diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 2229242502..f42e53c300 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -187,9 +187,17 @@ jobs:
         id: changed-files
         uses: tj-actions/changed-files@v47.0.6
         with:
+          # The ClickHouse config is mounted into both ch-server (via
+          # docker-compose.ci.yml) and ch-server-compat, which pins an older
+          # ClickHouse -- a config feature the old server rejects takes the
+          # whole suite down, so changes to it run these tests.
           files: |
             docker/otel-collector/**
             smoke-tests/otel-collector/**
+            packages/otel-collector/builder-config.yaml
+            docker/clickhouse/local/config.xml
+            docker/clickhouse/local/users.xml
+            docker-compose.ci.yml
       - name: Install required tooling
         if: steps.changed-files.outputs.any_changed == 'true'
         env:
diff --git a/.gitignore b/.gitignore
index 56ac35d259..c77d80ee0a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -79,6 +79,10 @@ e2e/cypress/results
 # storybook
 **/storybook-static/
 
+# otel smoke tests: OIDC issuer fixtures, regenerated on every run
+# (the matching private.pem is already covered by **/*.pem above)
+smoke-tests/otel-collector/data/oidc-auth/public/
+
 # scripts
 scripts/*.csv
 **/venv
diff --git a/smoke-tests/otel-collector/ch-compat-config.d/remove-prometheus-api.xml b/smoke-tests/otel-collector/ch-compat-config.d/remove-prometheus-api.xml
new file mode 100644
index 0000000000..1213f1ee17
--- /dev/null
+++ b/smoke-tests/otel-collector/ch-compat-config.d/remove-prometheus-api.xml
@@ -0,0 +1,7 @@
+<!-- The shared local config.xml declares a `prometheus_api_v1` HTTP handler,
+     which only exists in ClickHouse >= 26.2. On the older compat server the
+     unknown handler type aborts the whole HTTP listener (port 8123 never
+     opens, so the healthcheck fails), so drop the block here. -->
+<clickhouse>
+    <http_handlers remove="1"/>
+</clickhouse>
diff --git a/smoke-tests/otel-collector/docker-compose.yaml b/smoke-tests/otel-collector/docker-compose.yaml
index 54868e69fb..604ea99534 100644
--- a/smoke-tests/otel-collector/docker-compose.yaml
+++ b/smoke-tests/otel-collector/docker-compose.yaml
@@ -117,6 +117,7 @@ services:
     volumes:
       - ../../docker/clickhouse/local/config.xml:/etc/clickhouse-server/config.xml
       - ../../docker/clickhouse/local/users.xml:/etc/clickhouse-server/users.xml
+      - ./ch-compat-config.d/remove-prometheus-api.xml:/etc/clickhouse-server/config.d/remove-prometheus-api.xml:ro
     ports:
       - 29000:9000
       - 28123:8123