Live mode: optional timing of each request (QET_LIVE_PERF_LOG)

A request with "timing": true gets queue, confirm and exec times in its
answer; with QET_LIVE_PERF_LOG set, QElectroTech also appends one JSON
line per request, with the time until the folio is next painted. The
qet MCP server logs its side of each live call to the same file.

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

misc/qet-mcp/qet_mcp.py

@@ -64,6 +64,8 @@ import shutil
 import subprocess
 import sys
 import tempfile
+import time
+import uuid
 import xml.etree.ElementTree as ET
 from pathlib import Path, PurePath, PurePosixPath, PureWindowsPath
 
@@ -4016,9 +4018,21 @@ def _live_session() -> dict:
     return live
 
 
+_live_last_end = None
+
+
 def _live_call(request: dict, timeout: float = 60.0) -> dict:
+    # QET_LIVE_PERF_LOG: append one JSON line per request with where its
+    # time went (tools/live-perf/monitor.py in the docker harness reads it;
+    # QElectroTech writes its own half when started with the same variable).
+    perf_log = os.environ.get("QET_LIVE_PERF_LOG", "").strip()
+    started = time.perf_counter()
     session = _live_session()
-    request = dict(request, token=session.get("token", ""), id=1)
+    request_id = uuid.uuid4().hex[:12] if perf_log else 1
+    request = dict(request, token=session.get("token", ""), id=request_id)
+    if perf_log:
+        request["timing"] = True
+    t_session = time.perf_counter()
     line = (json.dumps(request) + "\n").encode("utf-8")
     name = session.get("socket", "")
     try:
@@ -4052,6 +4066,23 @@ def _live_call(request: dict, timeout: float = 60.0) -> dict:
         raise ValueError("QElectroTech closed the live channel without answering")
     answer = json.loads(data.decode("utf-8"))
     answer.pop("id", None)
+    if perf_log:
+        global _live_last_end
+        ended = time.perf_counter()
+        line = {"src": "client", "id": request_id, "cmd": request.get("cmd"),
+                "label": "mcp", "t": time.time(), "pid": os.getpid(),
+                "gap_ms": round((started - _live_last_end) * 1000, 2)
+                if _live_last_end is not None else None,
+                "session_ms": round((t_session - started) * 1000, 2),
+                "total_ms": round((ended - started) * 1000, 2),
+                "answer_bytes": len(data), "ok": answer.get("ok"),
+                "server": answer.pop("timing", None)}
+        _live_last_end = ended
+        try:
+            with open(perf_log, "a", encoding="utf-8") as f:
+                f.write(json.dumps(line) + "\n")
+        except OSError:
+            pass
     return answer