feat(cpp-object-oriented-modular-refactoring): step 11 - source-target-resolver

include/fesa/core/ascii.h

@@ -0,0 +1,28 @@
+#ifndef FESA_CORE_ASCII_H_
+#define FESA_CORE_ASCII_H_
+
+#include <cstdint>
+#include <string_view>
+
+#include "fesa/core/status.h"
+
+namespace fesa {
+
+/// @brief Converts one ASCII uppercase byte to lowercase.
+/// @return The lowercase ASCII byte, or the input byte when it is not A-Z.
+char AsciiLower(char value) noexcept;
+
+/// @brief Compares two byte strings with ASCII-only case folding.
+/// @return True when the strings have equal length and equal ASCII-folded
+/// bytes.
+bool AsciiCaseInsensitiveEquals(std::string_view lhs,
+                                std::string_view rhs) noexcept;
+
+/// @brief Parses a complete positive base-10 source label.
+/// @return The positive label or an input failure for malformed, nonpositive,
+/// or out-of-range text.
+Result<std::int64_t> ParsePositiveSourceLabel(std::string_view text);
+
+}  // namespace fesa
+
+#endif  // FESA_CORE_ASCII_H_

include/fesa/model/source_target_resolver.h

@@ -0,0 +1,81 @@
+#ifndef FESA_MODEL_SOURCE_TARGET_RESOLVER_H_
+#define FESA_MODEL_SOURCE_TARGET_RESOLVER_H_
+
+#include <cstddef>
+#include <string>
+#include <vector>
+
+#include "fesa/core/source_identity.h"
+#include "fesa/core/status.h"
+#include "fesa/model/model_types.h"
+
+namespace fesa {
+
+class Domain;
+
+/// @brief Selects the independent source node or element namespace.
+enum class SourceEntityKind { kNode, kElement };
+
+/// @brief Maps one direct label or named-target membership to stable identity.
+/// @note An empty target_name denotes a direct source-label entry.
+struct SourceTargetIndexEntry {
+  SourceEntityKind entity_kind;
+  std::string instance_name;
+  std::string target_name;
+  SourceEntityId source_id;
+  EntityIndex entity_index;
+  std::size_t declaration_order;
+};
+
+/// @brief Owns immutable compact source-target lookup entries.
+class SourceTargetIndex {
+ public:
+  /// @brief Takes ownership of compact entries from a validated model
+  /// candidate.
+  explicit SourceTargetIndex(std::vector<SourceTargetIndexEntry> entries);
+
+  /// @brief Builds compact entries from an immutable semantic Domain.
+  /// @return An owning index that preserves Domain declaration order.
+  static SourceTargetIndex FromDomain(const Domain& domain);
+
+  /// @brief Returns owned entries without exposing mutable index state.
+  const std::vector<SourceTargetIndexEntry>& Entries() const noexcept;
+
+ private:
+  std::vector<SourceTargetIndexEntry> entries_;
+};
+
+/// @brief Describes one source target lookup.
+struct SourceTargetQuery {
+  SourceEntityKind entity_kind;
+  std::string instance_name;
+  std::string target_name_or_label;
+};
+
+/// @brief Preserves both external source identity and stable internal index.
+struct ResolvedSourceTarget {
+  SourceEntityId source_id;
+  EntityIndex entity_index;
+};
+
+/// @brief Resolves source labels and named targets without owning model state.
+/// @note The referenced SourceTargetIndex must outlive this resolver.
+class SourceTargetResolver {
+ public:
+  /// @brief Creates a non-owning resolver over an immutable index.
+  /// @param index Index whose lifetime must exceed the resolver lifetime.
+  explicit SourceTargetResolver(const SourceTargetIndex& index) noexcept;
+
+  /// @brief Resolves one query in stable declaration order.
+  /// @return Stable source targets, or a deterministic input diagnostic for an
+  /// invalid, missing, duplicate, or ambiguous target.
+  Result<std::vector<ResolvedSourceTarget>> Resolve(
+      const SourceTargetQuery& query) const;
+
+ private:
+  const SourceTargetIndex* index_;
+};
+
+}  // namespace fesa
+
+#endif  // FESA_MODEL_SOURCE_TARGET_RESOLVER_H_

src/fesa/CMakeLists.txt

@@ -10,6 +10,7 @@ add_library(
     assembly/sparse_assembler.cpp
     build_info.cpp
     constraints/essential_constraints.cpp
+    core/ascii.cpp
     core/diagnostic.cpp
     core/status.cpp
     elements/euler_beam_3d.cpp
@@ -24,6 +25,7 @@ add_library(
     math/vector.cpp
     model/domain.cpp
     model/shell_geometry.cpp
+    model/source_target_resolver.cpp
     results/result_recovery.cpp
     solvers/linear/mkl_pardiso_solver.cpp
 )

src/fesa/assembly/load_assembler.cpp

@@ -1,17 +1,15 @@
 #include "fesa/assembly/load_assembler.h"
 
 #include <algorithm>
-#include <charconv>
 #include <cmath>
-#include <cstdint>
 #include <limits>
 #include <stdexcept>
 #include <string>
-#include <system_error>
 #include <utility>
 #include <vector>
 
 #include "fesa/constraints/essential_constraints.h"
+#include "fesa/model/source_target_resolver.h"
 
 namespace fesa {
 namespace {
@@ -27,28 +25,6 @@ Status LoadFailure(const std::string& code, const SourceLocation& location,
       {{Severity::kError, code, location, keyword, identity, message}});
 }
 
-char AsciiLower(const char value) {
-  if (value >= 'A' && value <= 'Z') {
-    return static_cast<char>(value + ('a' - 'A'));
-  }
-  return value;
-}
-
-bool EqualName(const std::string& left, const std::string& right) {
-  return left.size() == right.size() &&
-         std::equal(left.begin(), left.end(), right.begin(),
-                    [](const char left_value, const char right_value) {
-                      return AsciiLower(left_value) == AsciiLower(right_value);
-                    });
-}
-
-bool TryPositiveInteger(const std::string& text, std::int64_t& value) {
-  const char* const first = text.data();
-  const char* const last = first + text.size();
-  const auto parsed = std::from_chars(first, last, value);
-  return parsed.ec == std::errc{} && parsed.ptr == last && value > 0;
-}
-
 /// @brief Checks that equation-space indices preserve stable full-DOF order.
 bool IsStrictlyIncreasing(const std::vector<std::size_t>& values) {
   return std::adjacent_find(
@@ -122,36 +98,21 @@ Status ValidateDofOrder(const DofManager& dofs,
   return Status::Ok();
 }
 
-Result<std::vector<EntityIndex>> ResolveTarget(const Domain& domain,
+Result<std::vector<EntityIndex>> ResolveTarget(
+    const SourceTargetResolver& resolver, const Domain& domain,
     const NodalLoad& load) {
-  std::vector<const NodeSet*> matching_sets;
+  auto resolved = resolver.Resolve({SourceEntityKind::kNode, "", load.target});
-  for (const auto& set : domain.NodeSets()) {
+  if (!resolved.HasValue()) {
-    if (EqualName(set.name, load.target)) {
-      matching_sets.push_back(&set);
-    }
-  }
-
-  std::vector<EntityIndex> matching_nodes;
-  std::int64_t label = 0;
-  if (TryPositiveInteger(load.target, label)) {
-    for (std::size_t index = 0U; index < domain.Nodes().size(); ++index) {
-      if (domain.Nodes()[index].source_id.source_label == label) {
-        matching_nodes.push_back(static_cast<EntityIndex>(index));
-      }
-    }
-  }
-
-  if (matching_sets.size() > 1U || matching_nodes.size() > 1U ||
-      (!matching_sets.empty() && !matching_nodes.empty())) {
     return Result<std::vector<EntityIndex>>::Failure(
         LoadFailure("invalid-load-target", load.location, "CLOAD", load.target,
                     "The load target must resolve unambiguously to one node or "
                     "one expanded node set."));
   }
-  if (!matching_sets.empty()) {
+  std::vector<EntityIndex> nodes;
-    const auto& nodes = matching_sets.front()->node_indices;
+  nodes.reserve(resolved.Value().size());
   std::vector<unsigned char> seen(domain.Nodes().size(), 0U);
-    for (const EntityIndex node : nodes) {
+  for (const auto& target : resolved.Value()) {
+    const EntityIndex node = target.entity_index;
     if (node >= domain.Nodes().size() || seen[node] != 0U) {
       return Result<std::vector<EntityIndex>>::Failure(LoadFailure(
           "invalid-load-target", load.location, "CLOAD", load.target,
@@ -159,15 +120,9 @@ Result<std::vector<EntityIndex>> ResolveTarget(const Domain& domain,
           "identities."));
     }
     seen[node] = 1U;
+    nodes.push_back(node);
   }
-    return Result<std::vector<EntityIndex>>::Success(nodes);
+  return Result<std::vector<EntityIndex>>::Success(std::move(nodes));
-  }
-  if (!matching_nodes.empty()) {
-    return Result<std::vector<EntityIndex>>::Success(std::move(matching_nodes));
-  }
-  return Result<std::vector<EntityIndex>>::Failure(LoadFailure(
-      "invalid-load-target", load.location, "CLOAD", load.target,
-      "The load target must resolve to one semantic node or node set."));
 }
 
 Status ValidateFiniteVector(const Vector& values,
@@ -285,6 +240,8 @@ Result<Vector> LoadAssembler::AssembleFullNodalLoad(const AnalysisModel& model,
         "invalid-load-order", model.Step().location, "CLOAD", model.Step().name,
         "The active load view must include every sole-step load once."));
   }
+  const SourceTargetIndex target_index = SourceTargetIndex::FromDomain(domain);
+  const SourceTargetResolver target_resolver{target_index};
 
   Vector full_load{expected_full_count};
   // Active load indices are required to be the original source order; this
@@ -311,7 +268,7 @@ Result<Vector> LoadAssembler::AssembleFullNodalLoad(const AnalysisModel& model,
                       load.target, "A nodal load magnitude must be finite."));
     }
 
-    auto target = ResolveTarget(domain, load);
+    auto target = ResolveTarget(target_resolver, domain, load);
     if (!target.HasValue()) {
       return Result<Vector>::Failure(target.GetStatus());
     }

src/fesa/core/ascii.cpp

@@ -0,0 +1,49 @@
+#include "fesa/core/ascii.h"
+
+#include <charconv>
+#include <string>
+#include <system_error>
+
+namespace fesa {
+
+char AsciiLower(const char value) noexcept {
+  if (value >= 'A' && value <= 'Z') {
+    return static_cast<char>(value + ('a' - 'A'));
+  }
+  return value;
+}
+
+bool AsciiCaseInsensitiveEquals(const std::string_view lhs,
+                                const std::string_view rhs) noexcept {
+  if (lhs.size() != rhs.size()) {
+    return false;
+  }
+  for (std::size_t index = 0U; index < lhs.size(); ++index) {
+    if (AsciiLower(lhs[index]) != AsciiLower(rhs[index])) {
+      return false;
+    }
+  }
+  return true;
+}
+
+Result<std::int64_t> ParsePositiveSourceLabel(const std::string_view text) {
+  std::int64_t value = 0;
+  const char* const storage = text.empty() ? "" : text.data();
+  const char* const first = storage;
+  const char* const last = storage + text.size();
+  const auto parsed = std::from_chars(first, last, value, 10);
+  if (parsed.ec == std::errc{} && parsed.ptr == last && value > 0) {
+    return Result<std::int64_t>::Success(value);
+  }
+  const std::string identity{text};
+  return Result<std::int64_t>::Failure(Status::Failure(
+      FailureCategory::kInput,
+      {{Severity::kError,
+        "invalid-source-label",
+        {{}, 0U},
+        "SOURCE_LABEL",
+        identity,
+        "A source label must be a complete positive base-10 integer."}}));
+}
+
+}  // namespace fesa

src/fesa/fem/dof_manager.cpp

@@ -1,56 +1,29 @@
 #include "fesa/fem/dof_manager.h"
 
 #include <algorithm>
-#include <charconv>
 #include <stdexcept>
-#include <string>
-#include <system_error>
 #include <utility>
 
+#include "fesa/model/source_target_resolver.h"
+
 namespace fesa {
 namespace {
 
 constexpr std::size_t kDofsPerNode = 6U;
 
-char AsciiLower(char value) {
-  if (value >= 'A' && value <= 'Z') {
-    return static_cast<char>(value + ('a' - 'A'));
-  }
-  return value;
-}
-
-bool EqualName(const std::string& left, const std::string& right) {
-  return left.size() == right.size() &&
-         std::equal(left.begin(), left.end(), right.begin(),
-                    [](char left_value, char right_value) {
-                      return AsciiLower(left_value) == AsciiLower(right_value);
-                    });
-}
-
-bool TryPositiveInteger(const std::string& text, std::int64_t& value) {
-  const char* const first = text.data();
-  const char* const last = first + text.size();
-  const auto parsed = std::from_chars(first, last, value);
-  return parsed.ec == std::errc{} && parsed.ptr == last && value > 0;
-}
-
 std::vector<EntityIndex> ExpandBoundaryTarget(
-    const Domain& domain, const BoundaryCondition& boundary) {
+    const SourceTargetResolver& resolver, const BoundaryCondition& boundary) {
-  for (const auto& set : domain.NodeSets()) {
+  auto resolved =
-    if (EqualName(set.name, boundary.target)) {
+      resolver.Resolve({SourceEntityKind::kNode, "", boundary.target});
-      return set.node_indices;
+  if (!resolved.HasValue()) {
-    }
-  }
-
-  std::int64_t source_label = 0;
-  if (TryPositiveInteger(boundary.target, source_label)) {
-    for (std::size_t node = 0U; node < domain.Nodes().size(); ++node) {
-      if (domain.Nodes()[node].source_id.source_label == source_label) {
-        return {static_cast<EntityIndex>(node)};
-      }
-    }
-  }
     return {};
+  }
+  std::vector<EntityIndex> indices;
+  indices.reserve(resolved.Value().size());
+  for (const auto& target : resolved.Value()) {
+    indices.push_back(target.entity_index);
+  }
+  return indices;
 }
 
 template <std::size_t scatter_size>
@@ -94,12 +67,14 @@ SparsePattern BuildSparsePattern(
 
 Result<DofManager> DofManager::Create(const AnalysisModel& model) {
   const Domain& domain = model.GetDomain();
+  const SourceTargetIndex target_index = SourceTargetIndex::FromDomain(domain);
+  const SourceTargetResolver target_resolver{target_index};
   const std::size_t full_count = domain.Nodes().size() * kDofsPerNode;
 
   std::vector<std::optional<double>> prescribed_by_full_dof(full_count);
   for (const EntityIndex boundary_index : model.ActiveBoundaryConditions()) {
     const auto& boundary = model.Step().boundaries.at(boundary_index);
-    const auto target = ExpandBoundaryTarget(domain, boundary);
+    const auto target = ExpandBoundaryTarget(target_resolver, boundary);
     for (const EntityIndex node : target) {
       for (int component = boundary.first_dof; component <= boundary.last_dof;
            ++component) {

src/fesa/io/abaqus/domain_mapper.cpp

@@ -14,26 +14,14 @@
 #include <utility>
 #include <vector>
 
+#include "fesa/core/ascii.h"
 #include "fesa/math/vector3.h"
 #include "fesa/model/shell_geometry.h"
+#include "fesa/model/source_target_resolver.h"
 
 namespace fesa {
 namespace {
 
-std::string UppercaseAscii(std::string value) {
-  std::transform(value.begin(), value.end(), value.begin(), [](char character) {
-    if (character >= 'a' && character <= 'z') {
-      return static_cast<char>(character - 'a' + 'A');
-    }
-    return character;
-  });
-  return value;
-}
-
-bool EqualName(const std::string& left, const std::string& right) {
-  return UppercaseAscii(left) == UppercaseAscii(right);
-}
-
 std::vector<std::string> WithoutTrailingEmpty(std::vector<std::string> fields) {
   while (!fields.empty() && fields.back().empty()) {
     fields.pop_back();
@@ -254,20 +242,6 @@ class MappingContext {
     return true;
   }
 
-  bool TryPositiveInteger(const std::string& text, std::int64_t& value) const {
-    if (text.empty()) {
-      return false;
-    }
-    char* end = nullptr;
-    errno = 0;
-    const long long parsed = std::strtoll(text.c_str(), &end, 10);
-    if (errno == ERANGE || end != text.c_str() + text.size() || parsed <= 0) {
-      return false;
-    }
-    value = static_cast<std::int64_t>(parsed);
-    return true;
-  }
-
   bool ParseDouble(const std::string& text, double& value,
                    const SourceLocation& location, const std::string& keyword) {
     if (text.empty()) {
@@ -311,16 +285,17 @@ class MappingContext {
 
   bool ContainsName(const std::vector<RawPart>& values,
                     const std::string& name) const {
-    return std::any_of(
+    return std::any_of(values.begin(), values.end(),
-        values.begin(), values.end(),
+                       [&name](const RawPart& value) {
-        [&name](const RawPart& value) { return EqualName(value.name, name); });
+                         return AsciiCaseInsensitiveEquals(value.name, name);
+                       });
   }
 
   bool ContainsName(const std::vector<RawInstance>& values,
                     const std::string& name) const {
     return std::any_of(values.begin(), values.end(),
                        [&name](const RawInstance& value) {
-                         return EqualName(value.name, name);
+                         return AsciiCaseInsensitiveEquals(value.name, name);
                        });
   }
 
@@ -328,14 +303,14 @@ class MappingContext {
                     const std::string& name) const {
     return std::any_of(values.begin(), values.end(),
                        [&name](const RawMaterial& value) {
-                         return EqualName(value.name, name);
+                         return AsciiCaseInsensitiveEquals(value.name, name);
                        });
   }
 
   bool ContainsSetName(const std::vector<RawSet>& sets,
                        const std::string& name) const {
     const auto matches = [&name](const RawSet& set) {
-      return EqualName(set.name, name);
+      return AsciiCaseInsensitiveEquals(set.name, name);
     };
     return std::any_of(sets.begin(), sets.end(), matches);
   }
@@ -344,7 +319,7 @@ class MappingContext {
     return std::any_of(assembly_sets_.begin(), assembly_sets_.end(),
                        [node_set, &name](const RawAssemblySet& set) {
                          return set.is_node_set == node_set &&
-                                EqualName(set.name, name);
+                                AsciiCaseInsensitiveEquals(set.name, name);
                        });
   }
 
@@ -674,15 +649,15 @@ class MappingContext {
     RawElement::Type element_type{};
     ElementFamily element_family{};
     std::size_t expected_field_count = 0U;
-    if (EqualName(*type, "B33")) {
+    if (AsciiCaseInsensitiveEquals(*type, "B33")) {
       element_type = RawElement::Type::kB33;
       element_family = ElementFamily::kBeam;
       expected_field_count = 3U;
-    } else if (EqualName(*type, "S4")) {
+    } else if (AsciiCaseInsensitiveEquals(*type, "S4")) {
       element_type = RawElement::Type::kS4;
       element_family = ElementFamily::kShell;
       expected_field_count = 5U;
-    } else if (EqualName(*type, "S4R")) {
+    } else if (AsciiCaseInsensitiveEquals(*type, "S4R")) {
       element_type = RawElement::Type::kS4r;
       element_family = ElementFamily::kShell;
       expected_field_count = 5U;
@@ -803,9 +778,7 @@ class MappingContext {
       return;
     }
     if (block.data[0].fields.size() == 2U) {
-      std::int64_t ignored_integration_points = 0;
+      if (!ParsePositiveSourceLabel(block.data[0].fields[1]).HasValue()) {
-      if (!TryPositiveInteger(block.data[0].fields[1],
-                              ignored_integration_points)) {
         InputFailure("unsupported-shell-section-option", block.data[0].location,
                      block.canonical_name, block.data[0].fields[1],
                      "The optional shell integration-point field must be a "
@@ -932,7 +905,7 @@ class MappingContext {
     if (element_set == nullptr || material == nullptr || section == nullptr) {
       return;
     }
-    if (!EqualName(*section, "GENERAL")) {
+    if (!AsciiCaseInsensitiveEquals(*section, "GENERAL")) {
       InputFailure("unsupported-section-formulation", block.location,
                    block.canonical_name, *section,
                    "Only SECTION=GENERAL belongs to the approved subset.");
@@ -940,7 +913,8 @@ class MappingContext {
     }
     if (std::any_of(part.sections.begin(), part.sections.end(),
                     [element_set](const RawSection& existing) {
-                      return EqualName(existing.element_set_name, *element_set);
+                      return AsciiCaseInsensitiveEquals(
+                          existing.element_set_name, *element_set);
                     })) {
       InputFailure("duplicate-entity", block.location, block.canonical_name,
                    *element_set,
@@ -1332,7 +1306,7 @@ class MappingContext {
                      "NLGEOM requires NO in the approved subset.");
         return;
       }
-      if (!EqualName(*nlgeom->value, "NO")) {
+      if (!AsciiCaseInsensitiveEquals(*nlgeom->value, "NO")) {
         if (model_element_family_ == ElementFamily::kShell) {
           InputFailure("unsupported-nonlinear-geometry", block.location,
                        block.canonical_name, *nlgeom->value,
@@ -1510,22 +1484,24 @@ class MappingContext {
 
   const RawPart* FindPart(const std::string& name) const {
     const auto found = std::find_if(
-        parts_.begin(), parts_.end(),
+        parts_.begin(), parts_.end(), [&name](const RawPart& part) {
-        [&name](const RawPart& part) { return EqualName(part.name, name); });
+          return AsciiCaseInsensitiveEquals(part.name, name);
+        });
     return found == parts_.end() ? nullptr : &*found;
   }
 
   const RawInstance* FindInstance(const std::string& name) const {
-    const auto found = std::find_if(instances_.begin(), instances_.end(),
+    const auto found =
+        std::find_if(instances_.begin(), instances_.end(),
                      [&name](const RawInstance& instance) {
-                                      return EqualName(instance.name, name);
+                       return AsciiCaseInsensitiveEquals(instance.name, name);
                      });
     return found == instances_.end() ? nullptr : &*found;
   }
 
   std::optional<EntityIndex> FindMaterialIndex(const std::string& name) const {
     for (std::size_t index = 0U; index < materials_.size(); ++index) {
-      if (EqualName(materials_[index].name, name)) {
+      if (AsciiCaseInsensitiveEquals(materials_[index].name, name)) {
         return static_cast<EntityIndex>(index);
       }
     }
@@ -1534,9 +1510,10 @@ class MappingContext {
 
   const RawSet* FindSet(const std::vector<RawSet>& sets,
                         const std::string& name) const {
-    const auto found = std::find_if(
+    const auto found =
-        sets.begin(), sets.end(),
+        std::find_if(sets.begin(), sets.end(), [&name](const RawSet& set) {
-        [&name](const RawSet& set) { return EqualName(set.name, name); });
+          return AsciiCaseInsensitiveEquals(set.name, name);
+        });
     return found == sets.end() ? nullptr : &*found;
   }
 
@@ -2000,7 +1977,8 @@ class MappingContext {
       const auto definition_instance = std::find_if(
           definition_.instances.begin(), definition_.instances.end(),
           [&raw_instance](const InstanceDefinition& instance) {
-            return EqualName(instance.name, raw_instance->name);
+            return AsciiCaseInsensitiveEquals(instance.name,
+                                              raw_instance->name);
           });
       if (definition_instance == definition_.instances.end()) {
         InputFailure("unresolved-reference", raw_set.location,
@@ -2010,10 +1988,10 @@ class MappingContext {
       }
       if (raw_set.is_node_set) {
         definition_.node_sets.erase(
-            std::remove_if(definition_.node_sets.begin(),
+            std::remove_if(
-                           definition_.node_sets.end(),
+                definition_.node_sets.begin(), definition_.node_sets.end(),
                 [&raw_set](const NodeSet& set) {
-                             return EqualName(set.name, raw_set.name);
+                  return AsciiCaseInsensitiveEquals(set.name, raw_set.name);
                 }),
             definition_.node_sets.end());
         NodeSet set{
@@ -2040,7 +2018,8 @@ class MappingContext {
             std::remove_if(definition_.element_sets.begin(),
                            definition_.element_sets.end(),
                            [&raw_set](const ElementSet& set) {
-                             return EqualName(set.name, raw_set.name);
+                             return AsciiCaseInsensitiveEquals(set.name,
+                                                               raw_set.name);
                            }),
             definition_.element_sets.end());
         ElementSet set{
@@ -2066,68 +2045,57 @@ class MappingContext {
     }
   }
 
-  std::optional<std::vector<EntityIndex>> ResolveNodeTarget(
+  /// @brief Builds one stable node-target index from the completed candidate.
-      const std::string& target, const SourceLocation& location,
+  SourceTargetIndex BuildSourceTargetIndex() const {
-      const std::string& keyword) {
+    std::vector<SourceTargetIndexEntry> entries;
-    std::vector<const NodeSet*> matching_sets;
+    std::size_t declaration_order = 0U;
+    for (std::size_t node = 0U; node < definition_.nodes.size(); ++node) {
+      const auto& source_id = definition_.nodes[node].source_id;
+      entries.push_back({SourceEntityKind::kNode, source_id.instance_name, "",
+                         source_id, static_cast<EntityIndex>(node),
+                         declaration_order++});
+    }
     for (const auto& set : definition_.node_sets) {
-      if (EqualName(set.name, target)) {
+      for (const EntityIndex node : set.node_indices) {
-        matching_sets.push_back(&set);
+        const auto& source_id = definition_.nodes[node].source_id;
+        entries.push_back({SourceEntityKind::kNode,
+                           set.instance_name.value_or(source_id.instance_name),
+                           set.name, source_id, node, declaration_order++});
       }
     }
+    return SourceTargetIndex{std::move(entries)};
+  }
 
-    std::vector<EntityIndex> matching_nodes;
+  std::optional<std::vector<EntityIndex>> ResolveNodeTarget(
-    std::int64_t label = 0;
+      const SourceTargetResolver& resolver, const std::string& target,
-    if (TryPositiveInteger(target, label)) {
+      const SourceLocation& location, const std::string& keyword) {
-      for (std::size_t index = 0U; index < definition_.nodes.size(); ++index) {
+    auto resolved = resolver.Resolve({SourceEntityKind::kNode, "", target});
-        if (definition_.nodes[index].source_id.source_label == label) {
+    if (!resolved.HasValue()) {
-          matching_nodes.push_back(static_cast<EntityIndex>(index));
-        }
-      }
-    }
-
-    // A token is resolved only after both approved interpretations have
-    // been considered; declaration order never gives a node set priority
-    // over an equally valid direct source-label target.
-    if (matching_sets.size() > 1U) {
       InputFailure(
           "unresolved-reference", location, keyword, target,
-          "The node-set target is ambiguous across identity instances.");
+          "The boundary or load target must resolve unambiguously to one "
+          "node or one node set.");
       return std::nullopt;
     }
-    if (matching_nodes.size() > 1U) {
+    std::vector<EntityIndex> indices;
-      InputFailure("unresolved-reference", location, keyword, target,
+    indices.reserve(resolved.Value().size());
-                   "The direct node-label target is ambiguous across identity "
+    for (const auto& entry : resolved.Value()) {
-                   "instances.");
+      indices.push_back(entry.entity_index);
-      return std::nullopt;
     }
-    if (matching_sets.size() == 1U && matching_nodes.size() == 1U) {
+    return indices;
-      InputFailure("unresolved-reference", location, keyword, target,
-                   "The target is ambiguous between a node-set name and a "
-                   "direct node label.");
-      return std::nullopt;
-    }
-    if (matching_sets.size() == 1U) {
-      return matching_sets.front()->node_indices;
-    }
-    if (matching_nodes.size() == 1U) {
-      return matching_nodes;
-    }
-    InputFailure(
-        "unresolved-reference", location, keyword, target,
-        "The boundary or load target must resolve to one node or node set.");
-    return std::nullopt;
   }
 
   void FinalizeStep() {
     std::vector<BoundaryCondition> boundaries = model_boundaries_;
     boundaries.insert(boundaries.end(), step_.boundaries.begin(),
                       step_.boundaries.end());
+    const SourceTargetIndex target_index = BuildSourceTargetIndex();
+    const SourceTargetResolver target_resolver{target_index};
 
     std::map<std::pair<EntityIndex, int>, double> prescribed_values;
     for (const auto& boundary : boundaries) {
-      auto target =
+      auto target = ResolveNodeTarget(target_resolver, boundary.target,
-          ResolveNodeTarget(boundary.target, boundary.location, "BOUNDARY");
+                                      boundary.location, "BOUNDARY");
       if (!target) {
         return;
       }
@@ -2148,7 +2116,8 @@ class MappingContext {
       }
     }
     for (const auto& load : step_.loads) {
-      if (!ResolveNodeTarget(load.target, load.location, "CLOAD")) {
+      if (!ResolveNodeTarget(target_resolver, load.target, load.location,
+                             "CLOAD")) {
         return;
       }
     }

src/fesa/model/source_target_resolver.cpp

@@ -0,0 +1,227 @@
+#include "fesa/model/source_target_resolver.h"
+
+#include <algorithm>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "fesa/core/ascii.h"
+#include "fesa/model/domain.h"
+
+namespace fesa {
+namespace {
+
+struct Match {
+  const SourceTargetIndexEntry* entry;
+  bool named_target;
+  std::size_t input_order;
+};
+
+bool InstanceMatches(const std::string& query_instance,
+                     const std::string& entry_instance) {
+  return query_instance.empty() ||
+         AsciiCaseInsensitiveEquals(query_instance, entry_instance);
+}
+
+bool LooksLikeInteger(const std::string& text) {
+  if (text.empty()) {
+    return false;
+  }
+  std::size_t offset = 0U;
+  if (text.front() == '+' || text.front() == '-') {
+    offset = 1U;
+  }
+  if (offset == text.size()) {
+    return false;
+  }
+  return std::all_of(
+      text.begin() + static_cast<std::ptrdiff_t>(offset), text.end(),
+      [](const char value) { return value >= '0' && value <= '9'; });
+}
+
+Diagnostic TargetDiagnostic(const std::string& code,
+                            const std::string& identity,
+                            const std::string& message) {
+  return {Severity::kError, code, {{}, 0U}, "SOURCE_TARGET", identity, message};
+}
+
+Result<std::vector<ResolvedSourceTarget>> TargetFailure(
+    const std::string& code, const std::string& identity,
+    const std::string& message) {
+  return Result<std::vector<ResolvedSourceTarget>>::Failure(Status::Failure(
+      FailureCategory::kInput, {TargetDiagnostic(code, identity, message)}));
+}
+
+bool SpansInstances(const std::vector<Match>& matches, const bool named) {
+  const SourceTargetIndexEntry* first = nullptr;
+  for (const auto& match : matches) {
+    if (match.named_target != named) {
+      continue;
+    }
+    if (first == nullptr) {
+      first = match.entry;
+    } else if (!AsciiCaseInsensitiveEquals(first->instance_name,
+                                           match.entry->instance_name)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+}  // namespace
+
+SourceTargetIndex::SourceTargetIndex(
+    std::vector<SourceTargetIndexEntry> entries)
+    : entries_{std::move(entries)} {}
+
+SourceTargetIndex SourceTargetIndex::FromDomain(const Domain& domain) {
+  std::vector<SourceTargetIndexEntry> entries;
+  std::size_t declaration_order = 0U;
+  for (std::size_t index = 0U; index < domain.Nodes().size(); ++index) {
+    const auto& node = domain.Nodes()[index];
+    entries.push_back({SourceEntityKind::kNode, node.source_id.instance_name,
+                       "", node.source_id, static_cast<EntityIndex>(index),
+                       declaration_order++});
+  }
+  for (const auto& set : domain.NodeSets()) {
+    for (const EntityIndex node_index : set.node_indices) {
+      SourceEntityId source_id{set.instance_name.value_or(""), 0, ""};
+      if (node_index < domain.Nodes().size()) {
+        source_id = domain.Nodes()[node_index].source_id;
+      }
+      entries.push_back({SourceEntityKind::kNode,
+                         set.instance_name.value_or(source_id.instance_name),
+                         set.name, std::move(source_id), node_index,
+                         declaration_order++});
+    }
+  }
+
+  for (std::size_t index = 0U; index < domain.Elements().size(); ++index) {
+    const auto& element = domain.Elements()[index];
+    entries.push_back({SourceEntityKind::kElement,
+                       element.source_id.instance_name, "", element.source_id,
+                       static_cast<EntityIndex>(index), declaration_order++});
+  }
+  for (std::size_t index = 0U; index < domain.ShellElements().size(); ++index) {
+    const auto& element = domain.ShellElements()[index];
+    entries.push_back({SourceEntityKind::kElement,
+                       element.source_id.instance_name, "", element.source_id,
+                       static_cast<EntityIndex>(index), declaration_order++});
+  }
+  for (const auto& set : domain.ElementSets()) {
+    for (const EntityIndex element_index : set.element_indices) {
+      SourceEntityId source_id{set.instance_name.value_or(""), 0, ""};
+      if (domain.ShellElements().empty() &&
+          element_index < domain.Elements().size()) {
+        source_id = domain.Elements()[element_index].source_id;
+      } else if (domain.Elements().empty() &&
+                 element_index < domain.ShellElements().size()) {
+        source_id = domain.ShellElements()[element_index].source_id;
+      }
+      entries.push_back({SourceEntityKind::kElement,
+                         set.instance_name.value_or(source_id.instance_name),
+                         set.name, std::move(source_id), element_index,
+                         declaration_order++});
+    }
+  }
+  return SourceTargetIndex{std::move(entries)};
+}
+
+const std::vector<SourceTargetIndexEntry>& SourceTargetIndex::Entries()
+    const noexcept {
+  return entries_;
+}
+
+SourceTargetResolver::SourceTargetResolver(
+    const SourceTargetIndex& index) noexcept
+    : index_{&index} {}
+
+Result<std::vector<ResolvedSourceTarget>> SourceTargetResolver::Resolve(
+    const SourceTargetQuery& query) const {
+  const auto parsed_label =
+      ParsePositiveSourceLabel(query.target_name_or_label);
+  std::vector<Match> matches;
+  for (std::size_t input_order = 0U; input_order < index_->Entries().size();
+       ++input_order) {
+    const auto& entry = index_->Entries()[input_order];
+    if (entry.entity_kind != query.entity_kind ||
+        !InstanceMatches(query.instance_name, entry.instance_name)) {
+      continue;
+    }
+    const bool named = !entry.target_name.empty() &&
+                       AsciiCaseInsensitiveEquals(entry.target_name,
+                                                  query.target_name_or_label);
+    const bool direct = entry.target_name.empty() && parsed_label.HasValue() &&
+                        entry.source_id.source_label == parsed_label.Value();
+    if (named || direct) {
+      matches.push_back({&entry, named, input_order});
+    }
+  }
+
+  if (matches.empty()) {
+    if (!parsed_label.HasValue() &&
+        LooksLikeInteger(query.target_name_or_label)) {
+      return TargetFailure(
+          "invalid-source-target", query.target_name_or_label,
+          "A direct source target must be a positive base-10 label.");
+    }
+    return TargetFailure(
+        "unresolved-source-target", query.target_name_or_label,
+        "The source target does not resolve in its namespace.");
+  }
+
+  const bool has_named =
+      std::any_of(matches.begin(), matches.end(),
+                  [](const Match& match) { return match.named_target; });
+  const bool has_direct =
+      std::any_of(matches.begin(), matches.end(),
+                  [](const Match& match) { return !match.named_target; });
+  if ((has_named && has_direct) || SpansInstances(matches, true) ||
+      SpansInstances(matches, false)) {
+    return TargetFailure(
+        "ambiguous-source-target", query.target_name_or_label,
+        "The source target has more than one valid identity interpretation.");
+  }
+
+  std::stable_sort(
+      matches.begin(), matches.end(), [](const Match& lhs, const Match& rhs) {
+        if (lhs.entry->declaration_order != rhs.entry->declaration_order) {
+          return lhs.entry->declaration_order < rhs.entry->declaration_order;
+        }
+        return lhs.input_order < rhs.input_order;
+      });
+
+  std::vector<Diagnostic> duplicate_diagnostics;
+  std::vector<EntityIndex> seen_indices;
+  for (const auto& match : matches) {
+    const auto duplicate = std::find(seen_indices.begin(), seen_indices.end(),
+                                     match.entry->entity_index);
+    if (duplicate != seen_indices.end()) {
+      duplicate_diagnostics.push_back(TargetDiagnostic(
+          "duplicate-source-target", query.target_name_or_label,
+          "Duplicate resolved source target " +
+              match.entry->source_id.source_label_text + "."));
+    } else {
+      seen_indices.push_back(match.entry->entity_index);
+    }
+  }
+  if (!duplicate_diagnostics.empty()) {
+    return Result<std::vector<ResolvedSourceTarget>>::Failure(Status::Failure(
+        FailureCategory::kInput, std::move(duplicate_diagnostics)));
+  }
+  if (!has_named && seen_indices.size() > 1U) {
+    return TargetFailure(
+        "ambiguous-source-target", query.target_name_or_label,
+        "The direct source label resolves to multiple semantic entities.");
+  }
+
+  std::vector<ResolvedSourceTarget> resolved;
+  resolved.reserve(matches.size());
+  for (const auto& match : matches) {
+    resolved.push_back({match.entry->source_id, match.entry->entity_index});
+  }
+  return Result<std::vector<ResolvedSourceTarget>>::Success(
+      std::move(resolved));
+}
+
+}  // namespace fesa

src/fesa/results/result_recovery.cpp

@@ -2,21 +2,19 @@
 
 #include <algorithm>
 #include <array>
-#include <charconv>
 #include <cmath>
 #include <cstddef>
-#include <cstdint>
 #include <limits>
 #include <optional>
 #include <stdexcept>
 #include <string>
-#include <system_error>
 #include <utility>
 #include <vector>
 
 #include "fesa/elements/euler_beam_3d.h"
 #include "fesa/elements/mitc4_shell.h"
 #include "fesa/math/vector3.h"
+#include "fesa/model/source_target_resolver.h"
 
 namespace fesa {
 namespace {
@@ -324,70 +322,29 @@ Status ValidateRecoveryInputs(const AnalysisModel& model,
   return Status::Ok();
 }
 
-char AsciiLower(const char value) {
+Result<std::vector<EntityIndex>> ResolveLoadTarget(
-  if (value >= 'A' && value <= 'Z') {
+    const SourceTargetResolver& resolver, const Domain& domain,
-    return static_cast<char>(value + ('a' - 'A'));
-  }
-  return value;
-}
-
-bool EqualName(const std::string& left, const std::string& right) {
-  return left.size() == right.size() &&
-         std::equal(left.begin(), left.end(), right.begin(),
-                    [](const char left_value, const char right_value) {
-                      return AsciiLower(left_value) == AsciiLower(right_value);
-                    });
-}
-
-bool TryPositiveInteger(const std::string& text, std::int64_t& value) {
-  const char* const first = text.data();
-  const char* const last = first + text.size();
-  const auto parsed = std::from_chars(first, last, value);
-  return parsed.ec == std::errc{} && parsed.ptr == last && value > 0;
-}
-
-Result<std::vector<EntityIndex>> ResolveLoadTarget(const Domain& domain,
     const NodalLoad& load) {
-  std::vector<const NodeSet*> sets;
+  auto resolved = resolver.Resolve({SourceEntityKind::kNode, "", load.target});
-  for (const auto& set : domain.NodeSets()) {
+  if (!resolved.HasValue()) {
-    if (EqualName(set.name, load.target)) {
-      sets.push_back(&set);
-    }
-  }
-  std::vector<EntityIndex> nodes;
-  std::int64_t source_label = 0;
-  if (TryPositiveInteger(load.target, source_label)) {
-    for (std::size_t node = 0U; node < domain.Nodes().size(); ++node) {
-      if (domain.Nodes()[node].source_id.source_label == source_label) {
-        nodes.push_back(static_cast<EntityIndex>(node));
-      }
-    }
-  }
-  if (sets.size() > 1U || nodes.size() > 1U ||
-      (!sets.empty() && !nodes.empty())) {
     return RecoveryResultFailure<std::vector<EntityIndex>>(
         "invalid-node-station-entity", load.location, load.target,
         "A station-eligibility load target must resolve unambiguously.");
   }
-  if (!sets.empty()) {
+  std::vector<EntityIndex> nodes;
+  nodes.reserve(resolved.Value().size());
   std::vector<unsigned char> seen(domain.Nodes().size(), 0U);
-    for (const EntityIndex node : sets.front()->node_indices) {
+  for (const auto& target : resolved.Value()) {
+    const EntityIndex node = target.entity_index;
     if (node >= domain.Nodes().size() || seen[node] != 0U) {
       return RecoveryResultFailure<std::vector<EntityIndex>>(
           "invalid-node-station-entity", load.location, load.target,
           "A station-eligibility node set must contain unique valid nodes.");
     }
     seen[node] = 1U;
+    nodes.push_back(node);
   }
-    return Result<std::vector<EntityIndex>>::Success(
-        sets.front()->node_indices);
-  }
-  if (!nodes.empty()) {
   return Result<std::vector<EntityIndex>>::Success(std::move(nodes));
-  }
-  return RecoveryResultFailure<std::vector<EntityIndex>>(
-      "invalid-node-station-entity", load.location, load.target,
-      "A station-eligibility load target must resolve to a node or node set.");
 }
 
 bool AccumulateVectorAndScale(std::array<double, 3>& total, double& scale,
@@ -879,6 +836,8 @@ ResultRecovery::NormalizeSectionResultantsToNodeStations(
         "invalid-node-station-entity", model.Step().location, model.Step().name,
         "The active load view must preserve every sole-step load.");
   }
+  const SourceTargetIndex target_index = SourceTargetIndex::FromDomain(domain);
+  const SourceTargetResolver target_resolver{target_index};
   for (std::size_t order = 0U; order < model.ActiveLoads().size(); ++order) {
     const EntityIndex load_index = model.ActiveLoads()[order];
     if (load_index != order || load_index >= model.Step().loads.size()) {
@@ -893,7 +852,7 @@ ResultRecovery::NormalizeSectionResultantsToNodeStations(
           "nonfinite-node-station-value", load.location, load.target,
           "Station eligibility requires finite concentrated loads.");
     }
-    auto targets = ResolveLoadTarget(domain, load);
+    auto targets = ResolveLoadTarget(target_resolver, domain, load);
     if (!targets.HasValue()) {
       return Result<std::vector<NodeStationResultRow>>::Failure(
           targets.GetStatus());

tests/CMakeLists.txt

@@ -9,6 +9,7 @@ add_executable(
     unit/assembly/load_assembler_test.cpp
     unit/assembly/sparse_assembler_test.cpp
     unit/constraints/essential_constraints_test.cpp
+    unit/core/ascii_test.cpp
     unit/core/diagnostic_test.cpp
     unit/core/source_identity_test.cpp
     unit/core/status_test.cpp
@@ -27,6 +28,7 @@ add_executable(
     unit/model/domain_test.cpp
     unit/model/model_types_test.cpp
     unit/model/shell_geometry_test.cpp
+    unit/model/source_target_resolver_test.cpp
     unit/results/result_records_test.cpp
     unit/results/result_recovery_test.cpp
     unit/results/results_writer_test.cpp

tests/unit/core/ascii_test.cpp

@@ -0,0 +1,57 @@
+#include "fesa/core/ascii.h"
+
+#include <gtest/gtest.h>
+
+#include <cstdint>
+#include <limits>
+#include <string>
+#include <vector>
+
+TEST(Ascii, LowercasesOnlyAsciiUppercaseBytes) {
+  EXPECT_EQ(fesa::AsciiLower('A'), 'a');
+  EXPECT_EQ(fesa::AsciiLower('Z'), 'z');
+  EXPECT_EQ(fesa::AsciiLower('a'), 'a');
+  EXPECT_EQ(fesa::AsciiLower('0'), '0');
+
+  const char non_ascii = static_cast<char>(0xc0U);
+  EXPECT_EQ(fesa::AsciiLower(non_ascii), non_ascii);
+}
+
+TEST(Ascii, ComparesNamesWithoutLocaleOrUnicodeFolding) {
+  EXPECT_TRUE(fesa::AsciiCaseInsensitiveEquals("Beam-1", "bEaM-1"));
+  EXPECT_FALSE(fesa::AsciiCaseInsensitiveEquals("Beam-1", "Beam-10"));
+
+  const std::string uppercase_byte{static_cast<char>(0xc0U)};
+  const std::string lowercase_byte{static_cast<char>(0xe0U)};
+  EXPECT_FALSE(
+      fesa::AsciiCaseInsensitiveEquals(uppercase_byte, lowercase_byte));
+}
+
+TEST(Ascii, ParsesOnlyCompletePositiveBaseTenSourceLabels) {
+  auto one = fesa::ParsePositiveSourceLabel("1");
+  auto leading_zeroes = fesa::ParsePositiveSourceLabel("00042");
+  auto maximum = fesa::ParsePositiveSourceLabel(
+      std::to_string((std::numeric_limits<std::int64_t>::max)()));
+
+  ASSERT_TRUE(one.HasValue());
+  EXPECT_EQ(one.Value(), 1);
+  ASSERT_TRUE(leading_zeroes.HasValue());
+  EXPECT_EQ(leading_zeroes.Value(), 42);
+  ASSERT_TRUE(maximum.HasValue());
+  EXPECT_EQ(maximum.Value(), (std::numeric_limits<std::int64_t>::max)());
+
+  const std::string overflow =
+      std::to_string((std::numeric_limits<std::int64_t>::max)()) + "0";
+  const std::vector<std::string> invalid_values{"",   "0",  "-1", "+",     "+1",
+                                                " 1", "1 ", "1x", overflow};
+  for (const std::string& invalid : invalid_values) {
+    SCOPED_TRACE(invalid);
+    auto result = fesa::ParsePositiveSourceLabel(invalid);
+    ASSERT_FALSE(result.HasValue());
+    EXPECT_EQ(result.GetStatus().Category(), fesa::FailureCategory::kInput);
+    ASSERT_EQ(result.GetStatus().Diagnostics().size(), 1U);
+    EXPECT_EQ(result.GetStatus().Diagnostics()[0U].code,
+              "invalid-source-label");
+    EXPECT_EQ(result.GetStatus().Diagnostics()[0U].entity_identity, invalid);
+  }
+}

tests/unit/model/source_target_resolver_test.cpp

@@ -0,0 +1,135 @@
+#include "fesa/model/source_target_resolver.h"
+
+#include <gtest/gtest.h>
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace {
+
+fesa::SourceTargetIndexEntry Entry(const fesa::SourceEntityKind entity_kind,
+                                   std::string instance_name,
+                                   std::string target_name,
+                                   const std::int64_t source_label,
+                                   std::string source_label_text,
+                                   const fesa::EntityIndex entity_index,
+                                   const std::size_t declaration_order) {
+  fesa::SourceEntityId source_id{instance_name, source_label,
+                                 std::move(source_label_text)};
+  return {entity_kind,
+          std::move(instance_name),
+          std::move(target_name),
+          std::move(source_id),
+          entity_index,
+          declaration_order};
+}
+
+std::vector<fesa::EntityIndex> Indices(
+    const std::vector<fesa::ResolvedSourceTarget>& targets) {
+  std::vector<fesa::EntityIndex> indices;
+  indices.reserve(targets.size());
+  for (const auto& target : targets) {
+    indices.push_back(target.entity_index);
+  }
+  return indices;
+}
+
+void ExpectFailure(const fesa::SourceTargetIndex& index,
+                   fesa::SourceTargetQuery query, const std::string& code) {
+  const auto result = fesa::SourceTargetResolver{index}.Resolve(query);
+  ASSERT_FALSE(result.HasValue());
+  EXPECT_EQ(result.GetStatus().Category(), fesa::FailureCategory::kInput);
+  ASSERT_FALSE(result.GetStatus().Diagnostics().empty());
+  EXPECT_EQ(result.GetStatus().Diagnostics()[0U].code, code);
+  EXPECT_EQ(result.GetStatus().Diagnostics()[0U].entity_identity,
+            query.target_name_or_label);
+}
+
+}  // namespace
+
+TEST(SourceTargetResolver,
+     SeparatesNamespacesAndInstancesAndExpandsInDeclarationOrder) {
+  using fesa::SourceEntityKind;
+  fesa::SourceTargetIndex index{{
+      Entry(SourceEntityKind::kNode, "Beam-1", "Ends", 20, "0020", 1U, 30U),
+      Entry(SourceEntityKind::kElement, "Beam-1", "Ends", 700, "0700", 4U, 10U),
+      Entry(SourceEntityKind::kNode, "Beam-1", "Ends", 10, "0010", 0U, 20U),
+      Entry(SourceEntityKind::kNode, "Beam-2", "Ends", 10, "0010", 2U, 40U),
+      Entry(SourceEntityKind::kNode, "Beam-1", "", 10, "0010", 0U, 0U),
+  }};
+  const fesa::SourceTargetResolver resolver{index};
+
+  auto nodes = resolver.Resolve({SourceEntityKind::kNode, "bEaM-1", "eNdS"});
+  ASSERT_TRUE(nodes.HasValue());
+  EXPECT_EQ(Indices(nodes.Value()), (std::vector<fesa::EntityIndex>{0U, 1U}));
+  EXPECT_EQ(nodes.Value()[0U].source_id.instance_name, "Beam-1");
+  EXPECT_EQ(nodes.Value()[0U].source_id.source_label_text, "0010");
+
+  auto elements =
+      resolver.Resolve({SourceEntityKind::kElement, "BEAM-1", "ends"});
+  ASSERT_TRUE(elements.HasValue());
+  EXPECT_EQ(Indices(elements.Value()), (std::vector<fesa::EntityIndex>{4U}));
+
+  auto second_instance =
+      resolver.Resolve({SourceEntityKind::kNode, "beam-2", "ENDS"});
+  ASSERT_TRUE(second_instance.HasValue());
+  EXPECT_EQ(Indices(second_instance.Value()),
+            (std::vector<fesa::EntityIndex>{2U}));
+
+  auto direct = resolver.Resolve({SourceEntityKind::kNode, "Beam-1", "10"});
+  ASSERT_TRUE(direct.HasValue());
+  EXPECT_EQ(Indices(direct.Value()), (std::vector<fesa::EntityIndex>{0U}));
+}
+
+TEST(SourceTargetResolver, RejectsMissingAmbiguousAndNonpositiveTargets) {
+  using fesa::SourceEntityKind;
+  const fesa::SourceTargetIndex index{{
+      Entry(SourceEntityKind::kNode, "Beam-1", "", 10, "10", 0U, 0U),
+      Entry(SourceEntityKind::kNode, "Beam-2", "", 10, "10", 1U, 1U),
+      Entry(SourceEntityKind::kNode, "Beam-1", "10", 20, "20", 2U, 2U),
+      Entry(SourceEntityKind::kNode, "Beam-1", "Shared", 10, "10", 0U, 3U),
+      Entry(SourceEntityKind::kNode, "Beam-2", "Shared", 10, "10", 1U, 4U),
+  }};
+
+  ExpectFailure(index, {SourceEntityKind::kNode, "", "Missing"},
+                "unresolved-source-target");
+  ExpectFailure(index, {SourceEntityKind::kNode, "", "0"},
+                "invalid-source-target");
+  ExpectFailure(index, {SourceEntityKind::kNode, "", "-7"},
+                "invalid-source-target");
+  ExpectFailure(index, {SourceEntityKind::kNode, "", "10"},
+                "ambiguous-source-target");
+  ExpectFailure(index, {SourceEntityKind::kNode, "", "Shared"},
+                "ambiguous-source-target");
+  ExpectFailure(index, {SourceEntityKind::kNode, "Beam-1", "10"},
+                "ambiguous-source-target");
+}
+
+TEST(SourceTargetResolver,
+     ReportsDuplicateMembershipsInDeterministicDeclarationOrder) {
+  using fesa::SourceEntityKind;
+  const fesa::SourceTargetIndex index{{
+      Entry(SourceEntityKind::kNode, "Beam-1", "Duplicate", 10, "10", 0U, 1U),
+      Entry(SourceEntityKind::kNode, "Beam-1", "Duplicate", 10, "10", 0U, 9U),
+      Entry(SourceEntityKind::kNode, "Beam-1", "Duplicate", 20, "20", 1U, 2U),
+      Entry(SourceEntityKind::kNode, "Beam-1", "Duplicate", 20, "20", 1U, 7U),
+  }};
+
+  const auto result = fesa::SourceTargetResolver{index}.Resolve(
+      {SourceEntityKind::kNode, "Beam-1", "duplicate"});
+
+  ASSERT_FALSE(result.HasValue());
+  EXPECT_EQ(result.GetStatus().Category(), fesa::FailureCategory::kInput);
+  ASSERT_EQ(result.GetStatus().Diagnostics().size(), 2U);
+  EXPECT_EQ(result.GetStatus().Diagnostics()[0U].code,
+            "duplicate-source-target");
+  EXPECT_EQ(result.GetStatus().Diagnostics()[0U].message,
+            "Duplicate resolved source target 20.");
+  EXPECT_EQ(result.GetStatus().Diagnostics()[1U].code,
+            "duplicate-source-target");
+  EXPECT_EQ(result.GetStatus().Diagnostics()[1U].message,
+            "Duplicate resolved source target 10.");
+}