Stardew Valley engine reference notes

Engine mechanics that the server/mod relies on. Prescriptive contributor rules live at .claude/rules/cabin-system.md and .claude/rules/host-automation.md (the festival rule lives under host-automation, item 3).

For full source-of-truth, the decompiled game lives at decompiled/sdv-1.6.15-24356/.

Sleep / wakeup / day-end

GameLocation.startSleep() does NOT set player.isInBed. isInBed is set dynamically by Farmer.Update() from tile properties — so setTileLocation() to a bed tile MUST run BEFORE startSleep().
On clients (!IsMasterGame), doSleep() does NOT call Game1.NewDay(). It uses message type 14 (newDaySync).

Ready-check messages use message type 31. They are blocked by PasswordProtectionService for unauthenticated players.
isGameAvailable() returns false during newDaySync. It stays false until newDaySync.destroy() (which runs AFTER all barriers + save + PollForEndOfNewDaySync).
When isGameAvailable() == false, the server sends message type 11 (Client_WaitForHostAvailability); the client shows "Waiting for host event" in FarmhandMenu and times out after 45s.
checkFarmhandRequest with isGameAvailable() == false sends type 11 and registers a whenGameAvailable callback that calls sendAvailableFarmhands (NOT Check()); the client bounces back to FarmhandMenu.

When a client disconnects during the barrier: playerDisconnected() enqueues into disconnectingFarmers, removeDisconnectedFarmers() removes the entry from otherFarmers, and with empty otherFarmers the barrierReady() check returns true immediately.
Every instance runs the same barrierReady() against its own otherFarmers, farmhands included, and a farmhand is unmodded. A connected farmer that never checks in (an unauthenticated lobby player never receives newDaySync) therefore stalls every farmhand at the first barrier, and the host at the next one, however the host filters its own check. The server closes this by sending the barrier check-in on the excluded farmer's behalf (LobbyService.BarrierReady_Postfix).

Prescriptive cabin invariants are in .claude/rules/cabin-system.md. Reference-only:

BuildStartingCabins uses map-designated positions (tile 29/30 in the Paths layer), capped by Game1.startingCabins.

LAN-only servers (AllowIpConnections=true, no Steam account configured) never write an invite code. InviteCodeFile.Read() returns null in that configuration.