diff --git a/README.md b/README.md
index 3b0d316..1ca5182 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ puppet control model: leg orientation decoupled from body via procedural
 callback, foot-body-orientation ("tactical twist"), scale-deformation walk
 cycle, and inheritance-decoupled foot sprites.
 
-**Version:** 0.7.2
+**Version:** 0.7.3
 **Module-ID:** vagrant-skeleton
 **Requires:** lib-core.input >=0.4.0, lib-core.camera >=0.3.0, lib-core.render >=0.1.0, lib-core.maps >=0.1.2, lib-core.puppet >=0.4.4, lib-core.interaction >=0.1.0, lib-asset.prototype-subterrain >=0.1.0
 **Tags:** test-chamber, puppet, walking-sim, interaction
@@ -26,8 +26,11 @@ cycle, and inheritance-decoupled foot sprites.
 - **Q** — drop most-recent item from backpack at player position + re-register pickup trigger
 - **ESC** — return to launcher
 
-> **Note:** Q (drop) and E (item pickup) are groundwork for B.4 (rock on ground) and
-> B.5 (backpack-as-container) — not yet exercisable end-to-end until those slices land.
+> **Note:** The world now contains a rock (near the backpack, 80px to its left). Walk up
+> and press E to pick it up into the backpack; press Q to drop it back at your feet.
+> Picking up the rock currently throws a loud error because the backpack is not yet a
+> container — this confirms the pickup wiring is alive. Full pickup-into-backpack works
+> once the backpack becomes a container (next slice).
 
 ## Demonstrates
 
@@ -79,6 +82,16 @@ cycle, and inheritance-decoupled foot sprites.
 
 ## CHANGELOG
 
+### v0.7.3
+- **Rock entity**: `composition.define_template{id="rock"}` added (stack_mode=individual,
+  tags=renderable+item). One rock entity spawned at (270, 400) — 80px left of the backpack.
+  Uses `slot_00_isolated` UV from the `blob_rect_stone` atlas (lib-asset.prototype-blob-geom).
+  `register_pickup(state.rock)` wires an interaction trigger so pressing E near the rock
+  fires the pickup callback. The callback calls `inventory.add(state.backpack, …)` which
+  errors until the backpack becomes a container (next slice) — the error confirms the wiring
+  is alive. `render.draw_entities{tag="renderable"}` (existing Phase A render path) draws
+  the rock without any special-case render code.
+
 ### v0.4.4
 - **Sprint** (Shift+WASD): doubles `WALK_SPEED` (120 → 240) and walk-anim
   `speed` (0.45 → 0.9). Mid-walk sprint toggle uses `puppet.set_play_speed`
diff --git a/init.lua b/init.lua
index bdb29b8..302c292 100644
--- a/init.lua
+++ b/init.lua
@@ -1,4 +1,4 @@
--- sporel-module-vagrant-skeleton v0.7.2
+-- sporel-module-vagrant-skeleton v0.7.3
 -- 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,
@@ -55,6 +55,22 @@ composition.define_template{
     tags = {"renderable"},
 }
 
+-- Rock-Template: an item sitting in the world that the player can pick up.
+-- sprite_atlas + sprite_uv are filled in M.init after the blob_rect_stone atlas
+-- is loaded; placeholder defaults here keep the inert-declaration types correct.
+-- slot_00_isolated is a standalone isolated stone tile — visually reads as a
+-- single rock on the ground.
+composition.define_template{
+    id = "rock",
+    properties = {
+        stack_mode   = "individual",           -- required by inventory-list
+        sprite_atlas = "",
+        sprite_uv    = {x = 0, y = 0, w = 1, h = 1},
+        position     = {x = 0, y = 0},
+    },
+    tags = {"renderable", "item"},
+}
+
 -- Player-Actor-Template (Phase A.6). Vagrant's player is an actor whose
 -- position drives the puppet (sync each frame). NOT tagged renderable —
 -- the puppet handles rendering, render.draw_entities doesn't see this
@@ -95,6 +111,7 @@ local state = {
     world_tex = nil,             -- subterrain_world atlas diffuse handle (used for bed/bench)
     furniture_uvs = nil,         -- name -> { x, y, w, h } from atlas JSON
     backpack = nil,              -- composition-entity, created in M.init after atlas load
+    rock     = nil,              -- composition-entity (item), created in M.init after blob_rect_stone load
     -- Subterrain-style controller state:
     walk_anim_current = nil,     -- "walk_fwd_lower" / "walk_back_lower" / etc. (nil = idle_lower)
     lower_control_rot_deg = 0,
@@ -310,6 +327,37 @@ function M.init(ctx)
         },
     }
 
+    -- Blob-rect-stone atlas: load JSON + diffuse texture for the rock sprite.
+    -- blob_rect_stone alias resolves to lib-asset.prototype-blob-geom. The
+    -- "slot_00_isolated" tile is the standalone isolated stone shape — reads as
+    -- a single rock on the ground. Separate atlas/texture from world atlas
+    -- (lib-core.render's atlas-cache de-duplicates on path, no wasted load).
+    local stone_lib  = aliases.blob_rect_stone
+    local stone_base = stone_lib .. "/assets/atlases/blob_rect_stone"
+    local stone_atlas_png = stone_base .. "/tiles.diffuse.atlas.png"
+    local stone_meta = engine.asset.load_json(stone_base .. "/tiles.atlas.json")
+    local stone_uvs = {}
+    for _, t in ipairs(stone_meta.tiles) do
+        stone_uvs[t.name] = { x = t.uv[1], y = t.uv[2], w = t.uv[3], h = t.uv[4] }
+    end
+
+    -- Spawn Rock-Entity 80px to the left of the backpack so it sits in a
+    -- distinct position: visible to the player on first load, not overlapping
+    -- the backpack, reachable by walking left from spawn.
+    local ROCK_X, ROCK_Y = BACKPACK_X - 80, BACKPACK_Y
+    local rock_uv = stone_uvs["slot_00_isolated"]
+    state.rock = composition.create{
+        template = "rock",
+        properties = {
+            sprite_atlas = stone_atlas_png,
+            sprite_uv    = {x = rock_uv.x, y = rock_uv.y,
+                            w = rock_uv.w,  h = rock_uv.h},
+            position     = {x = ROCK_X, y = ROCK_Y},
+        },
+    }
+    register_pickup(state.rock)
+    if CI_FRAME_PERF then engine.print("vagrant: rock_spawned") end
+
     -- Input bindings.
     input.bind("walk_left",  { "a" })
     input.bind("walk_right", { "d" })
@@ -333,9 +381,9 @@ function M.init(ctx)
                 ctx.distance))
         end)
 
-    -- CI trace: assets loaded count (3 atlas textures: player + tiles + world).
+    -- CI trace: assets loaded count (4 atlas textures: player + tiles + world + stone).
     if CI_FRAME_PERF and not ci_assets_traced then
-        engine.print("vagrant: assets_loaded=3")
+        engine.print("vagrant: assets_loaded=4")
         ci_assets_traced = true
     end
 
diff --git a/manifest.module b/manifest.module
index 9239d44..29359a4 100644
--- a/manifest.module
+++ b/manifest.module
@@ -1,6 +1,6 @@
 {
     "id": "vagrant-skeleton",
-    "version": "0.7.2",
+    "version": "0.7.3",
     "kind": "module",
     "api": "^0.1",
     "ci_frames": 60,