Redesigns Lib\Db from a single global connection to a config-driven map
of named connections (config['db_connections']), each independently
lazy-connected, each with its own optional migrations_dir and its own
schema_migrations table. A sidecar can use more than one connection in
the same request (e.g. Db::query(...) against SQLite alongside
Db::query(..., 'legacy') against MySQL) — sidecars have full access to
any Lib\ class, so nothing stops a request from needing two databases
at once, which the original single-driver spec didn't account for.
Db::query()/Db::connection() both default to the 'default' connection
name so the common single-database case is unchanged at the call site.
Supersedes the flat db_driver/db_path/db_migrations_dir keys shipped in
the SQLite groundwork commit (a3b9967) — no downstream consumers yet,
so no migration path needed.
db_connections needed one deliberate exception to the project's usual
shallow config-merge rule: merged one level deeper, by connection name,
so App/config.php adding a connection doesn't delete 'default'. Verified
end-to-end against a real local MariaDB instance running alongside the
existing SQLite connection, which caught a real ordering bug in the
initial merge implementation (capturing defaults after they'd already
been overwritten) before it shipped.
Closes the "MySQL support" backlog item in novaconium/ISSUES.md.
code
3a59269eaa