diff --git a/tests/challenger-m4-inventory-audit.test.ts b/tests/challenger-m4-inventory-audit.test.ts
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+/**
+ * tests/challenger-m4-inventory-audit.test.ts
+ *
+ * EMPIRICAL CHALLENGER ADVERSARIAL TEST HARNESS
+ * Milestone M4 (Issue #149): Complete base item atlas resolution, bounding limits,
+ * transformed item dyes, authentic charm aspect ratios, and fallback guarantees.
+ */
+
+import { describe, expect, it } from 'vitest'
+import { join } from 'node:path'
+import { existsSync } from 'node:fs'
+import { BAKED_UI_MANIFEST } from '../src/ui/baked-ui-meta.ts'
+import {
+  resolveItemSpriteRect,
+  STARTER_BAG_ITEMS,
+  STARTER_EQUIPPED_GEAR,
+} from '../src/ui/inventory.ts'
+import { MountedArchives } from '../src/mpq/mount.ts'
+import { MpqArchive } from '../src/mpq/archive.ts'
+import { fileSource } from '../src/mpq/file-source.ts'
+import { parseTable } from '../src/game/tables.ts'
+
+describe('Challenger M4 Inventory & Item Atlas Audit (Issue #149)', () => {
+  const itemRects = BAKED_UI_MANIFEST.itemRects
+  const atlasWidth = BAKED_UI_MANIFEST.atlasWidth
+  const atlasHeight = BAKED_UI_MANIFEST.atlasHeight
+
+  describe('Objective 1: Atlas Bounding Limits & Integrity', () => {
+    it('contains at least 399 sprite rects in BAKED_UI_MANIFEST.itemRects', () => {
+      const keys = Object.keys(itemRects)
+      expect(keys.length).toBeGreaterThanOrEqual(399)
+    })
+
+    it('enforces that every sprite rect in itemRects is strictly within atlas bounds', () => {
+      expect(atlasWidth).toBe(1024)
+      expect(atlasHeight).toBeGreaterThanOrEqual(1024)
+
+      for (const [key, rect] of Object.entries(itemRects)) {
+        expect(rect, `Sprite ${key} must be defined`).toBeDefined()
+        expect(rect.w, `Sprite ${key} width must be > 0`).toBeGreaterThan(0)
+        expect(rect.h, `Sprite ${key} height must be > 0`).toBeGreaterThan(0)
+        expect(rect.x, `Sprite ${key} x must be >= 0`).toBeGreaterThanOrEqual(0)
+        expect(rect.y, `Sprite ${key} y must be >= 0`).toBeGreaterThanOrEqual(0)
+
+        // Strict boundary containment
+        const right = rect.x + rect.w
+        const bottom = rect.y + rect.h
+        expect(
+          right,
+          `Sprite ${key} exceeds atlas width: right edge ${right} > atlasWidth ${atlasWidth}`,
+        ).toBeLessThanOrEqual(atlasWidth)
+        expect(
+          bottom,
+          `Sprite ${key} exceeds atlas height: bottom edge ${bottom} > atlasHeight ${atlasHeight}`,
+        ).toBeLessThanOrEqual(atlasHeight)
+      }
+    })
+
+    it('enforces that questRects are strictly within questsAtlas bounds', () => {
+      const questRects = BAKED_UI_MANIFEST.questRects
+      const qW = BAKED_UI_MANIFEST.questsAtlasWidth
+      const qH = BAKED_UI_MANIFEST.questsAtlasHeight
+
+      expect(Object.keys(questRects).length).toBeGreaterThan(0)
+      for (const [key, rect] of Object.entries(questRects)) {
+        expect(rect.w).toBeGreaterThan(0)
+        expect(rect.h).toBeGreaterThan(0)
+        expect(rect.x).toBeGreaterThanOrEqual(0)
+        expect(rect.y).toBeGreaterThanOrEqual(0)
+        expect(rect.x + rect.w).toBeLessThanOrEqual(qW)
+        expect(rect.y + rect.h).toBeLessThanOrEqual(qH)
+      }
+    })
+  })
+
+  describe('Objective 2: Transformed Items (Dyes) Existence & Bounding', () => {
+    const transformedKeys = [
+      'invcap_cgrn', // Emerald Harlequin Crest Shako
+      'invgth_dpur', // Dark Purple Gothic Plate
+      'invtgl_lgry', // Light Grey Heavy Gloves
+      'invvbl_blac', // Black Vampirefang Belt
+      'invlbl_blac', // Black Light Belt
+    ]
+
+    it.each(transformedKeys)('transformed item sprite "%s" exists with non-zero dimensions inside atlas', (key) => {
+      const rect = itemRects[key]
+      expect(rect, `Transformed sprite "${key}" must exist in itemRects`).toBeDefined()
+      expect(rect!.w, `Transformed sprite "${key}" width must be > 0`).toBeGreaterThan(0)
+      expect(rect!.h, `Transformed sprite "${key}" height must be > 0`).toBeGreaterThan(0)
+      expect(rect!.x + rect!.w).toBeLessThanOrEqual(atlasWidth)
+      expect(rect!.y + rect!.h).toBeLessThanOrEqual(atlasHeight)
+    })
+
+    it('resolves transformed dyed items via resolveItemSpriteRect with case-insensitivity', () => {
+      const shako = resolveItemSpriteRect({ invFile: 'invcap', invtransform: 'cgrn' }, itemRects)
+      expect(shako).toEqual(itemRects['invcap_cgrn'])
+
+      const shakoUpper = resolveItemSpriteRect({ invFile: 'INVCAP', invtransform: 'CGRN' }, itemRects)
+      expect(shakoUpper).toEqual(itemRects['invcap_cgrn'])
+
+      const gothic = resolveItemSpriteRect({ invFile: 'invgth', invtransform: 'dpur' }, itemRects)
+      expect(gothic).toEqual(itemRects['invgth_dpur'])
+
+      const gloves = resolveItemSpriteRect({ invFile: 'invtgl', invtransform: 'lgry' }, itemRects)
+      expect(gloves).toEqual(itemRects['invtgl_lgry'])
+
+      const beltV = resolveItemSpriteRect({ invFile: 'invvbl', invtransform: 'blac' }, itemRects)
+      expect(beltV).toEqual(itemRects['invvbl_blac'])
+
+      const beltL = resolveItemSpriteRect({ invFile: 'invlbl', invtransform: 'blac' }, itemRects)
+      expect(beltL).toEqual(itemRects['invlbl_blac'])
+    })
+  })
+
+  describe('Objective 3: 100+ Base Items from weapons.txt, armor.txt, and misc.txt', () => {
+    it('empirically audits 100+ base items from 1.13c MPQ data tables', async () => {
+      const d2Path = join(process.cwd(), 'samples', 'd2')
+      if (!existsSync(join(d2Path, 'Patch_D2.mpq'))) {
+        throw new Error('Authoritative MPQ directory samples/d2 is missing or unmounted')
+      }
+
+      const archives = new MountedArchives()
+      for (const m of ['d2char.mpq', 'd2data.mpq', 'd2exp.mpq', 'Patch_D2.mpq']) {
+        archives.add(m, await MpqArchive.open(await fileSource(join(d2Path, m))))
+      }
+
+      let totalBaseItemsAudited = 0
+      const auditedCodes = new Set<string>()
+
+      for (const tblFile of ['weapons.txt', 'armor.txt', 'misc.txt']) {
+        const data = await archives.read(`data/global/excel/${tblFile}`)
+        const tbl = parseTable(new TextDecoder().decode(data))
+
+        for (const row of tbl.rows) {
+          const code = row['code']?.trim()
+          if (!code || auditedCodes.has(code)) continue
+          auditedCodes.add(code)
+
+          const invfile = row['invfile']?.trim()
+          const name = row['name']?.trim()
+
+          // 1. Resolve with full item info
+          const rectFull = resolveItemSpriteRect({ code, invFile: invfile, name }, itemRects)
+          expect(
+            rectFull,
+            `Base item code="${code}" (invFile="${invfile}", name="${name}") from ${tblFile} must resolve`,
+          ).not.toBeNull()
+          expect(rectFull!.w).toBeGreaterThan(0)
+          expect(rectFull!.h).toBeGreaterThan(0)
+          expect(rectFull!.x + rectFull!.w).toBeLessThanOrEqual(atlasWidth)
+          expect(rectFull!.y + rectFull!.h).toBeLessThanOrEqual(atlasHeight)
+
+          // 2. Resolve by code alone (Tier 3 lookup in codeToInvFile)
+          const rectByCode = resolveItemSpriteRect({ code }, itemRects)
+          expect(
+            rectByCode,
+            `Base item code="${code}" must resolve without invFile`,
+          ).not.toBeNull()
+
+          // 3. Strict charm aspect ratio and ground truth assertions
+          if (code === 'cm1') {
+            expect(rectFull!.w).toBe(28)
+            expect(rectFull!.h).toBe(28)
+            expect(rectByCode!.h).toBe(28)
+          } else if (code === 'cm2') {
+            expect(rectFull!.w).toBe(28)
+            expect(rectFull!.h).toBe(56)
+            expect(rectByCode!.h).toBe(56)
+            expect(rectFull).not.toEqual(itemRects['invwnd'])
+          } else if (code === 'cm3') {
+            expect(rectFull!.w).toBe(28)
+            expect(rectFull!.h).toBe(84)
+            expect(rectByCode!.h).toBe(84)
+            expect(rectFull).not.toEqual(itemRects['invsst'])
+          }
+
+          totalBaseItemsAudited++
+        }
+      }
+
+      console.log(`Empirically audited ${totalBaseItemsAudited} unique base items from MPQ data tables.`)
+      expect(totalBaseItemsAudited).toBeGreaterThanOrEqual(100)
+    })
+  })
+
+  describe('Objective 4: Dimension Fallbacks Stress Testing', () => {
+    it('w=1, h=2 resolves to 56px height', () => {
+      const item1x2 = resolveItemSpriteRect({ invWidth: 1, invHeight: 2 }, itemRects)
+      expect(item1x2).not.toBeNull()
+      expect(item1x2!.h).toBe(56)
+      expect(item1x2!.w).toBe(28)
+    })
+
+    it('w=1, h=3 resolves to 84px height', () => {
+      // Non-charm generic 1x3
+      const generic1x3 = resolveItemSpriteRect({ invWidth: 1, invHeight: 3 }, itemRects)
+      expect(generic1x3).not.toBeNull()
+      expect(generic1x3!.h).toBe(84)
+      expect(generic1x3!.w).toBe(28)
+
+      // Charm-designated 1x3
+      const charm1x3 = resolveItemSpriteRect({ name: 'Mystic Grand Charm', invWidth: 1, invHeight: 3 }, itemRects)
+      expect(charm1x3).not.toBeNull()
+      expect(charm1x3!.h).toBe(84)
+      expect(charm1x3!.w).toBe(28)
+      expect(charm1x3).toEqual(itemRects['invch3'])
+    })
+
+    it('exhaustively verifies all standard grid dimension fallbacks', () => {
+      const testCases = [
+        { w: 1, h: 1, expectedH: 28 },
+        { w: 1, h: 2, expectedH: 56 },
+        { w: 1, h: 3, expectedH: 84 },
+        { w: 1, h: 4, expectedH: 112 },
+        { w: 2, h: 1, expectedH: 28 },
+        { w: 2, h: 2, expectedH: 56 },
+        { w: 2, h: 3, expectedH: 84 },
+        { w: 2, h: 4, expectedH: 112 },
+      ]
+
+      for (const { w, h, expectedH } of testCases) {
+        const res = resolveItemSpriteRect({ invWidth: w, invHeight: h }, itemRects)
+        expect(res, `Fallback for w=${w}, h=${h} must resolve`).not.toBeNull()
+        expect(res!.h, `Fallback for w=${w}, h=${h} must match height ${expectedH}`).toBe(expectedH)
+      }
+    })
+  })
+
+  describe('Adversarial & Boundary Edge Cases', () => {
+    it('handles empty item object safely without crashing', () => {
+      const empty = resolveItemSpriteRect({}, itemRects)
+      expect(empty).not.toBeNull()
+      expect(empty!.w).toBeGreaterThan(0)
+      expect(empty!.h).toBeGreaterThan(0)
+    })
+
+    it('handles unmapped item with unknown code but valid dimensions', () => {
+      const unknownItem = resolveItemSpriteRect(
+        { code: 'nonexistent_code_9999', invWidth: 1, invHeight: 2 },
+        itemRects,
+      )
+      expect(unknownItem).not.toBeNull()
+      expect(unknownItem!.h).toBe(56)
+    })
+
+    it('handles adversarial keys without prototype pollution or exceptions', () => {
+      const badKeys = ['__proto__', 'constructor', 'toString', 'valueOf', '<script>', "'; DROP TABLE;"]
+      for (const bad of badKeys) {
+        expect(() => resolveItemSpriteRect({ code: bad }, itemRects)).not.toThrow()
+        expect(() => resolveItemSpriteRect({ invFile: bad }, itemRects)).not.toThrow()
+        expect(() => resolveItemSpriteRect({ invtransform: bad }, itemRects)).not.toThrow()
+      }
+    })
+
+    it('confirms starter inventory and equipped gear resolution integrity', () => {
+      for (const [slot, item] of Object.entries(STARTER_EQUIPPED_GEAR)) {
+        if (!item) continue
+        const rect = resolveItemSpriteRect(item, itemRects)
+        expect(rect, `Equipped item ${slot} (${item.name}) must resolve`).not.toBeNull()
+        expect(rect!.w).toBeGreaterThan(0)
+        expect(rect!.h).toBeGreaterThan(0)
+        expect(rect!.x + rect!.w).toBeLessThanOrEqual(atlasWidth)
+        expect(rect!.y + rect!.h).toBeLessThanOrEqual(atlasHeight)
+      }
+
+      for (const { item, col, row } of STARTER_BAG_ITEMS) {
+        const rect = resolveItemSpriteRect(item, itemRects)
+        expect(rect, `Bag item at (${col}, ${row}) (${item.name}) must resolve`).not.toBeNull()
+        expect(rect!.w).toBeGreaterThan(0)
+        expect(rect!.h).toBeGreaterThan(0)
+        expect(rect!.x + rect!.w).toBeLessThanOrEqual(atlasWidth)
+        expect(rect!.y + rect!.h).toBeLessThanOrEqual(atlasHeight)
+      }
+    })
+  })
+})