diff --git a/UNDF-REGISTRY.json b/UNDF-REGISTRY.json
index 377bd7e48..b3cf60175 100644
--- a/UNDF-REGISTRY.json
+++ b/UNDF-REGISTRY.json
@@ -943,5 +943,6 @@
   "monogame-0002-0002": "UNDF-2026-000000942",
   "monogame-0003-0003": "UNDF-2026-000000943",
   "supertuxkart-0001-0001": "UNDF-2026-000000944",
-  "supertuxkart-0002-0002": "UNDF-2026-000000945"
+  "supertuxkart-0002-0002": "UNDF-2026-000000945",
+  "minetest-0004-0004": "UNDF-2026-000000946"
 }
diff --git a/defects/cataclysm-0001/patch/cataclysm-0001.patch b/defects/cataclysm-0001/patch/cataclysm-0001.patch
new file mode 100644
index 000000000..704db2b5c
--- /dev/null
+++ b/defects/cataclysm-0001/patch/cataclysm-0001.patch
@@ -0,0 +1,31 @@
+# UNDF: UNDF-2026-000000935
+--- a/src/overmap_ui.cpp
++++ b/src/overmap_ui.cpp
+@@ -1,5 +1,6 @@
+ // ... (includes)
+ #include <algorithm>
++#include <unordered_set>
+
+ // In overmap_ui::search()
+ // BEFORE (CWE-407): overmap_checked is std::vector with std::find for dedup
+@@ -7,7 +8,7 @@
+ //   radius = OMAPX * 5 = 900, iterating ~3.24M points
+ //   Each std::find is O(M) where M = overmaps already checked
+ //   Total: O(P * M) where P = points in radius, M = distinct overmaps
+-    std::vector<point_abs_om> overmap_checked;
++    std::unordered_set<point_abs_om> overmap_checked;
+
+     const int radius = OMAPX * 5; // arbitrary
+     for( const tripoint_abs_omt &p : points_in_radius( curs, radius ) ) {
+@@ -16,9 +17,8 @@
+             tripoint_om_omt om_relative = om_loc.local;
+             point_abs_om om_cache = project_to<coords::om>( p.xy() );
+
+-            if( std::find( overmap_checked.begin(), overmap_checked.end(),
+-                           om_cache ) == overmap_checked.end() ) {
+-                overmap_checked.push_back( om_cache );
++            if( overmap_checked.find( om_cache ) == overmap_checked.end() ) {
++                overmap_checked.insert( om_cache );
+                 std::vector<point_abs_omt> notes = om_loc.om->find_notes( curs.z(), term );
+                 locations.insert( locations.end(), notes.begin(), notes.end() );
+             }
diff --git a/defects/cataclysm-0001/test/cataclysm-0001-test.cpp b/defects/cataclysm-0001/test/cataclysm-0001-test.cpp
new file mode 100644
index 000000000..4f162212f
--- /dev/null
+++ b/defects/cataclysm-0001/test/cataclysm-0001-test.cpp
@@ -0,0 +1,80 @@
+// Unit test for cataclysm-0001: overmap_ui search dedup
+// Verifies that unordered_set dedup matches vector+std::find dedup
+// and measures O(1) vs O(N) lookup performance.
+
+#include <algorithm>
+#include <cassert>
+#include <chrono>
+#include <cstdio>
+#include <unordered_set>
+#include <vector>
+
+// Simulate point_abs_om as a simple pair
+struct point_abs_om {
+    int x, y;
+    bool operator==( const point_abs_om &o ) const { return x == o.x && y == o.y; }
+};
+
+struct point_abs_om_hash {
+    size_t operator()( const point_abs_om &p ) const {
+        return std::hash<int>()( p.x ) ^ ( std::hash<int>()( p.y ) << 16 );
+    }
+};
+
+int main() {
+    // Generate overmap coordinates as if scanning radius 900
+    // In practice, distinct overmaps = (2*900/180+1)^2 ~ 100
+    const int num_overmaps = 100;
+    const int num_lookups = 50000; // simulating many points mapping to same overmaps
+
+    std::vector<point_abs_om> points;
+    for( int i = 0; i < num_lookups; i++ ) {
+        points.push_back( { i % num_overmaps, i / num_overmaps } );
+    }
+
+    // BEFORE: vector + std::find
+    {
+        std::vector<point_abs_om> checked;
+        int found_count = 0;
+        auto t0 = std::chrono::high_resolution_clock::now();
+        for( const auto &p : points ) {
+            if( std::find( checked.begin(), checked.end(), p ) == checked.end() ) {
+                checked.push_back( p );
+            } else {
+                found_count++;
+            }
+        }
+        auto t1 = std::chrono::high_resolution_clock::now();
+        double ms_before = std::chrono::duration<double, std::milli>( t1 - t0 ).count();
+        printf( "BEFORE (vector+find): %.3f ms, %d unique, %d dupes\n",
+                ms_before, (int)checked.size(), found_count );
+
+        // AFTER: unordered_set
+        std::unordered_set<point_abs_om, point_abs_om_hash> checked_set;
+        int found_count2 = 0;
+        auto t2 = std::chrono::high_resolution_clock::now();
+        for( const auto &p : points ) {
+            if( checked_set.find( p ) == checked_set.end() ) {
+                checked_set.insert( p );
+            } else {
+                found_count2++;
+            }
+        }
+        auto t3 = std::chrono::high_resolution_clock::now();
+        double ms_after = std::chrono::duration<double, std::milli>( t3 - t2 ).count();
+        printf( "AFTER  (unordered_set): %.3f ms, %zu unique, %d dupes\n",
+                ms_after, checked_set.size(), found_count2 );
+
+        // Verify correctness
+        assert( checked.size() == checked_set.size() );
+        assert( found_count == found_count2 );
+
+        double ratio = ms_before / ms_after;
+        printf( "Speedup ratio: %.1fx\n", ratio );
+        assert( ratio > 1.5 );  // Must be measurably faster
+
+        printf( "PASS: cataclysm-0001 overmap search dedup\n" );
+    }
+
+    return 0;
+}
diff --git a/defects/cataclysm-0002/patch/cataclysm-0002.patch b/defects/cataclysm-0002/patch/cataclysm-0002.patch
new file mode 100644
index 000000000..3b271772f
--- /dev/null
+++ b/defects/cataclysm-0002/patch/cataclysm-0002.patch
@@ -0,0 +1,74 @@
+# UNDF: UNDF-2026-000000936
+--- a/src/dependency_tree.cpp
++++ b/src/dependency_tree.cpp
+@@ -1,5 +1,6 @@
+ #include "dependency_tree.h"
+
+ #include <algorithm>
++#include <unordered_set>
+ #include <array>
+ #include <ostream>
+
+@@ -103,14 +104,15 @@
+ void dependency_node::inherit_errors()
+ {
+     std::stack<dependency_node * > nodes_to_check;
+     std::set<mod_id> nodes_visited;
+
+     // ... (BFS traversal) ...
+     // BEFORE (CWE-407): cur_errors is a copy of all_errors[error_type],
+     //   std::find scans it linearly for each node_error. O(E*N).
++    // Also note: cur_errors is a stale copy, dedup is partially broken.
+     //
+-            std::vector<std::string> cur_errors = all_errors[error_type];
+-            for( auto &node_error : node_errors ) {
+-                if( std::find( cur_errors.begin(), cur_errors.end(), node_error ) ==
+-                    cur_errors.end() ) {
++            std::unordered_set<std::string> cur_errors_set(
++                all_errors[error_type].begin(), all_errors[error_type].end() );
++            for( const auto &node_error : node_errors ) {
++                if( cur_errors_set.find( node_error ) == cur_errors_set.end() ) {
+                     all_errors[cerror.first].push_back( node_error );
++                    cur_errors_set.insert( node_error );
+                 }
+             }
+
+@@ -157,6 +159,7 @@
+ std::vector<dependency_node *> dependency_node::get_dependencies_as_nodes()
+ {
+     std::vector<dependency_node *> dependencies;
+     std::vector<dependency_node *> ret;
++    std::unordered_set<dependency_node *> ret_seen;
+     std::set<mod_id> found;
+
+     // ... (BFS collection into dependencies) ...
+@@ -188,8 +191,9 @@
+     // BEFORE (CWE-407): std::find on ret vector for dedup, O(N^2)
+     for( std::vector<dependency_node *>::reverse_iterator it =
+              dependencies.rbegin();
+          it != dependencies.rend(); ++it ) {
+-        if( std::find( ret.begin(), ret.end(), *it ) == ret.end() ) {
++        if( ret_seen.find( *it ) == ret_seen.end() ) {
+             ret.push_back( *it );
++            ret_seen.insert( *it );
+         }
+     }
+
+@@ -216,6 +220,7 @@
+ std::vector<dependency_node *> dependency_node::get_dependents_as_nodes()
+ {
+     std::vector<dependency_node *> dependents;
+     std::vector<dependency_node *> ret;
++    std::unordered_set<dependency_node *> ret_seen;
+     std::set<mod_id> found;
+
+     // ... (BFS collection into dependents) ...
+@@ -244,8 +249,9 @@
+     // BEFORE (CWE-407): std::find on ret vector for dedup, O(N^2)
+     for( dependency_node *&dependent : dependents ) {
+-        if( std::find( ret.begin(), ret.end(), dependent ) == ret.end() ) {
++        if( ret_seen.find( dependent ) == ret_seen.end() ) {
+             ret.push_back( dependent );
++            ret_seen.insert( dependent );
+         }
+     }
diff --git a/defects/cataclysm-0002/test/cataclysm-0002-test.cpp b/defects/cataclysm-0002/test/cataclysm-0002-test.cpp
new file mode 100644
index 000000000..f48c9758d
--- /dev/null
+++ b/defects/cataclysm-0002/test/cataclysm-0002-test.cpp
@@ -0,0 +1,130 @@
+// Unit test for cataclysm-0002: dependency_tree dedup
+// Verifies that unordered_set dedup matches vector+std::find dedup
+// for get_dependencies_as_nodes and get_dependents_as_nodes patterns.
+
+#include <algorithm>
+#include <cassert>
+#include <chrono>
+#include <cstdio>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+// Simulate dependency_node pointer dedup
+struct FakeNode {
+    int id;
+};
+
+int main() {
+    const int N = 500;  // Number of dependency nodes
+
+    // Create fake nodes
+    std::vector<FakeNode> nodes( N );
+    for( int i = 0; i < N; i++ ) {
+        nodes[i].id = i;
+    }
+
+    // Simulate dependencies list with duplicates (as in BFS traversal)
+    std::vector<FakeNode *> dependencies;
+    for( int i = 0; i < N; i++ ) {
+        dependencies.push_back( &nodes[i] );
+        // Add some duplicates
+        if( i % 3 == 0 ) {
+            dependencies.push_back( &nodes[i / 2] );
+        }
+    }
+
+    // BEFORE: vector + std::find for dedup
+    std::vector<FakeNode *> ret_before;
+    auto t0 = std::chrono::high_resolution_clock::now();
+    for( int run = 0; run < 1000; run++ ) {
+        ret_before.clear();
+        for( auto it = dependencies.rbegin(); it != dependencies.rend(); ++it ) {
+            if( std::find( ret_before.begin(), ret_before.end(), *it ) == ret_before.end() ) {
+                ret_before.push_back( *it );
+            }
+        }
+    }
+    auto t1 = std::chrono::high_resolution_clock::now();
+    double ms_before = std::chrono::duration<double, std::milli>( t1 - t0 ).count();
+
+    // AFTER: unordered_set + vector for dedup
+    std::vector<FakeNode *> ret_after;
+    auto t2 = std::chrono::high_resolution_clock::now();
+    for( int run = 0; run < 1000; run++ ) {
+        ret_after.clear();
+        std::unordered_set<FakeNode *> seen;
+        for( auto it = dependencies.rbegin(); it != dependencies.rend(); ++it ) {
+            if( seen.find( *it ) == seen.end() ) {
+                ret_after.push_back( *it );
+                seen.insert( *it );
+            }
+        }
+    }
+    auto t3 = std::chrono::high_resolution_clock::now();
+    double ms_after = std::chrono::duration<double, std::milli>( t3 - t2 ).count();
+
+    printf( "BEFORE (vector+find): %.3f ms\n", ms_before );
+    printf( "AFTER  (unordered_set): %.3f ms\n", ms_after );
+
+    // Verify correctness: same elements in same order
+    assert( ret_before.size() == ret_after.size() );
+    for( size_t i = 0; i < ret_before.size(); i++ ) {
+        assert( ret_before[i] == ret_after[i] );
+    }
+
+    double ratio = ms_before / ms_after;
+    printf( "Speedup ratio: %.1fx\n", ratio );
+    assert( ratio > 1.5 );
+
+    // Also test inherit_errors pattern (string dedup)
+    {
+        const int E = 200;
+        std::vector<std::string> errors;
+        for( int i = 0; i < E; i++ ) {
+            errors.push_back( "error_" + std::to_string( i ) );
+        }
+        // Add duplicates
+        std::vector<std::string> new_errors;
+        for( int i = 0; i < E; i++ ) {
+            new_errors.push_back( "error_" + std::to_string( i % ( E / 2 ) ) );
+        }
+
+        // BEFORE: vector copy + std::find
+        std::vector<std::string> result_before = errors;
+        auto t4 = std::chrono::high_resolution_clock::now();
+        for( int run = 0; run < 1000; run++ ) {
+            result_before = errors;
+            for( const auto &e : new_errors ) {
+                if( std::find( result_before.begin(), result_before.end(), e ) == result_before.end() ) {
+                    result_before.push_back( e );
+                }
+            }
+        }
+        auto t5 = std::chrono::high_resolution_clock::now();
+
+        // AFTER: unordered_set + vector
+        std::vector<std::string> result_after;
+        auto t6 = std::chrono::high_resolution_clock::now();
+        for( int run = 0; run < 1000; run++ ) {
+            result_after = errors;
+            std::unordered_set<std::string> seen_set( errors.begin(), errors.end() );
+            for( const auto &e : new_errors ) {
+                if( seen_set.find( e ) == seen_set.end() ) {
+                    result_after.push_back( e );
+                    seen_set.insert( e );
+                }
+            }
+        }
+        auto t7 = std::chrono::high_resolution_clock::now();
+
+        double ms_b = std::chrono::duration<double, std::milli>( t5 - t4 ).count();
+        double ms_a = std::chrono::duration<double, std::milli>( t7 - t6 ).count();
+        printf( "inherit_errors BEFORE: %.3f ms, AFTER: %.3f ms, ratio: %.1fx\n",
+                ms_b, ms_a, ms_b / ms_a );
+        assert( result_before.size() == result_after.size() );
+    }
+
+    printf( "PASS: cataclysm-0002 dependency_tree dedup\n" );
+    return 0;
+}
diff --git a/defects/cataclysm-0003/patch/cataclysm-0003.patch b/defects/cataclysm-0003/patch/cataclysm-0003.patch
new file mode 100644
index 000000000..c8989abcf
--- /dev/null
+++ b/defects/cataclysm-0003/patch/cataclysm-0003.patch
@@ -0,0 +1,45 @@
+# UNDF: UNDF-2026-000000937
+--- a/src/surroundings_menu.cpp
++++ b/src/surroundings_menu.cpp
+@@ -1,5 +1,6 @@
+ // ... (includes)
+ #include <algorithm>
++#include <unordered_set>
+
+ // In item_tab_data::add_item_recursive()
+ // BEFORE (CWE-407): item_order is std::vector<std::string> with std::find
+@@ -241,7 +242,8 @@
+ void item_tab_data::add_item_recursive( std::vector<std::string> &item_order, const item *it,
+                                         const tripoint_rel_ms &relative_pos )
+ {
++    // Also pass item_order_set for O(1) membership check
+     const std::string name = it->tname();
+
+-    if( std::find( item_order.begin(), item_order.end(), name ) == item_order.end() ) {
++    if( item_order_set.find( name ) == item_order_set.end() ) {
+         item_order.push_back( name );
++        item_order_set.insert( name );
+
+         items[name] = map_entity_stack<item>( it, relative_pos, it->count() );
+     } else {
+@@ -259,6 +261,7 @@
+ void item_tab_data::find_nearby_items( const Character &you, map &m )
+ {
+     std::vector<std::string> item_order;
++    // Add std::unordered_set<std::string> item_order_set as class member
+
+ // Similarly in terfurn_tab_data::add_terfurn()
+ // BEFORE:
+@@ -585,7 +588,8 @@
+ void terfurn_tab_data::add_terfurn( std::vector<std::string> &item_order,
+                                     const map_data_common_t *terfurn, const tripoint_rel_ms &relative_pos )
+ {
+     const std::string name = terfurn->name();
+
+-    if( std::find( item_order.begin(), item_order.end(), name ) == item_order.end() ) {
++    if( item_order_set.find( name ) == item_order_set.end() ) {
+         item_order.push_back( name );
++        item_order_set.insert( name );
+
+         terfurns[name] = map_entity_stack<map_data_common_t>( terfurn, relative_pos );
+     } else {
diff --git a/defects/cataclysm-0003/test/cataclysm-0003-test.cpp b/defects/cataclysm-0003/test/cataclysm-0003-test.cpp
new file mode 100644
index 000000000..0bbe73ff0
--- /dev/null
+++ b/defects/cataclysm-0003/test/cataclysm-0003-test.cpp
@@ -0,0 +1,86 @@
+// Unit test for cataclysm-0003: surroundings_menu item/terfurn dedup
+// Verifies that unordered_set dedup matches vector+std::find dedup
+// for add_item_recursive and add_terfurn patterns.
+
+#include <algorithm>
+#include <cassert>
+#include <chrono>
+#include <cstdio>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+int main() {
+    // Simulate nearby items: radius 12 means ~(25)^2 = 625 tiles
+    // Each tile may have 0-5 items. With item stacking, many names repeat.
+    const int num_items = 2000;
+    const int unique_names = 300;
+
+    std::vector<std::string> item_names;
+    for( int i = 0; i < num_items; i++ ) {
+        item_names.push_back( "item_type_" + std::to_string( i % unique_names ) );
+    }
+
+    // BEFORE: vector + std::find for dedup
+    auto t0 = std::chrono::high_resolution_clock::now();
+    for( int run = 0; run < 500; run++ ) {
+        std::vector<std::string> item_order;
+        for( const auto &name : item_names ) {
+            if( std::find( item_order.begin(), item_order.end(), name ) == item_order.end() ) {
+                item_order.push_back( name );
+            }
+        }
+    }
+    auto t1 = std::chrono::high_resolution_clock::now();
+    double ms_before = std::chrono::duration<double, std::milli>( t1 - t0 ).count();
+
+    // Capture result for correctness check
+    std::vector<std::string> result_before;
+    for( const auto &name : item_names ) {
+        if( std::find( result_before.begin(), result_before.end(), name ) == result_before.end() ) {
+            result_before.push_back( name );
+        }
+    }
+
+    // AFTER: unordered_set + vector for dedup
+    auto t2 = std::chrono::high_resolution_clock::now();
+    for( int run = 0; run < 500; run++ ) {
+        std::vector<std::string> item_order;
+        std::unordered_set<std::string> item_order_set;
+        for( const auto &name : item_names ) {
+            if( item_order_set.find( name ) == item_order_set.end() ) {
+                item_order.push_back( name );
+                item_order_set.insert( name );
+            }
+        }
+    }
+    auto t3 = std::chrono::high_resolution_clock::now();
+    double ms_after = std::chrono::duration<double, std::milli>( t3 - t2 ).count();
+
+    // Capture result for correctness check
+    std::vector<std::string> result_after;
+    std::unordered_set<std::string> result_set;
+    for( const auto &name : item_names ) {
+        if( result_set.find( name ) == result_set.end() ) {
+            result_after.push_back( name );
+            result_set.insert( name );
+        }
+    }
+
+    printf( "BEFORE (vector+find): %.3f ms\n", ms_before );
+    printf( "AFTER  (unordered_set): %.3f ms\n", ms_after );
+
+    // Verify correctness: same elements in same order
+    assert( result_before.size() == result_after.size() );
+    for( size_t i = 0; i < result_before.size(); i++ ) {
+        assert( result_before[i] == result_after[i] );
+    }
+    assert( result_before.size() == static_cast<size_t>( unique_names ) );
+
+    double ratio = ms_before / ms_after;
+    printf( "Speedup ratio: %.1fx\n", ratio );
+    assert( ratio > 2.0 );  // Must show clear improvement
+
+    printf( "PASS: cataclysm-0003 surroundings_menu dedup\n" );
+    return 0;
+}