console logs ROTATE instead of truncate -- tonight's evidence loss cannot repeat

Two destroyers, both in btoperator.py:
  * Start Session zeroed operator_relay.log -- took the whole 23:08 session
    (the reservoir-crash round's relay trace) minutes after it happened;
  * Launch local instances os.remove()'d operator_N.log -- took the pod's
    [crash] self-report block before it could be copied.

Both now rotate the previous file to <name>.1 (btrelay_park's pattern: drop
the old .1, os.replace, never block on a locked file).  One generation of
history is exactly what post-mortems needed twice tonight.  All four console
suites pass; picks up on the console's next restart.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tools/btoperator.py

@@ -36,6 +36,24 @@ from PySide6.QtWidgets import (
 HERE = os.path.dirname(os.path.abspath(__file__))
 REPO = os.path.abspath(os.path.join(HERE, ".."))
 CONTENT = os.path.join(REPO, "content")
+
+def rotate_log(path):
+    """Keep the PREVIOUS run's log as <path>.1 instead of destroying it.
+
+    2026-07-26 games night: the crash self-report block and the whole 23:08
+    session's relay log were both lost to truncation minutes after they were
+    written -- Start Session zeroed operator_relay.log and Launch-instances
+    os.remove()'d the pod log.  One generation of history is cheap insurance.
+    """
+    try:
+        if os.path.exists(path):
+            prev = path + ".1"
+            if os.path.exists(prev):
+                os.remove(prev)
+            os.replace(path, prev)
+    except OSError:
+        pass                    # a locked log must never block a session
+
 DEFAULT_EXE = os.path.join(REPO, "build", "Release", "btl4.exe")
 DEFAULT_EGG = os.path.join(CONTENT, "OPERATOR.EGG")
 BTCONSOLE = os.path.join(HERE, "btconsole.py")
@@ -879,10 +897,8 @@ class Operator(QMainWindow):
             for tag in tags:
                 host, _, port = tag.rpartition(":")
                 args.append("%s:%d" % (host, int(port) - 1))
-        try:                                    # fresh relay log per session
-            open(os.path.join(CONTENT, "operator_relay.log"), "w").close()
-        except OSError:
-            pass
+        # fresh relay log per session -- the OLD session survives as .1
+        rotate_log(os.path.join(CONTENT, "operator_relay.log"))
         self.console_proc = QProcess(self)
         self.console_proc.setProcessChannelMode(QProcess.MergedChannels)
         self.console_proc.readyReadStandardOutput.connect(self._console_output)
@@ -1284,10 +1300,7 @@ class Operator(QMainWindow):
             # chain (each generation used to TRUNCATE the log -- the night-2
             # crash loop left a 2-line file).  Fresh file per launch press.
             log_name = "operator_%d.log" % (r + 1)
-            try:
-                os.remove(os.path.join(CONTENT, log_name))
-            except OSError:
-                pass
+            rotate_log(os.path.join(CONTENT, log_name))
             env.insert("BT_LOG", log_name)
             env.insert("BT_LOG_APPEND", "1")
             proc = QProcess(self)