diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 055a0b95b..433880d1a 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -935,6 +935,22 @@ jobs:
     - name: Lint Helm chart
       run: helm lint helm/hindsight
 
+  test-standalone-start-script:
+    needs: [detect-changes]
+    if: >-
+      (github.event_name == 'workflow_dispatch' ||
+      needs.detect-changes.outputs.docker == 'true' ||
+      needs.detect-changes.outputs.ci == 'true')
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v6
+      with:
+        ref: ${{ github.event.pull_request.head.sha || '' }}
+
+    - name: Run standalone start script tests
+      run: bash docker/standalone/test-start-all.sh
+
   build-docker-images:
     needs: [detect-changes]
     if: >-
@@ -3651,6 +3667,7 @@ jobs:
       - build-docs
       - test-rust-cli
       - lint-helm-chart
+      - test-standalone-start-script
       - build-docker-images
       - test-api
       - test-api-oracle
diff --git a/docker/standalone/start-all.sh b/docker/standalone/start-all.sh
index b5f163e6c..045db38e1 100755
--- a/docker/standalone/start-all.sh
+++ b/docker/standalone/start-all.sh
@@ -10,19 +10,45 @@ set -e
 # loss scenarios where a container restart caused the data directory to be
 # wiped despite a volume mount being present.
 # =============================================================================
-PG0_DATA_DIR="${HOME}/.pg0"
-if [ -d "$PG0_DATA_DIR" ]; then
+pg0_has_pg_version() {
+    local pg0_data_dir="$1"
+
+    # pg0 has used more than one on-disk layout. Newer standalone images keep
+    # PostgreSQL data under instances/<name>/data, while older volumes may have
+    # placed PG_VERSION at or one level below the mount.
+    [ -f "$pg0_data_dir/PG_VERSION" ] && return 0
+    compgen -G "$pg0_data_dir"/*/PG_VERSION > /dev/null 2>&1 && return 0
+    compgen -G "$pg0_data_dir"/instances/*/data/PG_VERSION > /dev/null 2>&1 && return 0
+
+    return 1
+}
+
+check_pg0_data_integrity() {
+    local pg0_data_dir="$1"
+
+    if [ ! -d "$pg0_data_dir" ]; then
+        return 0
+    fi
+
     # Look for actual PostgreSQL data directories (pg0 creates subdirs per instance)
-    if compgen -G "$PG0_DATA_DIR"/*/PG_VERSION > /dev/null 2>&1; then
-        echo "✅ Existing pg0 data directory detected at $PG0_DATA_DIR"
-    elif [ "$(ls -A "$PG0_DATA_DIR" 2>/dev/null)" ]; then
-        echo "⚠️  WARNING: pg0 data directory exists at $PG0_DATA_DIR but no PG_VERSION found."
+    if pg0_has_pg_version "$pg0_data_dir"; then
+        echo "✅ Existing pg0 data directory detected at $pg0_data_dir"
+    elif [ "$(ls -A "$pg0_data_dir" 2>/dev/null)" ]; then
+        echo "⚠️  WARNING: pg0 data directory exists at $pg0_data_dir but no PG_VERSION found."
         echo "   This may indicate data corruption or an incomplete previous shutdown."
         echo "   If you see all migrations running from scratch after this, your data may have been lost."
         echo "   See: https://github.com/vectorize-io/hindsight/issues/675"
     fi
+
+    return 0
+}
+
+if [ "${HINDSIGHT_START_ALL_SOURCE_ONLY:-false}" = "true" ]; then
+    return 0 2>/dev/null || exit 0
 fi
 
+check_pg0_data_integrity "${HOME}/.pg0"
+
 # Service flags (default to true if not set)
 ENABLE_API="${HINDSIGHT_ENABLE_API:-true}"
 ENABLE_CP="${HINDSIGHT_ENABLE_CP:-true}"
diff --git a/docker/standalone/test-start-all.sh b/docker/standalone/test-start-all.sh
new file mode 100755
index 000000000..9f4f27e98
--- /dev/null
+++ b/docker/standalone/test-start-all.sh
@@ -0,0 +1,73 @@
+#!/bin/bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+HINDSIGHT_START_ALL_SOURCE_ONLY=true
+source "$SCRIPT_DIR/start-all.sh"
+unset HINDSIGHT_START_ALL_SOURCE_ONLY
+
+TMP_DIR="$(mktemp -d)"
+trap 'rm -rf "$TMP_DIR"' EXIT
+
+assert_contains() {
+    local output="$1"
+    local expected="$2"
+
+    if [[ "$output" != *"$expected"* ]]; then
+        echo "Expected output to contain: $expected"
+        echo "Actual output:"
+        echo "$output"
+        exit 1
+    fi
+}
+
+assert_not_contains() {
+    local output="$1"
+    local unexpected="$2"
+
+    if [[ "$output" == *"$unexpected"* ]]; then
+        echo "Expected output not to contain: $unexpected"
+        echo "Actual output:"
+        echo "$output"
+        exit 1
+    fi
+}
+
+assert_empty() {
+    local output="$1"
+
+    if [ -n "$output" ]; then
+        echo "Expected no output, got:"
+        echo "$output"
+        exit 1
+    fi
+}
+
+mkdir -p "$TMP_DIR/empty"
+assert_empty "$(check_pg0_data_integrity "$TMP_DIR/empty")"
+
+mkdir -p "$TMP_DIR/direct"
+touch "$TMP_DIR/direct/PG_VERSION"
+direct_output="$(check_pg0_data_integrity "$TMP_DIR/direct")"
+assert_contains "$direct_output" "Existing pg0 data directory detected"
+assert_not_contains "$direct_output" "WARNING"
+
+mkdir -p "$TMP_DIR/legacy/instance"
+touch "$TMP_DIR/legacy/instance/PG_VERSION"
+legacy_output="$(check_pg0_data_integrity "$TMP_DIR/legacy")"
+assert_contains "$legacy_output" "Existing pg0 data directory detected"
+assert_not_contains "$legacy_output" "WARNING"
+
+mkdir -p "$TMP_DIR/nested/instances/hindsight/data"
+touch "$TMP_DIR/nested/instances/hindsight/data/PG_VERSION"
+nested_output="$(check_pg0_data_integrity "$TMP_DIR/nested")"
+assert_contains "$nested_output" "Existing pg0 data directory detected"
+assert_not_contains "$nested_output" "WARNING"
+
+mkdir -p "$TMP_DIR/nonempty/instances/hindsight"
+touch "$TMP_DIR/nonempty/instances/hindsight/instance.json"
+nonempty_output="$(check_pg0_data_integrity "$TMP_DIR/nonempty")"
+assert_contains "$nonempty_output" "WARNING: pg0 data directory exists"
+
+echo "start-all pg0 integrity checks passed"