Run the local index in WAL mode with a busy timeout (closes #217)

The connection settings were passed as `_journal_mode=`-style
parameters, which the SQLite driver drops without an error, so the
index ran in rollback-journal mode with no busy timeout. `snapshot
list` or `info` reading during a backup could make the backup's next
write fail with "database is locked". Both open paths now pass
`_pragma=` parameters; foreign keys moved there too.

With WAL on, rows committed to the open index can still be in the
-wal file, which a copy of the main file misses. The metadata export
now copies the index with VACUUM INTO, into an empty 0600 file.

The retry after a failed open no longer claims a TRUNCATE recovery; it
retries with the same settings.

Model: opus-5-5

internal/database/database.go

@@ -42,9 +42,9 @@ var schemaFS embed.FS
 // table itself. It is applied before the normal migration loop.
 const bootstrapVersion = 0
 
-// busyTimeoutMsec is how long a connection to the index waits for another
+// busyTimeoutMs is how long a connection to the index waits for another
 // connection's lock before failing with "database is locked".
-const busyTimeoutMsec = 10000
+const busyTimeoutMs = 10000
 
 // DB represents the Vaultik local index database connection.
 // It uses SQLite to track file metadata, content-defined chunks, and blob associations.
@@ -108,7 +108,7 @@ func indexDSN(path string) string {
 	return fmt.Sprintf(
 		"%s?_pragma=busy_timeout(%d)&_pragma=journal_mode(WAL)"+
 			"&_pragma=synchronous(NORMAL)&_pragma=foreign_keys(1)",
-		path, busyTimeoutMsec)
+		path, busyTimeoutMs)
 }
 
 // New creates a new database connection at the specified path.
@@ -152,7 +152,7 @@ func New(ctx context.Context, path string) (*DB, error) {
 	}
 
 	// If the first attempt failed, try once more
-	return openWithRecovery(ctx, path)
+	return retryOpen(ctx, path)
 }
 
 // configureConnPool serializes all database access through one connection.
@@ -179,10 +179,10 @@ func finishOpen(ctx context.Context, conn *sql.DB, path string) (*DB, error) {
 	return db, nil
 }
 
-// openWithRecovery makes a second attempt to open the database, with the
-// same settings, after the first attempt failed, for example because
-// another process held a lock for longer than the busy timeout.
-func openWithRecovery(ctx context.Context, path string) (*DB, error) {
+// retryOpen makes a second attempt to open the database, with the same
+// settings, after the first attempt failed, for example because another
+// process held a lock for longer than the busy timeout.
+func retryOpen(ctx context.Context, path string) (*DB, error) {
 	log.Info("Database appears locked, retrying open", "path", path)
 
 	conn, err := sql.Open("sqlite", indexDSN(path))
@@ -202,7 +202,7 @@ func openWithRecovery(ctx context.Context, path string) (*DB, error) {
 		_ = conn.Close()
 
 		return nil, fmt.Errorf(
-			"database still locked after recovery attempt: %w",
+			"database still locked on retry: %w",
 			err,
 		)
 	}

internal/database/database_test.go

@@ -153,8 +153,8 @@ func TestNewSetsJournalModeAndBusyTimeout(t *testing.T) {
 		t.Fatalf("reading busy_timeout: %v", err)
 	}
 
-	if busyTimeout != busyTimeoutMsec {
-		t.Errorf("busy_timeout = %d, want %d", busyTimeout, busyTimeoutMsec)
+	if busyTimeout != busyTimeoutMs {
+		t.Errorf("busy_timeout = %d, want %d", busyTimeout, busyTimeoutMs)
 	}
 }