fix: SQLite WAL mode y busy_timeout para evitar SQLITE_BUSY

Registra un connection hook en el driver modernc/sqlite que ejecuta
PRAGMA journal_mode=WAL y PRAGMA busy_timeout=5000 en cada conexión nueva.

Esto previene errores SQLITE_BUSY cuando múltiples goroutines escriben
concurrentemente (crypto sync de mautrix + memory store + knowledge store).

Incluye tests que verifican:
- Pragmas aplicados correctamente en cada conexión
- Escrituras concurrentes sin error (mismo sql.DB y conexiones separadas)
- Archivo -wal creado en disco confirmando WAL activo

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/launcher/sqlite.go

@@ -1,12 +1,37 @@
 package main
 
 import (
+	"context"
 	"database/sql"
+	"database/sql/driver"
 
 	moderncsqlite "modernc.org/sqlite"
 )
 
 func init() {
-	// mautrix dbutil opens sqlite as "sqlite3"; register the pure-Go driver under that name.
-	sql.Register("sqlite3", &moderncsqlite.Driver{})
+	// mautrix dbutil opens sqlite as "sqlite3"; register the pure-Go driver
+	// under that name. We add a connection hook that sets WAL mode and a
+	// busy timeout on every connection to prevent SQLITE_BUSY crashes during
+	// concurrent writes (crypto store sync + memory store).
+	d := &moderncsqlite.Driver{}
+	d.RegisterConnectionHook(sqlitePragmaHook)
+	sql.Register("sqlite3", d)
+}
+
+// sqlitePragmaHook sets WAL journal mode and a 5-second busy timeout on
+// every new SQLite connection. This prevents SQLITE_BUSY errors when
+// multiple goroutines write concurrently (e.g. mautrix crypto sync +
+// memory/knowledge stores).
+func sqlitePragmaHook(conn moderncsqlite.ExecQuerierContext, _ string) error {
+	ctx := context.Background()
+	pragmas := []string{
+		"PRAGMA journal_mode=WAL",
+		"PRAGMA busy_timeout=5000",
+	}
+	for _, p := range pragmas {
+		if _, err := conn.ExecContext(ctx, p, []driver.NamedValue{}); err != nil {
+			return err
+		}
+	}
+	return nil
 }