diff --git a/README.md b/README.md
index b095e47..87630e1 100644
--- a/README.md
+++ b/README.md
@@ -5,7 +5,7 @@ property defaults; `create` spawns an `engine.entity` with template
 defaults + per-instance overrides; entities are indexed by template-id
 and tag for cheap reverse-lookup.
 
-**Version:** 0.1.0
+**Version:** 0.2.0
 **Lib-ID:** lib-core.composition
 **Requires:** (none — uses engine `entity.*`, `domain.contribute` only)
 **Tags:** composition, entity, template, tag-index
@@ -21,19 +21,22 @@ graph LR
 ```
 <!-- topology:end -->
 
-## Scope (v0.1.0 — Spine)
+## Scope (v0.2.0)
 
-Template-Only-Subset per [Phase-A Spec](../../../sporel-meta/docs/superpowers/specs/2026-06-09-phase-A-inactive-entities-composition-actor-reentry-design.md).
+Template-Only-Subset + set_tag + container declaration.
 
 **Supported:**
 - `define_template{id, properties, tags}`
+- `define_template{..., container={kind="list"}}` — v0.2: `kind="list"` accepted
 - `create{template, properties}`
 - `list_by_template(id)`, `list_by_tag(tag)`
 - `destroy(entity)`
+- `set_tag(entity, tag, present)` — v0.2: runtime tag add/remove
 
 **Deferred (Loud-Error if attempted):**
 - `slots` block → Phase D trigger (Composite Items with Sub-Items)
-- `container` block → Phase B trigger (Items + Inventory)
+- `container` constraint fields (`weight_max`, `volume_max`, `grid`,
+  `accepts_fluid`, `accepts_gas`, `restrictions`) → Phase F/G trigger
 - `quality`, `condition` → Phase J trigger (Damage / Wear)
 - `parent:` template-inheritance → no consumer yet
 
@@ -63,10 +66,31 @@ to dotted scalar keys (e.g. `position = {x, y}` → declares `position.x`
 and `position.y` as separate `number` properties). Tag-list registers
 the template in the tag-index used by `list_by_tag`.
 
+The optional `container` block declares this template as an item container.
+Only `kind = "list"` is supported in v0.2. Any constraint field
+(`weight_max`, `volume_max`, `grid`, `accepts_fluid`, `accepts_gas`,
+`restrictions`) loud-errors at template-load time (Capability-by-Declaration:
+no constraint is silently ignored).
+
+**Example with container:**
+```lua
+composition.define_template{
+    id         = "backpack",
+    properties = {
+        sprite_atlas = "sprites/items.png",
+        sprite_uv    = "0 0 32 32",
+        position     = {x = 0, y = 0},
+    },
+    tags      = {"renderable"},
+    container = { kind = "list" },
+}
+```
+
 Loud `error(...)` on: missing/non-string `id`, duplicate `id`,
 non-table `properties`, malformed `tags`, attempted `slots` /
-`container` / `quality` / `condition` / `parent:` block (each pointing
-to its re-entry phase).
+`quality` / `condition` / `parent:` block (each pointing to its
+re-entry phase); `container.kind` other than `"list"`; any
+unimplemented constraint field in `container`.
 
 ### `composition.create(spec)`
 
@@ -126,6 +150,28 @@ end
 declared `tag` in its `tags` array. Used by `lib-core.render`
 `draw_entities{tag="..."}` (see A.2). Empty list if tag has no entities.
 
+### `composition.set_tag(entity, tag, present)`
+
+**Syntax:** `composition.set_tag(entity, tag: string, present: boolean) -> void`
+
+**Example:**
+```lua
+-- Remove from renderable index (e.g. item picked up into inventory)
+composition.set_tag(item_entity, "renderable", false)
+
+-- Restore renderable index (e.g. item dropped back into world)
+composition.set_tag(item_entity, "renderable", true)
+```
+
+**Description:** Adds or removes `entity` from the tag-index for `tag`.
+`present=true` inserts the entity (idempotent — calling again with the
+same tag is a no-op). `present=false` removes it (idempotent — calling
+again when already absent is a no-op). Both `entity_meta` and
+`index_by_tag` are updated atomically. Loud-Error if `entity` was not
+created by composition (e.g. a raw `entity.create()` handle). Used by
+`lib-core.inventory` `add`/`remove` to flip the `"renderable"` tag
+when items move between world and inventory.
+
 ### `composition.destroy(entity)`
 
 **Syntax:** `composition.destroy(entity) -> void`
@@ -159,6 +205,7 @@ template-ids.
 
 | Phase | Triggers in Template | Spec |
 |---|---|---|
-| B (Items) | `container = true` | inventory-model.md |
+| B (Items) | `container={kind="list"}` — accepted in v0.2; constraint fields deferred to F/G | inventory-model.md |
 | D (Composites) | `slots = {...}` | composition-model.md (full Slot-System) |
+| F/G (Constraints) | `weight_max`, `volume_max`, `grid`, `accepts_fluid`, `accepts_gas`, `restrictions` | constraint-model.md |
 | J (Damage/Wear) | `quality`, `condition` | damage-model.md |
diff --git a/init.lua b/init.lua
index b46b4f3..2a5b4a5 100644
--- a/init.lua
+++ b/init.lua
@@ -1,5 +1,5 @@
 -- =====================================================================
--- lib-core.composition v0.1.0 — Template + Instantiation + Tag-Index
+-- lib-core.composition v0.2.0 — Template + Instantiation + Tag-Index
 -- See: meta/docs/superpowers/specs/2026-06-09-phase-A-inactive-entities-...
 --
 -- v0.1.0 Template-Only-Subset:
@@ -15,9 +15,18 @@
 --   - composition.destroy(entity) — removes from indices + destroys
 --     engine.entity.
 --
--- DEFERRED (loud-error if attempted in v0.1):
+-- v0.2.0 additions:
+--   - composition.set_tag(entity, tag, present) — adds (present=true) or
+--     removes (present=false) entity in index_by_tag + entity_meta.
+--     Idempotent. Loud-Error on entity not created by composition.
+--   - define_template accepts optional container={kind="list"} block.
+--     All constraint fields (weight_max, volume_max, grid, accepts_fluid,
+--     accepts_gas, restrictions) → Loud-Error (Phase F/G deferred).
+--
+-- DEFERRED (loud-error if attempted):
 --   - slots         → Phase D Trigger (Composite Items with Sub-Items)
---   - container     → Phase B Trigger (Items + Inventory)
+--   - container constraint fields (weight_max, volume_max, grid,
+--     accepts_fluid, accepts_gas, restrictions) → Phase F/G Trigger
 --   - quality       → Phase J Trigger (Damage / Wear)
 --   - condition     → Phase J Trigger (Damage / Wear)
 --   - parent:       → Template-Inheritance, no consumer yet
@@ -145,25 +154,59 @@ function M.define_template(def)
     if def.slots ~= nil then
         error(string.format(
             "composition.define_template '%s': 'slots' block is Phase-D " ..
-            "trigger (Composite Items with Sub-Items); not supported in v0.1",
+            "trigger (Composite Items with Sub-Items); not supported in v0.2",
             def.id))
     end
     if def.container ~= nil then
-        error(string.format(
-            "composition.define_template '%s': 'container' block is " ..
-            "Phase-B trigger (Items + Inventory); not supported in v0.1",
-            def.id))
+        if type(def.container) ~= "table" then
+            error(string.format(
+                "composition.define_template '%s': 'container' must be a table",
+                def.id))
+        end
+        if def.container.kind ~= "list" then
+            error(string.format(
+                "composition.define_template '%s': container.kind must be " ..
+                "'list' (only kind='list' is supported in v0.2; got %s)",
+                def.id, tostring(def.container.kind)))
+        end
+        -- Reject each unimplemented constraint field individually so the
+        -- error message names the offending field (Capability-by-Declaration:
+        -- no silent ignorance of declared constraints).
+        local deferred_fields = {
+            "weight_max", "volume_max", "grid",
+            "accepts_fluid", "accepts_gas", "restrictions",
+        }
+        for _, field in ipairs(deferred_fields) do
+            if def.container[field] ~= nil then
+                error(string.format(
+                    "composition.define_template '%s': container.%s is a " ..
+                    "Phase-F/G trigger (Constraint fields not implemented in v0.2)",
+                    def.id, field))
+            end
+        end
+        -- Reject any unknown container keys (forward-protects against typos).
+        local known_container_keys = { kind = true,
+            weight_max = true, volume_max = true, grid = true,
+            accepts_fluid = true, accepts_gas = true, restrictions = true }
+        for k, _ in pairs(def.container) do
+            if not known_container_keys[k] then
+                error(string.format(
+                    "composition.define_template '%s': unknown container " ..
+                    "field '%s'",
+                    def.id, tostring(k)))
+            end
+        end
     end
     if def.quality ~= nil or def.condition ~= nil then
         error(string.format(
             "composition.define_template '%s': 'quality' / 'condition' " ..
-            "are Phase-J triggers (Damage / Wear); not supported in v0.1",
+            "are Phase-J triggers (Damage / Wear); not supported in v0.2",
             def.id))
     end
     if def.parent ~= nil then
         error(string.format(
             "composition.define_template '%s': 'parent:' inheritance has " ..
-            "no consumer in v0.1; declare inline until a real use-case appears",
+            "no consumer in v0.2; declare inline until a real use-case appears",
             def.id))
     end
 
@@ -206,6 +249,7 @@ function M.define_template(def)
         id          = def.id,
         props_flat  = props_flat,
         tags        = tags_set,
+        container   = def.container,  -- nil when not declared; B.2 reads this
     }
     index_by_template[def.id] = index_by_template[def.id] or {}
 end
@@ -264,9 +308,13 @@ function M.create(spec)
     end
 
     -- Register in indices + meta.
+    -- Copy tpl.tags so per-entity set_tag calls don't mutate the template's
+    -- tag-set (which would affect future create() calls for the same template).
     local reg_id = next_reg_id
     next_reg_id = next_reg_id + 1
-    entity_meta[reg_id] = { template_id = tpl.id, tags = tpl.tags, handle = entity }
+    local entity_tags = {}
+    for t, v in pairs(tpl.tags) do entity_tags[t] = v end
+    entity_meta[reg_id] = { template_id = tpl.id, tags = entity_tags, handle = entity }
 
     table.insert(index_by_template[tpl.id], entity)
     for tag, _ in pairs(tpl.tags) do
@@ -335,6 +383,39 @@ function M.destroy(target_entity)
     entity.destroy(target_entity)
 end
 
+function M.set_tag(target_entity, tag, present)
+    -- Validate tag argument.
+    if type(tag) ~= "string" or tag == "" then
+        error("composition.set_tag: 'tag' must be a non-empty string")
+    end
+    -- Validate present argument.
+    if type(present) ~= "boolean" then
+        error("composition.set_tag: 'present' must be a boolean")
+    end
+    -- Resolve entity → meta via the composition.reg_id property.
+    local reg_id = target_entity and target_entity:get_property("composition.reg_id")
+    if not reg_id or reg_id == 0 then
+        error("composition.set_tag: entity was not created by composition")
+    end
+    local meta = entity_meta[reg_id]
+    if not meta then
+        error("composition.set_tag: entity was not created by composition")
+    end
+
+    if present then
+        -- Idempotent add.
+        if meta.tags[tag] then return end
+        meta.tags[tag] = true
+        index_by_tag[tag] = index_by_tag[tag] or {}
+        table.insert(index_by_tag[tag], target_entity)
+    else
+        -- Idempotent remove.
+        if meta.tags[tag] == nil then return end
+        meta.tags[tag] = nil
+        remove_from_list(index_by_tag[tag], target_entity)
+    end
+end
+
 -- ---------- introspection (debug/testing) ----------
 
 -- Returns the set of declared template-ids (for tests + debug).
diff --git a/manifest.lib b/manifest.lib
index 9a81d26..b4d60e4 100644
--- a/manifest.lib
+++ b/manifest.lib
@@ -1 +1 @@
-{"id":"lib-core.composition","version":"0.1.0","api_min":"0.1","deps":[]}
+{"id":"lib-core.composition","version":"0.2.0","api_min":"0.1","deps":[]}