op-node: add more comments, fix flag description

op-node/flags/flags.go

@@ -74,8 +74,9 @@ var (
 		Category: RollupCategory,
 	}
 	SupervisorAddr = &cli.StringFlag{
-		Name:    "supervisor",
-		Usage:   "Experimental feature. Do not use. Address of interop supervisor service for cross-chain safety verification.",
+		Name: "supervisor",
+		Usage: "RPC address of interop supervisor service for cross-chain safety verification." +
+			"Applies only to Interop-enabled networks.",
 		Hidden:  true, // hidden for now during early testing.
 		EnvVars: prefixEnvVars("SUPERVISOR"),
 	}

op-node/node/config.go

@@ -143,7 +143,7 @@ func (cfg *Config) Check() error {
 			return fmt.Errorf("the Interop upgrade is scheduled (timestamp = %d) but no supervisor RPC endpoint is configured", *cfg.Rollup.InteropTime)
 		}
 		if err := cfg.Supervisor.Check(); err != nil {
-			return fmt.Errorf("misconfigured supervsiro RPC endpoint: %w", err)
+			return fmt.Errorf("misconfigured supervisor RPC endpoint: %w", err)
 		}
 	}
 	if err := cfg.Rollup.Check(); err != nil {

op-node/rollup/driver/driver.go

@@ -183,6 +183,9 @@ func NewDriver(
 
 	opts := event.DefaultRegisterOpts()
 
+	// If interop is scheduled we start the driver.
+	// It will then be ready to pick up verification work
+	// as soon as we reach the upgrade time (if the upgrade is not already active).
 	if cfg.InteropTime != nil {
 		interopDeriver := interop.NewInteropDeriver(log, cfg, driverCtx, supervisor, l2)
 		sys.Register("interop", interopDeriver, opts)

op-node/rollup/interop/interop.go

@@ -83,7 +83,8 @@ func (d *InteropDeriver) OnEvent(ev event.Event) bool {
 		if x.CrossUnsafe.Number >= x.LocalUnsafe.Number {
 			break // nothing left to promote
 		}
-		// pre-interop the engine itself handles promotion to cross-unsafe
+		// Pre-interop the engine itself handles promotion to cross-unsafe.
+		// Check if the next block (still unsafe) can be promoted to cross-unsafe.
 		if !d.cfg.IsInterop(d.cfg.TimestampForBlock(x.CrossUnsafe.Number + 1)) {
 			return false
 		}
@@ -112,7 +113,8 @@ func (d *InteropDeriver) OnEvent(ev event.Event) bool {
 		if x.CrossSafe.Number >= x.LocalSafe.Number {
 			break // nothing left to promote
 		}
-		// pre-interop the engine itself handles promotion to cross-safe
+		// Pre-interop the engine itself handles promotion to cross-safe.
+		// Check if the next block (not yet cross-safe) can be promoted to cross-safe.
 		if !d.cfg.IsInterop(d.cfg.TimestampForBlock(x.CrossSafe.Number + 1)) {
 			return false
 		}