feat(core): programs' threads, and FILIUS' echo server and generic client after Java, measured against Java

Programs run as generators that yield what they wait for (threads.ts); the
engine resumes them after every event. TCP connect, send, receive, accept
and name resolution exist as such steps; the blocking calls wrap them.
EchoRun records eight stories in Java FILIUS, frames, tables and each
program's window lines; echoJava.test.ts plays them card by card. Not
taken from Java: a connection without a route hangs for ever; a server
switched off leaves its connections' last FIN unanswered.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/src/runtime/snapshot.ts

@@ -12,14 +12,21 @@ import type {
   DhcpClientConfiguration,
   DhcpServerConfiguration,
   DnsServerConfiguration,
+  EchoServerConfiguration,
   FirewallConfiguration,
   GatewayPortForwardingRow,
   InterfaceConfiguration,
   InterfaceKey,
   ManualRoute,
+  SimpleClientConfiguration,
   SwitchConfiguration,
 } from './config.js';
 
+/** An installed echo server: its port, and whether it is switched on (Java: ServerBaustein.aktiv). */
+export interface EchoServerSnapshot extends EchoServerConfiguration {
+  readonly isActive: boolean;
+}
+
 export interface PortSnapshot {
   readonly id: Id;
   readonly label: string;
@@ -65,6 +72,10 @@ export interface TopologySnapshot {
   readonly switchConfigurationsByNodeId: ReadonlyMap<Id, SwitchConfiguration>;
   /** Nodes whose IP forwarding differs from their kind's (forwardsIPv4ByDefault): a host that forwards. */
   readonly ipForwardingByNodeId: ReadonlyMap<Id, boolean>;
+  /** The installed echo servers (ServerBaustein), by node. */
+  readonly echoServersByNodeId: ReadonlyMap<Id, EchoServerSnapshot>;
+  /** The installed generic clients (ClientBaustein) with the server they last talked to, by node. */
+  readonly simpleClientsByNodeId: ReadonlyMap<Id, SimpleClientConfiguration>;
 }
 
 export interface TopologySnapshotInput {
@@ -81,6 +92,8 @@ export interface TopologySnapshotInput {
   portForwardingRowsByNodeId?: ReadonlyMap<Id, readonly GatewayPortForwardingRow[]>;
   switchConfigurationsByNodeId?: ReadonlyMap<Id, SwitchConfiguration>;
   ipForwardingByNodeId?: ReadonlyMap<Id, boolean>;
+  echoServersByNodeId?: ReadonlyMap<Id, EchoServerSnapshot>;
+  simpleClientsByNodeId?: ReadonlyMap<Id, SimpleClientConfiguration>;
 }
 
 export function topologySnapshot(input: TopologySnapshotInput): TopologySnapshot {
@@ -98,6 +111,8 @@ export function topologySnapshot(input: TopologySnapshotInput): TopologySnapshot
     portForwardingRowsByNodeId: input.portForwardingRowsByNodeId ?? new Map(),
     switchConfigurationsByNodeId: input.switchConfigurationsByNodeId ?? new Map(),
     ipForwardingByNodeId: input.ipForwardingByNodeId ?? new Map(),
+    echoServersByNodeId: input.echoServersByNodeId ?? new Map(),
+    simpleClientsByNodeId: input.simpleClientsByNodeId ?? new Map(),
   };
 }