test(827): capture Gate0 runtime evidence

docs/compaction-refresh/probes/p1_anchor_exec.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+"""Register this PID as anchor, then exec the real `mosaic yolo` launcher."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import os
+import socket
+import sys
+
+
+def request(socket_path: str, payload: dict[str, object]) -> dict[str, object]:
+    conn = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+    conn.connect(socket_path)
+    conn.sendall((json.dumps(payload) + "\n").encode())
+    response = json.loads(conn.makefile("r", encoding="utf-8").readline())
+    conn.close()
+    return response
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--socket", required=True)
+    parser.add_argument("runtime", choices=["pi", "claude"])
+    parser.add_argument("args", nargs=argparse.REMAINDER)
+    ns = parser.parse_args()
+
+    response = request(ns.socket, {"action": "register-anchor", "runtime": ns.runtime})
+    if response.get("decision") != "ACCEPT":
+        raise SystemExit("anchor registration refused")
+    os.environ["GATE0_SESSION_ID"] = str(response["session_id"])
+    argv = ["mosaic", "yolo", ns.runtime, *ns.args]
+    print(
+        json.dumps(
+            {
+                "event": "anchor-exec",
+                "pid": os.getpid(),
+                "argv": ["mosaic", "yolo", ns.runtime, f"<{len(ns.args)} runtime args>"],
+                "note": "os.execvpe retains pid and /proc starttime",
+            },
+            sort_keys=True,
+        ),
+        file=sys.stderr,
+        flush=True,
+    )
+    os.execvpe("mosaic", argv, os.environ)
+
+
+if __name__ == "__main__":
+    main()