✨ feat(user): foundation for parallel-safe BDD isolation (T12 stage 1/2) (#34)

NewPostgresRepositoryFromDSN factory + BuildSchemaIsolatedDSN helper + integration test proving per-schema isolation works at repo level. Foundation for T12. Wiring into testserver is stage 2/2.

Co-authored-by: Gabriel Radureau <arcodange@gmail.com>
Co-committed-by: Gabriel Radureau <arcodange@gmail.com>

pkg/user/postgres_repository_isolated_test.go

@@ -0,0 +1,118 @@
+package user
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"testing"
+
+	"dance-lessons-coach/pkg/config"
+
+	_ "github.com/lib/pq"
+)
+
+// TestNewPostgresRepositoryFromDSN_SchemaIsolation verifies that the factory
+// + BuildSchemaIsolatedDSN combo produces a repository whose AutoMigrate
+// creates the users table inside a per-scenario schema (NOT public).
+//
+// This is the foundation block for parallel-safe BDD tests (T12).
+// Wiring it into the BDD testserver's SetupScenarioSchema is a follow-up.
+//
+// Skipped if Postgres is not available (no env vars / connection refused).
+func TestNewPostgresRepositoryFromDSN_SchemaIsolation(t *testing.T) {
+	host := os.Getenv("DLC_DATABASE_HOST")
+	if host == "" {
+		t.Skip("DLC_DATABASE_HOST not set, skipping integration test")
+	}
+
+	cfg := &config.Config{}
+	cfg.Database.Host = host
+	cfg.Database.Port = parsePortOrDefault(os.Getenv("DLC_DATABASE_PORT"), 5432)
+	cfg.Database.User = envOr("DLC_DATABASE_USER", "postgres")
+	cfg.Database.Password = envOr("DLC_DATABASE_PASSWORD", "postgres")
+	cfg.Database.Name = envOr("DLC_DATABASE_NAME", "dance_lessons_coach_bdd_test")
+	cfg.Database.SSLMode = envOr("DLC_DATABASE_SSL_MODE", "disable")
+
+	schemaName := "test_isolated_dsn_factory"
+
+	// Open default repo (public schema) just to manage the schema lifecycle
+	defaultRepo, err := NewPostgresRepository(cfg)
+	if err != nil {
+		t.Skipf("Postgres unavailable: %v", err)
+	}
+	defer defaultRepo.Close()
+
+	// Drop schema if it exists from a previous run
+	if err := defaultRepo.db.Exec(fmt.Sprintf("DROP SCHEMA IF EXISTS %s CASCADE", schemaName)).Error; err != nil {
+		t.Fatalf("DROP SCHEMA setup failed: %v", err)
+	}
+	defer func() {
+		_ = defaultRepo.db.Exec(fmt.Sprintf("DROP SCHEMA IF EXISTS %s CASCADE", schemaName)).Error
+	}()
+
+	// CREATE SCHEMA
+	if err := defaultRepo.db.Exec(fmt.Sprintf("CREATE SCHEMA %s", schemaName)).Error; err != nil {
+		t.Fatalf("CREATE SCHEMA failed: %v", err)
+	}
+
+	// Now use the factory to open a repo whose connection has search_path=schemaName
+	dsn := BuildSchemaIsolatedDSN(cfg, schemaName)
+	isolatedRepo, err := NewPostgresRepositoryFromDSN(cfg, dsn)
+	if err != nil {
+		t.Fatalf("NewPostgresRepositoryFromDSN failed: %v", err)
+	}
+	defer isolatedRepo.Close()
+
+	// Verify the users table now exists in our schema (not just in public)
+	var count int64
+	q := fmt.Sprintf("SELECT count(*) FROM information_schema.tables WHERE table_schema='%s' AND table_name='users'", schemaName)
+	if err := isolatedRepo.db.Raw(q).Scan(&count).Error; err != nil {
+		t.Fatalf("information_schema query failed: %v", err)
+	}
+	if count != 1 {
+		t.Fatalf("expected users table in schema %s after AutoMigrate, count=%d", schemaName, count)
+	}
+
+	// Verify a CreateUser via the isolated repo writes into the new schema, NOT public
+	u := &User{Username: "isolated_factory_user", PasswordHash: "x"}
+	if err := isolatedRepo.CreateUser(context.Background(), u); err != nil {
+		t.Fatalf("CreateUser via isolated repo failed: %v", err)
+	}
+
+	var publicCount int64
+	if err := defaultRepo.db.Raw(fmt.Sprintf("SELECT count(*) FROM public.users WHERE username='%s'", u.Username)).Scan(&publicCount).Error; err != nil {
+		t.Fatalf("query public.users failed: %v", err)
+	}
+	if publicCount != 0 {
+		t.Fatalf("isolation leak: expected 0 rows in public.users for username=%s, got %d", u.Username, publicCount)
+	}
+
+	var schemaCount int64
+	if err := isolatedRepo.db.Raw(fmt.Sprintf("SELECT count(*) FROM %s.users WHERE username='%s'", schemaName, u.Username)).Scan(&schemaCount).Error; err != nil {
+		t.Fatalf("query schema users failed: %v", err)
+	}
+	if schemaCount != 1 {
+		t.Fatalf("expected 1 row in %s.users, got %d", schemaName, schemaCount)
+	}
+}
+
+// envOr returns the env var value or the fallback if empty.
+func envOr(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}
+
+// parsePortOrDefault parses a port string or returns the fallback.
+func parsePortOrDefault(s string, fallback int) int {
+	if s == "" {
+		return fallback
+	}
+	var n int
+	_, err := fmt.Sscanf(s, "%d", &n)
+	if err != nil || n <= 0 {
+		return fallback
+	}
+	return n
+}