fix(endgame): "Continue in Singleplayer" resumes the run instead of starting a new one

lib/continue_singleplayer.lua

@@ -0,0 +1,28 @@
+-- Pure decision for G.FUNCS:continue_in_singleplayer (ui/game/functions.lua).
+--
+-- Context: vanilla save_run() synchronously fills in G.ARGS.save_run, but the
+-- actual save.jkr write is dispatched to the async SAVE_MANAGER worker thread
+-- on a later Game:update tick. The old "continue in singleplayer" handler read
+-- save.jkr back off disk immediately after calling save_run(), racing that
+-- write. Because G.F_NO_SAVING is true for an entire MP match, there is also no
+-- prior save on disk to fall back on -- the read reliably came back nil and
+-- G:start_run silently began a brand-new run instead of resuming the match.
+--
+-- The fix captures the in-memory snapshot (G.ARGS.save_run, deep-copied before
+-- G:delete_run() can mutate the live G.GAME table it still references) instead
+-- of round-tripping through disk. This function is the pure "what do we do
+-- with the captured snapshot" decision, so it's testable without any I/O.
+--
+-- savetext: the captured save table, or nil if save_run() didn't produce one.
+-- Returns a plain-data command:
+--   { action = "continue", savetext = <table> }
+--   { action = "abort", reason = <string> }
+function MP.UTILS.decide_continue_singleplayer(savetext)
+	if type(savetext) ~= "table" then
+		return {
+			action = "abort",
+			reason = "continue_in_singleplayer: no save snapshot captured, aborting to avoid starting a fresh run",
+		}
+	end
+	return { action = "continue", savetext = savetext }
+end

tests/test_continue_singleplayer.lua

@@ -0,0 +1,94 @@
+--[[
+  "Continue in singleplayer" resume decision.
+
+  Bug: the end-of-match "Continue in singleplayer" handler
+  (G.FUNCS:continue_in_singleplayer, ui/game/functions.lua) used to call
+  save_run() then immediately read save.jkr back off disk and hand that to
+  G:start_run(). Vanilla save_run() only synchronously fills in
+  G.ARGS.save_run -- the actual disk write is dispatched to the async
+  SAVE_MANAGER worker thread on a later Game:update tick. Reading the file
+  back immediately raced that write, and because G.F_NO_SAVING is true for
+  the whole MP match there was no prior save on disk to fall back on either,
+  so the read reliably came back nil and G:start_run silently began a brand
+  new run instead of resuming.
+
+  The fix (lib/continue_singleplayer.lua) captures G.ARGS.save_run in memory
+  right after save_run() returns and skips the disk round trip entirely.
+  MP.UTILS.decide_continue_singleplayer is the pure "what do we do with the
+  captured snapshot" decision extracted out of that handler: given a captured
+  save table (or nil), decide whether to continue with it or abort rather
+  than silently starting a fresh run.
+
+  This test asserts the new decision function's behavior (green), and -- since
+  the function is newly extracted and has no pre-fix equivalent to run
+  unmodified -- also runs an inlined reproduction of the OLD racy-disk-read
+  logic through the same assertion to demonstrate it fails for the documented
+  reason (red control).
+
+  Run from the repo root:
+    luajit tests/test_continue_singleplayer.lua
+]]
+
+MP = { UTILS = {} }
+
+dofile("lib/continue_singleplayer.lua")
+local decide = assert(MP.UTILS.decide_continue_singleplayer, "MP.UTILS.decide_continue_singleplayer not defined after load")
+
+-- ─── New (fixed) logic: table in vs continue-with-that-table out ───────────
+
+do
+	local savetext = { GAME = { dollars = 4 }, BLIND = { name = "Small Blind" } }
+	local decision = decide(savetext)
+	assert(decision.action == "continue", "expected continue, got " .. tostring(decision.action))
+	assert(decision.savetext == savetext, "decision must carry through the exact captured table")
+end
+
+-- ─── New (fixed) logic: nil guard -- abort, never silently start fresh ─────
+
+do
+	local decision = decide(nil)
+	assert(decision.action == "abort", "expected abort for nil savetext, got " .. tostring(decision.action))
+	assert(type(decision.reason) == "string" and #decision.reason > 0, "abort must carry a non-empty reason")
+	assert(decision.savetext == nil, "abort must not carry a savetext to start_run with")
+end
+
+-- ─── New (fixed) logic: non-table savetext also aborts (defensive) ─────────
+
+do
+	local decision = decide(false)
+	assert(decision.action == "abort", "expected abort for non-table savetext, got " .. tostring(decision.action))
+end
+
+print("continue_singleplayer (fixed): all assertions passed")
+
+-- ─── Regression control: the OLD racy-disk-read logic, inlined ────────────
+--
+-- Mirrors the removed handler body exactly:
+--   G.SAVED_GAME = get_compressed(save_path)
+--   if G.SAVED_GAME ~= nil then G.SAVED_GAME = STR_UNPACK(G.SAVED_GAME) end
+--   G:start_run({ savetext = G.SAVED_GAME })
+--
+-- It always proceeds to start_run (no abort path existed), with whatever the
+-- disk read produced. disk_read_result models get_compressed()+STR_UNPACK():
+-- nil when the async save.jkr write from THIS run hasn't landed yet -- which,
+-- per the bug, is every time, since G.F_NO_SAVING held for the entire MP
+-- match and there's no earlier save.jkr to fall back on.
+local function decide_continue_singleplayer_OLD(disk_read_result)
+	return { action = "continue", savetext = disk_read_result }
+end
+
+do
+	local ok, err = pcall(function()
+		local disk_read_result = nil -- the async write hasn't flushed; no prior save.jkr exists either
+		local decision = decide_continue_singleplayer_OLD(disk_read_result)
+		assert(decision.savetext ~= nil, "BUG: continuing with a nil savetext starts a brand-new run instead of resuming")
+	end)
+	assert(not ok, "control: OLD logic was expected to fail this assertion (nil savetext -> fresh run bug), but it passed")
+	assert(
+		tostring(err):find("BUG: continuing with a nil savetext starts a brand-new run instead of resuming", 1, true),
+		"control failed for the wrong reason: " .. tostring(err)
+	)
+	print("continue_singleplayer (OLD, control): failed as expected -- " .. tostring(err))
+end
+
+print("continue_singleplayer: all checks complete (fix green, pre-fix control red)")

ui/game/functions.lua

@@ -247,30 +247,44 @@ end
 function G.FUNCS:continue_in_singleplayer(e)
 	-- Detach from the multiplayer lobby (the API owns leave now; the legacy
 	-- MP.ACTIONS.leave_lobby() is a no-op here), then update UI. The run itself is kept
-	-- and reloaded below so the player continues solo.
+	-- and reloaded below so the player continues solo. lobby:leave() is async
+	-- (server round trip) for a live lobby, but its completion only clears mod
+	-- focus/UI state (see BalatroMultiplayerAPI on_lobby_disconnected) -- it
+	-- never touches G.GAME/G.ARGS, so it's safe regardless of when it lands
+	-- relative to the reload below.
 	MP.LOBBY.code = nil
 	local lobby = MPAPI.get_current_lobby()
 	if lobby then
 		lobby:leave()
 	end
 	MP.UI.update_connection_status()
 
-	-- Allow saving, save the run, and set up for continuation
+	-- Allow saving and build the save table. save_run() synchronously fills in
+	-- G.ARGS.save_run; the disk write it queues happens later, off-thread, so we
+	-- don't wait for it (see MP.UTILS.decide_continue_singleplayer for why the
+	-- old disk round trip was racy). Deep-copy the snapshot now, before
+	-- G:delete_run() mutates the live G.GAME table it still references
+	-- (e.g. G.GAME.won = false).
 	G.F_NO_SAVING = false
 	G.SETTINGS.current_setup = "Continue"
-	G.FUNCS.wipe_on()
 	save_run()
+	local savetext = G.ARGS and G.ARGS.save_run and copy_table(G.ARGS.save_run) or nil
+
+	local decision = MP.UTILS.decide_continue_singleplayer(savetext)
+	if decision.action == "abort" then
+		sendWarnMessage(decision.reason, "MULTIPLAYER")
+		return
+	end
+
+	G.FUNCS.wipe_on()
 	G:delete_run()
 
-	-- Load the saved game and start a new run in singleplayer
+	-- Resume the captured run in-memory -- no disk round trip.
 	G.E_MANAGER:add_event(Event({
 		trigger = "immediate",
 		no_delete = true,
 		func = function()
-			local profile = G.SETTINGS.profile
-			local save_path = profile .. "/save.jkr"
-			G.SAVED_GAME = get_compressed(save_path)
-			if G.SAVED_GAME ~= nil then G.SAVED_GAME = STR_UNPACK(G.SAVED_GAME) end
+			G.SAVED_GAME = decision.savetext
 			G:start_run({ savetext = G.SAVED_GAME })
 			return true
 		end,