fix(827): isolate D4 lease broker fixture

docs/compaction-refresh/probes/p3_generation_broker.py

@@ -6,6 +6,7 @@ from __future__ import annotations
 import argparse
 import json
 import os
+import secrets
 import socket
 import struct
 from pathlib import Path
@@ -41,6 +42,9 @@ def main() -> None:
     server.listen(8)
     generations: dict[tuple[int, int], int] = {}
     lease_state: dict[tuple[int, int], str] = {}
+    # The gated launcher registers its own exec-preserved PID here.  This is
+    # deliberately volatile fixture state; nothing is written outside root.
+    launcher_sessions: dict[tuple[int, int], str] = {}
     emit(log_path, {"event": "listen", "pid": os.getpid(), "socket": str(socket_path)})
 
     while True:
@@ -54,6 +58,27 @@ def main() -> None:
                 conn.sendall(b'{"ok":true}\n')
                 break
             identity = (pid, starttime)
+            if request.get("action") == "register_anchor":
+                generation = request.get("runtime_generation")
+                if type(generation) is not int or generation < 0:
+                    conn.sendall(b'{"ok":false,"code":"INVALID_GENERATION"}\n')
+                    continue
+                session_id = launcher_sessions.setdefault(identity, secrets.token_hex(32))
+                record = {
+                    "event": "lease_anchor_registered",
+                    "peercred": {"pid": pid, "uid": uid, "gid": gid},
+                    "starttime_ticks": starttime,
+                    "runtime_generation": generation,
+                    "session_id_shape": "hex-256",
+                }
+                emit(log_path, record)
+                reply = {
+                    "ok": True,
+                    "session_id": session_id,
+                    "peer": {"pid": pid, "uid": uid, "gid": gid, "starttime": str(starttime)},
+                }
+                conn.sendall((json.dumps(reply, sort_keys=True) + "\n").encode())
+                continue
             if request.get("action") == "promote-probe":
                 generation = generations.get(identity, 0)
                 lease_state[identity] = "VERIFIED"