chore(db): Swap lib/pq for jackc/pgx/v5

[Amund211]

Summary

Two commits:

1. 9459243 Swap lib/pq for jackc/pgx/v5 as the sql driver. database/sql driver name "postgres" → "pgx" via _ "github.com/jackc/pgx/v5/stdlib". Every pq.QuoteIdentifier(...) call becomes pgx.Identifier{...}.Sanitize(). CloudSQL DSN keyword database= → dbname= (pgx doesn't accept the pq-only alias).
2. 37abad5 Run migrations via database/pgx/v5 with per-schema DSN. Migrations now run through a one-off *sql.DB built by stdlib.OpenDB(*cfg) where RuntimeParams["search_path"] is set to the target schema. NewDatabaseMigrator takes a connection string instead of an *sqlx.DB. NewCloudsqlPostgresDatabase lost its only caller and was removed; ConnectionString(conf) was extracted.

Why

lib/pq is in maintenance mode — README and issue #1010 explicitly point users at pgx. flashlight's direct usage was limited to pq.QuoteIdentifier, so the swap is minimal-risk.

Caveats / things a reviewer should know

• pgx.Identifier{name}.Sanitize() is the canonical pgx-native identifier quoter (pgx.Identifier []string with a Sanitize() method). Multi-part identifiers like {"schema","table"} produce "schema"."table". Same semantics as the old pq.QuoteIdentifier for single names.
• DSN keyword database= is pq-only. pgx's libpq-style parser uses dbname= (matches PostgreSQL's own keyword set). The CloudSQL helper was changed.
• migrate database/pgx/v5 only exposes WithInstance(*sql.DB) — no WithConnection(*sql.Conn). So per-schema search_path can't ride on a single borrowed conn anymore; it has to be a property of every conn in the pool, which is why the throwaway DB / RuntimeParams approach.
• search_path must be quoted inside RuntimeParams. First implementation set it to the bare schema name. Postgres parses each comma-separated entry of search_path as a SQL identifier — unquoted names get lower-cased and reject -. Test schemas like find_milestone_Single_milestone_reached and find_milestone_Milestones_skipped_-_final_reached silently resolved to a non-existent schema; unqualified DDL then failed with SQLSTATE 3F000 ("no schema has been selected to create in"), while SHOW search_path happily echoed the raw value back. Wrapping the value in pgx.Identifier{...}.Sanitize() fixes it. There's a comment on openSchemaScopedDB explaining this.
• migrate driver name passed to migrate.NewWithInstance is "pgx5", not "pgx" or "postgres" — that's what database/pgx/v5 registers itself as.
• lib/pq is still in go.sum as // indirect, but only because jmoiron/sqlx's own test suite imports it (flashlight → sqlx → sqlx.test → lib/pq). It is never compiled into flashlight's binary or its tests. Fully removing it would require dropping sqlx itself; out of scope here.
• PgBouncer note (no action needed): pgx defaults to cache_statement which is incompatible with PgBouncer transaction/statement pooling on older PgBouncer (< 1.21). flashlight talks to Cloud SQL directly over Unix socket — no PgBouncer in the path — so the default is fine. If that changes, append ?default_query_exec_mode=exec to the DSN.

Test plan

• go build ./...
• go vet ./...
• go test ./... — all 19 packages pass, including the four Postgres-backed integration suites (accountrepository, database, playerrepository, userrepository) that exercise schema creation, migrations, and per-schema search_path under the new driver.
• Smoke-test in staging before prod rollout.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR migrates the project’s PostgreSQL integration from lib/pq to jackc/pgx/v5, including updating identifier quoting and switching migrations to use the golang-migrate pgx/v5 database driver with schema-scoped connections.

Changes:

• Switched database/sql driver from "postgres" (lib/pq) to "pgx" (pgx stdlib) and replaced pq.QuoteIdentifier usages with pgx.Identifier{...}.Sanitize().
• Updated Cloud SQL DSN keyword database= → dbname= for pgx compatibility.
• Reworked migrations to run via database/pgx/v5 using a per-schema search_path startup parameter on a temporary *sql.DB.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
main.go	Uses a shared connection string for both repository DB creation and migrator initialization.
internal/adapters/userrepository/postgres.go	Replaces schema identifier quoting with pgx sanitizer.
internal/adapters/userrepository/postgres_test.go	Updates schema DDL/search_path quoting and migrator construction API.
internal/adapters/playerrepository/repository.go	Updates SET search_path quoting to pgx sanitizer.
internal/adapters/playerrepository/repository_test.go	Updates schema setup/search_path quoting and migrator construction API.
internal/adapters/database/postgres.go	Switches sql driver to pgx, introduces ConnectionString, and adds schema-scoped DB helper for migrations.
internal/adapters/database/postgres_test.go	Updates tests to connect using the pgx driver name.
internal/adapters/database/migrator.go	Switches migrate DB driver from postgres to pgx/v5 and uses schema-scoped DB instances.
internal/adapters/database/migrator_test.go	Updates migration test setup to use pgx/v5 migrate driver and schema-scoped DB helper.
internal/adapters/database/cloudsql.go	Updates DSN to use dbname= instead of database=.
internal/adapters/accountrepository/postgres.go	Replaces schema identifier quoting with pgx sanitizer.
internal/adapters/accountrepository/postgres_test.go	Updates schema setup/search_path quoting and migrator construction API.
go.mod	Adds pgx/v5 and moves lib/pq to indirect dependency.
go.sum	Adds checksums for pgx and related indirect dependencies.