diff --git a/.devcontainer/setup.sh b/.devcontainer/setup.sh
index 312ef8e4d08bc..dd36d03e365cf 100755
--- a/.devcontainer/setup.sh
+++ b/.devcontainer/setup.sh
@@ -3,22 +3,59 @@
 # SPDX-FileCopyrightText: 2021 Nextcloud GmbH and Nextcloud contributors
 # SPDX-License-Identifier: AGPL-3.0-or-later
 #
+# Fail loudly. Without this, a failure here leaves a half-configured codespace
+# that looks like it started correctly: Apache serves, but Nextcloud is not
+# installed, so the browser shows the database setup wizard instead.
+set -euo pipefail
+
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )/../" >/dev/null 2>&1 && pwd )"
 
-cd $DIR/
+cd "$DIR"
 
+# Nextcloud does not boot without 3rdparty, and Codespaces does not clone
+# submodules for us.
 git submodule update --init
 
+if [ ! -f 3rdparty/autoload.php ]; then
+    echo "error: 3rdparty is empty after 'git submodule update --init'." >&2
+    echo "       Nextcloud cannot start without it. Re-run this script once" >&2
+    echo "       the network is available." >&2
+    exit 1
+fi
+
 # Codespace config
 cp .devcontainer/codespace.config.php config/codespace.config.php
 
 # VSCode debugger profile
 mkdir -p .vscode && cp .devcontainer/launch.json .vscode/launch.json
 
+# The db service has no healthcheck, and compose only guarantees that the
+# container was started, not that Postgres finished initialising. On a first
+# create that takes a few seconds, and maintenance:install fails if it gets
+# there first.
+# Checked with PHP rather than pg_isready: the image installs php8.4-pgsql but
+# not postgresql-client, so pg_isready is not available here.
+wait_for_database() {
+    local attempt
+    for attempt in $(seq 1 30); do
+        if php -r 'exit(@pg_connect("host=127.0.0.1 port=5432 user=postgres password=postgres dbname=postgres connect_timeout=2") ? 0 : 1);'; then
+            return 0
+        fi
+        echo "Waiting for the database to accept connections ($attempt/30)"
+        sleep 2
+    done
+    return 1
+}
+
+if ! wait_for_database; then
+    echo "error: the database did not become available within 60 seconds." >&2
+    exit 1
+fi
+
 # Onetime installation setup
-if [[ ! $(sudo -u ${APACHE_RUN_USER} php occ status) =~ installed:[[:space:]]*true ]]; then
+if [[ ! $(sudo -u "${APACHE_RUN_USER}" php occ status) =~ installed:[[:space:]]*true ]]; then
     echo "Running NC installation"
-    sudo -u ${APACHE_RUN_USER} php occ maintenance:install \
+    sudo -u "${APACHE_RUN_USER}" php occ maintenance:install \
         --verbose \
         --database=pgsql \
         --database-name=postgres \
@@ -30,4 +67,11 @@ if [[ ! $(sudo -u ${APACHE_RUN_USER} php occ status) =~ installed:[[:space:]]*tr
         --admin-pass admin
 fi
 
+# Confirm the instance is actually usable before handing it over, so a failed
+# install is reported here rather than discovered in the browser.
+if [[ ! $(sudo -u "${APACHE_RUN_USER}" php occ status) =~ installed:[[:space:]]*true ]]; then
+    echo "error: Nextcloud is still not installed after running maintenance:install." >&2
+    exit 1
+fi
+
 sudo service apache2 restart