fix: preserve local env overrides in shell pipelines

scripts/env_precedence_test.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$ROOT_DIR"
+
+TMP_DIR="$(mktemp -d)"
+trap 'rm -rf "$TMP_DIR"' EXIT
+
+cat > "$TMP_DIR/.env.local" <<'EOF'
+LOCAL_ALPHA=test-placeholder-value
+LOCAL_BETA=real-db
+EOF
+cat > "$TMP_DIR/.env" <<'EOF'
+LOCAL_ALPHA=
+LOCAL_BETA=
+EOF
+
+
+
+unset LOCAL_ALPHA LOCAL_BETA || true
+while IFS= read -r kv; do export "$kv"; done < <(scripts/load_project_env.sh "$TMP_DIR/.env.local")
+while IFS= read -r kv; do key="${kv%%=*}"; [[ -n "$key" && -n "${!key:-}" ]] && continue; export "$kv"; done < <(scripts/load_project_env.sh "$TMP_DIR/.env")
+[[ "$LOCAL_ALPHA" == "test-placeholder-value" ]]
+[[ "$LOCAL_BETA" == "real-db" ]]