launcher logs: rotate, never delete -- and solo/joyconfig must stop destroying the MULTIPLAYER log

Prompted by "does the steam path still generate our logs?".  Answer: yes --
play_steam.bat sets BT_LOG=steam.log with append, and matchlogs arm because both
Steam launch paths pass -net (the default trigger).  But the audit found two
evidence-destroying bugs on the way:

1. play_steam.bat DELETED the previous steam.log at every launch -- the same
   pattern fixed in join.bat/join_lan.bat last night.  A Steam player who
   crashes and relaunches loses the stack.  Now rotates to steam.old.log.

2. WORSE: play_solo.bat and joyconfig.bat deleted content\join.log -- the
   MULTIPLAYER log, not theirs.  A player who crashed in MP and then ran solo
   to investigate (or ran the joystick wizard) DESTROYED THEIR OWN CRASH
   EVIDENCE.  That is a very plausible part of how Conn Man's owens-laser stack
   vanished (#35) -- he had every reason to poke around after crashing.  Each
   bat now writes its OWN log (solo.log / joyconfig.log), rotates it, and never
   touches join.log.  Their launch-forensics + "send the operator" lines are
   repointed to match.

VERIFIED in the zip layout (the bats need build\ + content\ beside them, so a
repo-relative test is meaningless -- my first two attempts hit the badpath
guard and proved nothing):
  solo.log     = [boot] btl4 4.11.599 ... (the NEW run)
  solo.old.log = OLD-SOLO-CONTENT        (rotated, not deleted)
  join.log     = SEEDED-MP-EVIDENCE      (untouched by the solo run)

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

players/joyconfig.bat

@@ -15,8 +15,13 @@ set BT_START_INSIDE=1
 set BT_DEV_GAUGES=1
 rem one fresh log per bat run; the menu->game relaunch chain APPENDS
 rem so every generation's lines survive (0-byte logs = killed pre-start)
-if exist content\join.log del content\join.log
-set BT_LOG=join.log
+rem KEEP the previous run's log (a crash report died 2026-07-26 because a
+rem re-run deleted the only evidence).  Rotate, never delete.
+rem ...and do NOT touch join.log (the MULTIPLAYER log) -- the wizard used to
+rem delete a player's MP crash evidence.  The wizard writes joyconfig.log.
+if exist content\joyconfig.old.log del content\joyconfig.old.log
+if exist content\joyconfig.log ren content\joyconfig.log joyconfig.old.log
+set BT_LOG=joyconfig.log
 set BT_LOG_APPEND=1
 set BT_FE_SOLO=1
 cd content
@@ -27,8 +32,8 @@ echo [%DATE% %TIME%] launching btl4.exe > launch_report.txt
 ..\build\Release\btl4.exe
 set BT_EXITCODE=%ERRORLEVEL%
 echo [%DATE% %TIME%] btl4.exe exited with code %BT_EXITCODE% >> launch_report.txt
-if not exist join.log echo join.log WAS NEVER CREATED: the exe was blocked before it could run (loader failure or antivirus) >> launch_report.txt
-if exist join.log for %%A in (join.log) do echo join.log size: %%~zA bytes >> launch_report.txt
+if not exist joyconfig.log echo joyconfig.log WAS NEVER CREATED: the exe was blocked before it could run (loader failure or antivirus) >> launch_report.txt
+if exist joyconfig.log for %%A in (joyconfig.log) do echo joyconfig.log size: %%~zA bytes >> launch_report.txt
 exit /b
 :badpath
 echo.

players/play_solo.bat

@@ -14,8 +14,14 @@ set BT_START_INSIDE=1
 set BT_DEV_GAUGES=1
 rem one fresh log per bat run; the menu->game relaunch chain APPENDS
 rem so every generation's lines survive (0-byte logs = killed pre-start)
-if exist content\join.log del content\join.log
-set BT_LOG=join.log
+rem KEEP the previous run's log (a crash report died 2026-07-26 because a
+rem re-run deleted the only evidence).  Rotate, never delete.
+rem ...and do NOT touch join.log: that is the MULTIPLAYER log.  A player who
+rem crashed in MP and then ran solo to investigate used to destroy their own
+rem crash evidence.  Solo writes solo.log.
+if exist content\solo.old.log del content\solo.old.log
+if exist content\solo.log ren content\solo.log solo.old.log
+set BT_LOG=solo.log
 set BT_LOG_APPEND=1
 set BT_FE_SOLO=1
 cd content
@@ -26,8 +32,8 @@ echo [%DATE% %TIME%] launching btl4.exe > launch_report.txt
 ..\build\Release\btl4.exe
 set BT_EXITCODE=%ERRORLEVEL%
 echo [%DATE% %TIME%] btl4.exe exited with code %BT_EXITCODE% >> launch_report.txt
-if not exist join.log echo join.log WAS NEVER CREATED: the exe was blocked before it could run (loader failure or antivirus) >> launch_report.txt
-if exist join.log for %%A in (join.log) do echo join.log size: %%~zA bytes >> launch_report.txt
+if not exist solo.log echo solo.log WAS NEVER CREATED: the exe was blocked before it could run (loader failure or antivirus) >> launch_report.txt
+if exist solo.log for %%A in (solo.log) do echo solo.log size: %%~zA bytes >> launch_report.txt
 
 rem ------------------------------------------------------------------
 rem HANDOFF WAIT (2026-07-25).  The front end does NOT stay resident: it
@@ -59,7 +65,7 @@ if defined BT_STILL_RUNNING (
 )
 echo.
 echo The game has exited.  If it closed unexpectedly,
-echo send the operator content\join.log.
+echo send the operator content\solo.log.
 pause
 exit /b
 :badpath

players/play_steam.bat

@@ -9,7 +9,10 @@ if not exist "build\Release\btl4.exe" goto badpath
 if not exist "content\BTL4.RES" goto badpath
 set BT_PLATFORM=glass
 set BT_STEAM_NET=1
-if exist content\steam.log del content\steam.log
+rem KEEP the previous run's log (a crash report died 2026-07-26 because a
+rem re-run deleted the only evidence).  Rotate, never delete.
+if exist content\steam.old.log del content\steam.old.log
+if exist content\steam.log ren content\steam.log steam.old.log
 set BT_LOG=steam.log
 set BT_LOG_APPEND=1
 rem Cockpit view + MFD gauges -- the same client flags the join bats set