require-sqlite-blocks-pg-for-guarded-commands

Summary

Certain subcommands like hash-sources are hardcoded to only work with SQLite. The _require_sqlite function acts as a guard that checks both command-line flags and environment variables for any sign of a Postgres connection, and kills the process immediately if one is found. This means these commands can never accidentally run against a production Postgres database, but it also means any future Postgres support for those commands requires explicitly removing or updating this guard.