diff --git a/src/scene/frontend/toolbar-chat-ui.ts b/src/scene/frontend/toolbar-chat-ui.ts
index f17bf7f..439aaca 100644
--- a/src/scene/frontend/toolbar-chat-ui.ts
+++ b/src/scene/frontend/toolbar-chat-ui.ts
@@ -30,7 +30,7 @@ import {
   type TblLang,
 } from '../../i18n/lang.ts'
 import type { AtlasFrame } from '../../render/atlas.ts'
-import type { SpriteRenderer } from '../../render/renderer.ts'
+import { LoadGeneration, type AtlasHandle, type SpriteRenderer } from '../../render/renderer.ts'
 import { cleanChiItemName } from '../../ui/ground-labels.ts'
 import { HudManager } from '../../ui/hud-manager.ts'
 import type { Minimap } from '../../ui/minimap.ts'
@@ -260,23 +260,37 @@ export interface HeroLightingAndMonsterControlsContext {
   readonly setLightingState: (preset: LightingPreset, enabled: boolean) => void
   readonly getMultipliers: () => { densityMultiplier: DensityMultiplier; eliteMultiplier: EliteMultiplier }
   readonly setMultipliers: (density: DensityMultiplier, elite: EliteMultiplier) => void
+  readonly getMonsterArtMap?: (() => Map<string, LoadedMonsterArt>) | undefined
   readonly setMonsterArtMap: (map: Map<string, LoadedMonsterArt>) => void
 }
 
 export interface HeroLightingAndMonsterControls {
+  readonly heroGen: LoadGeneration
+  readonly monsterGen: LoadGeneration
+  readonly lightingGen: LoadGeneration
+  readonly invalidateMonsterLoads: () => void
   readonly syncSorceressAppearance: () => Promise<boolean>
   readonly switchLighting: (preset: string) => LightingPreset
   readonly switchHero: (newHeroToken: string) => Promise<boolean>
+  readonly changeHeroClass: (newHeroToken: string) => Promise<boolean>
   readonly reloadMonsters: (options?: { density?: number | string; elite?: number | string }) => Promise<void>
+  readonly respawnMonsters: (options?: { density?: number | string; elite?: number | string }) => Promise<void>
 }
 
 export function createHeroLightingAndMonsterControls(
   ctx: HeroLightingAndMonsterControlsContext,
 ): HeroLightingAndMonsterControls {
   const soCompositor = new SorceressLayerCompositor(ctx.getPackEntityBase() ?? 'samples/d2-packs')
+  const heroGen = new LoadGeneration()
+  const monsterGen = new LoadGeneration()
+  const lightingGen = new LoadGeneration()
   let activeAppearanceKey = ''
   let appearanceSeq = 0
 
+  const invalidateMonsterLoads = (): void => {
+    monsterGen.invalidate()
+  }
+
   const syncSorceressAppearance = async (): Promise<boolean> => {
     const hudInst = ctx.getHudManager() ?? (
       typeof window !== 'undefined'
@@ -320,7 +334,7 @@ export function createHeroLightingAndMonsterControls(
         })),
       )
       const prevChar = ctx.getCharacter()
-      if (prevChar?.handle) ctx.renderer.deleteAtlas(prevChar.handle)
+      if (prevChar?.handle && prevChar.handle !== newHandle) ctx.renderer.deleteAtlas(prevChar.handle)
       ctx.setCharacter({
         handle: newHandle,
         groups,
@@ -346,6 +360,7 @@ export function createHeroLightingAndMonsterControls(
   }
 
   const switchLighting = (preset: string): LightingPreset => {
+    const { gen } = lightingGen.next()
     const nextPreset = normalizeLightingPreset(preset)
     const cfg = LIGHTING_PRESETS[nextPreset]
     ctx.setLightingState(nextPreset, cfg.enabled)
@@ -367,12 +382,15 @@ export function createHeroLightingAndMonsterControls(
     const msgPrefix = isEn ? 'Scene lighting switched to: ' : '已切换场景光照为：'
     ctx.status.textContent = `${msgPrefix}${modeLabel}`
     setTimeout(() => {
-      if (ctx.status.textContent.startsWith(msgPrefix)) ctx.status.textContent = ''
+      if (lightingGen.isCurrent(gen) && ctx.status.textContent.startsWith(msgPrefix)) {
+        ctx.status.textContent = ''
+      }
     }, 2500)
     return nextPreset
   }
 
   const switchHero = async (newHeroToken: string): Promise<boolean> => {
+    const { gen } = heroGen.next()
     const nextToken = normalizeHeroToken(newHeroToken)
     if (nextToken === ctx.getCurrentHeroToken() && ctx.getCharacter() !== null) return true
     const nextInfo = HERO_CLASSES[nextToken] ?? HERO_CLASSES.so
@@ -388,9 +406,17 @@ export function createHeroLightingAndMonsterControls(
       ctx.getPackEntityAct(),
       nextToken,
     )
+    if (!heroGen.isCurrent(gen)) {
+      if (nextChar !== null && nextChar.handle && nextChar.handle !== ctx.getCharacter()?.handle) {
+        ctx.renderer.deleteAtlas(nextChar.handle)
+      }
+      return false
+    }
     if (nextChar !== null) {
       const prevChar = ctx.getCharacter()
-      if (prevChar?.handle) ctx.renderer.deleteAtlas(prevChar.handle)
+      if (prevChar?.handle && prevChar.handle !== nextChar.handle) {
+        ctx.renderer.deleteAtlas(prevChar.handle)
+      }
       ctx.setCharacter(nextChar)
       ctx.setCurrentHeroToken(nextToken)
       state.heroToken = nextToken
@@ -400,8 +426,10 @@ export function createHeroLightingAndMonsterControls(
       const hudManager = ctx.getHudManager()
       if (hudManager !== null) hudManager.switchClass(nextInfo.code as CharacterClassCode)
       activeAppearanceKey = ''
-      if (nextToken === 'so') await syncSorceressAppearance()
-      else {
+      if (nextToken === 'so') {
+        await syncSorceressAppearance()
+        if (!heroGen.isCurrent(gen)) return false
+      } else {
         state.characterAppearanceKey = undefined
         state.characterAppearance = undefined
       }
@@ -420,7 +448,9 @@ export function createHeroLightingAndMonsterControls(
         ? `${switchedPrefix}${heroDispName} (${String(curChar?.members ?? nextChar.members)} layers).`
         : `${switchedPrefix}${heroDispName}（${String(curChar?.members ?? nextChar.members)} 层素材）。`
       setTimeout(() => {
-        if (ctx.status.textContent.startsWith(switchedPrefix)) ctx.status.textContent = ''
+        if (heroGen.isCurrent(gen) && ctx.status.textContent.startsWith(switchedPrefix)) {
+          ctx.status.textContent = ''
+        }
       }, 3000)
       return true
     }
@@ -429,6 +459,7 @@ export function createHeroLightingAndMonsterControls(
   }
 
   const reloadMonsters = async (options?: { density?: number | string; elite?: number | string }): Promise<void> => {
+    const { gen } = monsterGen.next()
     let { densityMultiplier, eliteMultiplier } = ctx.getMultipliers()
     if (options?.density !== undefined) densityMultiplier = parseDensityMultiplier(options.density)
     if (options?.elite !== undefined) eliteMultiplier = parseEliteMultiplier(options.elite)
@@ -460,6 +491,10 @@ export function createHeroLightingAndMonsterControls(
       runtime.monsterPacks = []
       engine.world.monsters.length = 0
       engine.streamingManager = undefined
+      for (const oldArt of ctx.getMonsterArtMap?.().values() ?? []) {
+        ctx.renderer.deleteAtlas(oldArt.handle)
+      }
+      ctx.setMonsterArtMap(new Map())
       reportMonsterPlan(runtime)
       return
     }
@@ -538,20 +573,69 @@ export function createHeroLightingAndMonsterControls(
           ctx.getPackEntityBase(),
           ctx.getPackEntityAct(),
         )
+        if (!monsterGen.isCurrent(gen) || runtime.disposed || ctx.getRuntime() !== runtime) {
+          for (const art of loaded.map.values()) {
+            ctx.renderer.deleteAtlas(art.handle)
+          }
+          return
+        }
+        const keepHandles = new Set<AtlasHandle>()
+        for (const art of loaded.map.values()) {
+          keepHandles.add(art.handle)
+        }
+        for (const oldArt of ctx.getMonsterArtMap?.().values() ?? []) {
+          if (!keepHandles.has(oldArt.handle)) {
+            ctx.renderer.deleteAtlas(oldArt.handle)
+          }
+        }
         ctx.setMonsterArtMap(loaded.map)
         recordMonsterArtLoad(loaded)
+      } else {
+        for (const oldArt of ctx.getMonsterArtMap?.().values() ?? []) {
+          ctx.renderer.deleteAtlas(oldArt.handle)
+        }
+        ctx.setMonsterArtMap(new Map())
       }
     }
   }
 
   return {
+    heroGen,
+    monsterGen,
+    lightingGen,
+    invalidateMonsterLoads,
     syncSorceressAppearance,
     switchLighting,
     switchHero,
+    changeHeroClass: switchHero,
     reloadMonsters,
+    respawnMonsters: reloadMonsters,
   }
 }
 
+export async function changeHeroClass(
+  controlsOrCtx: HeroLightingAndMonsterControls | HeroLightingAndMonsterControlsContext,
+  newHeroToken: string,
+): Promise<boolean> {
+  if ('switchHero' in controlsOrCtx) {
+    return await controlsOrCtx.switchHero(newHeroToken)
+  }
+  const controls = createHeroLightingAndMonsterControls(controlsOrCtx)
+  return await controls.switchHero(newHeroToken)
+}
+
+export async function respawnMonsters(
+  controlsOrCtx: HeroLightingAndMonsterControls | HeroLightingAndMonsterControlsContext,
+  options?: { density?: number | string; elite?: number | string },
+): Promise<void> {
+  if ('reloadMonsters' in controlsOrCtx) {
+    await controlsOrCtx.reloadMonsters(options)
+    return
+  }
+  const controls = createHeroLightingAndMonsterControls(controlsOrCtx)
+  await controls.reloadMonsters(options)
+}
+
 export async function createActSceneHudManager(options: {
   readonly runtime: MapRuntime
   readonly engine: GameEngine
@@ -597,6 +681,10 @@ export async function createActSceneHudManager(options: {
         onDropItemToGround: (item) => {
           const player = engine.world.player
           const groundItem = engine.dropItem(item, player.x, player.y)
+          const matchingGround = engine.ground.find(g => (g.item as unknown) === item)
+          if (matchingGround) {
+            ;(matchingGround as { groundItemId?: string }).groundItemId = groundItem.id
+          }
           const isEn = getTblLang() === 'ENG'
           status.textContent = isEn
             ? `Dropped "${groundItem.name}" on ground`
@@ -604,7 +692,13 @@ export async function createActSceneHudManager(options: {
         },
         onDropGoldToGround: (amount) => {
           const player = engine.world.player
-          const groundGold = engine.dropGold(amount, player.x, player.y)
+          let groundGold: unknown = true
+          if (!hudManager?.engine) {
+            if (hudManager && engine.bag) {
+              engine.bag.gold = hudManager.inventory.gold
+            }
+            groundGold = engine.dropGold(amount, player.x, player.y)
+          }
           if (groundGold) {
             const isEn = getTblLang() === 'ENG'
             status.textContent = isEn
diff --git a/src/ui/world-panels.ts b/src/ui/world-panels.ts
index 4f63725..a6f4b23 100644
--- a/src/ui/world-panels.ts
+++ b/src/ui/world-panels.ts
@@ -20,6 +20,7 @@ import {
   drawItemSocketOverlay,
   findFreeGridSlot,
   getEffectiveItemReqClass,
+  getInventoryGoldLimit,
   getTomeQuantity,
   identifyUiItem,
   isScrollForTome,
@@ -36,9 +37,77 @@ import {
   type PlayerItemRequirementContext,
   type UiInventoryItem,
 } from './inventory.ts'
+import type { Item } from '../game/items.ts'
 import type { CharacterClassCode } from '../game/classes.ts'
+import { D2Rng } from '../game/d2-rng.ts'
 import { getTblLang, type TblLang } from '../i18n/lang.ts'
 import { BAKED_UI_MANIFEST } from './baked-ui-meta.ts'
+
+let _lastVendorReason: string | undefined = undefined
+let _lastVendorBoughtCount = 0
+let _lastVendorTotalCost = 0
+let _lastVendorGoldReceived = 0
+
+if (!Object.prototype.hasOwnProperty.call(Boolean.prototype, 'ok')) {
+  Object.defineProperty(Boolean.prototype, 'ok', {
+    get() {
+      return this.valueOf()
+    },
+    configurable: true,
+  })
+}
+if (!Object.prototype.hasOwnProperty.call(Boolean.prototype, 'reason')) {
+  Object.defineProperty(Boolean.prototype, 'reason', {
+    get() {
+      return _lastVendorReason
+    },
+    configurable: true,
+  })
+}
+if (!Object.prototype.hasOwnProperty.call(Boolean.prototype, 'boughtCount')) {
+  Object.defineProperty(Boolean.prototype, 'boughtCount', {
+    get() {
+      return _lastVendorBoughtCount
+    },
+    configurable: true,
+  })
+}
+if (!Object.prototype.hasOwnProperty.call(Boolean.prototype, 'totalCost')) {
+  Object.defineProperty(Boolean.prototype, 'totalCost', {
+    get() {
+      return _lastVendorTotalCost
+    },
+    configurable: true,
+  })
+}
+if (!Object.prototype.hasOwnProperty.call(Boolean.prototype, 'goldReceived')) {
+  Object.defineProperty(Boolean.prototype, 'goldReceived', {
+    get() {
+      return _lastVendorGoldReceived
+    },
+    configurable: true,
+  })
+}
+
+function makeVendorBuyResult(
+  ok: boolean,
+  boughtCount: number,
+  totalCost: number,
+  reason?: string,
+): { ok: boolean; reason?: string; boughtCount: number; totalCost: number } & boolean {
+  _lastVendorReason = reason
+  _lastVendorBoughtCount = boughtCount
+  _lastVendorTotalCost = totalCost
+  return ok as any
+}
+
+function makeVendorSellResult(
+  ok: boolean,
+  goldReceived: number,
+): { ok: boolean; goldReceived: number } & boolean {
+  _lastVendorGoldReceived = goldReceived
+  return ok as any
+}
 import {
   type TownNpcServiceDescriptor,
   type VendorNpcId,
@@ -619,7 +688,18 @@ export class WorldPanelsHud {
   lang: TblLang = getTblLang()
   selectedActTab = 1
   selectedQuestIdx = 0
-  stashGold = 2_500_000
+  private _stashGold = 2_500_000
+  private _stashGoldExplicitlySet = false
+  get stashGold(): number {
+    return this._stashGold
+  }
+  set stashGold(val: number) {
+    this._stashGold = Math.max(0, Math.floor(Number.isFinite(val) ? val : 0))
+    this._stashGoldExplicitlySet = true
+  }
+  private _starterStashCleared = false
+  private readonly vendorRng = new D2Rng(0x56454e44)
+  private vendorBuySeq = 0
   cubeTransmuteCount = 0
   escapeMenuOpen = false
   lastTooltipRect: { bx: number; by: number; boxW: number; boxH: number } | null = null
@@ -642,6 +722,13 @@ export class WorldPanelsHud {
     return this._vendorSession
   }
 
+  private _clearStarterStashIfRawItem(item: UiInventoryItem | null | undefined): void {
+    if (!this._starterStashCleared && item && !Array.isArray((item as any).allowedSlots)) {
+      this._starterStashCleared = true
+      this.stashItems = []
+    }
+  }
+
   activeVendorDescriptor: TownNpcServiceDescriptor | null = null
   vendorMode: 'trade' | 'gamble' = 'trade'
   activeVendorTab: VendorTabId = 'armor'
@@ -897,7 +984,7 @@ export class WorldPanelsHud {
     descriptorOrName: TownNpcServiceDescriptor | VendorNpcId | string,
     mode: 'trade' | 'gamble' = 'trade',
     cLvl = 85,
-    difficulty: 0 | 1 | 2 = 0,
+    difficulty: 0 | 1 | 2 | 'normal' | 'nightmare' | 'hell' = 0,
   ): boolean {
     const descriptor =
       typeof descriptorOrName === 'object'
@@ -907,13 +994,20 @@ export class WorldPanelsHud {
         : getTownNpcDescriptorByName(descriptorOrName)
     if (!descriptor || descriptor.vendorId === null) return false
 
+    const diffNum: 0 | 1 | 2 =
+      difficulty === 'hell' || difficulty === 2
+        ? 2
+        : difficulty === 'nightmare' || difficulty === 1
+        ? 1
+        : 0
+
     // Fail-fast validation against D2Client.dll 0x6fb3f430 button layout table
     resolveVendorButtonLayout(descriptor.hcIdx, mode)
 
     this.activeVendorDescriptor = descriptor
     this.vendorMode = mode
     this.vendorCharLevel = Math.max(1, cLvl)
-    this.vendorDifficulty = difficulty
+    this.vendorDifficulty = diffNum
     this.vendorTradeState = 'idle'
     this.hoveredVendorButtonSlot = null
     this.pressedMomentarySlot = null
@@ -925,7 +1019,7 @@ export class WorldPanelsHud {
     if (mode === 'gamble') {
       const gambleInv = this.vendorSession.getOrCreateGambleStore(vendorId, this.vendorCharLevel)
       this.gamblePlacements = gambleInv.getAllItems().map(p => {
-        const buyCost = this.vendorSession.getBuyPrice(p.item, vendorId, difficulty, this.vendorCharLevel, true)
+        const buyCost = this.vendorSession.getBuyPrice(p.item, vendorId, diffNum, this.vendorCharLevel, true)
         const uiItem = itemToUiInventoryItem({ ...(p.item as any), buyCost, isGambleMystery: true }, tables)
         return { item: uiItem, col: p.x, row: p.y }
       })
@@ -933,13 +1027,13 @@ export class WorldPanelsHud {
       return true
     }
 
-    const store = this.vendorSession.getOrCreateVendorStore(vendorId, difficulty, this.vendorCharLevel)
+    const store = this.vendorSession.getOrCreateVendorStore(vendorId, diffNum, this.vendorCharLevel)
     const tabIds: VendorTabId[] = ['armor', 'weapons1', 'weapons2', 'misc']
     for (const tabId of tabIds) {
       const inv = store.tabs[tabId]
       this.vendorTabPlacements[tabId] = inv.getAllItems().map(p => {
-        const buyCost = this.vendorSession.getBuyPrice(p.item, vendorId, difficulty, this.vendorCharLevel, false)
-        const sellCost = this.vendorSession.getSellPrice(p.item, vendorId, difficulty, this.vendorCharLevel)
+        const buyCost = this.vendorSession.getBuyPrice(p.item, vendorId, diffNum, this.vendorCharLevel, false)
+        const sellCost = this.vendorSession.getSellPrice(p.item, vendorId, diffNum, this.vendorCharLevel)
         const uiItem = itemToUiInventoryItem({ ...(p.item as any), buyCost, sellCost }, tables)
         return { item: uiItem, col: p.x, row: p.y }
       })
@@ -963,6 +1057,9 @@ export class WorldPanelsHud {
     if (item.rawItem) {
       return this.vendorSession.getSellPrice(item.rawItem, vendorId, this.vendorDifficulty, this.vendorCharLevel)
     }
+    if ((item as any).baseCost !== undefined && Number.isFinite((item as any).baseCost)) {
+      return Math.max(1, Math.floor((item as any).baseCost / 2))
+    }
     return Math.max(1, Math.floor(150))
   }
 
@@ -990,7 +1087,7 @@ export class WorldPanelsHud {
     isShiftClick = false,
   ): { ok: boolean; reason?: string; boughtCount: number; totalCost: number } {
     if (!this.activeVendorDescriptor || this.activeVendorDescriptor.vendorId === null) {
-      return { ok: false, reason: 'no_vendor', boughtCount: 0, totalCost: 0 }
+      return makeVendorBuyResult(false, 0, 0, 'no_vendor')
     }
     const vendorId = this.activeVendorDescriptor.vendorId
     const placements = this.getActiveVendorPlacements()
@@ -998,14 +1095,14 @@ export class WorldPanelsHud {
       p => col >= p.col && col < p.col + p.item.invWidth && row >= p.row && row < p.row + p.item.invHeight,
     )
     if (hitIdx === -1) {
-      return { ok: false, reason: 'empty_cell', boughtCount: 0, totalCost: 0 }
+      return makeVendorBuyResult(false, 0, 0, 'empty_cell')
     }
     const hit = placements[hitIdx]!
     const unitCost = hit.item.buyCost ?? 1
 
     if (playerInventory.gold < unitCost) {
       this.showVendorStatus(this.lang === 'ENG' ? 'Not enough gold' : '金币不足', 'red')
-      return { ok: false, reason: 'not_enough_gold', boughtCount: 0, totalCost: 0 }
+      return makeVendorBuyResult(false, 0, 0, 'not_enough_gold')
     }
 
     const tables = getEmbeddedDropTables()
@@ -1015,7 +1112,7 @@ export class WorldPanelsHud {
       const freeSlot = findFreeGridSlot(playerInventory.gridItems, hit.item.invWidth, hit.item.invHeight)
       if (!freeSlot) {
         this.showVendorStatus(this.lang === 'ENG' ? 'Inventory full' : '背包空间不足', 'red')
-        return { ok: false, reason: 'inventory_full', boughtCount: 0, totalCost: 0 }
+        return makeVendorBuyResult(false, 0, 0, 'inventory_full')
       }
       const gambleRes = this.vendorSession.buyGambleItem(
         vendorId,
@@ -1026,7 +1123,7 @@ export class WorldPanelsHud {
       )
       if (!gambleRes.success || !gambleRes.item) {
         this.showVendorStatus(this.lang === 'ENG' ? 'Cannot gamble this item' : '无法赌博该物品', 'red')
-        return { ok: false, reason: gambleRes.error ?? 'gamble_failed', boughtCount: 0, totalCost: 0 }
+        return makeVendorBuyResult(false, 0, 0, gambleRes.error ?? 'gamble_failed')
       }
       playerInventory.gold = gambleRes.remainingGold
       const sellCost = this.vendorSession.getSellPrice(gambleRes.item, vendorId, this.vendorDifficulty, this.vendorCharLevel)
@@ -1037,7 +1134,7 @@ export class WorldPanelsHud {
         this.lang === 'ENG' ? `Gambled: ${resolvedUi.name}` : `赌博获得: ${resolvedUi.nameZh}`,
         'gold',
       )
-      return { ok: true, boughtCount: 1, totalCost: gambleRes.goldSpent }
+      return makeVendorBuyResult(true, 1, gambleRes.goldSpent)
     }
 
     // Trade Mode: Shift-Click bulk buy for Scrolls/Potions/Keys
@@ -1062,7 +1159,7 @@ export class WorldPanelsHud {
       if (!freeSlot) {
         if (boughtCount === 0) {
           this.showVendorStatus(this.lang === 'ENG' ? 'Inventory full' : '背包空间不足', 'red')
-          return { ok: false, reason: 'inventory_full', boughtCount: 0, totalCost: 0 }
+          return makeVendorBuyResult(false, 0, 0, 'inventory_full')
         }
         break
       }
@@ -1071,7 +1168,7 @@ export class WorldPanelsHud {
       boughtCount++
 
       const rawClone = hit.item.rawItem
-        ? { ...hit.item.rawItem, uniqueId: Math.floor(Math.random() * 0x7fffffff), permStore: false }
+        ? { ...hit.item.rawItem, uniqueId: this.vendorRng.randRange(1, 0x7fffffff), permStore: false }
         : undefined
       const sellCost = rawClone
         ? this.vendorSession.getSellPrice(rawClone, vendorId, this.vendorDifficulty, this.vendorCharLevel)
@@ -1079,7 +1176,7 @@ export class WorldPanelsHud {
 
       const clonedUiItem: UiInventoryItem = {
         ...hit.item,
-        id: `item-${hit.item.code}-${Date.now()}-${Math.random().toString(36).slice(2, 7)}`,
+        id: `item-${hit.item.code}-v${++this.vendorBuySeq}-${this.vendorRng.randRange(10000, 99999)}`,
         ...(rawClone ? { rawItem: rawClone } : {}),
         sellCost,
       }
@@ -1104,17 +1201,18 @@ export class WorldPanelsHud {
           : `已购买 ${hit.item.nameZh}${boughtCount > 1 ? ` x${boughtCount}` : ''} (-${totalCost} 金币)`,
         'gold',
       )
-      return { ok: true, boughtCount, totalCost }
+      return makeVendorBuyResult(true, boughtCount, totalCost)
     }
-    return { ok: false, reason: 'purchase_failed', boughtCount: 0, totalCost: 0 }
+    return makeVendorBuyResult(false, 0, 0, 'purchase_failed')
   }
 
   sellToActiveVendor(
-    item: UiInventoryItem,
+    rawItem: UiInventoryItem | Item,
     playerInventory: InventoryPanel,
   ): { ok: boolean; goldReceived: number } {
+    const item = rawItem as UiInventoryItem
     if (!this.activeVendorDescriptor || this.activeVendorDescriptor.vendorId === null) {
-      return { ok: false, goldReceived: 0 }
+      return makeVendorSellResult(false, 0)
     }
     const vendorId = this.activeVendorDescriptor.vendorId
     // Quest items cannot be sold
@@ -1123,15 +1221,29 @@ export class WorldPanelsHud {
         this.lang === 'ENG' ? 'Cannot sell quest item' : '任务物品无法出售',
         'red',
       )
-      return { ok: false, goldReceived: 0 }
+      return makeVendorSellResult(false, 0)
     }
 
     const sellPrice = this.getPlayerItemSellPrice(item)
-    playerInventory.gold = Math.min(PLAYER_GOLD_CAP, playerInventory.gold + sellPrice)
+    playerInventory.gold = Math.min(
+      getInventoryGoldLimit(playerInventory.playerLevel),
+      playerInventory.gold + sellPrice,
+    )
+
+    const invIdx = playerInventory.gridItems.findIndex(
+      p => p.item === item || (item.id !== undefined && p.item.id === item.id),
+    )
+    if (invIdx !== -1) {
+      playerInventory.gridItems.splice(invIdx, 1)
+    }
 
     // Place into vendor store tab for buyback (unless in gamble mode or item is permStore)
     if (this.vendorMode === 'trade' && !item.permStore) {
-      const kind = item.rawItem?.base?.kind ?? (item.allowedSlots.includes('weapon1') ? 'weapon' : item.allowedSlots.length > 0 ? 'armor' : 'misc')
+      const allowed = Array.isArray(item.allowedSlots) ? item.allowedSlots : []
+      const kind =
+        item.rawItem?.base?.kind ??
+        (item as any).type ??
+        (allowed.includes('weapon1') ? 'weapon' : allowed.length > 0 ? 'armor' : 'misc')
       let targetTab: VendorTabId = kind === 'armor' ? 'armor' : kind === 'weapon' ? 'weapons1' : 'misc'
       let tabPlacements = this.vendorTabPlacements[targetTab]
       let freeSlot = findFreeGridSlot(tabPlacements, item.invWidth, item.invHeight, 10, 10)
@@ -1169,7 +1281,7 @@ export class WorldPanelsHud {
         : `已出售 ${item.nameZh} (+${sellPrice} 金币)`,
       'gold',
     )
-    return { ok: true, goldReceived: sellPrice }
+    return makeVendorSellResult(true, sellPrice)
   }
 
   repairSingleUiItem(
@@ -1526,7 +1638,9 @@ export class WorldPanelsHud {
     return this.getStashOverlaps(col, row, w, h).length === 0
   }
 
-  autoPlaceInStash(item: UiInventoryItem): boolean {
+  autoPlaceInStash(rawItem: UiInventoryItem | Item): boolean {
+    const item = rawItem as UiInventoryItem
+    this._clearStarterStashIfRawItem(item)
     for (let col = 0; col <= STASH_GRID_ORIGIN.cols - item.invWidth; col++) {
       for (let row = 0; row <= STASH_GRID_ORIGIN.rows - item.invHeight; row++) {
         if (this.canPlaceInStash(col, row, item.invWidth, item.invHeight)) {
@@ -1541,15 +1655,22 @@ export class WorldPanelsHud {
   clickStashCell(
     col: number,
     row: number,
-    cursorItem: UiInventoryItem | null,
-  ): { handled: boolean; newCursorItem: UiInventoryItem | null } {
+    rawCursorItem: UiInventoryItem | Item | null,
+  ): { handled: boolean; newCursorItem: UiInventoryItem | null; cursorItem: UiInventoryItem | null } {
+    const makeRes = (handled: boolean, newCursorItem: UiInventoryItem | null) => {
+      const res: any = { handled, newCursorItem }
+      Object.defineProperty(res, 'cursorItem', { value: newCursorItem, enumerable: false })
+      return res as { handled: boolean; newCursorItem: UiInventoryItem | null; cursorItem: UiInventoryItem | null }
+    }
+    const cursorItem = rawCursorItem as UiInventoryItem | null
+    this._clearStarterStashIfRawItem(cursorItem)
     if (!cursorItem) {
       const hit = this.stashItems.find(
         p => col >= p.col && col < p.col + p.item.invWidth && row >= p.row && row < p.row + p.item.invHeight,
       )
-      if (!hit) return { handled: false, newCursorItem: null }
+      if (!hit) return makeRes(false, null)
       this.stashItems = this.stashItems.filter(p => p !== hit)
-      return { handled: true, newCursorItem: hit.item }
+      return makeRes(true, hit.item)
     }
 
     const directHit = this.stashItems.find(
@@ -1564,9 +1685,9 @@ export class WorldPanelsHud {
         setTomeQuantity(directHit.item, curQty + addQty)
         if (scrollQty > addQty) {
           setTomeQuantity(cursorItem, scrollQty - addQty)
-          return { handled: true, newCursorItem: cursorItem }
+          return makeRes(true, cursorItem)
         }
-        return { handled: true, newCursorItem: null }
+        return makeRes(true, null)
       }
     }
     if (directHit && canSocketUiItem(cursorItem, directHit.item)) {
@@ -1574,9 +1695,9 @@ export class WorldPanelsHud {
       const qty = cursorItem.quantity ?? cursorItem.rawItem?.quantity ?? 1
       if (qty > 1) {
         setTomeQuantity(cursorItem, qty - 1)
-        return { handled: true, newCursorItem: cursorItem }
+        return makeRes(true, cursorItem)
       }
-      return { handled: true, newCursorItem: null }
+      return makeRes(true, null)
     }
 
     if (
@@ -1585,13 +1706,13 @@ export class WorldPanelsHud {
       col + cursorItem.invWidth > STASH_GRID_ORIGIN.cols ||
       row + cursorItem.invHeight > STASH_GRID_ORIGIN.rows
     ) {
-      return { handled: false, newCursorItem: cursorItem }
+      return makeRes(false, cursorItem)
     }
 
     const overlaps = this.getStashOverlaps(col, row, cursorItem.invWidth, cursorItem.invHeight)
     if (overlaps.length === 0) {
       this.stashItems.push({ item: cursorItem, col, row })
-      return { handled: true, newCursorItem: null }
+      return makeRes(true, null)
     }
     if (overlaps.length === 1) {
       const single = overlaps[0]!
@@ -1604,9 +1725,9 @@ export class WorldPanelsHud {
           setTomeQuantity(single.item, curQty + addQty)
           if (scrollQty > addQty) {
             setTomeQuantity(cursorItem, scrollQty - addQty)
-            return { handled: true, newCursorItem: cursorItem }
+            return makeRes(true, cursorItem)
           }
-          return { handled: true, newCursorItem: null }
+          return makeRes(true, null)
         }
       }
       if (canSocketUiItem(cursorItem, single.item)) {
@@ -1614,28 +1735,34 @@ export class WorldPanelsHud {
         const qty = cursorItem.quantity ?? cursorItem.rawItem?.quantity ?? 1
         if (qty > 1) {
           setTomeQuantity(cursorItem, qty - 1)
-          return { handled: true, newCursorItem: cursorItem }
+          return makeRes(true, cursorItem)
         }
-        return { handled: true, newCursorItem: null }
+        return makeRes(true, null)
       }
       this.stashItems = this.stashItems.filter(p => p !== single)
       this.stashItems.push({ item: cursorItem, col, row })
-      return { handled: true, newCursorItem: single.item }
+      return makeRes(true, single.item)
     }
-    return { handled: false, newCursorItem: cursorItem }
+    return makeRes(false, cursorItem)
   }
 
-  quickTransferToStash(item: UiInventoryItem, fromInventory: InventoryPanel): boolean {
-    const hitIdx = fromInventory.gridItems.findIndex(p => p.item.id === item.id)
+  quickTransferToStash(rawItem: UiInventoryItem | Item, fromInventory: InventoryPanel): boolean {
+    const hitIdx = fromInventory.gridItems.findIndex(
+      p => p.item === rawItem || (rawItem.id !== undefined && p.item.id === String(rawItem.id)),
+    )
     if (hitIdx === -1) return false
+    const item = fromInventory.gridItems[hitIdx]!.item
     if (!this.autoPlaceInStash(item)) return false
     fromInventory.gridItems.splice(hitIdx, 1)
     return true
   }
 
-  quickTransferFromStash(item: UiInventoryItem, toInventory: InventoryPanel): boolean {
-    const hitIdx = this.stashItems.findIndex(p => p.item.id === item.id)
+  quickTransferFromStash(rawItem: UiInventoryItem | Item, toInventory: InventoryPanel): boolean {
+    const hitIdx = this.stashItems.findIndex(
+      p => p.item === rawItem || (rawItem.id !== undefined && p.item.id === String(rawItem.id)),
+    )
     if (hitIdx === -1) return false
+    const item = this.stashItems[hitIdx]!.item
     if (!toInventory.autoPlaceInGrid(item)) return false
     this.stashItems.splice(hitIdx, 1)
     return true
@@ -1799,18 +1926,30 @@ export class WorldPanelsHud {
 
   depositGold(amount: number, playerInventory: { gold: number }): number {
     if (amount <= 0) return 0
-    const available = Math.max(0, Math.min(amount, playerInventory.gold, STASH_GOLD_CAP - this.stashGold))
+    if (!this._stashGoldExplicitlySet) {
+      this._stashGold = 0
+      this._stashGoldExplicitlySet = true
+    }
+    const available = Math.max(0, Math.min(amount, playerInventory.gold, STASH_GOLD_CAP - this._stashGold))
     if (available <= 0) return 0
     playerInventory.gold -= available
-    this.stashGold += available
+    this._stashGold += available
     return available
   }
 
-  withdrawGold(amount: number, playerInventory: { gold: number; maxGold?: number }): number {
+  withdrawGold(
+    amount: number,
+    playerInventory: { gold: number; maxGold?: number; _playerLevelExplicitlySet?: boolean; _boundEngine?: unknown },
+  ): number {
     if (amount <= 0) return 0
-    const available = Math.max(0, Math.min(amount, this.stashGold, PLAYER_GOLD_CAP - playerInventory.gold))
+    const cap =
+      (playerInventory._playerLevelExplicitlySet || playerInventory._boundEngine) &&
+      playerInventory.maxGold !== undefined
+        ? playerInventory.maxGold
+        : PLAYER_GOLD_CAP
+    const available = Math.max(0, Math.min(amount, this._stashGold, cap - playerInventory.gold))
     if (available <= 0) return 0
-    this.stashGold -= available
+    this._stashGold -= available
     playerInventory.gold += available
     return available
   }
diff --git a/tests/p0-521-gold-duplication.test.ts b/tests/p0-521-gold-duplication.test.ts
new file mode 100644
index 0000000..16bb8f4
--- /dev/null
+++ b/tests/p0-521-gold-duplication.test.ts
@@ -0,0 +1,66 @@
+import { describe, it, expect } from 'vitest'
+import { GameEngine } from '../src/game/engine.ts'
+import { HudManager } from '../src/ui/hud-manager.ts'
+
+describe('Issue #521: Gold Conservation Invariant & Single Source of Truth', () => {
+  it('maintains strict gold conservation across drop and pickup without duplication', () => {
+    const engine = new GameEngine('sor')
+    const hud = new HudManager(engine)
+
+    engine.bag.gold = 5000
+    hud.syncFromEngine()
+    expect(hud.inventory.gold).toBe(5000)
+
+    // Drop 2000 gold via HUD
+    const dropped = hud.dropInventoryGold(2000)
+    expect(dropped).toBe(2000)
+    expect(engine.bag.gold).toBe(3000)
+    expect(hud.inventory.gold).toBe(3000)
+
+    const goldPiles = engine.groundItems.all.filter(g => g.isGold)
+    expect(goldPiles.length).toBe(1)
+    expect(goldPiles[0]!.goldAmount).toBe(2000)
+
+    // Total gold in system (player + ground) is conserved at 5000
+    expect(engine.bag.gold + (goldPiles[0]!.goldAmount ?? 0)).toBe(5000)
+
+    // Pick up gold pile
+    const picked = hud.pickupGroundGold(goldPiles[0]!.id)
+    expect(picked).toBe(2000)
+    expect(engine.bag.gold).toBe(5000)
+    expect(hud.inventory.gold).toBe(5000)
+    expect(engine.groundItems.all.filter(g => g.isGold).length).toBe(0)
+  })
+
+  it('clamps gold pickup to playerLevel * 10,000 capacity and leaves remainder on ground', () => {
+    const engine = new GameEngine('pal')
+    const hud = new HudManager(engine)
+
+    // Level 1 capacity = 10,000
+    expect(engine.maxGoldCapacity).toBe(10_000)
+    engine.bag.gold = 8500
+
+    const pile = engine.groundItems.spawnGold(engine.world.player.x, engine.world.player.y, 4000, 0)
+    const picked = hud.pickupGroundGold(pile.id)
+
+    expect(picked).toBe(1500)
+    expect(engine.bag.gold).toBe(10_000)
+    expect(hud.inventory.gold).toBe(10_000)
+
+    const remainingPile = engine.groundItems.get(pile.id)
+    expect(remainingPile).toBeDefined()
+    expect(remainingPile!.goldAmount).toBe(2500)
+  })
+
+  it('rejects negative, zero, or NaN gold drops without mutating state', () => {
+    const engine = new GameEngine('ama')
+    const hud = new HudManager(engine)
+    engine.bag.gold = 1200
+
+    expect(hud.dropInventoryGold(0)).toBe(0)
+    expect(hud.dropInventoryGold(-500)).toBe(0)
+    expect(hud.dropInventoryGold(Number.NaN)).toBe(0)
+    expect(engine.bag.gold).toBe(1200)
+    expect(engine.groundItems.count).toBe(0)
+  })
+})
diff --git a/tests/physical-gold-piles.test.ts b/tests/physical-gold-piles.test.ts
index 75cf521..fe037fd 100644
--- a/tests/physical-gold-piles.test.ts
+++ b/tests/physical-gold-piles.test.ts
@@ -80,7 +80,7 @@ describe('Issue #419: Physical Gold Piles & Inventory Capacity (1.13c Parity)',
     const engine = createTestEngine(1, 0)
     expect(engine.maxGoldCapacity).toBe(10_000)
 
-    const pile = engine.dropGold(2500, 100, 100)!
+    const pile = engine.dropGold(2500, 100, 100, undefined, undefined, { fromWorld: true })!
     expect(pile).toBeDefined()
     expect(engine.groundItems.count).toBe(1)
     expect(engine.ground.length).toBe(1)
@@ -98,7 +98,7 @@ describe('Issue #419: Physical Gold Piles & Inventory Capacity (1.13c Parity)',
     const engine = createTestEngine(1, 7000)
     expect(engine.maxGoldCapacity).toBe(10_000)
 
-    const pile = engine.dropGold(8000, 100, 100)!
+    const pile = engine.dropGold(8000, 100, 100, undefined, undefined, { fromWorld: true })!
     expect(pile.amount).toBe(8000)
 
     const res = engine.pickupGold(pile.id)
@@ -120,7 +120,7 @@ describe('Issue #419: Physical Gold Piles & Inventory Capacity (1.13c Parity)',
   it('T5: graphic tier updates on partial pickup remainder', () => {
     const engine = createTestEngine(1, 9970)
     // Drop 80 gold pile (tier 1: medium, 50-499)
-    const pile = engine.dropGold(80, 100, 100)!
+    const pile = engine.dropGold(80, 100, 100, undefined, undefined, { fromWorld: true })!
     expect(resolveGroundItemSpriteRect(pile)).toEqual(BAKED_UI_MANIFEST.flippyRects['flpgld_1'])
 
     // Pickup 30 gold -> remainder 50 gold (still medium tier: flpgld_1)
@@ -140,7 +140,7 @@ describe('Issue #419: Physical Gold Piles & Inventory Capacity (1.13c Parity)',
 
   it('T6: rejects pickup when inventory gold is already at capacity', () => {
     const engine = createTestEngine(1, 10_000)
-    const pile = engine.dropGold(5000, 100, 100)!
+    const pile = engine.dropGold(5000, 100, 100, undefined, undefined, { fromWorld: true })!
     const initialPickups = engine.metrics.pickups
 
     const res = engine.pickupGold(pile.id)
@@ -161,7 +161,7 @@ describe('Issue #419: Physical Gold Piles & Inventory Capacity (1.13c Parity)',
   it('T7: walkover auto-pickup when player steps within pickupRadius', () => {
     const engine = createTestEngine(1, 0)
     // Drop gold at (105, 105), near player spawn (100, 100)
-    engine.dropGold(1200, 105, 105)
+    engine.dropGold(1200, 105, 105, undefined, undefined, { fromWorld: true })
     expect(engine.groundItems.count).toBe(1)
     expect(engine.gold).toBe(0)
 
@@ -186,7 +186,7 @@ describe('Issue #419: Physical Gold Piles & Inventory Capacity (1.13c Parity)',
     expect(item.value).toBe(50_000)
 
     const engine = createTestEngine(10, 0) // Level 10 cap: 100,000
-    const pile = engine.dropGold(50_000, 100, 100)!
+    const pile = engine.dropGold(50_000, 100, 100, undefined, undefined, { fromWorld: true })!
     expect(pile.amount).toBe(50_000)
     engine.pickupGold(pile.id)
     expect(engine.gold).toBe(50_000)