feat(core): event queue, Ethernet, switch, ARP, IPv4, ICMP, routing and firewall

First slice of the TypeScript port of the filius-ipad runtime engine,
with 29 tests ported from the Swift suite. Parts not ported yet throw
NotPortedError instead of guessing.

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

packages/core/src/runtime/trace.ts

@@ -0,0 +1,58 @@
+// Ported from filius-ipad (GPLv2/GPLv3):
+//   State/TopologyNetworkRuntimeEngine.swift (packet trace model)
+// Java counterpart: filius.rahmenprogramm.nachrichten.Lauscher — here every
+// step a frame or packet takes is one trace event; the packet viewer groups them.
+
+import type { Id } from '../ids.js';
+
+export type TraceDirection = 'inbound' | 'outbound' | 'local';
+
+export type TraceLayer = 'application' | 'transport' | 'network' | 'dataLink' | 'physical';
+
+export type TraceOperation =
+  | 'created'
+  | 'sent'
+  | 'received'
+  | 'forwarded'
+  | 'accepted'
+  | 'dropped'
+  | 'rewritten'
+  | 'retransmitted'
+  | 'compatibilityAdapter';
+
+export interface HeaderField {
+  readonly name: string;
+  readonly value: string;
+}
+
+export interface TraceEvent {
+  readonly id: number;
+  readonly timeMilliseconds: number;
+  readonly frameIdentity?: number;
+  readonly packetIdentity?: number;
+  readonly nodeId: Id;
+  readonly interfaceId?: Id;
+  readonly direction: TraceDirection;
+  readonly layer: TraceLayer;
+  readonly operation: TraceOperation;
+  readonly beforeHeaders: readonly HeaderField[];
+  readonly afterHeaders: readonly HeaderField[];
+  readonly detail?: string;
+}
+
+/** How many trace events the runtime keeps, and how many it drops at once when full. */
+export interface TraceRetentionPolicy {
+  readonly maximumEventCount: number;
+  readonly evictionBatchSize: number;
+}
+
+export function traceRetentionPolicy(maximumEventCount: number, evictionBatchSize: number): TraceRetentionPolicy {
+  if (!(maximumEventCount > 0)) throw new RangeError('Packet-trace retention must keep at least one event');
+  if (!(evictionBatchSize > 0)) throw new RangeError('Packet-trace eviction must remove at least one event');
+  if (evictionBatchSize > maximumEventCount) {
+    throw new RangeError('Packet-trace eviction cannot exceed the retention limit');
+  }
+  return { maximumEventCount, evictionBatchSize };
+}
+
+export const PRODUCTION_TRACE_RETENTION = traceRetentionPolicy(10_000, 1_000);