Adv 2.0 D&D Phase 12 E1b: supply system (procurement, burn, depletion)

Pure logic per gogobee_expedition_system.md §4. Tier→base SU/day and
harsh-conditions multiplier tables (§4.1). Standard pack 10 SU/50c
(max 3) and deluxe pack 20 SU/90c (max 1) per §4.2. SupplyPurchase
struct with Validate / Total / Cost. Depletion brackets (>25 / 10–25
/ 1–9 / 0) → roll modifier and long-rest gate per §4.3. applyDailyBurn
deducts and clamps; resets the per-day forage flag.

Procurement is exposed as a pure helper here; the !expedition start
flow wires it interactively in E1c.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/dnd_expedition_supplies.go

@@ -0,0 +1,176 @@
+package plugin
+
+import (
+	"fmt"
+)
+
+// Phase 12 E1b — Supply procurement, daily burn, and depletion effects.
+// Spec: gogobee_expedition_system.md §4.
+
+// Pack pricing/yield. §4.2.
+const (
+	SupplyPackStandardSU    = 10
+	SupplyPackStandardCoins = 50
+	SupplyPackStandardMax   = 3 // per expedition
+
+	SupplyPackDeluxeSU    = 20
+	SupplyPackDeluxeCoins = 90
+	SupplyPackDeluxeMax   = 1 // per expedition
+
+	SupplyForageMaxSU = 4 // 1d4 cap (Ranger, WIS DC 12) — §4.2
+)
+
+// supplyDailyBurn returns the base SU/day for a zone tier (§4.1).
+// Tier 1: 1, Tier 2: 1.5, Tier 3: 2, Tier 4: 3, Tier 5: 4.
+func supplyDailyBurn(tier ZoneTier) float32 {
+	switch tier {
+	case ZoneTierBeginner:
+		return 1.0
+	case ZoneTierApprentice:
+		return 1.5
+	case ZoneTierJourneyman:
+		return 2.0
+	case ZoneTierVeteran:
+		return 3.0
+	case ZoneTierLegendary:
+		return 4.0
+	}
+	return 1.0
+}
+
+// supplyHarshMultiplier returns the harsh-conditions multiplier (§4.1).
+// Tier 1×1, Tier 2×1.5, Tier 3×2, Tier 4×2.5, Tier 5×3.
+func supplyHarshMultiplier(tier ZoneTier) float32 {
+	switch tier {
+	case ZoneTierBeginner:
+		return 1.0
+	case ZoneTierApprentice:
+		return 1.5
+	case ZoneTierJourneyman:
+		return 2.0
+	case ZoneTierVeteran:
+		return 2.5
+	case ZoneTierLegendary:
+		return 3.0
+	}
+	return 1.0
+}
+
+// SupplyDepletionState classifies remaining supply ratio (§4.3).
+type SupplyDepletionState int
+
+const (
+	SupplyNormal SupplyDepletionState = iota
+	SupplyRationing
+	SupplySevereRationing
+	SupplyStarvation
+)
+
+// supplyDepletion returns the depletion state for a supplies snapshot.
+// Brackets: >25% normal, 10–25% rationing, 1–9% severe, 0 starvation.
+func supplyDepletion(s ExpeditionSupplies) SupplyDepletionState {
+	if s.Max <= 0 {
+		return SupplyNormal
+	}
+	if s.Current <= 0 {
+		return SupplyStarvation
+	}
+	pct := (s.Current / s.Max) * 100
+	switch {
+	case pct >= 25:
+		return SupplyNormal
+	case pct >= 10:
+		return SupplyRationing
+	default:
+		return SupplySevereRationing
+	}
+}
+
+// supplyRollModifier maps depletion state to the universal roll penalty
+// applied to attack/skill rolls (§4.3). Starvation has its own CON bleed
+// handled elsewhere; the roll mod for starvation matches severe rationing
+// floor so combat math doesn't divide by zero.
+func supplyRollModifier(state SupplyDepletionState) int {
+	switch state {
+	case SupplyRationing:
+		return -1
+	case SupplySevereRationing, SupplyStarvation:
+		return -2
+	}
+	return 0
+}
+
+// supplyAllowsLongRest returns false when severe rationing (§4.3) blocks
+// long rests. Starvation also blocks (forced extraction is the next step).
+func supplyAllowsLongRest(state SupplyDepletionState) bool {
+	return state == SupplyNormal || state == SupplyRationing
+}
+
+// SupplyPurchase represents an expedition outfitting choice.
+type SupplyPurchase struct {
+	StandardPacks int
+	DeluxePacks   int
+}
+
+// Total SU yield from a purchase.
+func (p SupplyPurchase) Total() float32 {
+	return float32(p.StandardPacks*SupplyPackStandardSU + p.DeluxePacks*SupplyPackDeluxeSU)
+}
+
+// Total cost in coins.
+func (p SupplyPurchase) Cost() int {
+	return p.StandardPacks*SupplyPackStandardCoins + p.DeluxePacks*SupplyPackDeluxeCoins
+}
+
+// Validate enforces §4.2 caps (max 3 standard, max 1 deluxe, no negatives,
+// at least one pack purchased — an expedition without supplies is not a
+// legal start).
+func (p SupplyPurchase) Validate() error {
+	if p.StandardPacks < 0 || p.DeluxePacks < 0 {
+		return fmt.Errorf("supply pack counts must be non-negative")
+	}
+	if p.StandardPacks > SupplyPackStandardMax {
+		return fmt.Errorf("standard packs capped at %d (got %d)", SupplyPackStandardMax, p.StandardPacks)
+	}
+	if p.DeluxePacks > SupplyPackDeluxeMax {
+		return fmt.Errorf("deluxe packs capped at %d (got %d)", SupplyPackDeluxeMax, p.DeluxePacks)
+	}
+	if p.StandardPacks == 0 && p.DeluxePacks == 0 {
+		return fmt.Errorf("expedition requires at least one supply pack")
+	}
+	return nil
+}
+
+// makeSupplies builds an ExpeditionSupplies from a purchase, sized for the
+// given zone tier. Harsh-conditions multiplier defaults to 1 (off);
+// upgraded by E2/E3 events.
+func makeSupplies(tier ZoneTier, p SupplyPurchase) ExpeditionSupplies {
+	total := p.Total()
+	return ExpeditionSupplies{
+		Current:       total,
+		Max:           total,
+		DailyBurn:     supplyDailyBurn(tier),
+		HarshMod:      1.0,
+		PacksStandard: p.StandardPacks,
+		PacksDeluxe:   p.DeluxePacks,
+	}
+}
+
+// applyDailyBurn deducts one day's supplies from the snapshot (caller
+// persists). Returns the new snapshot and the SU consumed.
+func applyDailyBurn(s ExpeditionSupplies, harshActive bool) (ExpeditionSupplies, float32) {
+	burn := s.DailyBurn
+	if harshActive {
+		burn *= s.HarshMod
+		if burn == s.DailyBurn { // HarshMod was 0 / unset
+			burn = s.DailyBurn
+		}
+	}
+	s.Current -= burn
+	if s.Current < 0 {
+		s.Current = 0
+	}
+	// Reset per-day forage flag.
+	s.ForagedToday = false
+	return s, burn
+}