fix: improve endgame clock and gameplay stability

docs/endgame-faketime.md

@@ -21,8 +21,15 @@ Use the command field in GaC-Srtool:
 - `/faketime 1791748801` sets Unix seconds.
 - `/faketime 2026-10-12T03:00:01+07:00` sets an explicit zoned date.
 - `/faketime off` restores real time (`reset` and `real` are equivalent).
+- `/faketime window <begin Unix seconds> <end Unix seconds>` keeps game time
+  inside a Client-observed overlap. It starts at the midpoint, advances, and
+  wraps to the beginning when the end is reached. Use only bounds verified for
+  the installed Client; changing Client revision requires checking them again.
 
-The fake clock keeps advancing. Its offset is atomically saved to
+The fake clock keeps advancing. Window mode wraps the shared game calendar for
+all game features, so the displayed time moves backwards at the boundary and
+other time-based activities may be affected. `/faketime off` or setting a new
+single time disables the window. Its state is atomically saved to
 `game_clock.state_file`, configured in `server.json`, local overrides, or
 `GAC_GAME_CLOCK_STATE_FILE`. With no state file configured, reads use real time
 and attempts to set fake time fail with a configuration error. Login and