Fix Grid::remove_object to validate object ID before clearing grid cell

Prevents inconsistent state where grid cell is cleared but object may still
exist in memory if obj.id >= objects.size(). Now returns false instead of
true when the ID is invalid.

Author: daveey

packages/mettagrid/cpp/include/mettagrid/core/grid.hpp

@@ -104,13 +104,16 @@ class Grid {
       return false;  // Object not at expected location
     }
 
+    // Validate object ID first
+    if (obj.id >= objects.size()) {
+      return false;
+    }
+
     // Clear the grid cell
     grid[obj.location.r][obj.location.c] = nullptr;
 
     // Release the object (unique_ptr becomes null but slot remains)
-    if (obj.id < objects.size()) {
-      objects[obj.id].reset();
-    }
+    objects[obj.id].reset();
     return true;
   }
 

packages/mettagrid/cpp/include/mettagrid/core/grid_object.hpp

@@ -84,18 +84,13 @@ class GridObject : public HasVibe {
 
   virtual ~GridObject() = default;
 
-  void init(TypeId object_type_id,
-            const std::string& object_type_name,
-            const GridLocation& object_location,
-            const std::vector<int>& tags,
-            ObservationType object_vibe = 0,
-            const DemolishConfig* demolish = nullptr) {
-    this->type_id = object_type_id;
-    this->type_name = object_type_name;
+  void init(const GridObjectConfig& cfg, const GridLocation& object_location) {
+    this->type_id = cfg.type_id;
+    this->type_name = cfg.type_name;
     this->location = object_location;
-    this->tag_ids = tags;
-    this->vibe = object_vibe;
-    this->demolish_config = demolish;
+    this->tag_ids = cfg.tag_ids;
+    this->vibe = cfg.initial_vibe;
+    this->demolish_config = cfg.demolish.has_value() ? &cfg.demolish.value() : nullptr;
   }
 
   // Called when this object is demolished. Override for cleanup.

packages/mettagrid/cpp/include/mettagrid/objects/assembler.hpp

@@ -266,8 +266,7 @@ class Assembler : public GridObject, public Usable {
         allow_partial_usage(cfg.allow_partial_usage),
         chest_search_distance(cfg.chest_search_distance),
         clipper_ptr(nullptr) {
-    const DemolishConfig* demolish = cfg.demolish.has_value() ? &cfg.demolish.value() : nullptr;
-    GridObject::init(cfg.type_id, cfg.type_name, GridLocation(r, c), cfg.tag_ids, cfg.initial_vibe, demolish);
+    GridObject::init(cfg, GridLocation(r, c));
   }
   virtual ~Assembler() = default;
 

packages/mettagrid/cpp/include/mettagrid/objects/chest.hpp

@@ -78,8 +78,7 @@ class Chest : public GridObject, public Usable, public HasInventory {
         vibe_transfers(cfg.vibe_transfers),
         stats_tracker(stats_tracker),
         grid(nullptr) {
-    const DemolishConfig* demolish = cfg.demolish.has_value() ? &cfg.demolish.value() : nullptr;
-    GridObject::init(cfg.type_id, cfg.type_name, GridLocation(r, c), cfg.tag_ids, cfg.initial_vibe, demolish);
+    GridObject::init(cfg, GridLocation(r, c));
     // Set initial inventory for all configured resources (ignore limits for initial setup)
     for (const auto& [resource, amount] : cfg.initial_inventory) {
       if (amount > 0) {

packages/mettagrid/cpp/include/mettagrid/objects/protocol.hpp

@@ -4,8 +4,6 @@
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 
-#include <algorithm>
-#include <cmath>
 #include <memory>
 #include <unordered_map>
 
@@ -18,40 +16,13 @@ class Protocol {
   std::unordered_map<InventoryItem, InventoryQuantity> input_resources;
   std::unordered_map<InventoryItem, InventoryQuantity> output_resources;
   unsigned short cooldown;
-  float slope;     // Linear component: adds slope * activation_count to the multiplier
-  float exponent;  // Exponential component: multiplies by (1 + exponent)^activation_count
-
-  // Track activation count for inflation calculation
-  mutable unsigned int activation_count;
 
   Protocol(unsigned short min_agents = 0,
            const std::vector<ObservationType>& vibes = {},
            const std::unordered_map<InventoryItem, InventoryQuantity>& inputs = {},
            const std::unordered_map<InventoryItem, InventoryQuantity>& outputs = {},
-           unsigned short cooldown = 0,
-           float slope = 0.0f,
-           float exponent = 0.0f)
-      : min_agents(min_agents),
-        vibes(vibes),
-        input_resources(inputs),
-        output_resources(outputs),
-        cooldown(cooldown),
-        slope(slope),
-        exponent(exponent),
-        activation_count(0) {}
-
-  // Calculate cost multiplier based on activation count
-  // Formula: max(0, 1 + slope * n) * (1 + exponent)^n
-  // - slope < 0: discounting (starts at 1, decreases linearly, floors at 0)
-  // - slope > 0: linear cost increase
-  // - exponent > 0: exponential cost increase
-  // - exponent < 0: exponential cost decrease
-  float get_cost_multiplier() const {
-    float n = static_cast<float>(activation_count);
-    float linear_component = std::max(0.0f, 1.0f + slope * n);
-    float exponential_component = std::pow(1.0f + exponent, n);
-    return linear_component * exponential_component;
-  }
+           unsigned short cooldown = 0)
+      : min_agents(min_agents), vibes(vibes), input_resources(inputs), output_resources(outputs), cooldown(cooldown) {}
 };
 
 inline void bind_protocol(py::module& m) {
@@ -61,10 +32,7 @@ inline void bind_protocol(py::module& m) {
       .def_readwrite("vibes", &Protocol::vibes)
       .def_readwrite("input_resources", &Protocol::input_resources)
       .def_readwrite("output_resources", &Protocol::output_resources)
-      .def_readwrite("cooldown", &Protocol::cooldown)
-      .def_readwrite("slope", &Protocol::slope)
-      .def_readwrite("exponent", &Protocol::exponent)
-      .def_readwrite("activation_count", &Protocol::activation_count);
+      .def_readwrite("cooldown", &Protocol::cooldown);
 }
 
 #endif  // PACKAGES_METTAGRID_CPP_INCLUDE_METTAGRID_OBJECTS_PROTOCOL_HPP_

packages/mettagrid/cpp/include/mettagrid/objects/wall.hpp

@@ -20,8 +20,7 @@ struct WallConfig : public GridObjectConfig {
 class Wall : public GridObject {
 public:
   Wall(GridCoord r, GridCoord c, const WallConfig& cfg) {
-    const DemolishConfig* demolish = cfg.demolish.has_value() ? &cfg.demolish.value() : nullptr;
-    GridObject::init(cfg.type_id, cfg.type_name, GridLocation(r, c), cfg.tag_ids, cfg.initial_vibe, demolish);
+    GridObject::init(cfg, GridLocation(r, c));
   }
 
   std::vector<PartialObservationToken> obs_features() const override {

packages/mettagrid/cpp/src/mettagrid/objects/agent.cpp

@@ -41,7 +41,7 @@ Agent::Agent(GridCoord r,
     }
   }
   populate_initial_inventory(config.initial_inventory);
-  GridObject::init(config.type_id, config.type_name, GridLocation(r, c), config.tag_ids, config.initial_vibe);
+  GridObject::init(config, GridLocation(r, c));
 }
 
 void Agent::init(RewardType* reward_ptr) {

packages/mettagrid/nim/mettascope/libmettascope.dylib

@@ -289,8 +289,6 @@ def convert_to_cpp_game_config(game_config: GameConfig):
                 cpp_protocol.input_resources = input_res
                 cpp_protocol.output_resources = output_res
                 cpp_protocol.cooldown = protocol_config.cooldown
-                cpp_protocol.slope = protocol_config.slope
-                cpp_protocol.exponent = protocol_config.exponent
                 protocols.append(cpp_protocol)
 
             # Convert tag names to IDs
@@ -571,8 +569,6 @@ def process_action_config(action_name: str, action_config):
                 output_res[key] = val
             cpp_protocol.output_resources = output_res
             cpp_protocol.cooldown = protocol_config.cooldown
-            cpp_protocol.slope = protocol_config.slope
-            cpp_protocol.exponent = protocol_config.exponent
             clipper_protocols.append(cpp_protocol)
         clipper_config = CppClipperConfig()
         clipper_config.unclipping_protocols = clipper_protocols

packages/mettagrid/python/src/mettagrid/config/mettagrid_c_config.py

@@ -422,20 +422,6 @@ class ProtocolConfig(Config):
     input_resources: dict[str, int] = Field(default_factory=dict)
     output_resources: dict[str, int] = Field(default_factory=dict)
     cooldown: int = Field(ge=0, default=0)
-    slope: float = Field(
-        default=0.0,
-        description=(
-            "Linear component of cost multiplier. "
-            "Negative = discounting (starts at 1x, decreases linearly). "
-            "Positive = linear cost increase."
-        ),
-    )
-    exponent: float = Field(
-        default=0.0,
-        description=(
-            "Exponential component of cost multiplier. Cost multiplier = max(0, 1 + slope * n) * (1 + exponent)^n."
-        ),
-    )
 
 
 class AssemblerConfig(GridObjectConfig):