From 87040c55bb5f23af824914823f96c5bc01b44e51 Mon Sep 17 00:00:00 2001
From: Houmgaor <contact@houmgaor.com>
Date: Sat, 21 Feb 2026 00:53:10 +0100
Subject: [PATCH] fix(channelserver): prevent guild RP rollover race and
 redundant stepup query

RolloverDailyRP now locks the guild row with SELECT FOR UPDATE and
re-checks rp_reset_at inside the transaction, so concurrent callers
cannot double-rollover and zero out freshly donated RP.

Gacha stepup entry-type check is now skipped when the row was already
deleted as stale, avoiding a redundant DELETE on step 0.
---
 server/channelserver/handlers_gacha.go | 15 ++++++++-------
 server/channelserver/repo_guild.go     | 15 +++++++++++++++
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/server/channelserver/handlers_gacha.go b/server/channelserver/handlers_gacha.go
index 4245be3f2..d9e6cbbf2 100644
--- a/server/channelserver/handlers_gacha.go
+++ b/server/channelserver/handlers_gacha.go
@@ -327,14 +327,15 @@ func handleMsgMhfGetStepupStatus(s *Session, p mhfpacket.MHFPacket) {
 			s.logger.Error("Failed to reset stale gacha stepup", zap.Error(err))
 		}
 		step = 0
-	}
-
-	hasEntry, _ := s.server.gachaRepo.HasEntryType(pkt.GachaID, step)
-	if !hasEntry {
-		if err := s.server.gachaRepo.DeleteStepup(pkt.GachaID, s.charID); err != nil {
-			s.logger.Error("Failed to reset gacha stepup state", zap.Error(err))
+	} else if err == nil {
+		// Only check for valid entry type if the stepup is fresh
+		hasEntry, _ := s.server.gachaRepo.HasEntryType(pkt.GachaID, step)
+		if !hasEntry {
+			if err := s.server.gachaRepo.DeleteStepup(pkt.GachaID, s.charID); err != nil {
+				s.logger.Error("Failed to reset gacha stepup state", zap.Error(err))
+			}
+			step = 0
 		}
-		step = 0
 	}
 	bf := byteframe.NewByteFrame()
 	bf.WriteUint8(step)
diff --git a/server/channelserver/repo_guild.go b/server/channelserver/repo_guild.go
index 734de2969..68087a3d0 100644
--- a/server/channelserver/repo_guild.go
+++ b/server/channelserver/repo_guild.go
@@ -942,11 +942,26 @@ func (r *GuildRepository) ListInvitedCharacters(guildID uint32) ([]*ScoutedChara
 
 // RolloverDailyRP moves rp_today into rp_yesterday for all members of a guild,
 // then updates the guild's rp_reset_at timestamp.
+// Uses SELECT FOR UPDATE to prevent concurrent rollovers from racing.
 func (r *GuildRepository) RolloverDailyRP(guildID uint32, noon time.Time) error {
 	tx, err := r.db.Begin()
 	if err != nil {
 		return err
 	}
+	// Lock the guild row and re-check whether rollover is still needed.
+	var rpResetAt time.Time
+	if err := tx.QueryRow(
+		`SELECT COALESCE(rp_reset_at, '2000-01-01'::timestamptz) FROM guilds WHERE id = $1 FOR UPDATE`,
+		guildID,
+	).Scan(&rpResetAt); err != nil {
+		_ = tx.Rollback()
+		return err
+	}
+	if !rpResetAt.Before(noon) {
+		// Another goroutine already rolled over; nothing to do.
+		_ = tx.Rollback()
+		return nil
+	}
 	if _, err := tx.Exec(
 		`UPDATE guild_characters SET rp_yesterday = rp_today, rp_today = 0 WHERE guild_id = $1`,
 		guildID,