N5/D1c: the finale — !expedition start epilogue

Closes the Hollow King arc with a solo one-shot boss fight, reached via
`!expedition start epilogue` (intercepted before the zone/loadout
machinery). Unlock: all 24 journal pages found + both Tier-5 zones cleared.

- Encounter: runZoneCombat + renderBossOutcome, the arena's own pattern —
  no supplies, no walk, no party, no new mechanics. The stat block is
  Belaxath's (the abyss boss whose gate "lets one thing come home")
  re-dressed as the King returned in full, HP ×1.25 for a capstone; the
  ability/AC/CR carry over unchanged.
- Reward-once: first clear grants a unique title ("Kingsbane") + one
  Legendary + a games-room notice; later clears are a flavour-only
  rematch. The flag is a dedicated player_meta.epilogue_cleared column,
  latched by an atomic UPDATE (never the bulk save) so the monotonic
  false→true can't be clobbered — same discipline as D1a's journal
  bitmask. A loss costs a death, as any boss fight does.
- Title is written after a fresh character reload so runZoneCombat's
  post-fight HP persist isn't overwritten (the survivalist-milestone
  gotcha).

Golden byte-identical; go test ./... green.

Claude-Session: https://claude.ai/code/session_017mEwUmmS7aQTP2NQXj6rUa

internal/db/db.go

@@ -386,6 +386,13 @@ func runMigrations(d *sql.DB) error {
 		// character save. DEFAULT 0 == "no pages found", correct for every
 		// pre-existing row, so no bootstrap backfill.
 		`ALTER TABLE player_meta ADD COLUMN journal_pages INTEGER NOT NULL DEFAULT 0`,
+		// N5/D1c the Hollow King finale (gogobee_engagement_plan.md §D1). Set once,
+		// the first time a player closes the account — the reward (unique title +
+		// one Legendary) drops only on that first clear; later rematches are
+		// flavour-only. Written by a dedicated atomic UPDATE, never the bulk
+		// character save, so a monotonic false→true flag can't be clobbered.
+		// DEFAULT 0 correct for every pre-existing row, so no bootstrap.
+		`ALTER TABLE player_meta ADD COLUMN epilogue_cleared INTEGER NOT NULL DEFAULT 0`,
 	}
 	for _, stmt := range columnMigrations {
 		if _, err := d.Exec(stmt); err != nil {

internal/plugin/adventure_character.go

@@ -115,6 +115,9 @@ type AdventureCharacter struct {
 	// == page i+1). Read-only overlay from player_meta.journal_pages; writes go
 	// through the atomic grantJournalPageDB, never the bulk character save.
 	JournalPages int64
+	// N5/D1c the finale reward-once flag. True after the first finale clear;
+	// overlay-read, written by the atomic markEpilogueClearedDB.
+	EpilogueCleared bool
 }
 
 type AdvEquipment struct {

internal/plugin/adventure_flavor_campaign.go

@@ -2,9 +2,12 @@ package plugin
 
 import (
 	"fmt"
+	"log/slog"
 	"math/rand/v2"
 	"strings"
 
+	"gogobee/internal/db"
+
 	"maunium.net/go/mautrix/id"
 )
 
@@ -229,7 +232,7 @@ func renderJournal(mask int64) string {
 	}
 
 	if journalComplete(mask) {
-		b.WriteString("\nThe ledger is whole. Every page you needed, you have. What remains is to bring it to him.")
+		b.WriteString("\nThe ledger is whole. Clear both Tier-5 zones and you can follow him to the end — `!expedition start epilogue`.")
 	} else {
 		b.WriteString(fmt.Sprintf("\n_%d pages still scattered._", journalTotalPages-found))
 	}
@@ -246,6 +249,155 @@ func romanNumeral(n int) string {
 	return romanNumerals[n-1]
 }
 
+// ── D1c: the finale ─────────────────────────────────────────────────────────
+
+// finaleTitle is the unique role awarded for the first finale clear.
+const finaleTitle = "Kingsbane"
+
+const epilogueEntryFlavor = "You bring the whole ledger to the Empty Throne. The shape kept warm against his return stirs, and stands, and is finally, fully here."
+
+// hollowKingFinaleMonster is the finale stat block: Belaxath's block — the abyss
+// boss whose gate "was meant to let one thing come home" — re-dressed as the
+// King returned in full, with HP bumped for a capstone. A variant stat block
+// with no new mechanics, per the plan. Built on the fly (not registered in
+// dndBestiary) because runZoneCombat takes the template directly, exactly as the
+// arena bosses do.
+func hollowKingFinaleMonster() DnDMonsterTemplate {
+	m := dndBestiary["boss_belaxath"]
+	m.ID = "boss_hollow_king_finale"
+	m.Name = "The Hollow King, Unhoused"
+	m.HP = int(float64(m.HP) * 1.25)
+	m.Notes = "Finale encounter — the Hollow King returned in full through the abyss gate. Variant of the Balor stat block; no new mechanics."
+	return m
+}
+
+// epilogueUnlocked gates the finale on the whole ledger plus both Tier-5 clears.
+func (p *AdventurePlugin) epilogueUnlocked(char *AdventureCharacter) (bool, string) {
+	if !journalComplete(char.JournalPages) {
+		return false, fmt.Sprintf(
+			"The trail runs cold. You've recovered **%d of %d** journal pages — find them all before you can follow him to the end. (`!adventure journal`)",
+			journalPageCount(char.JournalPages), journalTotalPages)
+	}
+	if !clearedEveryZoneOfTier(db.Get(), char.UserID, ZoneTier(5)) {
+		return false, "You hold the whole ledger, but not the standing to use it. Clear **both** Tier-5 zones — the Dragon's Lair and the Abyss Portal — then come back to the throne."
+	}
+	return true, ""
+}
+
+// handleEpilogueEncounter runs the finale: a single auto-resolved boss fight
+// against the Hollow King's true form, reached via `!expedition start epilogue`.
+// Reward drops only on the first clear (reward-once); later clears are a
+// flavour-only rematch. A loss costs a death, as any boss fight does.
+func (p *AdventurePlugin) handleEpilogueEncounter(ctx MessageContext) error {
+	char, _, err := p.ensureCharacter(ctx.Sender)
+	if err != nil {
+		return p.SendReply(ctx.RoomID, ctx.EventID, "Failed to load your character. Try `!adventure` first.")
+	}
+	if !char.Alive {
+		return p.SendDM(ctx.Sender, "You're in no shape to face him. Mend at `!hospital` first.")
+	}
+	if ok, why := p.epilogueUnlocked(char); !ok {
+		return p.SendDM(ctx.Sender, why)
+	}
+	// Busy guards — the finale is a synchronous auto-resolved fight, so refuse if
+	// anything else is in flight and could collide on HP or run state.
+	if exp, _ := getActiveExpedition(ctx.Sender); exp != nil {
+		return p.SendDM(ctx.Sender, "Finish your expedition before you walk to the Empty Throne.")
+	}
+	if run, _ := getActiveZoneRun(ctx.Sender); run != nil {
+		return p.SendDM(ctx.Sender, "Finish your current zone run first.")
+	}
+	if sess, _ := getActiveCombatSession(ctx.Sender); sess != nil {
+		return p.SendDM(ctx.Sender, "You're already in a fight. Finish it first.")
+	}
+
+	monster := hollowKingFinaleMonster()
+	displayName, _ := loadDisplayName(ctx.Sender)
+	if displayName == "" {
+		displayName = "You"
+	}
+
+	preHP, _ := dndHPSnapshot(ctx.Sender)
+	result, err := p.runZoneCombat(ctx.Sender, monster, 5, bossCombatPhases, 50)
+	if err != nil {
+		slog.Error("epilogue: combat failed", "user", ctx.Sender, "err", err)
+		return p.SendDM(ctx.Sender, "Something went wrong at the throne. Try again in a moment.")
+	}
+	postHP, maxHP := dndHPSnapshot(ctx.Sender)
+	nat20s, nat1s := countNat20sAnd1s(result)
+
+	intro := fmt.Sprintf("👑 **The Empty Throne — %s** (HP %d, AC %d)\n_%s_",
+		monster.Name, monster.HP, monster.AC, epilogueEntryFlavor)
+	phases := RenderCombatLog(result, displayName, monster.Name)
+	outcome := renderBossOutcome(BossOutcomeInputs{
+		// Synthetic ZoneArena keeps twinBeeLine's deterministic pickers off any
+		// real zone's pool, exactly as the arena does.
+		ZoneID:          ZoneArena,
+		RunID:           "epilogue-" + string(ctx.Sender),
+		RoomIdx:         0,
+		Monster:         monster,
+		Result:          result,
+		PreHP:           preHP,
+		PostHP:          postHP,
+		MaxHP:           maxHP,
+		PhaseTwoAt:      0.40,
+		Nat20s:          nat20s,
+		Nat1s:           nat1s,
+		DefeatHeadline:  "💀 The Hollow King folds you into the quiet he keeps. The account goes unpaid a while longer.",
+		VictoryHeadline: fmt.Sprintf("🏆 **The Hollow King falls — and this time stays down.** You finished at **%d/%d HP**.", postHP, maxHP),
+	})
+
+	var tail string
+	if !result.PlayerWon {
+		markAdventureDead(ctx.Sender, "adventure", "the Empty Throne")
+	} else {
+		tail = p.finishEpilogueWin(ctx.Sender, char.EpilogueCleared)
+	}
+
+	_ = p.sendZoneCombatMessages(ctx.Sender, append([]string{intro}, phases...), joinLootLines(outcome, tail))
+	return nil
+}
+
+// finishEpilogueWin grants the reward on a first clear and returns the reward
+// narration; a repeat clear is flavour only. The character is reloaded before
+// the title write so runZoneCombat's post-fight HP persist isn't clobbered.
+func (p *AdventurePlugin) finishEpilogueWin(userID id.UserID, alreadyCleared bool) string {
+	if alreadyCleared {
+		return "_The throne stays empty. You came to be sure. You are sure._"
+	}
+
+	var b strings.Builder
+	b.WriteString("🎖️ **The account is closed.** You are named **" + finaleTitle + "** — the one who unhoused the Hollow King.\n")
+	if mi, ok := pickMagicItemForRarity(RarityLegendary, nil); ok {
+		if line := p.dropMagicItemLoot(userID, mi, LootTierLegendary); line != "" {
+			b.WriteString(line + "\n")
+		}
+	} else {
+		slog.Error("epilogue: no legendary in registry", "user", userID)
+	}
+
+	if fresh, err := loadAdvCharacter(userID); err == nil && fresh != nil {
+		if fresh.Title != finaleTitle {
+			fresh.Title = finaleTitle
+			if err := saveAdvCharacter(fresh); err != nil {
+				slog.Error("epilogue: title save failed", "user", userID, "err", err)
+			}
+		}
+	}
+	if err := markEpilogueClearedDB(userID); err != nil {
+		slog.Error("epilogue: mark cleared failed", "user", userID, "err", err)
+	}
+
+	if gr := gamesRoom(); gr != "" {
+		if dn, _ := loadDisplayName(userID); dn != "" {
+			p.SendMessage(id.RoomID(gr), fmt.Sprintf(
+				"👑 **%s** carried the whole ledger to the Empty Throne and closed the account. The Hollow King is ended. **%s.**",
+				dn, finaleTitle))
+		}
+	}
+	return b.String()
+}
+
 var romanNumerals = []string{
 	"I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX", "X",
 	"XI", "XII", "XIII", "XIV", "XV", "XVI", "XVII", "XVIII", "XIX", "XX",

internal/plugin/adventure_flavor_campaign_test.go

@@ -188,6 +188,97 @@ func TestBossEpilogues_EveryRegisteredZoneHasOne(t *testing.T) {
 	}
 }
 
+func TestHollowKingFinaleMonster_ClonesBelaxathWithBump(t *testing.T) {
+	base := dndBestiary["boss_belaxath"]
+	if base.ID == "" {
+		t.Fatal("boss_belaxath missing from bestiary — finale clones it")
+	}
+	m := hollowKingFinaleMonster()
+	if m.ID != "boss_hollow_king_finale" {
+		t.Errorf("finale ID = %q", m.ID)
+	}
+	if m.Name == base.Name || m.Name == "" {
+		t.Errorf("finale name should differ from Belaxath: %q", m.Name)
+	}
+	if m.HP <= base.HP {
+		t.Errorf("finale HP %d should exceed base %d (capstone bump)", m.HP, base.HP)
+	}
+	// No new mechanics: the ability and defensive profile carry over unchanged.
+	if m.Ability != base.Ability {
+		t.Errorf("finale ability pointer changed — should reuse Belaxath's, no new mechanics")
+	}
+	if m.AC != base.AC || m.CR != base.CR {
+		t.Errorf("finale AC/CR drifted from base: AC %d/%d CR %v/%v", m.AC, base.AC, m.CR, base.CR)
+	}
+}
+
+func TestEpilogueRewardOnce_FlagRoundTrip(t *testing.T) {
+	townTestDB(t)
+	u := id.UserID("@finale:test.invalid")
+
+	if got, err := loadEpilogueCleared(u); err != nil || got {
+		t.Fatalf("fresh player: cleared=%v err=%v, want false/nil", got, err)
+	}
+	if err := markEpilogueClearedDB(u); err != nil {
+		t.Fatalf("mark cleared: %v", err)
+	}
+	if got, err := loadEpilogueCleared(u); err != nil || !got {
+		t.Fatalf("after mark: cleared=%v err=%v, want true/nil", got, err)
+	}
+	// Idempotent.
+	if err := markEpilogueClearedDB(u); err != nil {
+		t.Fatalf("re-mark: %v", err)
+	}
+
+	var c AdventureCharacter
+	c.UserID = u
+	applyPlayerMetaOverlay(&c)
+	if !c.EpilogueCleared {
+		t.Fatalf("overlay did not carry EpilogueCleared")
+	}
+}
+
+func TestEpilogueUnlocked_Gates(t *testing.T) {
+	townTestDB(t)
+	p := &AdventurePlugin{}
+
+	// Incomplete journal → refused, page-count message.
+	partial := &AdventureCharacter{UserID: id.UserID("@u1:test.invalid")}
+	partial.JournalPages = setJournalPageBit(0, 1)
+	ok, why := p.epilogueUnlocked(partial)
+	if ok {
+		t.Fatalf("incomplete journal should not unlock")
+	}
+	if !strings.Contains(why, "journal pages") {
+		t.Errorf("expected page-count refusal, got: %s", why)
+	}
+
+	// Complete journal but no Tier-5 clears → refused, T5 message.
+	full := &AdventureCharacter{UserID: id.UserID("@u2:test.invalid")}
+	for i := 1; i <= journalTotalPages; i++ {
+		full.JournalPages = setJournalPageBit(full.JournalPages, i)
+	}
+	ok, why = p.epilogueUnlocked(full)
+	if ok {
+		t.Fatalf("no T5 clears should not unlock")
+	}
+	if !strings.Contains(why, "Tier-5") {
+		t.Errorf("expected Tier-5 refusal, got: %s", why)
+	}
+}
+
+func TestFinishEpilogueWin_RepeatIsFlavorOnly(t *testing.T) {
+	// The already-cleared branch is pure flavour: no reward, no client calls.
+	p := &AdventurePlugin{}
+	repeat := p.finishEpilogueWin(id.UserID("@u:test.invalid"), true)
+	if strings.Contains(repeat, finaleTitle) {
+		t.Errorf("a repeat clear must not re-award the title: %s", repeat)
+	}
+	if strings.TrimSpace(repeat) == "" {
+		t.Errorf("a repeat clear should still say something")
+	}
+}
+
 func TestTwinBeeJournalReaction_DeterministicAndGuarded(t *testing.T) {
 	if twinBeeJournalReaction(3, 0) != "" {
 		t.Errorf("zero pages should produce no reaction")

internal/plugin/dnd_expedition_cmd.go

@@ -283,6 +283,12 @@ func (p *AdventurePlugin) expeditionCmdStart(ctx MessageContext, c *DnDCharacter
 			formatRespecDuration(remaining)))
 	}
 	zoneTok, packTok := splitFirstWord(rest)
+	// N5/D1c: the campaign finale is reached here but is not a normal zone — it
+	// runs a single auto-resolved boss fight with its own unlock gate, no
+	// supplies, no walk. Intercept before the zone/loadout machinery.
+	if strings.EqualFold(zoneTok, "epilogue") {
+		return p.handleEpilogueEncounter(ctx)
+	}
 	available := zonesForLevel(c.Level)
 	zoneID, ok := resolveZoneInput(zoneTok, available)
 	if !ok {

internal/plugin/player_meta.go

@@ -421,6 +421,33 @@ func grantJournalPageDB(userID id.UserID, page int) error {
 	return err
 }
 
+// loadEpilogueCleared reads the finale reward-once flag (N5/D1c).
+func loadEpilogueCleared(userID id.UserID) (bool, error) {
+	var cleared int
+	err := db.Get().QueryRow(
+		`SELECT epilogue_cleared FROM player_meta WHERE user_id = ?`,
+		string(userID),
+	).Scan(&cleared)
+	if err == sql.ErrNoRows {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+	return cleared != 0, nil
+}
+
+// markEpilogueClearedDB latches the finale reward-once flag atomically, so the
+// monotonic false→true set survives any concurrent character save.
+func markEpilogueClearedDB(userID id.UserID) error {
+	_, err := db.Get().Exec(
+		`INSERT INTO player_meta (user_id, epilogue_cleared) VALUES (?, 1)
+		 ON CONFLICT(user_id) DO UPDATE SET epilogue_cleared = 1`,
+		string(userID),
+	)
+	return err
+}
+
 // HouseState is the in-memory mirror of player_meta's house_* columns. Phase
 // L4e ports housing/mortgage off AdvCharacter (gogobee_legacy_migration.md
 // §6.5). All six fields mutate together at known sites (purchase, payoff,
@@ -1319,6 +1346,9 @@ func applyPlayerMetaOverlay(c *AdventureCharacter) {
 	if mask, err := loadJournalPages(uid); err == nil {
 		c.JournalPages = mask
 	}
+	if cleared, err := loadEpilogueCleared(uid); err == nil {
+		c.EpilogueCleared = cleared
+	}
 	if s, err := loadHouseState(uid); err == nil {
 		c.HouseTier = s.Tier
 		c.HouseLoanBalance = s.LoanBalance