feat(vagrant): pickup/drop glue + lib-core.inventory-list dep

- Add lib-core.inventory-list v0.1.0 to manifest deps; bump module
  version 0.7.1 -> 0.7.2
- Import inventory = require("lib-core.inventory-list") in init.lua
- Add Item-Template-Convention comment block after vagrant_player
  template: documents stack_mode/tags/sprite/position contract that
  B.4 (rock) and B.5 (backpack-as-container) will fulfill
- Add register_pickup(item) factory: reads item position, registers
  interaction trigger; callback calls inventory.add + unregisters
  trigger on pickup
- Bind "drop" action to Q; drop handler in M.update pops last item
  from backpack via inventory.remove (renderable tag restored by
  library), repositions item at player pos +30px, re-registers pickup
- Update README Controls section: document E (pickup) and Q (drop)
  with note that end-to-end use requires B.4 + B.5

init.lua

@@ -1,4 +1,4 @@
--- sporel-module-vagrant-skeleton v0.7.0
+-- sporel-module-vagrant-skeleton v0.7.2
 -- Sprite-mode test-chamber: 13-bone humanoid puppet + sprite-tilemap +
 -- hardcoded furniture. Subterrain-style puppet control model:
 -- multi-look-target (aim/soft), slerp body rotation, hip-static legs,
@@ -24,6 +24,7 @@ local puppet      = require("lib-core.puppet")
 local interaction = require("lib-core.interaction")
 local composition = require("lib-core.composition")
 local actor       = require("lib-core.actor")
+local inventory   = require("lib-core.inventory-list")
 
 local M = {}
 
@@ -68,6 +69,25 @@ composition.define_template{
     tags = {},                         -- intentionally untagged: not renderable
 }
 
+-- Item-Template-Convention (Phase B):
+-- An "item" is a composition-template with:
+--   - properties.stack_mode = "individual"     (required by inventory-list)
+--   - properties.sprite_atlas + sprite_uv      (Atlas-UV render path)
+--   - properties.position = {x = 0, y = 0}    (world anchor)
+--   - tags = {"renderable", "item"}            ("renderable" → drawn by
+--                                               render.draw_entities;
+--                                               "item" → reserved/visible to
+--                                               future inventory queries)
+-- Pickup: register_pickup(item) registers an interaction-trigger at the
+-- item's current position; on interact, the item moves into state.backpack
+-- via inventory.add (renderable-tag flips off → world stops drawing it).
+-- Drop: input-action "drop" pops the last item out of state.backpack,
+-- re-parents it to the world at the player position, and re-registers a
+-- pickup-trigger at the new location.
+--
+-- Rock template (B.4) and container block on backpack (B.5) activate this
+-- convention end-to-end. B.3 establishes the glue only.
+
 local state = {
     player = nil,                -- puppet handle (state-bearing for animation)
     actor  = nil,                -- composition-entity owning position
@@ -96,6 +116,24 @@ local ci_assets_traced = false
 -- All 4 directional walk animation ids.
 local WALK_ANIMS = {"walk_fwd_lower", "walk_back_lower", "walk_left_lower", "walk_right_lower"}
 
+-- register_pickup(item)
+-- Registers an interaction-trigger at the item's current world position.
+-- When the player presses E within INTERACTION_RANGE, the item is moved
+-- into state.backpack via inventory.add (renderable-tag flips off) and
+-- the trigger is unregistered so the item no longer shows as interactable.
+-- Called by B.4 after placing the rock, and by drop-glue after relocation.
+local function register_pickup(item)
+    local x = item:get_property("position.x")
+    local y = item:get_property("position.y")
+    local trigger_id
+    trigger_id = interaction.register(x, y, INTERACTION_RANGE, "interact",
+        function()
+            inventory.add(state.backpack, item)
+            interaction.unregister(trigger_id)
+            if CI_FRAME_PERF then engine.print("vagrant: event=pickup") end
+        end)
+end
+
 -- Signed angle between two 2D vectors (in degrees, range [-180, 180]).
 -- Sporel uses Y-down screen-coords. Substrate's math assumes Y-up; the cross
 -- component is flipped so "positive num = move-direction is CCW from body-fwd
@@ -279,6 +317,7 @@ function M.init(ctx)
     input.bind("walk_down",  { "s" })
     input.bind("sprint",     { "shift" })   -- held while walking → 2x speed
     input.bind("interact",   { "e" })       -- fires nearest proximity-trigger
+    input.bind("drop",       { "q" })       -- drop most-recent item from backpack
     input.bind("quit_to_launcher", { "escape" })
 
     -- Proximity trigger on the backpack-Entity. Anchor read from the
@@ -311,6 +350,22 @@ function M.update(ctx, dt)
         return
     end
 
+    -- Drop: Q pops the most-recently-added item from backpack, relocates
+    -- it to world at player position + 30px right offset, and re-registers
+    -- a pickup-trigger. inventory.remove restores the renderable tag.
+    if input.was_action_pressed("drop") then
+        local items = inventory.contents(state.backpack)
+        if #items > 0 then
+            local item = inventory.remove(state.backpack, items[#items])
+            local px = state.actor:get_property("position.x")
+            local py = state.actor:get_property("position.y")
+            item:set_property("position.x", px + 30)
+            item:set_property("position.y", py)
+            register_pickup(item)
+            if CI_FRAME_PERF then engine.print("vagrant: event=drop") end
+        end
+    end
+
     -- WASD input → normalized move vector.
     local dx, dy = 0, 0
     if input.is_action_down("walk_left")  then dx = dx - 1 end