diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index b3aaa06..fcb64a6 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -23,5 +23,8 @@ jobs:
         env:
           DJANGO_ENV: dev
           DJANGO_SECRET_KEY: test-secret-key
+          # Explicitly clear DB vars so host/prod DATABASE_URL cannot leak in.
+          DATABASE_URL: ""
+          DB_HOST: ""
         run: |
           uv run python manage.py test
diff --git a/.gitea/workflows/deploy.yml b/.gitea/workflows/deploy.yml
index e4afa2f..9a1c3d0 100644
--- a/.gitea/workflows/deploy.yml
+++ b/.gitea/workflows/deploy.yml
@@ -20,15 +20,27 @@ jobs:
       - name: Build Docker image
         run: docker compose build
 
+      # Ephemeral local Postgres only — never inherit host DATABASE_URL (prod).
       - name: Run containerized tests
         run: |
-          docker compose up -d db
-          docker compose run --rm --entrypoint "" \
+          set -euo pipefail
+          # Drop host/prod DB secrets so compose cannot interpolate them.
+          unset DATABASE_URL DB_HOST DB_NAME DB_USER DB_PASSWORD DB_PORT \
+            COMPOSE_DATABASE_URL DJANGO_ENV DJANGO_SECRET_KEY DJANGO_DEBUG \
+            DJANGO_ALLOWED_HOSTS || true
+
+          PROJECT="scha-ci-${{ gitea.event.workflow_run.head_sha }}"
+          cleanup() { docker compose -p "$PROJECT" down -v --remove-orphans || true; }
+          trap cleanup EXIT
+
+          docker compose -p "$PROJECT" up -d --wait db
+          docker compose -p "$PROJECT" run --rm --no-deps --entrypoint "" \
             -e DJANGO_ENV=dev \
             -e DJANGO_SECRET_KEY=test-secret-key \
+            -e DJANGO_DEBUG=true \
+            -e DJANGO_ALLOWED_HOSTS=localhost,127.0.0.1,testserver \
             -e DATABASE_URL=postgres://scha:scha@db:5432/scha \
             web uv run python manage.py test
-          docker compose down
 
   deploy:
     if: gitea.event.workflow_run.conclusion == 'success' && gitea.event.workflow_run.event == 'push'
diff --git a/.gitea/workflows/unittests.yml b/.gitea/workflows/unittests.yml
index 74a8437..7edcf73 100644
--- a/.gitea/workflows/unittests.yml
+++ b/.gitea/workflows/unittests.yml
@@ -25,5 +25,8 @@ jobs:
         env:
           DJANGO_ENV: dev
           DJANGO_SECRET_KEY: test-secret-key
+          # Explicitly clear DB vars so host/prod DATABASE_URL cannot leak in.
+          DATABASE_URL: ""
+          DB_HOST: ""
         run: |
           uv run python manage.py test
diff --git a/README.md b/README.md
index 60ec80a..d4a9cc9 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,8 @@ Without `DATABASE_URL` / `DB_HOST`, settings fall back to SQLite (`db.sqlite3`).
 docker compose up --build
 ```
 
-App: http://localhost:8000 — Postgres via `DATABASE_URL=postgres://scha:scha@db:5432/scha`.
+App: http://localhost:8000 — Postgres via bundled `db` (`postgres://scha:scha@db:5432/scha`).
+Compose does **not** read host `DATABASE_URL` (avoids CI/prod leaks); override with `COMPOSE_DATABASE_URL` if needed.
 
 ## Environment variables
 
@@ -69,7 +70,7 @@ Validate with:
 |----------|---------|--------|
 | `unittests.yml` | push + PR → `master` | `uv sync` + `manage.py test` |
 | `ci.yml` | PR → `master` | same unit tests |
-| `deploy.yml` | after Unit Tests succeeds on `master` **push** | docker build/test → `deploy.sh` |
+| `deploy.yml` | after Unit Tests succeeds on `master` **push** | docker build + tests on **ephemeral compose Postgres** → `deploy.sh` |
 
 Deploy never runs on PRs.
 
diff --git a/docker-compose.yml b/docker-compose.yml
index 96621be..34612f2 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -20,12 +20,16 @@ services:
       - "8000:8000"
     # No required env_file — CI has no .env. Defaults below; for local secrets:
     #   docker compose --env-file .env up
+    #
+    # Do NOT interpolate ${DATABASE_URL} here. On the Act runner / control node that
+    # var often points at shared prod/beta Postgres; compose would bake it into
+    # containerized tests. Use COMPOSE_DATABASE_URL only if you need to override.
     environment:
       DJANGO_ENV: ${DJANGO_ENV:-dev}
       DJANGO_SECRET_KEY: ${DJANGO_SECRET_KEY:-dev-only-change-me}
       DJANGO_DEBUG: ${DJANGO_DEBUG:-true}
       DJANGO_ALLOWED_HOSTS: ${DJANGO_ALLOWED_HOSTS:-localhost,127.0.0.1,0.0.0.0}
-      DATABASE_URL: ${DATABASE_URL:-postgres://scha:scha@db:5432/scha}
+      DATABASE_URL: ${COMPOSE_DATABASE_URL:-postgres://scha:scha@db:5432/scha}
     depends_on:
       db:
         condition: service_healthy