Keep foreign keys on for every database connection (closes #207)

SQLite keeps the foreign keys setting per connection, and the server
turned it on once with a PRAGMA. A query cancelled while it runs makes
the pool close its only connection and open a new one, which then ran
without foreign keys until a restart.

connect now adds `_pragma=foreign_keys(1)` to the database URL. The
driver runs every `_pragma` parameter on each connection it opens, so
this also holds for a `DBURL` without `_pragma` parameters. The new
test cancels a query on a file database, then checks that the tables
are still there and that foreign keys are on.

Model: opus-5-5

internal/db/db.go

@@ -90,6 +90,17 @@ func (database *Database) connect(ctx context.Context) error {
 		dbURL = config.DefaultDBURL
 	}
 
+	// SQLite keeps the foreign keys setting per connection. The driver
+	// runs each _pragma parameter on every connection it opens. A
+	// PRAGMA run once would miss the connection the pool opens after a
+	// cancelled query breaks the old one.
+	separator := "?"
+	if strings.Contains(dbURL, "?") {
+		separator = "&"
+	}
+
+	dbURL += separator + "_pragma=foreign_keys(1)"
+
 	database.log.Info(
 		"connecting to database", "url", dbURL,
 	)
@@ -109,13 +120,6 @@ func (database *Database) connect(ctx context.Context) error {
 	database.conn = conn
 	database.log.Info("database connected")
 
-	_, err = database.conn.ExecContext(
-		ctx, "PRAGMA foreign_keys = ON",
-	)
-	if err != nil {
-		return fmt.Errorf("enable foreign keys: %w", err)
-	}
-
 	return database.runMigrations(ctx)
 }