diff --git a/src/ui/BagMenu.lua b/src/ui/BagMenu.lua
index e8cb6630..5d6807f1 100644
--- a/src/ui/BagMenu.lua
+++ b/src/ui/BagMenu.lua
@@ -4,6 +4,7 @@
 
 local ItemEffects = require("src.inventory.ItemEffects")
 local ListMenu = require("src.ui.ListMenu")
+local Runtime = require("src.mods.Runtime")
 local TextBox = require("src.render.TextBox")
 
 local BagMenu = {}
@@ -46,7 +47,16 @@ end
 -- the stack, so every exit that prints has to close it afterwards.  For
 -- every other item the picker popped itself first and closePicker's identity
 -- check makes it a no-op (#252).
-local function useOn(game, battle, id, target, list, moveIndex, picker)
+--
+-- Every result string used to fall through to this one unconditional
+-- function with no seam around it: a mod could not suppress a message,
+-- delay it behind a screen of its own, or replace the outcome for one item
+-- id.  The "item.use" hook wraps the whole dispatch (not a name per
+-- result -- a mod deciding what a Poké Doll or a stone does needs the
+-- SAME reach a vanilla `if result == ...` branch has, not a narrower one),
+-- the way "battle.overlay" and "ui.party.submenu" already wrap a
+-- screen's own default behavior elsewhere in src/ui.
+local function vanillaUseOn(game, battle, id, target, list, moveIndex, picker)
   local result, payload, extra = ItemEffects.use(game.data, game.save, id, target,
                                                  battle, moveIndex, game.overworld)
   local function closePicker()
@@ -375,6 +385,11 @@ local function useOn(game, battle, id, target, list, moveIndex, picker)
   showMessages(game, payload, closePicker) -- failed
 end
 
+local function useOn(game, battle, id, target, list, moveIndex, picker)
+  return Runtime.call("item.use", vanillaUseOn,
+    game, battle, id, target, list, moveIndex, picker)
+end
+
 local function pickTargetAndUse(game, battle, id, list)
   -- pick a target from the party
   -- the ETHERs and PP UP open the move menu after picking a mon
diff --git a/tests/engine/item_use_hook.lua b/tests/engine/item_use_hook.lua
new file mode 100644
index 00000000..9107a32c
--- /dev/null
+++ b/tests/engine/item_use_hook.lua
@@ -0,0 +1,101 @@
+-- Public mod-API coverage for the "item.use" hook (src/ui/BagMenu.lua).
+--
+-- Before this hook existed, every result ItemEffects.use returned fell
+-- through to one unconditional call with nothing wrapped around it: a mod
+-- could not suppress a message, delay it behind a screen of its own, or
+-- replace what a specific item id does after the bag decides to use it.
+-- This exercises the seam end to end through the public mod API -- a real
+-- BagMenu list, a real USE selection -- rather than calling the hook
+-- machinery directly.
+
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+local Bag = require("src.inventory.Bag")
+
+-- Real TextBoxes want a Font atlas; this only cares that useOn reaches the
+-- no-effect fallthrough, so the same stand-in tests/parity_rare_candy_menu.lua
+-- uses for a ROM-backed run works here too.
+local realTextBox = package.loaded["src.render.TextBox"]
+package.loaded["src.render.TextBox"] = {
+  new = function(_, text, done) return { textBox = true, text = text, done = done } end,
+}
+package.loaded["src.ui.BagMenu"] = nil
+local BagMenu = require("src.ui.BagMenu")
+
+local FIXTURE = {
+  ["mods/item_hook_probe/manifest.json"] = [[{
+    "id": "item_hook_probe",
+    "name": "Item Hook Probe",
+    "version": "1.0.0",
+    "entry": "main.lua",
+    "api": 2
+  }]],
+  ["mods/item_hook_probe/main.lua"] = [[
+    local mod = ...
+    mod.hooks:wrap("item.use",
+      function(vanilla, game, battle, id, target, list, moveIndex, picker)
+        mod.exports.calls = (mod.exports.calls or 0) + 1
+        mod.exports.id = id
+        mod.exports.battle = battle
+        mod.exports.target = target
+        return vanilla(game, battle, id, target, list, moveIndex, picker)
+      end)
+  ]],
+}
+
+local function newStack()
+  local stack = { states = {} }
+  function stack:push(s) self.states[#self.states + 1] = s end
+  function stack:pop() return table.remove(self.states) end
+  function stack:top() return self.states[#self.states] end
+  return stack
+end
+
+local run = T.sdk.loadMods({ "mods/item_hook_probe" }, {
+  fs = T.sdk.memfs(FIXTURE),
+})
+T.eq(#run.errors, 0,
+  "the probe mod loads clean (" .. tostring(run.errors[1]) .. ")")
+
+local game = {
+  data = run.data,
+  stack = newStack(),
+  save = {
+    player = { name = "RED" }, inventory = {}, money = 0,
+    options = { battleStyle = "set", battleAnim = "on" },
+    pokedex = { seen = {}, owned = {} }, flags = {},
+  },
+}
+Bag.add(game.save, "FIX_POTION", 1)
+
+local list = BagMenu.new(game, {})
+game.stack:push(list)
+local row
+for i, r in ipairs(list.items) do
+  if r.value == "FIX_POTION" then row = i end
+end
+T.check(row ~= nil, "the fixture item is in the bag")
+list.index = row
+list.onChoose(list.items[row], list)
+
+-- out of battle the bag offers USE / TOSS first (start_sub_menus.asm)
+local sub = game.stack:top()
+T.check(sub ~= nil and sub.items and sub.items[1] and sub.items[1].onSelect,
+  "the USE/TOSS submenu opened")
+sub.items[1].onSelect()
+
+local out = run.loader.exports.item_hook_probe or {}
+T.eq(out.calls, 1, "the hook fires exactly once for a bag item use")
+T.eq(out.id, "FIX_POTION", "the hook sees the item id")
+T.eq(out.battle, nil, "the hook sees the field-use battle argument (nil)")
+
+local top = game.stack:top()
+T.check(type(top) == "table" and top.textBox == true,
+  "vanilla still ran: the no-effect message box landed on the stack")
+
+run.release()
+package.loaded["src.render.TextBox"] = realTextBox
+package.loaded["src.ui.BagMenu"] = nil
+
+T.finish()