feat(core): TCP in the simulation core

engine.ts ports Swift's "Java-compatible TCP sockets" in one piece, since
half a state machine could not be checked: server and client sockets (a
free port from Java's random numbers on their own seed), the three-way
handshake with its result (connected, invalid socket, unreachable, timed
out), segments of 1460 bytes, messages up to the push, a timeout of
3 × 2.5 s with at most three attempts, closing through every Java state
including TIME_WAIT (2.5 s), sequence numbers modulo 2^32.

Three scenarios match the Swift engine trace for trace: a LAN with data
over three segments, closing from both ends, a closed port and an
unreachable host; two networks through a router with a firewall rule,
data lost until the connection closes, and an accepted socket that does
not hold the port of its closed listener; CLOSING, reached by a lost FIN.
The engine delivers a FIN within the same close, so both ends close at
once only with packet loss; an empty message does not arrive in Swift (it
does not advance the sequence number), nor here.

Swift's four TCP engine tests are ported, with tests for stopping, a
foreign SYN+ACK at a listener and the flag names. 17 mutation probes, 16
caught; the other (delivered, not waited, not connected gives unreachable)
cannot be reached through Swift's engine, which never sends a reset and
always acknowledges correctly.

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

packages/core/test/scenarios/tcp-routed-loss.scenario.json

@@ -0,0 +1,166 @@
+{
+  "seed": 32,
+  "nodes": [
+    {
+      "id": "00000000-0000-0000-0000-000000000201",
+      "kind": "pc",
+      "ports": [
+        {
+          "id": "00000000-0000-0000-0000-000000000211",
+          "label": "eth0"
+        }
+      ]
+    },
+    {
+      "id": "00000000-0000-0000-0000-000000000202",
+      "kind": "router",
+      "ports": [
+        {
+          "id": "00000000-0000-0000-0000-000000000221",
+          "label": "rt1"
+        },
+        {
+          "id": "00000000-0000-0000-0000-000000000222",
+          "label": "rt2"
+        }
+      ]
+    },
+    {
+      "id": "00000000-0000-0000-0000-000000000203",
+      "kind": "pc",
+      "ports": [
+        {
+          "id": "00000000-0000-0000-0000-000000000213",
+          "label": "eth0"
+        }
+      ]
+    }
+  ],
+  "links": [
+    {
+      "id": "00000000-0000-0000-0000-00000000F004",
+      "sourceNode": "00000000-0000-0000-0000-000000000201",
+      "sourcePort": "00000000-0000-0000-0000-000000000211",
+      "targetNode": "00000000-0000-0000-0000-000000000202",
+      "targetPort": "00000000-0000-0000-0000-000000000221"
+    },
+    {
+      "id": "00000000-0000-0000-0000-00000000F005",
+      "sourceNode": "00000000-0000-0000-0000-000000000202",
+      "sourcePort": "00000000-0000-0000-0000-000000000222",
+      "targetNode": "00000000-0000-0000-0000-000000000203",
+      "targetPort": "00000000-0000-0000-0000-000000000213"
+    }
+  ],
+  "devices": {
+    "00000000-0000-0000-0000-000000000201": {
+      "ip": "10.0.0.2",
+      "mask": "255.255.255.0",
+      "gateway": "10.0.0.1"
+    },
+    "00000000-0000-0000-0000-000000000202": {
+      "ip": "10.0.0.1",
+      "mask": "255.255.255.0"
+    },
+    "00000000-0000-0000-0000-000000000203": {
+      "ip": "20.0.0.2",
+      "mask": "255.255.255.0",
+      "gateway": "20.0.0.1"
+    }
+  },
+  "interfaces": [
+    {
+      "node": "00000000-0000-0000-0000-000000000202",
+      "port": "00000000-0000-0000-0000-000000000221",
+      "ip": "10.0.0.1",
+      "mask": "255.255.255.0"
+    },
+    {
+      "node": "00000000-0000-0000-0000-000000000202",
+      "port": "00000000-0000-0000-0000-000000000222",
+      "ip": "20.0.0.1",
+      "mask": "255.255.255.0"
+    }
+  ],
+  "steps": [
+    {
+      "op": "openTcpServer",
+      "node": "00000000-0000-0000-0000-000000000203",
+      "port": 80
+    },
+    {
+      "op": "openTcpServer",
+      "node": "00000000-0000-0000-0000-000000000203",
+      "port": 81
+    },
+    {
+      "op": "openTcpClient",
+      "node": "00000000-0000-0000-0000-000000000201",
+      "target": "20.0.0.2",
+      "port": 80
+    },
+    {
+      "op": "connectTcp",
+      "socket": "00000000-0000-0000-0000-000000000003"
+    },
+    {
+      "op": "sendTcp",
+      "socket": "00000000-0000-0000-0000-000000000003",
+      "payload": "durch den Router"
+    },
+    {
+      "op": "receiveTcp",
+      "socket": "00000000-0000-0000-0000-000000000004"
+    },
+    {
+      "op": "openTcpClient",
+      "node": "00000000-0000-0000-0000-000000000201",
+      "target": "20.0.0.2",
+      "port": 81
+    },
+    {
+      "op": "connectTcp",
+      "socket": "00000000-0000-0000-0000-000000000005"
+    },
+    {
+      "op": "packetLoss",
+      "enabled": true
+    },
+    {
+      "op": "sendTcp",
+      "socket": "00000000-0000-0000-0000-000000000003",
+      "payload": "verloren"
+    },
+    {
+      "op": "packetLoss",
+      "enabled": false
+    },
+    {
+      "op": "sendTcp",
+      "socket": "00000000-0000-0000-0000-000000000003",
+      "payload": "zu spaet"
+    },
+    {
+      "op": "closeSocket",
+      "socket": "00000000-0000-0000-0000-000000000001"
+    },
+    {
+      "op": "openTcpServer",
+      "node": "00000000-0000-0000-0000-000000000203",
+      "port": 80
+    }
+  ],
+  "firewalls": {
+    "00000000-0000-0000-0000-000000000202": {
+      "active": true,
+      "defaultPolicy": "accept",
+      "rules": [
+        {
+          "protocol": "tcp",
+          "port": 81,
+          "action": "drop"
+        }
+      ]
+    }
+  }
+}