fix(nexus-db): cross-review findings

- source build.func (script was unrunnable without it)
- validate DB_NAME/DB_USER/DB_PORT/NEXUS_APP_IP before SQL/pg_hba use
- rotate password when role exists but credentials file is missing

ct/nexus-db.sh

@@ -28,6 +28,8 @@ DEFAULT_DB_NAME="nexus"
 DEFAULT_DB_USER="nexus"
 DEFAULT_DB_PORT="5432"
 
+source <(curl -fsSL "$LIB_URL/build.func")
+
 # ── app-specific prompts (host TTY; each skipped if the var is preset) ───────
 prompt_app_config() {
   echo

install/nexus-db-install.sh

@@ -24,6 +24,13 @@ DB_NAME="${DB_NAME:-nexus}"
 DB_USER="${DB_USER:-nexus}"
 DB_PORT="${DB_PORT:-5432}"
 
+# Values land verbatim in SQL and pg_hba.conf — accept only safe shapes.
+[[ "$DB_NAME" =~ ^[a-z_][a-z0-9_]*$ ]] || { msg_err "DB_NAME must be a plain lowercase identifier: $DB_NAME"; exit 1; }
+[[ "$DB_USER" =~ ^[a-z_][a-z0-9_]*$ ]] || { msg_err "DB_USER must be a plain lowercase identifier: $DB_USER"; exit 1; }
+[[ "$DB_PORT" =~ ^[0-9]{2,5}$ ]] || { msg_err "DB_PORT must be numeric: $DB_PORT"; exit 1; }
+[[ "$NEXUS_APP_IP" =~ ^[0-9]{1,3}(\.[0-9]{1,3}){3}$ || "$NEXUS_APP_IP" =~ ^[0-9a-fA-F:]+$ ]] \
+  || { msg_err "NEXUS_APP_IP must be a single host IP: $NEXUS_APP_IP"; exit 1; }
+
 PG_MAJOR=16
 CRED_FILE="/root/nexus-db.credentials"
 
@@ -92,6 +99,14 @@ if [[ "$(run_psql -c "SELECT 1 FROM pg_roles WHERE rolname='$DB_USER'")" != "1"
   DB_PASS="$(openssl rand -base64 32 | tr -d '/+=' | head -c 32)"
   run_psql -c "CREATE ROLE $DB_USER LOGIN PASSWORD '$DB_PASS' NOSUPERUSER NOCREATEDB NOCREATEROLE"
   msg_ok "Role $DB_USER created (least privilege)"
+elif [[ ! -f "$CRED_FILE" ]]; then
+  # Recovery: role exists but the generated password was never persisted
+  # (first run died between CREATE ROLE and credentials write). Rotate so
+  # the credentials file is authoritative again.
+  msg_warn "Role $DB_USER exists but $CRED_FILE is missing — rotating password"
+  DB_PASS="$(openssl rand -base64 32 | tr -d '/+=' | head -c 32)"
+  run_psql -c "ALTER ROLE $DB_USER PASSWORD '$DB_PASS'"
+  msg_ok "Password rotated"
 else
   DB_PASS=""
   msg_warn "Role $DB_USER already exists, password unchanged"