diff --git a/cmd/launcher/sqlite.go b/cmd/launcher/sqlite.go
index 20be13d..941a512 100644
--- a/cmd/launcher/sqlite.go
+++ b/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
 }
diff --git a/cmd/launcher/sqlite_test.go b/cmd/launcher/sqlite_test.go
new file mode 100644
index 0000000..5988cc7
--- /dev/null
+++ b/cmd/launcher/sqlite_test.go
@@ -0,0 +1,198 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"os"
+	"path/filepath"
+	"sync"
+	"testing"
+)
+
+// TestSQLitePragmaHook verifies that every connection opened via the registered
+// "sqlite3" driver has WAL journal mode and a busy_timeout set.
+func TestSQLitePragmaHook(t *testing.T) {
+	dir := t.TempDir()
+	dbPath := filepath.Join(dir, "test.db")
+
+	db, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	defer db.Close()
+
+	// Force a real connection to be created (Open is lazy).
+	if err := db.Ping(); err != nil {
+		t.Fatalf("ping: %v", err)
+	}
+
+	var journalMode string
+	if err := db.QueryRow("PRAGMA journal_mode").Scan(&journalMode); err != nil {
+		t.Fatalf("query journal_mode: %v", err)
+	}
+	if journalMode != "wal" {
+		t.Errorf("journal_mode = %q, want %q", journalMode, "wal")
+	}
+
+	var busyTimeout int
+	if err := db.QueryRow("PRAGMA busy_timeout").Scan(&busyTimeout); err != nil {
+		t.Fatalf("query busy_timeout: %v", err)
+	}
+	if busyTimeout != 5000 {
+		t.Errorf("busy_timeout = %d, want %d", busyTimeout, 5000)
+	}
+}
+
+// TestSQLiteConcurrentWrites verifies that concurrent writers do not get
+// SQLITE_BUSY errors thanks to WAL mode and busy_timeout.
+func TestSQLiteConcurrentWrites(t *testing.T) {
+	dir := t.TempDir()
+	dbPath := filepath.Join(dir, "concurrent.db")
+
+	db, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	defer db.Close()
+
+	// Create a table to write to.
+	if _, err := db.Exec(`CREATE TABLE kv (k TEXT PRIMARY KEY, v TEXT)`); err != nil {
+		t.Fatalf("create table: %v", err)
+	}
+
+	// Simulate the scenario: multiple goroutines writing concurrently,
+	// like mautrix crypto sync + memory store + knowledge store.
+	const writers = 5
+	const writesPerWriter = 50
+	ctx := context.Background()
+
+	var wg sync.WaitGroup
+	errs := make(chan error, writers*writesPerWriter)
+
+	for w := 0; w < writers; w++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for i := 0; i < writesPerWriter; i++ {
+				_, err := db.ExecContext(ctx,
+					`INSERT OR REPLACE INTO kv (k, v) VALUES (?, ?)`,
+					// Use writer+iteration as key so they conflict
+					"key", "value",
+				)
+				if err != nil {
+					errs <- err
+				}
+			}
+		}()
+	}
+
+	wg.Wait()
+	close(errs)
+
+	for err := range errs {
+		t.Errorf("concurrent write error: %v", err)
+	}
+}
+
+// TestSQLiteConcurrentWritesSeparateConnections tests with separate sql.DB
+// instances (like crypto.db being opened by both mautrix and our code).
+func TestSQLiteConcurrentWritesSeparateConnections(t *testing.T) {
+	dir := t.TempDir()
+	dbPath := filepath.Join(dir, "shared.db")
+
+	// Open two separate connections to the same file (simulates mautrix +
+	// our memory store sharing a DB, or separate processes).
+	db1, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		t.Fatalf("open db1: %v", err)
+	}
+	defer db1.Close()
+
+	db2, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		t.Fatalf("open db2: %v", err)
+	}
+	defer db2.Close()
+
+	// Create table via db1
+	if _, err := db1.Exec(`CREATE TABLE t (id INTEGER PRIMARY KEY, data TEXT)`); err != nil {
+		t.Fatalf("create table: %v", err)
+	}
+
+	ctx := context.Background()
+	const iterations = 100
+
+	var wg sync.WaitGroup
+	errs := make(chan error, iterations*2)
+
+	// Writer 1 (simulates mautrix SaveNextBatch)
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for i := 0; i < iterations; i++ {
+			_, err := db1.ExecContext(ctx,
+				`INSERT INTO t (data) VALUES (?)`, "from_crypto_sync",
+			)
+			if err != nil {
+				errs <- err
+			}
+		}
+	}()
+
+	// Writer 2 (simulates our memory store SaveMessage)
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for i := 0; i < iterations; i++ {
+			_, err := db2.ExecContext(ctx,
+				`INSERT INTO t (data) VALUES (?)`, "from_memory_store",
+			)
+			if err != nil {
+				errs <- err
+			}
+		}
+	}()
+
+	wg.Wait()
+	close(errs)
+
+	for err := range errs {
+		t.Errorf("concurrent write error (separate conns): %v", err)
+	}
+
+	// Verify all writes succeeded
+	var count int
+	if err := db1.QueryRow("SELECT COUNT(*) FROM t").Scan(&count); err != nil {
+		t.Fatalf("count: %v", err)
+	}
+	expected := iterations * 2
+	if count != expected {
+		t.Errorf("row count = %d, want %d", count, expected)
+	}
+}
+
+// TestSQLiteWALFileCreated verifies that WAL mode actually creates the -wal file,
+// confirming the pragma took effect at the filesystem level.
+func TestSQLiteWALFileCreated(t *testing.T) {
+	dir := t.TempDir()
+	dbPath := filepath.Join(dir, "walcheck.db")
+
+	db, err := sql.Open("sqlite3", dbPath)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	defer db.Close()
+
+	// Create a table and write data to trigger WAL file creation.
+	if _, err := db.Exec(`CREATE TABLE x (id INTEGER PRIMARY KEY)`); err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if _, err := db.Exec(`INSERT INTO x (id) VALUES (1)`); err != nil {
+		t.Fatalf("insert: %v", err)
+	}
+
+	walPath := dbPath + "-wal"
+	if _, err := os.Stat(walPath); os.IsNotExist(err) {
+		t.Errorf("WAL file not created at %s — PRAGMA journal_mode=WAL may not be taking effect", walPath)
+	}
+}