diff --git a/src/lib/sim/CMakeLists.txt b/src/lib/sim/CMakeLists.txt
index d2eac1f..c4ebed0 100644
--- a/src/lib/sim/CMakeLists.txt
+++ b/src/lib/sim/CMakeLists.txt
@@ -19,6 +19,7 @@ SET(HDRS
     ${CMAKE_CURRENT_SOURCE_DIR}/ShipStatsCalculator.h
     ${CMAKE_CURRENT_SOURCE_DIR}/StateChecksum.h
     ${CMAKE_CURRENT_SOURCE_DIR}/ThreatCostCalculator.h
+    ${CMAKE_CURRENT_SOURCE_DIR}/UnlockState.h
     ${CMAKE_CURRENT_SOURCE_DIR}/WaveSystem.h
     PARENT_SCOPE
 )
@@ -40,6 +41,7 @@ SET(SRCS
     ${CMAKE_CURRENT_SOURCE_DIR}/ShipStatsCalculator.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/StateChecksum.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/ThreatCostCalculator.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/UnlockState.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/WaveSystem.cpp
     PARENT_SCOPE
 )
diff --git a/src/lib/sim/UnlockState.cpp b/src/lib/sim/UnlockState.cpp
new file mode 100644
index 0000000..3ab8591
--- /dev/null
+++ b/src/lib/sim/UnlockState.cpp
@@ -0,0 +1,352 @@
+#include "UnlockState.h"
+
+#include <algorithm>
+
+#include "DisplayName.h"
+#include "StateChecksum.h"
+
+UnlockState::UnlockState(const GameConfig& config)
+    : m_config(config)
+{
+}
+
+void UnlockState::initializeUnlockState()
+{
+    // Cache the ids granted by some unlock group (REQ-LOCK-EXPLICIT); an item
+    // starts locked iff it is granted by a group.
+    m_grantedShipIds.clear();
+    m_grantedModuleIds.clear();
+    m_grantedBuildingIds.clear();
+    m_grantedRecipeIds.clear();
+    for (const UnlockGroupDef& group : m_config.unlocks.groups)
+    {
+        m_grantedShipIds.insert(group.ships.begin(), group.ships.end());
+        m_grantedModuleIds.insert(group.modules.begin(), group.modules.end());
+        m_grantedBuildingIds.insert(group.buildings.begin(), group.buildings.end());
+        m_grantedRecipeIds.insert(group.recipes.begin(), group.recipes.end());
+    }
+
+    m_awardedUnlockGroupIds.clear();
+
+    m_schematicLevels.clear();
+    for (const ShipDef& def : m_config.ships.ships)
+    {
+        SchematicState state;
+        state.unlocked = (m_grantedShipIds.count(def.id) == 0);
+        m_schematicLevels[def.id] = state;
+    }
+
+    m_moduleSchematicLevels.clear();
+    for (const ModuleDef& def : m_config.modules.modules)
+    {
+        SchematicState state;
+        state.unlocked = (m_grantedModuleIds.count(def.id) == 0);
+        m_moduleSchematicLevels[def.id] = state;
+    }
+
+    m_buildingLevels.clear();
+    for (const BuildingDef& def : m_config.buildings.buildings)
+    {
+        SchematicState state;
+        state.unlocked = (m_grantedBuildingIds.count(def.id) == 0);
+        m_buildingLevels[def.id] = state;
+    }
+
+    // Gated assembler recipes start locked; unlocked_at_start recipes are handled
+    // in the REQ-LOCK-IMPLICIT traversal, not tracked here.
+    m_unlockedRecipeSchematicIds.clear();
+
+    recomputeUnlocked();
+}
+
+bool UnlockState::isSchematicUnlocked(const std::string& shipId) const
+{
+    const std::map<std::string, SchematicState>::const_iterator it =
+        m_schematicLevels.find(shipId);
+    if (it == m_schematicLevels.end())
+    {
+        return false;
+    }
+    return it->second.unlocked;
+}
+
+bool UnlockState::isModuleSchematicUnlocked(const std::string& moduleId) const
+{
+    const std::map<std::string, SchematicState>::const_iterator it =
+        m_moduleSchematicLevels.find(moduleId);
+    if (it == m_moduleSchematicLevels.end())
+    {
+        return false;
+    }
+    return it->second.unlocked;
+}
+
+bool UnlockState::isRecipeUnlocked(const std::string& recipeId) const
+{
+    return m_unlockedRecipeIds.count(recipeId) > 0;
+}
+
+bool UnlockState::isItemUnlocked(const std::string& itemId) const
+{
+    return m_unlockedItemIds.count(itemId) > 0;
+}
+
+bool UnlockState::isBuildingUnlocked(BuildingType type) const
+{
+    const BuildingDef* def = m_config.buildings.findBuildingDef(type);
+    if (def == nullptr)
+    {
+        // Types without a config entry (e.g. HQ, defence stations) are unrestricted.
+        return true;
+    }
+    const std::map<std::string, SchematicState>::const_iterator it =
+        m_buildingLevels.find(def->id);
+    return it == m_buildingLevels.end() ? true : it->second.unlocked;
+}
+
+bool UnlockState::isUnlockGroupAwarded(const std::string& groupId) const
+{
+    return m_awardedUnlockGroupIds.count(groupId) > 0;
+}
+
+bool UnlockState::prerequisitesSatisfied(const std::vector<std::string>& requiredGroupIds) const
+{
+    // A prerequisite is satisfied only once the named unlock group has been
+    // awarded (REQ-LOCK-PREREQ).
+    for (const std::string& groupId : requiredGroupIds)
+    {
+        if (m_awardedUnlockGroupIds.count(groupId) == 0) { return false; }
+    }
+    return true;
+}
+
+SchematicChoiceOption UnlockState::makeUnlockOption(const UnlockGroupDef& group) const
+{
+    SchematicChoiceOption option;
+    option.isArtifact    = false;
+    option.unlockGroupId = group.id;
+    option.displayName   = toDisplayName(group.id);
+
+    for (const std::string& id : group.ships)
+    {
+        option.grantedItems.push_back({SchematicType::Ship, id, toDisplayName(id)});
+    }
+    for (const std::string& id : group.modules)
+    {
+        option.grantedItems.push_back({SchematicType::Module, id, toDisplayName(id)});
+    }
+    for (const std::string& id : group.buildings)
+    {
+        option.grantedItems.push_back({SchematicType::Building, id, toDisplayName(id)});
+    }
+    for (const std::string& id : group.recipes)
+    {
+        option.grantedItems.push_back({SchematicType::Recipe, id, toDisplayName(id)});
+    }
+
+    // REQ-DEF-SCHEMATIC-DROP: preview recipes newly implicitly unlocked by
+    // awarding this whole group. Seed the hypothetical explicit-unlock sets with
+    // every grant (ship + module materials via step 1a, recipe outputs via step
+    // 1b), then diff against the current implicit set.
+    std::set<std::string> hypotheticalShipIds            = getUnlockedShipSchematicIds();
+    std::set<std::string> hypotheticalModuleIds          = getUnlockedModuleSchematicIds();
+    std::set<std::string> hypotheticalRecipeSchematicIds = m_unlockedRecipeSchematicIds;
+    for (const std::string& id : group.ships)   { hypotheticalShipIds.insert(id); }
+    for (const std::string& id : group.modules) { hypotheticalModuleIds.insert(id); }
+    for (const std::string& id : group.recipes) { hypotheticalRecipeSchematicIds.insert(id); }
+
+    const UnlockedSets hypothetical = computeUnlockedSets(
+        hypotheticalShipIds, hypotheticalModuleIds, hypotheticalRecipeSchematicIds);
+    option.newlyUnlockedRecipeIds = computeNewlyUnlockedRecipeIds(hypothetical);
+
+    return option;
+}
+
+void UnlockState::awardUnlockGroup(const SchematicChoiceOption& chosen)
+{
+    // Award the whole unlock group (REQ-DEF-SCHEMATIC-DROP): unlock every granted
+    // ship, module, building, and assembler recipe at once.
+    m_awardedUnlockGroupIds.insert(chosen.unlockGroupId);
+    for (const GrantedSchematic& grant : chosen.grantedItems)
+    {
+        switch (grant.type)
+        {
+        case SchematicType::Ship:     m_schematicLevels.at(grant.id).unlocked = true;       break;
+        case SchematicType::Module:   m_moduleSchematicLevels.at(grant.id).unlocked = true; break;
+        case SchematicType::Building: m_buildingLevels.at(grant.id).unlocked = true;        break;
+        case SchematicType::Recipe:   m_unlockedRecipeSchematicIds.insert(grant.id);        break;
+        }
+    }
+
+    recomputeUnlocked();
+}
+
+// ---------------------------------------------------------------------------
+// Implicit unlock computation (REQ-LOCK-IMPLICIT)
+// ---------------------------------------------------------------------------
+
+void UnlockState::recomputeUnlocked()
+{
+    const UnlockedSets result = computeUnlockedSets(
+        getUnlockedShipSchematicIds(), getUnlockedModuleSchematicIds(), m_unlockedRecipeSchematicIds);
+    m_unlockedItemIds   = result.itemIds;
+    m_unlockedRecipeIds = result.recipeIds;
+}
+
+std::set<std::string> UnlockState::getUnlockedShipSchematicIds() const
+{
+    std::set<std::string> ids;
+    for (const auto& [id, state] : m_schematicLevels)
+    {
+        if (state.unlocked) { ids.insert(id); }
+    }
+    return ids;
+}
+
+std::set<std::string> UnlockState::getUnlockedModuleSchematicIds() const
+{
+    std::set<std::string> ids;
+    for (const auto& [id, state] : m_moduleSchematicLevels)
+    {
+        if (state.unlocked) { ids.insert(id); }
+    }
+    return ids;
+}
+
+UnlockState::UnlockedSets UnlockState::computeUnlockedSets(
+    const std::set<std::string>& unlockedShipSchematicIds,
+    const std::set<std::string>& unlockedModuleSchematicIds,
+    const std::set<std::string>& unlockedRecipeSchematicIds) const
+{
+    UnlockedSets result;
+
+    for (const ShipDef& def : m_config.ships.ships)
+    {
+        if (unlockedShipSchematicIds.count(def.id) == 0) { continue; }
+        for (const RecipeIngredient& mat : def.schematic.materials)
+        {
+            result.itemIds.insert(mat.item);
+        }
+    }
+    for (const ModuleDef& def : m_config.modules.modules)
+    {
+        if (unlockedModuleSchematicIds.count(def.id) == 0) { continue; }
+        for (const RecipeIngredient& mat : def.materials)
+        {
+            result.itemIds.insert(mat.item);
+        }
+    }
+    for (const RecipeDef& def : m_config.recipes.recipes)
+    {
+        // An assembler recipe seeds the base set when it is explicitly available:
+        // flagged unlocked_at_start (base recipes the graph can't reach), or a
+        // gated recipe whose unlock group has been awarded (REQ-LOCK-EXPLICIT).
+        if (def.building == BuildingType::Assembler
+            && (def.unlockedAtStart || unlockedRecipeSchematicIds.count(def.id) > 0))
+        {
+            for (const RecipeOutput& out : def.outputs)
+            {
+                result.itemIds.insert(out.item);
+            }
+        }
+    }
+
+    bool changed = true;
+    while (changed)
+    {
+        changed = false;
+        for (const RecipeDef& recipe : m_config.recipes.recipes)
+        {
+            if (recipe.building != BuildingType::Miner
+                && recipe.building != BuildingType::Smelter
+                && recipe.building != BuildingType::Assembler)
+            {
+                continue;
+            }
+            // Skip a gated assembler recipe (granted by an unlock group) whose
+            // group has not yet been awarded (REQ-LOCK-IMPLICIT step 2).
+            if (recipe.building == BuildingType::Assembler
+                && m_grantedRecipeIds.count(recipe.id) > 0
+                && unlockedRecipeSchematicIds.count(recipe.id) == 0)
+            {
+                continue;
+            }
+            bool producesUnlocked = false;
+            for (const RecipeOutput& out : recipe.outputs)
+            {
+                if (result.itemIds.count(out.item) > 0)
+                {
+                    producesUnlocked = true;
+                    break;
+                }
+            }
+            if (!producesUnlocked) { continue; }
+
+            if (recipe.building == BuildingType::Miner
+                || recipe.building == BuildingType::Assembler)
+            {
+                result.recipeIds.insert(recipe.id);
+            }
+            for (const RecipeIngredient& ing : recipe.inputs)
+            {
+                if (result.itemIds.insert(ing.item).second)
+                {
+                    changed = true;
+                }
+            }
+        }
+    }
+
+    return result;
+}
+
+std::vector<std::string> UnlockState::computeNewlyUnlockedRecipeIds(const UnlockedSets& hypothetical) const
+{
+    std::vector<std::string> recipeIds;
+    for (const std::string& recipeId : hypothetical.recipeIds)
+    {
+        if (m_unlockedRecipeIds.count(recipeId) > 0) { continue; }
+        recipeIds.push_back(recipeId);
+    }
+    std::sort(recipeIds.begin(), recipeIds.end(),
+              [](const std::string& lhs, const std::string& rhs)
+              {
+                  return toDisplayName(lhs) < toDisplayName(rhs);
+              });
+    return recipeIds;
+}
+
+// ---------------------------------------------------------------------------
+// Determinism (see docs/replay_design.md)
+// ---------------------------------------------------------------------------
+
+void UnlockState::appendSchematicMap(Hasher& hasher,
+                                     const std::map<std::string, SchematicState>& levels)
+{
+    hasher.append(levels.size());
+    for (const std::pair<const std::string, SchematicState>& entry : levels)
+    {
+        hasher.append(entry.first);
+        hasher.append(entry.second.unlocked);
+    }
+}
+
+void UnlockState::appendStringSet(Hasher& hasher, const std::set<std::string>& ids)
+{
+    hasher.append(ids.size());
+    for (const std::string& id : ids)
+    {
+        hasher.append(id);
+    }
+}
+
+void UnlockState::appendChecksum(Hasher& hasher) const
+{
+    appendSchematicMap(hasher, m_schematicLevels);
+    appendSchematicMap(hasher, m_moduleSchematicLevels);
+    appendSchematicMap(hasher, m_buildingLevels);
+    appendStringSet(hasher, m_awardedUnlockGroupIds);
+    appendStringSet(hasher, m_unlockedRecipeSchematicIds);
+    appendStringSet(hasher, m_unlockedRecipeIds);
+    appendStringSet(hasher, m_unlockedItemIds);
+}
diff --git a/src/lib/sim/UnlockState.h b/src/lib/sim/UnlockState.h
new file mode 100644
index 0000000..5e013f7
--- /dev/null
+++ b/src/lib/sim/UnlockState.h
@@ -0,0 +1,129 @@
+#pragma once
+
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+#include "BuildingType.h"
+#include "GameConfig.h"
+#include "SchematicChoiceOption.h"
+
+class Hasher;
+
+// Owns schematic/unlock bookkeeping for one run: which ship, module, and
+// building schematics are unlocked (REQ-LOCK-EXPLICIT), which assembler recipe
+// schematics have been explicitly granted, and the implicit recipe/item unlock
+// sets derived from that state (REQ-LOCK-IMPLICIT). Reads config the same way
+// BuildingSystem does (a bound const reference to Simulation::m_config, which is
+// safe across restart because that member's storage address never changes —
+// reset() move-assigns into it rather than replacing it).
+//
+// Simulation forwards its isXUnlocked-style public queries here and drives
+// state changes (awarding an unlock group) here; the RNG-touching schematic
+// choice generation itself stays in Simulation (call ordering of m_rng is the
+// determinism backbone and must not move).
+class UnlockState
+{
+public:
+    explicit UnlockState(const GameConfig& config);
+
+    // Builds the granted-id sets and initializes all per-item unlock maps from
+    // them (shared by the constructor and Simulation::reset). Ends with
+    // recomputeUnlocked().
+    void initializeUnlockState();
+
+    // Ship schematic state query.
+    bool isSchematicUnlocked(const std::string& shipId) const;
+
+    // Module schematic state query.
+    bool isModuleSchematicUnlocked(const std::string& moduleId) const;
+
+    // Implicit recipe/item unlock queries (REQ-LOCK-IMPLICIT).
+    bool isRecipeUnlocked(const std::string& recipeId) const;
+    bool isItemUnlocked(const std::string& itemId) const;
+
+    // Building unlock query (REQ-LOCK-BUILDING). True if the building type is not
+    // gated by any unlock group, or its granting group has been awarded.
+    bool isBuildingUnlocked(BuildingType type) const;
+
+    // True if the unlock group has already been awarded to the player.
+    bool isUnlockGroupAwarded(const std::string& groupId) const;
+
+    // True if every prerequisite unlock group has been awarded (REQ-LOCK-PREREQ).
+    bool prerequisitesSatisfied(const std::vector<std::string>& requiredGroupIds) const;
+
+    // Builds a schematic choice option for one unlock group (REQ-DEF-SCHEMATIC-DROP).
+    SchematicChoiceOption makeUnlockOption(const UnlockGroupDef& group) const;
+
+    // Awards the unlock group backing `chosen` (REQ-DEF-SCHEMATIC-DROP): marks
+    // every granted ship/module/building schematic unlocked, records granted
+    // recipe schematics, marks the group as awarded, and recomputes the implicit
+    // unlock sets. Mirrors the non-artifact branch of the original
+    // Simulation::applySchematicChoice exactly; callers still special-case
+    // chosen.isArtifact themselves before calling this.
+    void awardUnlockGroup(const SchematicChoiceOption& chosen);
+
+    // Determinism helper (see Simulation::computeStateChecksum): folds unlock
+    // state into the hasher via the same seven calls, in the same order, that
+    // used to live at the Simulation::computeStateChecksum call site.
+    void appendChecksum(Hasher& hasher) const;
+
+private:
+    // Schematic unlock state (REQ-DEF-SCHEMATIC-DROP).
+    struct SchematicState
+    {
+        bool unlocked;
+    };
+
+    // Recomputes m_unlockedRecipeIds and m_unlockedItemIds from current schematic state.
+    void recomputeUnlocked();
+
+    // Result of the REQ-LOCK-IMPLICIT traversal.
+    struct UnlockedSets
+    {
+        std::set<std::string> itemIds;
+        std::set<std::string> recipeIds;
+    };
+
+    // Pure REQ-LOCK-IMPLICIT traversal given hypothetical explicit-unlock sets.
+    UnlockedSets computeUnlockedSets(const std::set<std::string>& unlockedShipSchematicIds,
+                                      const std::set<std::string>& unlockedModuleSchematicIds,
+                                      const std::set<std::string>& unlockedRecipeSchematicIds) const;
+
+    // Current explicit-unlock id sets, derived from m_schematicLevels / m_moduleSchematicLevels.
+    std::set<std::string> getUnlockedShipSchematicIds() const;
+    std::set<std::string> getUnlockedModuleSchematicIds() const;
+
+    // Ids (sorted alphabetically by display name) of the recipes in
+    // hypothetical.recipeIds that are not yet in m_unlockedRecipeIds.
+    std::vector<std::string> computeNewlyUnlockedRecipeIds(const UnlockedSets& hypothetical) const;
+
+    // Determinism helpers — fold sub-state into the hasher in deterministic order.
+    static void appendSchematicMap(Hasher& hasher,
+                                   const std::map<std::string, SchematicState>& levels);
+    static void appendStringSet(Hasher& hasher, const std::set<std::string>& ids);
+
+    const GameConfig& m_config;
+
+    std::map<std::string, SchematicState> m_schematicLevels;
+    std::map<std::string, SchematicState> m_moduleSchematicLevels;
+    std::map<std::string, SchematicState> m_buildingLevels;
+
+    // Unlock groups awarded so far (REQ-LOCK-EXPLICIT). Group ids.
+    std::set<std::string> m_awardedUnlockGroupIds;
+
+    // Ids granted by some unlock group, per kind — cached from config at init.
+    // An item starts locked iff it appears in the corresponding set.
+    std::set<std::string> m_grantedShipIds;
+    std::set<std::string> m_grantedModuleIds;
+    std::set<std::string> m_grantedBuildingIds;
+    std::set<std::string> m_grantedRecipeIds;
+
+    // Explicitly unlocked assembler recipe schematics (REQ-LOCK-EXPLICIT).
+    std::set<std::string> m_unlockedRecipeSchematicIds;
+
+    // Implicit unlock sets derived from schematic state (REQ-LOCK-IMPLICIT).
+    std::set<std::string> m_unlockedRecipeIds;
+    std::set<std::string> m_unlockedItemIds;
+};