N7/E4: Seasonal events — 1-week holiday skins

Four anchor holidays (Hallowtide, Midwinter Feast, Sweethearts' Revel,
First Bloom) each get a 7-day window (anchor ±3 days) that layers three
things on the world, all reusing existing machinery:

  1. A themed Omen that overrides the weekly rotation. Reuses the B3 omen
     effect fields, so the non-combat rule holds; kept behind activeOmen's
     simOmenDisabled guard (and activeSeason honours it too) so no season
     path can reach the balance sim or move the golden.
  2. A curated curio shelf at Luigi's — existing registry items rotated to
     the front of dailyCuriosStock, so no net-new power enters the economy.
     Off-season output is byte-identical to before.
  3. A themed road visitor via the ambient seam — a season_visitor event
     that leaves a sellable keepsake + coin gift. No combat: the ambient
     seam still never opens a fight.

Pure function of the UTC date + anchor calendar — no schema, ticker, or
persistence, same discipline as the Omen and holiday calendar. Season
banner rides the existing morning DM (no net-new scheduled message).

go test ./internal/plugin ./internal/db green; combat golden byte-identical.

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

internal/plugin/adventure_omen.go

@@ -84,6 +84,11 @@ func activeOmen() omen {
 	if simOmenDisabled {
 		return omen{Key: "none", Name: "None"}
 	}
+	// N7/E4 — a live season's themed omen overrides the weekly rotation. Kept
+	// behind the simOmenDisabled guard above so the balance sim never sees it.
+	if s, ok := activeSeason(); ok {
+		return s.Omen
+	}
 	y, w := time.Now().UTC().ISOWeek()
 	return omenForWeek(y, w)
 }

internal/plugin/adventure_render.go

@@ -318,6 +318,14 @@ func renderAdvMorningDM(userID id.UserID, equip map[EquipmentSlot]*AdvEquipment,
 	sb.WriteString(omenMorningLine(activeOmen()))
 	sb.WriteString("\n\n")
 
+	// N7/E4 — a live season adds a "what's live this week" banner under the Omen
+	// line (its themed omen already rode the line above). Same morning DM, no
+	// net-new scheduled message.
+	if s, ok := activeSeason(); ok {
+		sb.WriteString(seasonBannerLine(s))
+		sb.WriteString("\n\n")
+	}
+
 	// Pick a morning greeting
 	greeting, _ := advPickFlavor(MorningDM, userID, "morning_dm")
 	displayName, _ := loadDisplayName(userID)

internal/plugin/adventure_season.go

@@ -0,0 +1,199 @@
+package plugin
+
+import (
+	"time"
+)
+
+// N7/E4 — Seasonal events (gogobee_engagement_plan.md §E4).
+//
+// A season is a 1-week skin anchored to a real holiday. Unlike isHolidayToday()
+// (a single UTC day, worth a double-action) and unlike the Omen (an ISO-week
+// rotation), a season spans a window around its anchor date and layers three
+// things on top of the world for that week:
+//
+//   1. A themed world modifier — a reskinned Omen that OVERRIDES the weekly
+//      rotation (see activeOmen). It reuses the omen effect fields, so the same
+//      non-combat rule holds: a season never touches SimulateCombat or the turn
+//      engine. That is enforced structurally — activeSeason() honours
+//      simOmenDisabled exactly as activeOmen() does, so the balance sim never
+//      sees a season through any path, and the season Omen only reaches the sim's
+//      omen seams behind activeOmen's own simOmenDisabled guard.
+//   2. A limited-time curio shelf at Luigi's — a curated selection of existing
+//      registry items (dailyCuriosStock). No new power enters the game; the shelf
+//      just changes which items rotate in for the week.
+//   3. A themed visitor on the road — a season-gated ambient event that leaves a
+//      small keepsake and a coin gift (expedition_ambient.go). No combat: the
+//      ambient seam has never opened a fight and this does not change that.
+//
+// A season is a pure function of the UTC date and the anchor calendar, so it
+// needs no schema, no ticker state, and no persistence — the same discipline as
+// the Omen and the holiday calendar.
+
+// seasonHalfWidth is the number of days on each side of the anchor date that the
+// season is live. 3 → a 7-day window (anchor ± 3).
+const seasonHalfWidth = 3
+
+// seasonVisitor is the themed ambient event a season adds to the road. It never
+// resolves combat — it leaves a sellable keepsake and a small coin gift.
+type seasonVisitor struct {
+	Weight        int      // relative weight in the ambient pick
+	FlavorPool    []string // scene narration lines for the visit
+	Keepsake      string   // sellable trophy left behind
+	KeepsakeValue int64    // coin baseline of the keepsake
+	Coins         int      // flat coin gift
+}
+
+// season is one holiday skin.
+type season struct {
+	Key      string                   // stable id (tests, logs)
+	Name     string                   // player-facing, e.g. "Hallowtide"
+	Emoji    string                   // banner emoji
+	Anchor   func(year int) time.Time // the anchor date for a given year (UTC)
+	Blurb    string                   // one-line "what's live this week" banner copy
+	Omen     omen                     // themed override omen (non-combat fields only)
+	CurioIDs []string                 // curated registry IDs for Luigi's shelf
+	Visitor  seasonVisitor            // the road visitor
+}
+
+// fixedAnchor builds an Anchor for a fixed month/day holiday.
+func fixedAnchor(month time.Month, day int) func(int) time.Time {
+	return func(year int) time.Time {
+		return time.Date(year, month, day, 0, 0, 0, 0, time.UTC)
+	}
+}
+
+// seasonTable is the set of anchor holidays that get a skin. Order is match
+// order; the windows are disjoint so it never matters, but keep them disjoint.
+var seasonTable = []season{
+	{
+		Key: "hallowtide", Name: "Hallowtide", Emoji: "🎃",
+		Anchor: fixedAnchor(time.October, 31),
+		Blurb:  "the veil's thin — spooky curios at Luigi's and things going bump on the road, all week",
+		Omen: omen{
+			Key: "hallowtide", Name: "Hallowtide",
+			TwinBee:              "The veil's gone thin for Hallowtide — reagents and oddments are spilling through from somewhere I'd rather not name. I'm grabbing them while they're here.",
+			ConsumableChanceMult: 2.0,
+		},
+		CurioIDs: []string{
+			"cloak_of_arachnida", "demon_armor", "goggles_of_night",
+			"slippers_of_spider_climbing", "staff_of_swarming_insects",
+			"sword_of_life_stealing", "dagger_of_venom", "cloak_of_the_bat",
+		},
+		Visitor: seasonVisitor{
+			Weight: 12,
+			FlavorPool: []string{
+				"A gourd-headed thing shuffles out of the dark, sets a little carved lantern on your bedroll, and shuffles right back into it.",
+				"Something small and many-legged skitters past, drops a trinket at your feet as if in tribute, and is gone before you can look twice.",
+				"A cold draft carries a whisper and a gift — a carved gourd, still faintly warm, left where you'll find it come morning.",
+			},
+			Keepsake: "Carved Gourd Lantern", KeepsakeValue: 60, Coins: 8,
+		},
+	},
+	{
+		Key: "midwinter", Name: "Midwinter Feast", Emoji: "❄️",
+		Anchor: fixedAnchor(time.December, 25),
+		Blurb:  "gifts by every door — a free pack for anyone heading out, warm curios at Luigi's, all week",
+		Omen: omen{
+			Key: "midwinter", Name: "Midwinter Feast",
+			TwinBee:            "It's Midwinter, and someone's been leaving gifts by the outfitter's door. There's a free pack in it for anyone heading out — and I set off in high spirits.",
+			SupplyFreebiePacks: 1,
+			StartMoodBonus:     5,
+		},
+		CurioIDs: []string{
+			"boots_of_the_winterlands", "frost_brand", "ring_of_warmth",
+			"staff_of_frost", "potion_of_healing", "staff_of_healing",
+		},
+		Visitor: seasonVisitor{
+			Weight: 12,
+			FlavorPool: []string{
+				"A bundled figure passes your camp without a word, leaves a frost-glass bauble hanging where the firelight catches it, and trudges on into the snow.",
+				"You wake to find your pack a little heavier — a wrapped bauble and a handful of coin, and a single set of bootprints leading away.",
+				"Bells, faint and far off. By the time they fade there's a bauble on your bedroll that wasn't there before.",
+			},
+			Keepsake: "Frost-Glass Bauble", KeepsakeValue: 60, Coins: 10,
+		},
+	},
+	{
+		Key: "sweethearts", Name: "Sweethearts' Revel", Emoji: "💗",
+		Anchor: fixedAnchor(time.February, 14),
+		Blurb:  "the arena crowd's throwing coin — fat purses, charming curios at Luigi's, all week",
+		Omen: omen{
+			Key: "sweethearts", Name: "Sweethearts' Revel",
+			TwinBee:         "The whole town's giddy for Sweethearts' week — the arena crowd's throwing coin like confetti. Win pretty and the purse pays twenty over the odds.",
+			ArenaPayoutMult: 1.20,
+		},
+		CurioIDs: []string{
+			"eyes_of_charming", "philter_of_love", "staff_of_charming",
+			"luck_blade", "stone_of_good_luck_luckstone", "pearl_of_power",
+			"glamoured_studded_leather",
+		},
+		Visitor: seasonVisitor{
+			Weight: 12,
+			FlavorPool: []string{
+				"A courier in festival colours finds you even out here, presses a ribbon-wrapped token into your hand with a wink, and hurries back the way they came.",
+				"A paper heart, pinned to a token and left on your pack — 'from an admirer,' it says, and nothing else.",
+				"Someone's left a ribbon-wrapped keepsake by the trail marker, addressed to no one and everyone. You pocket it.",
+			},
+			Keepsake: "Ribbon-Wrapped Token", KeepsakeValue: 55, Coins: 10,
+		},
+	},
+	{
+		Key: "first_bloom", Name: "First Bloom", Emoji: "🌷",
+		Anchor: func(year int) time.Time { return easterDate(year) },
+		Blurb:  "everything's growing eager — fuller harvests, green curios at Luigi's, all week",
+		Omen: omen{
+			Key: "first_bloom", Name: "First Bloom",
+			TwinBee:           "First Bloom's on us — everything's growing twice as eager and the woods feel calm with it. Every gather comes up fuller, and the dread's slow to rise.",
+			HarvestYieldBonus: 1,
+			ThreatDriftReduce: 1,
+		},
+		CurioIDs: []string{
+			"bag_of_beans", "potion_of_growth", "potion_of_animal_friendship",
+			"ring_of_animal_influence", "horn_of_valhalla", "sword_of_life_stealing",
+		},
+		Visitor: seasonVisitor{
+			Weight: 12,
+			FlavorPool: []string{
+				"A hare the size of a hound lopes up, regards you with unsettling calm, and leaves a pressed blossom on the ground before bounding off.",
+				"New vines have crept over your gear in the night — and tucked among them, a perfect pressed blossom and a little coin, as if the woods were paying rent.",
+				"The undergrowth parts on its own, sets a spring blossom at your feet, and closes again. You decide not to question it.",
+			},
+			Keepsake: "Pressed Spring Blossom", KeepsakeValue: 50, Coins: 8,
+		},
+	},
+}
+
+// activeSeason returns the season whose window contains today (UTC), or false.
+// Honours simOmenDisabled so the balance sim never observes a season through any
+// path — the same neutralisation activeOmen applies to the weekly rotation.
+func activeSeason() (season, bool) {
+	if simOmenDisabled {
+		return season{}, false
+	}
+	now := time.Now().UTC()
+	today := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, time.UTC)
+	return seasonForDate(today)
+}
+
+// seasonForDate is the pure core of activeSeason, split out for tests. The
+// anchor is checked against the target year and its neighbours so a window that
+// straddles a year boundary still resolves.
+func seasonForDate(today time.Time) (season, bool) {
+	for _, s := range seasonTable {
+		for _, yr := range []int{today.Year() - 1, today.Year(), today.Year() + 1} {
+			a := s.Anchor(yr)
+			lo := a.AddDate(0, 0, -seasonHalfWidth)
+			hi := a.AddDate(0, 0, seasonHalfWidth)
+			if !today.Before(lo) && !today.After(hi) {
+				return s, true
+			}
+		}
+	}
+	return season{}, false
+}
+
+// seasonBannerLine is the "what's live this week" one-liner surfaced under the
+// Omen line in the morning DM. Empty when no season is active.
+func seasonBannerLine(s season) string {
+	return s.Emoji + " **" + s.Name + "** is here — " + s.Blurb + "."
+}

internal/plugin/adventure_season_test.go

@@ -0,0 +1,120 @@
+package plugin
+
+import (
+	"testing"
+	"time"
+)
+
+func date(y int, m time.Month, d int) time.Time {
+	return time.Date(y, m, d, 0, 0, 0, 0, time.UTC)
+}
+
+// TestSeasonForDate_ActiveOnAnchor — every season resolves on its own anchor day
+// and both window edges (±seasonHalfWidth), and is dark one day past each edge.
+func TestSeasonForDate_ActiveOnAnchor(t *testing.T) {
+	for _, s := range seasonTable {
+		a := s.Anchor(2026)
+		for _, off := range []int{-seasonHalfWidth, 0, seasonHalfWidth} {
+			got, ok := seasonForDate(a.AddDate(0, 0, off))
+			if !ok || got.Key != s.Key {
+				t.Errorf("%s: day offset %d → (%v, %q), want (true, %q)",
+					s.Key, off, ok, got.Key, s.Key)
+			}
+		}
+		for _, off := range []int{-seasonHalfWidth - 1, seasonHalfWidth + 1} {
+			if got, ok := seasonForDate(a.AddDate(0, 0, off)); ok {
+				t.Errorf("%s: day offset %d should be dark, got %q", s.Key, off, got.Key)
+			}
+		}
+	}
+}
+
+// TestSeasonForDate_WindowsDisjoint — no calendar day resolves to two seasons, so
+// the first-match order in seasonForDate never hides overlapping content.
+func TestSeasonForDate_WindowsDisjoint(t *testing.T) {
+	for y := 2024; y <= 2030; y++ {
+		day := date(y, time.January, 1)
+		end := date(y+1, time.January, 1)
+		for day.Before(end) {
+			matches := 0
+			for _, s := range seasonTable {
+				for _, yr := range []int{day.Year() - 1, day.Year(), day.Year() + 1} {
+					a := s.Anchor(yr)
+					if !day.Before(a.AddDate(0, 0, -seasonHalfWidth)) &&
+						!day.After(a.AddDate(0, 0, seasonHalfWidth)) {
+						matches++
+						break
+					}
+				}
+			}
+			if matches > 1 {
+				t.Fatalf("%s resolves to %d seasons (windows must be disjoint)",
+					day.Format("2006-01-02"), matches)
+			}
+			day = day.AddDate(0, 0, 1)
+		}
+	}
+}
+
+// TestSeasonTable_CuratedItemsExist — every curated curio ID is a real registry
+// item, so a season's shelf never lists a phantom the buyer can't purchase. Guards
+// against typos and registry edits (mirrors TestTemperMaterialsAreObtainable).
+func TestSeasonTable_CuratedItemsExist(t *testing.T) {
+	for _, s := range seasonTable {
+		if len(s.CurioIDs) == 0 {
+			t.Errorf("%s has no curated curios", s.Key)
+		}
+		for _, id := range s.CurioIDs {
+			if _, ok := magicItemRegistry[id]; !ok {
+				t.Errorf("%s curio %q is not in magicItemRegistry", s.Key, id)
+			}
+		}
+	}
+}
+
+// TestSeasonTable_OmenIsNonCombat — a season's themed omen carries an effect and
+// only touches the non-combat omen levers, so overriding the weekly rotation with
+// it can never move the combat golden or the balance corpus. §E4/§B3.
+func TestSeasonTable_OmenIsNonCombat(t *testing.T) {
+	for _, s := range seasonTable {
+		o := s.Omen
+		hasEffect := o.HarvestYieldBonus > 0 || o.SupplyFreebiePacks > 0 ||
+			o.StartMoodBonus > 0 || o.ArenaPayoutMult > 1.0 ||
+			o.ConsumableChanceMult > 1.0 || o.ThreatDriftReduce > 0
+		if !hasEffect {
+			t.Errorf("%s omen has no active effect", s.Key)
+		}
+		if o.Name == "" || o.TwinBee == "" {
+			t.Errorf("%s omen missing player-facing copy", s.Key)
+		}
+	}
+}
+
+// TestSeasonTable_VisitorRewardComplete — every season's road visitor has flavor,
+// a named keepsake, and a positive keepsake value, so applyAmbientEffect always
+// has a real reward to grant.
+func TestSeasonTable_VisitorRewardComplete(t *testing.T) {
+	for _, s := range seasonTable {
+		v := s.Visitor
+		if len(v.FlavorPool) == 0 {
+			t.Errorf("%s visitor has no flavor", s.Key)
+		}
+		if v.Keepsake == "" || v.KeepsakeValue <= 0 {
+			t.Errorf("%s visitor keepsake incomplete: %q value %d", s.Key, v.Keepsake, v.KeepsakeValue)
+		}
+		if v.Weight <= 0 {
+			t.Errorf("%s visitor has non-positive weight %d", s.Key, v.Weight)
+		}
+	}
+}
+
+// TestActiveSeason_NeutralizedInSim — the balance sim must never observe a season
+// through any path; activeSeason honours simOmenDisabled exactly as activeOmen does.
+func TestActiveSeason_NeutralizedInSim(t *testing.T) {
+	prev := simOmenDisabled
+	simOmenDisabled = true
+	defer func() { simOmenDisabled = prev }()
+	if s, ok := activeSeason(); ok {
+		t.Fatalf("activeSeason returned %q while simOmenDisabled", s.Key)
+	}
+}

internal/plugin/adventure_shop.go

@@ -1146,13 +1146,38 @@ func dailyCuriosStock() []MagicItem {
 	rng := rand.New(rand.NewPCG(seed, seed^0x9e3779b97f4a7c15))
 	rng.Shuffle(len(ids), func(i, j int) { ids[i], ids[j] = ids[j], ids[i] })
 
-	n := curiosStockSize
-	if n > len(ids) {
-		n = len(ids)
+	target := curiosStockSize
+	if target > len(ids) {
+		target = len(ids)
+	}
+	stock := make([]MagicItem, 0, target)
+	seen := make(map[string]bool)
+
+	// N7/E4 — a live season features its curated items at the front of the shelf,
+	// displacing the day's rotation. They are existing registry items, so no
+	// net-new power enters the economy for the week; only which items rotate in.
+	if s, ok := activeSeason(); ok {
+		for _, id := range s.CurioIDs {
+			if mi, ok := magicItemRegistry[id]; ok && !seen[id] {
+				stock = append(stock, mi)
+				seen[id] = true
+			}
+		}
+		if len(stock) > target {
+			target = len(stock)
+		}
+	}
+
+	// Fill the remaining slots from the day's deterministic rotation.
+	for _, id := range ids {
+		if len(stock) >= target {
+			break
+		}
+		if seen[id] {
+			continue
 		}
-	stock := make([]MagicItem, 0, n)
-	for _, id := range ids[:n] {
 		stock = append(stock, magicItemRegistry[id])
+		seen[id] = true
 	}
 	// Stable display order: rarity ascending, then name.
 	sort.Slice(stock, func(i, j int) bool {
@@ -1167,7 +1192,11 @@ func dailyCuriosStock() []MagicItem {
 
 func (p *AdventurePlugin) luigiCuriosView(userID id.UserID, balance float64) string {
 	var sb strings.Builder
+	if s, ok := activeSeason(); ok {
+		sb.WriteString(fmt.Sprintf("%s **Curios** — %s stock, this week only\n", s.Emoji, s.Name))
+	} else {
 		sb.WriteString("🔮 **Curios** — fresh stock daily at dawn\n")
+	}
 	sb.WriteString(fmt.Sprintf("💰 Balance: €%.0f\n\n", balance))
 
 	factor := p.shopSessionPriceFactor(userID)

internal/plugin/expedition_ambient.go

@@ -230,7 +230,7 @@ func ambientEventMonologue() ambientEvent {
 // it's cheap to test in isolation and free of package-level state.
 func ambientEvents() []ambientEvent {
 	always := func(*Expedition) bool { return true }
-	return []ambientEvent{
+	events := []ambientEvent{
 		ambientEventMonologue(),
 		{
 			Kind:     "small_find",
@@ -280,6 +280,19 @@ func ambientEvents() []ambientEvent {
 			},
 		},
 	}
+	// N7/E4 — a live season adds a themed road visitor. Non-combat: it leaves a
+	// keepsake and a coin gift, resolved in applyAmbientEffect. The pool and
+	// reward come from activeSeason(); the ambient seam is production-only, so
+	// this never reaches the balance sim.
+	if s, ok := activeSeason(); ok && len(s.Visitor.FlavorPool) > 0 {
+		events = append(events, ambientEvent{
+			Kind:     "season_visitor",
+			Pool:     s.Visitor.FlavorPool,
+			Weight:   s.Visitor.Weight,
+			Eligible: func(*Expedition) bool { return true },
+		})
+	}
+	return events
 }
 
 // pickAmbientEvent runs a weighted pick over eligible events. avoidKind
@@ -395,6 +408,39 @@ func (p *AdventurePlugin) applyAmbientEffect(e *Expedition, ev ambientEvent) str
 			return ""
 		}
 		return "+1 HP"
+	case "season_visitor":
+		// N7/E4 — the visitor leaves a sellable keepsake and a coin gift. Re-read
+		// the season so the reward matches the current window even if it turned
+		// over between pick and apply; bail quietly if it just ended.
+		s, ok := activeSeason()
+		if !ok {
+			return ""
+		}
+		v := s.Visitor
+		uid := id.UserID(e.UserID)
+		if err := addAdvInventoryItem(uid, AdvItem{
+			Name:  v.Keepsake,
+			Type:  "trophy",
+			Tier:  1,
+			Value: v.KeepsakeValue,
+		}); err != nil {
+			slog.Warn("expedition: ambient season keepsake", "user", uid, "err", err)
+			return ""
+		}
+		if v.Coins > 0 {
+			if p.euro != nil {
+				p.euro.Credit(uid, float64(v.Coins), "expedition ambient: "+s.Key+" visitor")
+			}
+			if _, err := db.Get().Exec(`
+				UPDATE dnd_expedition
+				   SET coins_earned = coins_earned + ?,
+				       last_activity = CURRENT_TIMESTAMP
+				 WHERE expedition_id = ?`, v.Coins, e.ID); err != nil {
+				slog.Warn("expedition: ambient season coin tally", "expedition", e.ID, "err", err)
+			}
+			return fmt.Sprintf("You keep the %s. +%d coins", v.Keepsake, v.Coins)
+		}
+		return fmt.Sprintf("You keep the %s.", v.Keepsake)
 	}
 	return ""
 }