failed jobs across those pipelines.
+: > failed_jobs.txt
+for pid in "${pipelines[@]}"; do
+  for page in 1 2 3 4 5; do
+    data=$(curl -g -sf -H "${AUTH}" \
+      "${GITLAB_API}/projects/${CI_PROJECT_ID}/pipelines/${pid}/jobs?scope[]=failed&per_page=100&page=${page}" || echo "[]")
+    echo "${data}" | jq -r '.[] | select(.status == "failed") | .name' >> failed_jobs.txt
+    [ "$(echo "${data}" | jq 'length')" -lt 100 ] && break
+  done
+done
+sort -u failed_jobs.txt -o failed_jobs.txt
+
+# Load flaky globs and classify each failure.
+mapfile -t GLOBS < <(grep -vE '^[[:space:]]*(#|$)' .gitlab/flaky-jobs.txt)
+echo "Loaded ${#GLOBS[@]} flaky patterns; $(wc -l < failed_jobs.txt) distinct failed job(s)."
+blocking=0
+while IFS= read -r job; do
+  [ -z "${job}" ] && continue
+  [ "${job}" = "merge-gate" ] && continue
+  ok=0
+  for g in "${GLOBS[@]}"; do
+    if [[ "${job}" == $g ]]; then ok=1; break; fi
+  done
+  if [ "${ok}" -eq 0 ]; then
+    echo "  ✗ non-flaky failure: ${job}"
+    blocking=1
+  else
+    echo "  ✓ known-flaky:       ${job}"
+  fi
+done < failed_jobs.txt
+
+if [ "${blocking}" -ne 0 ]; then
+  echo ""
+  echo "Merge gate FAILED — a required (non-flaky) job failed. See ✗ lines above."
+  exit 1
+fi
+echo ""
+echo "Merge gate PASSED — no failures, or all failures are known-flaky."