diff --git a/package.json b/package.json
index 5a721af..138e93b 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,7 @@
         "format": "prettier --write .",
         "test": "turbo test",
         "test:integration": "pnpm --filter @sammo-ts/integration-tests test:integration",
+        "test:integration:conditional": "./tools/run-conditional-integration.sh",
         "build": "turbo build",
         "typecheck": "turbo typecheck",
         "dev": "turbo dev",
diff --git a/tools/run-conditional-integration.sh b/tools/run-conditional-integration.sh
new file mode 100755
index 0000000..64d20f7
--- /dev/null
+++ b/tools/run-conditional-integration.sh
@@ -0,0 +1,122 @@
+#!/bin/sh
+set -eu
+
+usage() {
+    echo "usage: $0 [env-file]" >&2
+    exit 64
+}
+
+[ "$#" -le 1 ] || usage
+
+script_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+workspace_root=$(CDPATH= cd -- "$script_dir/.." && pwd)
+env_file=${1:-"$workspace_root/.env.ci"}
+
+if [ ! -f "$env_file" ]; then
+    echo "missing integration environment file: $env_file" >&2
+    exit 66
+fi
+env_file=$(CDPATH= cd -- "$(dirname -- "$env_file")" && pwd)/$(basename -- "$env_file")
+
+# .env.ci is generated by the sam_rebuild development Compose helper and is a
+# shell-compatible, credential-bearing local file. Never print its contents.
+set -a
+# shellcheck disable=SC1090
+. "$env_file"
+set +a
+
+: "${POSTGRES_HOST:?POSTGRES_HOST is required in $env_file}"
+: "${POSTGRES_PORT:?POSTGRES_PORT is required in $env_file}"
+: "${POSTGRES_DB:?POSTGRES_DB is required in $env_file}"
+: "${POSTGRES_USER:?POSTGRES_USER is required in $env_file}"
+: "${POSTGRES_PASSWORD:?POSTGRES_PASSWORD is required in $env_file}"
+: "${REDIS_URL:?REDIS_URL is required in $env_file}"
+
+integration_schema=${CONDITIONAL_INTEGRATION_SCHEMA:-conditional_integration}
+scenario_schema=${SCENARIO_SEED_INTEGRATION_SCHEMA:-conditional_scenario_seed}
+
+for schema in "$integration_schema" "$scenario_schema"; do
+    case "$schema" in
+        ''|[!a-z_]*|*[!a-z0-9_]*)
+            echo "integration schema must be a lowercase PostgreSQL identifier: $schema" >&2
+            exit 64
+            ;;
+    esac
+done
+
+build_database_url() {
+    SCHEMA_NAME=$1 node --input-type=module -e '
+        const required = [
+            "POSTGRES_HOST",
+            "POSTGRES_PORT",
+            "POSTGRES_DB",
+            "POSTGRES_USER",
+            "POSTGRES_PASSWORD",
+            "SCHEMA_NAME",
+        ];
+        for (const name of required) {
+            if (!process.env[name]) {
+                throw new Error(`missing ${name}`);
+            }
+        }
+        const url = new URL("postgresql://localhost");
+        url.hostname = process.env.POSTGRES_HOST;
+        url.port = process.env.POSTGRES_PORT;
+        url.username = process.env.POSTGRES_USER;
+        url.password = process.env.POSTGRES_PASSWORD;
+        url.pathname = `/${process.env.POSTGRES_DB}`;
+        url.searchParams.set("schema", process.env.SCHEMA_NAME);
+        process.stdout.write(url.href);
+    '
+}
+
+run_marked_tests() {
+    package_dir=$1
+    marker=$2
+    label=$3
+    test_files=$(cd "$workspace_root/$package_dir" && rg -l "$marker" test -g '*.test.ts' | sort)
+    if [ -z "$test_files" ]; then
+        echo "no $label tests found under $package_dir" >&2
+        exit 65
+    fi
+    echo "running $label tests in $package_dir"
+    (
+        cd "$workspace_root/$package_dir"
+        printf '%s\n' "$test_files" |
+            xargs -r pnpm exec vitest run --no-file-parallelism --maxWorkers=1
+    )
+}
+
+cd "$workspace_root"
+pnpm install --frozen-lockfile
+pnpm --filter @sammo-ts/infra prisma:generate
+pnpm --filter @sammo-ts/common build
+
+database_url=$(build_database_url "$integration_schema")
+export POSTGRES_SCHEMA=$integration_schema
+export DATABASE_URL=$database_url
+export INPUT_EVENT_DATABASE_URL=$database_url
+export GENERAL_LIFECYCLE_DATABASE_URL=$database_url
+export TURN_DAEMON_LEASE_DATABASE_URL=$database_url
+export TURN_DIFFERENTIAL_DATABASE_URL=$database_url
+
+pnpm --filter @sammo-ts/infra prisma:db:push:game
+
+database_markers='INPUT_EVENT_DATABASE_URL|GENERAL_LIFECYCLE_DATABASE_URL|TURN_DAEMON_LEASE_DATABASE_URL'
+run_marked_tests app/game-api "$database_markers" "PostgreSQL"
+run_marked_tests app/game-engine "$database_markers" "PostgreSQL"
+run_marked_tests tools/integration-tests \
+    'TURN_DIFFERENTIAL_DATABASE_URL|INPUT_EVENT_DATABASE_URL' \
+    "PostgreSQL snapshot"
+run_marked_tests app/game-api 'process\.env\.REDIS_URL' "Redis"
+
+scenario_database_url=$(build_database_url "$scenario_schema")
+(
+    export POSTGRES_SCHEMA=$scenario_schema
+    export DATABASE_URL=$scenario_database_url
+    pnpm --filter @sammo-ts/infra prisma:db:push:game
+    cd "$workspace_root/app/game-engine"
+    pnpm exec vitest run --no-file-parallelism --maxWorkers=1 test/scenarioSeeder.test.ts
+)
+
+echo "conditional PostgreSQL and Redis integration tests passed"