ABI/API taxonomy coverage

Phases 2 and 3 of ABI/API knowledge and corpus: every leaf mechanism in the ABI/API failure taxonomy resolved against the three things this repository already has -- the docs/learn/ page(s) that explain it, the catalog/cases/ case(s) that demonstrate it, and the ChangeKind(s) that would produce a finding for it -- and then classified with exactly one coverage status.

The taxonomy is deliberately independent of abicheck's own vocabulary, which is what lets this page find a gap on either side rather than defining the domain in abicheck's image and then trivially covering it. A column may legitimately be empty; an empty one is recorded, not filled in with the nearest plausible match.

The mapping itself is hand-maintained in docs/_meta/abi-taxonomy-coverage.json (the single source of truth this page renders and scripts/check_ai_readiness.py's abi-taxonomy-coverage check gates). Only two facts on this page are derived: each ChangeKind's owning abicheck/model/change_catalog/ module and its minimum evidence tier (scripts/evidence_tiers.py), read from those sources so they cannot go stale here.

Headline

65 of 88 known ABI/API failure mechanisms are COVERED -- explained by a docs/learn/ page, demonstrated by a catalog/cases/ case, and detected by at least one ChangeKind. The remaining 23: 3 KNOWN_UNDETECTABLE, 1 NOT_IMPLEMENTED, 11 MISSING_CASE, 8 PARTIALLY_COVERED.

This is the plan's intended metric: completeness against the domain, not a case count. A corpus can grow indefinitely without moving this number, and can look complete while a whole mechanism class has no case at all.

Status	Leaves	Meaning
NOT_APPLICABLE	0	outside abicheck's stated scope
KNOWN_UNDETECTABLE	3	real and explained, but no static evidence distinguishes it
NOT_IMPLEMENTED	1	no detector claims it at any evidence tier -- a tractable product gap
MISSING_CASE	11	a detector exists, but no catalog case demonstrates it
PARTIALLY_COVERED	8	detected and demonstrated, but only a narrower sub-case, or unexplained
COVERED	65	explained, demonstrated, and detected
Total	88

The six statuses are evaluated in the order listed (first match wins) -- see the plan's own Phase 3 table in ABI/API knowledge and corpus for each definition. The order, not the prose, is what keeps them mutually exclusive: a mechanism with a detector but no case satisfies both "detection is real" and "no case exists".

Phase 4 backlog

The 11 MISSING_CASE leaves below are Phase 4's concrete work list: a detector already claims each one, so the gap is a corpus gap. Phase 4 closes each with a paired positive/negative control through the ordinary case-authoring path (catalog/CLAUDE.md) -- it is not started, and this page does not require the list to reach zero (a tracked, visible gap is preferred to a manufactured closure).

Leaf	Why it is open
calling-contract.variadic-change	Four detectors claim the fixed-arity/variadic transition, none has a case, and no docs/learn/ page mentions variadic functions at all -- so this leaf is a corpus gap and a documentation gap at once.
dependency-abi.version-range-widening	Four detectors reason about a dependency constraint admitting an incompatible version, and learn/dependency-floors.md explains the mechanism, but no case widens a range and shows the consequence.
ecosystem-specific.cpython-limited-api-tag-change	Three detectors (plus the vendored Stable-ABI membership set) claim the limited-API contract, and learn/packages-and-consumers.md explains abi3, but no catalog case is a CPython extension module changing its stable-ABI tag.
ecosystem-specific.cpython-object-layout-change	python_gil_abi_changed covers the free-threaded/no-GIL build split and python_stable_abi_violation covers reaching into a non-guaranteed field, but no case exercises either, and CPython's own object-layout evolution across interpreter versions has no fixture.
ecosystem-specific.sycl-device-binary-format-change	The SYCL plugin/runtime detectors exist, but the two SYCL cases in the catalog are host-side (an overload set and a device-impl pointer field); no case changes the packaged device-binary format or target list.
export-surface.documented-contract-drift	The surface-growth detectors exist and learn/surface-growth.md explains the mechanism, but no case exercises accretion of an undocumented surface across releases.
export-surface.version-script-map-change	Three detectors claim the export-map surface (an absent version script, a changed export policy, a retargeted PE ordinal), but the corpus has no case where a version script or .def file -- and nothing else -- changes the export set.
source-abi.macro-driven-layout-change	case164 is the false-positive control (a #ifdef-guarded field where both releases define the macro, so the correct answer is NO_CHANGE). No case demonstrates the positive mechanism -- two consumers compiling the same header under different macro state and getting different layouts -- which the context-mismatch detectors claim.
source-api.signature-change-source-only	case186 is the ABI-neutral negative control (a char* parameter becoming const char*, which must stay NO_CHANGE). No case demonstrates the positive mechanism: a binary-identical change that still breaks recompilation of consumer source.
symbol-identity.alias-change	Detection exists for the .symver alias half (plus the PE forwarder and Mach-O re-export analogues), but no catalog case exercises any of them, and no detector claims a plain __attribute__((alias)) repoint.
toolchain-platform.endianness-change	elf_endianness_changed claims the mechanism outright, but no case pairs a little-endian and a big-endian build -- the catalog's build fixtures are all produced on one host.

Separately, 1 leaf is NOT_IMPLEMENTED -- a product gap rather than a corpus gap, tracked in known gaps: dependency-abi.linking-mode-change. And 3 leaves are KNOWN_UNDETECTABLE -- accepted limitations, cross-referenced from Limitations: header-only.include-guard-macro-collision, header-only.template-heavy-recompilation-drift, symbol-identity.ifunc-resolver-change.

Per-leaf mapping

One row per taxonomy leaf, in the taxonomy's own branch and row order. Each detector cell names the ChangeKind, the abicheck/model/change_catalog/ module that owns its registry entry, and its minimum evidence tier; -- there means the kind carries no entry in scripts/evidence_tiers.py's EVIDENCE_TIER_BY_KIND (that table covers the kinds the example catalog exercises, not every kind in the registry). A case cell marked (control only) maps a case that exercises the mechanism's non-breaking sibling -- a negative or false-positive control -- without demonstrating the mechanism itself.

1. Symbol identity (symbol-identity)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
symbol-identity.removal Symbol removal	abi-cheat-sheet 02-symbol-contracts	case01_symbol_removal case12_function_removed case182_accidental_export_removed_still_breaking case58_var_removed	func_removed (symbols, L0) func_removed_elf_only (symbols, L0) type_removed (types, L1) var_removed (symbols, L0)	COVERED
symbol-identity.rename Symbol rename	02-symbol-contracts	case194_header_graph_rename_reconciled case86_tag_struct_renamed	declaration_renamed (source, L5) func_likely_renamed (symbols, --) symbol_renamed_batch (symbols, --) tag_type_renamed (types, L0)	PARTIALLY_COVERED
symbol-identity.mangling-scheme-change Mangling-scheme change	04-cpp-abi modern-cpp-toolchain-hazards msvc-pe-abi-model system-library-discipline	case104_glibcxx_dual_abi_flip case113_abi_tag_changed	abi_tag_changed (platform, L0) glibcxx_dual_abi_flip_detected (platform, L0) libcpp_abi_version_changed (types, --)	COVERED
symbol-identity.mangling-signature-change Mangling-signature change	02-symbol-contracts 04-cpp-abi	case02_param_type_change case10_return_type case166_ref_qualifier_added case22_method_const_changed	func_cv_changed (types, L1) func_params_changed (symbols, L1) func_ref_qual_changed (types, L2) func_return_changed (symbols, L1)	COVERED
symbol-identity.linkage-change Linkage change	02-symbol-contracts 05-linker-elf	case157_inline_function_removed case59_func_became_inline case66_language_linkage_changed	func_became_inline (symbols, --) func_language_linkage_changed (symbols, L0) func_lost_inline (symbols, --) func_removed_elf_only (symbols, L0) inline_function_removed (source, L4)	COVERED
symbol-identity.visibility-change Visibility attribute change	05-linker-elf abi-surface elf-symbol-filtering	case06_visibility case51_protected_visibility	func_visibility_changed (symbols, L0) func_visibility_protected_changed (platform, --) protected_visibility_changed (platform, --) symbol_elf_visibility_changed (platform, L0) type_visibility_changed (types, --) visibility_leak (platform, --)	COVERED
symbol-identity.version-node-change Symbol-version-node change	05-linker-elf system-library-discipline	case139_symbol_version_node_removed case13_symbol_versioning case183_internal_version_node_churn case65_symbol_version_removed	symbol_moved_version_node (platform, --) symbol_version_defined_added (platform, L0) symbol_version_defined_removed (platform, L0) symbol_version_node_removed (platform, L0) symbol_version_required_added (platform, L0) symbol_version_required_removed (platform, --)	COVERED
symbol-identity.weak-strong-binding-change Weak/strong binding change	abi-cheat-sheet	case128_symbol_binding_strengthened case180_symbol_binding_lost_unique case27_symbol_binding_weakened	common_symbol_risk (platform, --) symbol_binding_became_unique (platform, L0) symbol_binding_changed (platform, L0) symbol_binding_lost_unique (platform, L0) symbol_binding_strengthened (platform, L0)	PARTIALLY_COVERED
symbol-identity.alias-change Symbol alias change	02-symbol-contracts system-library-discipline	none	macho_reexport_changed (platform, L0) pe_forwarder_changed (platform, L0) symbol_version_alias_changed (platform, --)	MISSING_CASE
symbol-identity.ifunc-resolver-change Indirect-function resolver change	dependency-floors modern-cpp-toolchain-hazards verdicts	case29_ifunc_transition	ifunc_introduced (platform, L0) ifunc_removed (platform, --)	KNOWN_UNDETECTABLE

• symbol-identity.rename (PARTIALLY_COVERED) — The catalog demonstrates rename reconciliation at the L5 source-graph tier (case194) and a tag-type rename, but no case exercises the flat exported-symbol rename detectors (func_likely_renamed/symbol_renamed_batch) on a binary pair.
• symbol-identity.weak-strong-binding-change (PARTIALLY_COVERED) — Detection and cases are complete, but the only docs/learn/ material is a pair of cheat-sheet table rows -- no narrative page explains weak/strong binding, interposition, or when relaxing it matters.
• symbol-identity.alias-change (MISSING_CASE) — Detection exists for the .symver alias half (plus the PE forwarder and Mach-O re-export analogues), but no catalog case exercises any of them, and no detector claims a plain __attribute__((alias)) repoint.
• symbol-identity.ifunc-resolver-change (KNOWN_UNDETECTABLE) — abicheck observes ifunc adoption and removal (ifunc_introduced/ifunc_removed, case29), but the mechanism as stated is a change inside the resolver's own selection logic: which implementation binds is decided at load time from CPU features, so no static evidence from two artifacts distinguishes an unchanged resolver from one that now selects differently.

2. Function calling contract (calling-contract)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
calling-contract.parameter-type-change Parameter type change	02-symbol-contracts	case02_param_type_change case189_public_function_private_parameter_type case33_pointer_level case46_pointer_chain_type_change	func_params_changed (symbols, L1) param_pointer_level_changed (symbols, L1) template_param_type_changed (types, --)	COVERED
calling-contract.parameter-count-change Parameter count (arity) change	02-symbol-contracts	case199_public_function_parameter_added case200_new_entry_point_instead_of_parameter_added	func_params_changed (symbols, L1) mandatory_template_param_added (types, --)	COVERED
calling-contract.parameter-order-change Parameter order change	02-symbol-contracts	case201_public_function_parameters_reordered case202_public_header_declaration_order_changed	func_params_changed (symbols, L1)	COVERED
calling-contract.return-type-change Return type change	02-symbol-contracts	case102_frozen_runtime_signature_changed case10_return_type case46_pointer_chain_type_change	func_return_changed (symbols, L1) return_pointer_level_changed (symbols, --) template_return_type_changed (types, --) unspecified_return_now_named (types, --)	COVERED
calling-contract.calling-convention-change Calling-convention change	05-linker-elf msvc-pe-abi-model	case64_calling_convention_changed	calling_convention_changed (symbols, L1)	COVERED
calling-contract.exception-specification-abi-change Exception-specification ABI change	04-cpp-abi exception-unwinding-abi	case130_exceptions_mode_flip case15_noexcept_change	exceptions_mode_changed (platform, L3) func_exception_spec_changed (symbols, L2) func_noexcept_added (symbols, --) func_noexcept_removed (symbols, --)	COVERED
calling-contract.variadic-change Variadic/fixed-arity change	none	none	func_variadic_added (symbols, L2) func_variadic_removed (symbols, L2) param_became_va_list (symbols, --) param_lost_va_list (symbols, --)	MISSING_CASE
calling-contract.implicit-this-change Implicit this change	04-cpp-abi	case21_method_became_static	func_static_changed (types, L1)	COVERED
calling-contract.aggregate-classification-change Aggregate-classification change	04-cpp-abi class-layout-abi	case129_struct_return_convention case69_trivial_to_nontrivial	standard_layout_lost (types, --) struct_return_convention_changed (platform, L1) trivially_copyable_lost (types, --) value_abi_trait_changed (platform, L1)	COVERED
calling-contract.pass-by-value-threshold-change Pass-by-value size-threshold crossing	04-cpp-abi class-layout-abi	case129_struct_return_convention	struct_return_convention_changed (platform, L1)	PARTIALLY_COVERED

• calling-contract.variadic-change (MISSING_CASE) — Four detectors claim the fixed-arity/variadic transition, none has a case, and no docs/learn/ page mentions variadic functions at all -- so this leaf is a corpus gap and a documentation gap at once.
• calling-contract.pass-by-value-threshold-change (PARTIALLY_COVERED) — Detection covers the return-value register-vs-memory transition only. A by-value aggregate parameter growing across the same platform threshold is reported as an ordinary size change, with no finding stating that the argument moved from registers to an invisible reference.

3. Data layout (data-layout)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
data-layout.size-change Type size change	03-type-layout class-layout-abi	case07_struct_layout case14_cpp_class_size case17_template_abi case40_field_layout case48_leaf_struct_through_pointer	struct_size_changed (types, L1) symbol_size_changed (symbols, L0) symbol_size_changed_const_object (symbols, --) type_size_changed (types, L1)	COVERED
data-layout.alignment-change Alignment change	03-type-layout class-layout-abi	case42_type_alignment_changed	exported_object_alignment_reduced (platform, L0) struct_alignment_changed (types, --) type_alignment_changed (types, L1) var_alignment_changed (symbols, L2)	COVERED
data-layout.field-offset-change Field offset change	03-type-layout class-layout-abi	case117_no_unique_address case43_base_class_member_added case77_detail_templated_base_changed	base_class_offset_changed (types, L1) struct_field_offset_changed (types, --) type_field_offset_changed (types, L1)	COVERED
data-layout.field-reorder Field reorder	03-type-layout	case120_internal_struct_reordered_scoped case198_public_struct_field_reorder	field_renamed (types, L1) struct_field_type_changed (types, L1) type_field_offset_changed (types, L1)	COVERED
data-layout.padding-change Packing/padding change	03-type-layout class-layout-abi	case153_struct_packing_flip case56_struct_packing_changed	struct_packing_changed (types, L1) struct_packing_mode_changed (platform, L3)	COVERED
data-layout.bitfield-allocation-change Bitfield allocation change	03-type-layout class-layout-abi	case63_bitfield_changed	field_bitfield_changed (types, L1)	COVERED
data-layout.enum-underlying-type-change Enum underlying-type change	03-type-layout	case152_enum_size_flag_flip case57_enum_underlying_size_changed	enum_became_scoped (types, L2) enum_lost_scoped (types, L2) enum_size_flag_changed (platform, L3) enum_underlying_size_changed (platform, L1)	COVERED
data-layout.union-active-member-change Union member change	03-type-layout	case24_union_field_removed case26_union_field_added case26b_union_field_added_compatible	union_field_added (types, L1) union_field_removed (types, L1) union_field_type_changed (types, --)	COVERED
data-layout.embedded-array-dimension-change Embedded fixed-array dimension change	03-type-layout	case45_multi_dim_array_change	type_field_type_changed (types, L1) type_size_changed (types, L1)	COVERED
data-layout.flexible-array-member-change Flexible array member change	03-type-layout	case70_flexible_array_member_changed	flexible_array_member_changed (types, L1)	COVERED
data-layout.tail-padding-reuse-change Tail-padding reuse change	03-type-layout class-layout-abi modern-cpp-toolchain-hazards	case117_no_unique_address case140_empty_base_optimization_lost	base_class_offset_changed (types, L1) tail_padding_reuse_changed (types, --) type_field_offset_changed (types, L1)	COVERED

4. C++ object model (cpp-object-model)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
cpp-object-model.base-class-addition-removal Base class addition/removal	04-cpp-abi class-layout-abi	case188_public_class_private_base_class case37_base_class case60_base_class_position_changed	base_class_offset_changed (types, L1) base_class_position_changed (types, L1) type_base_changed (types, L1)	COVERED
cpp-object-model.virtual-function-insertion-reorder Virtual function insertion/reorder	04-cpp-abi class-layout-abi	case09_cpp_vtable case142_vtable_slot_count_binary_only case185_inherited_override_reuses_slot case38_virtual_methods case68_virtual_method_added	func_virtual_added (symbols, L1) type_vtable_changed (types, L1) virtual_method_added (types, --) vtable_slot_count_changed (types, L0) vtable_symbol_identity_changed (platform, --)	COVERED
cpp-object-model.virtual-function-removal Virtual function removal	04-cpp-abi class-layout-abi	case168_virtual_method_devirtualized	func_virtual_removed (symbols, L2) vtable_slot_count_changed (types, L0)	COVERED
cpp-object-model.pure-virtual-transition Pure/non-pure virtual transition	04-cpp-abi	case23_pure_virtual_added	func_pure_virtual_added (types, L1) func_virtual_became_pure (types, L1) type_became_abstract (types, L2) type_lost_abstract (types, L2)	COVERED
cpp-object-model.multiple-inheritance-thunk-change Multiple-inheritance thunk/vtable change	04-cpp-abi class-layout-abi	case172_vtable_thunk_offset_changed case173_vtt_slot_count_changed case174_secondary_vtable_group_changed	secondary_vtable_group_changed (types, L1) vtable_thunk_offset_changed (types, L0) vtable_thunk_set_changed (types, L0) vtt_slot_count_changed (types, L0)	COVERED
cpp-object-model.rtti-representation-change RTTI representation change	04-cpp-abi class-layout-abi msvc-pe-abi-model	case131_rtti_mode_flip case146_audit_rtti_for_internal	rtti_for_internal_type (source, L2) rtti_inheritance_changed (types, L0) rtti_mode_changed (platform, L3)	PARTIALLY_COVERED
cpp-object-model.virtual-base-layout-change Virtual base layout change	04-cpp-abi msvc-pe-abi-model	case167_base_became_virtual	base_class_virtual_changed (types, L1) virtual_base_offset_changed (types, L1)	COVERED
cpp-object-model.covariant-return-type-change Covariant return-type change	04-cpp-abi	case72_covariant_return_changed	func_return_changed (symbols, L1) type_vtable_changed (types, L1) vtable_thunk_set_changed (types, L0)	COVERED
cpp-object-model.vptr-presence-change Vptr presence change	03-type-layout class-layout-abi	case203_class_gained_vtable_pointer case204_class_gained_non_virtual_method	type_field_offset_changed (types, L1) type_size_changed (types, L1) vptr_introduced (types, L1)	COVERED

• cpp-object-model.rtti-representation-change (PARTIALLY_COVERED) — Detection covers RTTI being switched on/off (rtti_mode_changed), an inheritance-shape change reflected in the RTTI records, and RTTI emitted for an internal type. The type_info record's own layout or mangled type-name representation changing -- the Itanium-vs-MSVC representation question this leaf names -- has no detector and no case.

5. Inline/template/source ABI (source-abi)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
source-abi.inline-function-body-change Inline function body change	04-cpp-abi limitations static-and-header-only	case157_inline_function_removed case16_inline_to_non_inline case47_inline_to_outlined case89_inline_accessor_renamed_pimpl_member	func_became_inline (symbols, --) func_lost_inline (symbols, --) inline_body_changed (source, --) inline_body_references_renamed_member (types, L2) inline_function_removed (source, L4)	COVERED
source-abi.template-instantiation-set-change Template instantiation-set change	04-cpp-abi limitations template-heavy-libraries	case122_template_signature_uninstantiated case79_missing_template_instantiation case93_bundle_manifest_drift	bundle_manifest_instantiation_added (build, --) bundle_manifest_instantiation_removed (build, L0) instantiation_missing_from_binary (types, L2) template_body_changed (source, L4) uninstantiated_template_removed (source, --)	COVERED
source-abi.odr-violation One Definition Rule violation	04-cpp-abi consumer-models static-and-header-only	case149_xcheck_odr_variant	identity_collision_detected (source, L4) odr_source_conflict (source, --) odr_type_variant (source, L4)	COVERED
source-abi.constexpr-evaluation-change constexpr evaluation change	06-transitive-breaks abi-surface limitations	case124_header_constant_value_changed case190_public_inline_function_references_internal_constant	constant_added (symbols, --) constant_changed (symbols, L2) constant_removed (symbols, --) constexpr_value_changed (source, --)	COVERED
source-abi.macro-driven-layout-change Macro-driven layout/signature change	build-profile-comparability build-source-data limitations	case164_preproc_conditional_field (control only)	compile_context_conflict (build, L3) header_binary_context_mismatch (build, L2) header_build_context_mismatch (build, L3) header_parse_context_drift (build, --) public_macro_value_changed (source, --)	MISSING_CASE
source-abi.default-template-argument-change Default template-argument change	04-cpp-abi template-heavy-libraries	case87_default_template_arg_changed	default_template_arg_changed (types, L2) mandatory_template_param_added (types, --)	COVERED

• source-abi.macro-driven-layout-change (MISSING_CASE) — case164 is the false-positive control (a #ifdef-guarded field where both releases define the macro, so the correct answer is NO_CHANGE). No case demonstrates the positive mechanism -- two consumers compiling the same header under different macro state and getting different layouts -- which the context-mismatch detectors claim.

6. Export/public-surface contract (export-surface)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
export-surface.header-export-divergence Header/export divergence	abi-surface evidence-and-detectability graph-coverage	case144_audit_private_header_leak case150_xcheck_export_public_pair case151_xcheck_provider_matrix	exported_not_public (source, L2) private_header_leak (source, L2) public_not_exported (source, L2) source_decl_binary_symbol_mismatch (source, --) source_surface_dso_mismatch (source, L4)	COVERED
export-surface.visibility-demotion-without-header-change Visibility demotion without header change	07-designing-for-stability abi-surface elf-symbol-filtering	case182_accidental_export_removed_still_breaking case59_func_became_inline	func_removed_elf_only (symbols, L0) func_visibility_changed (symbols, L0) link_export_policy_changed (build, --) visibility_leak (platform, --)	COVERED
export-surface.accidental-export Accidental export	07-designing-for-stability abi-surface surface-growth	case143_audit_accidental_export case145_audit_unversioned_export	exported_not_public (source, L2) undocumented_export_ratio_increased (source, --) unversioned_exported_symbol (source, L0)	COVERED
export-surface.version-script-map-change Version-script/export-map change	05-linker-elf 07-designing-for-stability system-library-discipline	none	link_export_policy_changed (build, --) pe_ordinal_retargeted (platform, L0) version_script_missing (platform, --)	MISSING_CASE
export-surface.documented-contract-drift Documented-contract drift	abi-surface rollout-and-governance surface-growth	none	abi_surface_explosion (platform, --) public_surface_grew (source, --) public_surface_shrank (source, --) undocumented_export_ratio_increased (source, --)	MISSING_CASE

• export-surface.version-script-map-change (MISSING_CASE) — Three detectors claim the export-map surface (an absent version script, a changed export policy, a retargeted PE ordinal), but the corpus has no case where a version script or .def file -- and nothing else -- changes the export set.
• export-surface.documented-contract-drift (MISSING_CASE) — The surface-growth detectors exist and learn/surface-growth.md explains the mechanism, but no case exercises accretion of an undocumented surface across releases.

7. Dynamic linker contract (dynamic-linker)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
dynamic-linker.soname-change SONAME change	05-linker-elf compatibility-direction system-library-discipline	case05_soname case50_soname_inconsistent case84_bundle_soname_skew	compat_version_changed (platform, --) soname_bump_recommended (platform, --) soname_bump_unnecessary (platform, --) soname_changed (platform, L0) soname_missing (platform, L0)	COVERED
dynamic-linker.symbol-versioning-scheme-change Symbol-versioning scheme change	05-linker-elf system-library-discipline	case139_symbol_version_node_removed case141_versioned_symbol_scheme	symbol_version_node_removed (platform, L0) unversioned_exported_symbol (source, L0) versioned_symbol_scheme_detected (platform, L0)	COVERED
dynamic-linker.dt-needed-change DT_NEEDED/dependency-list change	abi-cheat-sheet 05-linker-elf environment-drift	case138_needed_added	imported_symbol_added (platform, L0) imported_symbol_removed (platform, L0) needed_added (platform, L0) needed_order_changed (platform, L0) needed_removed (platform, L0)	COVERED
dynamic-linker.rpath-runpath-change RPATH/RUNPATH change	05-linker-elf environment-drift	case137_runpath_changed case52_rpath_leak	rpath_changed (platform, --) rpath_type_changed (platform, L0) runpath_changed (platform, L0) wheel_rpath_not_portable (build, L0)	COVERED
dynamic-linker.binding-mode-change Binding-mode change	abi-cheat-sheet 05-linker-elf	case134_relro_weakened	bind_now_disabled (platform, L0) dynamic_loading_flags_changed (platform, L0) pe_import_load_mode_changed (platform, L0) relro_weakened (platform, L0) symbolic_binding_mode_changed (platform, L0)	COVERED
dynamic-linker.plt-got-representation-change PLT/GOT representation change	01-foundations 05-linker-elf	case29_ifunc_transition	dt_relr_introduced (platform, L0) dt_relr_removed (platform, L0) hash_style_removed (platform, L0) ifunc_introduced (platform, L0) text_relocation_introduced (platform, L0) text_relocation_removed (platform, L0)	PARTIALLY_COVERED

• dynamic-linker.plt-got-representation-change (PARTIALLY_COVERED) — Six detectors cover the relocation/hash-table representation surface, but the only case is the ifunc transition -- the DT_RELR, text-relocation and hash-style changes the same leaf names have no case, and no learn page explains what changing the relocation representation costs a consumer.

8. Dependency ABI (dependency-abi)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
dependency-abi.transitive-break Transitive dependency break	06-transitive-breaks dependency-floors packages-and-consumers	case18_dependency_leak case91_bundle_intra_signature_drift	bundle_intra_dep_signature_changed (build, L0) bundle_intra_type_changed (build, --) runtime_symbol_provider_changed (source, L0) symbol_leaked_from_dependency_changed (platform, --)	COVERED
dependency-abi.version-range-widening Dependency version-range widening	dependency-floors packages-and-consumers	none	bundle_intra_dep_resolved_to_different_version (build, --) library_version_downgraded (platform, L0) numpy_metadata_understates_required_version (build, L0) wheel_closure_dependency_violation (build, L0)	MISSING_CASE
dependency-abi.incompatible-substitution ABI-incompatible dependency substitution	environment-drift products-not-libraries system-library-discipline	case92_bundle_provider_changed	bundle_duplicate_provider (build, L0) bundle_provider_changed (build, L0) runtime_symbol_provider_changed (source, L0) stdlib_implementation_changed (types, --)	COVERED
dependency-abi.linking-mode-change Dependency linking-mode change	01-foundations static-and-header-only	none	none	NOT_IMPLEMENTED

• dependency-abi.version-range-widening (MISSING_CASE) — Four detectors reason about a dependency constraint admitting an incompatible version, and learn/dependency-floors.md explains the mechanism, but no case widens a range and shows the consequence.
• dependency-abi.linking-mode-change (NOT_IMPLEMENTED) — No ChangeKind states that a dependency moved between static and dynamic linking. The consequences are partly observable through unrelated kinds (needed_removed when the dependency leaves DT_NEEDED, symbol_leaked_from_dependency_changed when its symbols appear in the artifact's own export table), but nothing names the transition itself, so a reader gets two unexplained findings instead of one that says what happened. Tractable: both sides' DT_NEEDED/import tables and export sets are already collected at L0.

9. Toolchain/platform ABI (toolchain-platform)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
toolchain-platform.compiler-abi-epoch-change Compiler ABI-epoch change	build-profile-comparability modern-cpp-toolchain-hazards system-library-discipline	case104_glibcxx_dual_abi_flip case113_abi_tag_changed case98_cxx_standard_floor_raised	cxx_standard_floor_raised (build, --) glibcxx_dual_abi_flip_detected (platform, L0) libcpp_abi_version_changed (types, --) stdlib_implementation_changed (types, --) toolchain_version_changed (build, --)	COVERED
toolchain-platform.target-triple-change Target-triple change	build-profile-comparability modern-cpp-toolchain-hazards	case112_lp64_ilp64	elf_abi_flags_changed (platform, L0) elf_class_changed (platform, L0) elf_machine_changed (platform, L0) elf_osabi_changed (platform, L0) integer_model_changed (platform, L1) macho_cpu_type_changed (platform, L0) pe_machine_changed (platform, L0) wheel_tag_architecture_mismatch (build, L0)	COVERED
toolchain-platform.abi-relevant-flag-change ABI-relevant compiler-flag change	build-profile-comparability build-source-data environment-drift	case103_toolchain_flag_drift case152_enum_size_flag_flip case153_struct_packing_flip case154_lto_mode_flip case155_char_signedness_flip case98_cxx_standard_floor_raised	abi_relevant_build_flag_changed (build, L3) build_option_reaches_public_symbol (source, --) char_signedness_changed (platform, L3) enum_size_flag_changed (platform, L3) float_abi_changed (platform, L3) lto_mode_changed (platform, L3) sanitizer_mode_changed (platform, L3) struct_packing_mode_changed (platform, L3) toolchain_flag_drift (platform, L1)	COVERED
toolchain-platform.libc-runtime-abi-change libc/runtime ABI change	dependency-floors environment-drift system-library-discipline	case170_env_runtime_floor_raised case97_api_depends_on_consumer_env	macos_deployment_target_raised (build, L0) musllinux_glibc_dependency_detected (build, L0) os_deployment_floor_raised (platform, L0) platform_baseline_floor_raised (platform, L0) runtime_floor_raised (build, L0) time64_abi_changed (platform, L1)	COVERED
toolchain-platform.endianness-change Endianness change	build-profile-comparability data-wire-compatibility	none	elf_endianness_changed (platform, L0)	MISSING_CASE
toolchain-platform.word-size-change Word-size (32-bit/64-bit) change	abi-cheat-sheet build-profile-comparability modern-cpp-toolchain-hazards	case112_lp64_ilp64	elf_class_changed (platform, L0) integer_model_changed (platform, L1) long_double_abi_changed (platform, L0) wchar_model_changed (platform, L1)	COVERED
toolchain-platform.hardening-flag-change Hardening/mitigation flag change	abi-cheat-sheet 05-linker-elf	case134_relro_weakened case135_stack_canary_removed case136_executable_stack_removed case179_cet_protection_weakened case49_executable_stack	branch_protection_improved (platform, L0) branch_protection_weakened (platform, L0) cet_protection_improved (platform, L0) cet_protection_weakened (platform, L0) executable_stack (platform, --) executable_stack_removed (platform, L0) fortify_source_weakened (platform, --) pe_hardening_improved (platform, L0) pe_hardening_weakened (platform, L0) pie_disabled (platform, --) stack_canary_removed (platform, L0)	COVERED

• toolchain-platform.endianness-change (MISSING_CASE) — elf_endianness_changed claims the mechanism outright, but no case pairs a little-endian and a big-endian build -- the catalog's build fixtures are all produced on one host.

10. Multi-library/product ABI (product-abi)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
product-abi.cross-component-contract-break Cross-component contract break	06-transitive-breaks products-not-libraries	case90_bundle_intra_dep_removed case91_bundle_intra_signature_drift	bundle_intra_dep_removed (build, L0) bundle_intra_dep_signature_changed (build, L0) bundle_intra_dep_signature_unverified (build, L0) bundle_intra_type_changed (build, --) bundle_unresolved_intra_dependency (build, L0)	COVERED
product-abi.version-skew-within-release Version skew within a release	products-not-libraries rollout-and-governance	case84_bundle_soname_skew case93_bundle_manifest_drift	bundle_library_added (build, --) bundle_library_removed (build, --) bundle_manifest_entry_unsatisfied (build, L0) bundle_soname_skew (types, L0) bundle_variant_coverage_regressed (build, L0)	COVERED
product-abi.plugin-interface-break Plugin interface break	07-designing-for-stability consumer-models products-not-libraries	case82_sycl_overload_set_removed	consumer_required_symbol_removed (source, L0) sycl_overload_set_removed (types, L0) sycl_pi_entrypoint_added (platform, --) sycl_pi_entrypoint_removed (platform, --) sycl_plugin_added (platform, --) sycl_plugin_removed (platform, --)	PARTIALLY_COVERED

• product-abi.plugin-interface-break (PARTIALLY_COVERED) — The one demonstrated plugin boundary is SYCL's. A generic host/plugin ABI break -- third-party plugins outside the release, which is the case this leaf is about -- is reachable only through the explicit --used-by/--required-symbol consumer path (consumer_required_symbol_removed), with no case demonstrating it.

11. Source-level API compatibility (source-api)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
source-api.signature-change-source-only Source-only signature change	06-transitive-breaks limitations verdicts	case186_c_api_pointee_const_abi_neutral (control only)	func_cv_changed (types, L1) func_params_changed (symbols, L1) param_renamed (symbols, --) removed_const_overload (types, --) source_level_kind_changed (types, --)	MISSING_CASE
source-api.header-macro-removal Public macro removal	06-transitive-breaks abi-surface	case156_public_macro_removed	public_macro_removed (source, L4) public_macro_value_changed (source, --)	COVERED
source-api.deprecation-attribute-addition Deprecation-attribute addition	02-symbol-contracts rollout-and-governance	case205_public_function_marked_deprecated case206_deprecation_documented_without_attribute	enum_deprecated_added (types, L2) field_deprecated_added (types, L2) func_deprecated_added (symbols, L2) func_deprecated_removed (symbols, L2) type_deprecated_added (types, L2) var_deprecated_added (symbols, L2)	COVERED
source-api.default-argument-value-change Default-argument value change	abi-cheat-sheet 06-transitive-breaks	case123_default_argument_removed case32_param_defaults	default_argument_changed (source, --) param_default_value_changed (symbols, L2) param_default_value_removed (symbols, L2) python_api_default_removed (symbols, L2)	COVERED
source-api.overload-resolution-change Overload-resolution change	06-transitive-breaks modern-cpp-toolchain-hazards	case111_enumerable_thread_specific_lambda_ambiguity case169_overload_added	ctor_explicit_added (symbols, L2) ctor_explicit_removed (symbols, --) ctor_overload_ambiguity_risk (symbols, L2) overload_added (types, L0) overload_set_rerouted (types, --) removed_const_overload (types, --)	COVERED

• source-api.signature-change-source-only (MISSING_CASE) — case186 is the ABI-neutral negative control (a char* parameter becoming const char*, which must stay NO_CHANGE). No case demonstrates the positive mechanism: a binary-identical change that still breaks recompilation of consumer source.

12. Header-only compatibility (header-only)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
header-only.multiple-version-odr Multiple-version ODR violation	consumer-models limitations static-and-header-only	case149_xcheck_odr_variant	odr_source_conflict (source, --) odr_type_variant (source, L4)	PARTIALLY_COVERED
header-only.include-guard-macro-collision Include-guard/macro collision	limitations static-and-header-only	none	none	KNOWN_UNDETECTABLE
header-only.inline-namespace-version-stamp-change Inline-namespace version-stamp change	07-designing-for-stability modern-cpp-toolchain-hazards system-library-discipline	case100_experimental_removed_without_replacement case101_inline_namespace_version_bumped case71_inline_namespace_moved	experimental_graduated (types, L0) experimental_removed_without_replacement (types, L0) inline_namespace_moved (platform, L0) inline_namespace_version_bumped (types, L0)	COVERED
header-only.template-heavy-recompilation-drift Per-TU recompilation drift	limitations static-and-header-only template-heavy-libraries	case122_template_signature_uninstantiated	header_binary_context_mismatch (build, L2) layout_unverifiable (types, --) template_body_changed (source, L4)	KNOWN_UNDETECTABLE

• header-only.multiple-version-odr (PARTIALLY_COVERED) — The ODR detectors compare translation units within one analyzed build (case149). Two different releases of the same header-only library being included by different TUs of one consumer program is a whole-program property of an artifact abicheck is not given, so only the narrower sub-case is detected.
• header-only.include-guard-macro-collision (KNOWN_UNDETECTABLE) — A collision only exists relative to some other library's macro namespace in a consumer's include closure. abicheck compares two versions of one library; nothing in either snapshot -- at any evidence tier -- can establish that an unrelated third party defines the same guard, and the symptom (one definition silently suppressed) leaves no trace in the compared artifacts.
• header-only.template-heavy-recompilation-drift (KNOWN_UNDETECTABLE) — The mechanism is defined by the absence of the thing abicheck compares: with no compiled artifact, each consumer TU's own instantiation is the ABI, and abicheck never sees those TUs. The header-side signature change is observable (case122, template_body_changed), but per-TU drift across consumers abicheck is not given cannot be established from any evidence tier.

13. Language/ecosystem-specific mechanisms (ecosystem-specific)

Leaf	learn_pages	catalog_cases	detector (kind, module, min evidence)	Status
ecosystem-specific.c-restrict-qualifier-change restrict qualifier change	impact-analysis	case207_pointer_parameter_gained_restrict case208_restrict_added_to_definition_only	param_restrict_changed (symbols, L2)	COVERED
ecosystem-specific.cpp-stdlib-abi-variant C++ standard-library ABI variant mismatch	build-profile-comparability modern-cpp-toolchain-hazards system-library-discipline	case104_glibcxx_dual_abi_flip	glibcxx_dual_abi_flip_detected (platform, L0) libcpp_abi_version_changed (types, --) public_api_exposes_stl_by_value (symbols, --) stdlib_debug_mode_changed (build, L3) stdlib_implementation_changed (types, --)	COVERED
ecosystem-specific.cpython-limited-api-tag-change CPython limited-API/stable-ABI tag change	packages-and-consumers	none	python_abi3_dropped (symbols, L0) python_abi3_floor_raised (symbols, L0) python_stable_abi_violation (symbols, L0)	MISSING_CASE
ecosystem-specific.cpython-object-layout-change CPython object layout change	packages-and-consumers	none	numpy_abi_major_incompatible (build, L0) numpy_target_floor_raised (build, L0) python_gil_abi_changed (symbols, L0) python_stable_abi_violation (symbols, L0)	MISSING_CASE
ecosystem-specific.sycl-kernel-abi-change SYCL kernel ABI change	06-transitive-breaks packages-and-consumers	case126_sycl_device_impl_ptr case82_sycl_overload_set_removed	sycl_implementation_changed (platform, --) sycl_overload_set_removed (types, L0) sycl_pi_entrypoint_added (platform, --) sycl_pi_entrypoint_removed (platform, --) sycl_pi_version_changed (platform, --)	COVERED
ecosystem-specific.sycl-device-binary-format-change SYCL device-binary format change	environment-drift packages-and-consumers	none	sycl_backend_driver_req_changed (platform, --) sycl_plugin_added (platform, --) sycl_plugin_removed (platform, --) sycl_plugin_search_path_changed (platform, --) sycl_runtime_version_changed (platform, --)	MISSING_CASE
ecosystem-specific.kernel-symbol-versioning-crc-change Kernel MODVERSIONS CRC change	packages-and-consumers system-library-discipline	case175_kabi_crc_changed case176_kabi_symbol_namespace_changed	kabi_crc_changed (platform, L0) kabi_export_type_changed (platform, L0) kabi_symbol_added (platform, L0) kabi_symbol_namespace_changed (platform, L0) kabi_symbol_removed (platform, L0)	COVERED
ecosystem-specific.kernel-btf-type-id-change Kernel BTF type-ID/graph change	evidence-and-detectability packages-and-consumers	case121_kernel_btf_struct_field_added	struct_field_offset_changed (types, --) struct_field_type_changed (types, L1) struct_size_changed (types, L1)	PARTIALLY_COVERED

• ecosystem-specific.cpython-limited-api-tag-change (MISSING_CASE) — Three detectors (plus the vendored Stable-ABI membership set) claim the limited-API contract, and learn/packages-and-consumers.md explains abi3, but no catalog case is a CPython extension module changing its stable-ABI tag.
• ecosystem-specific.cpython-object-layout-change (MISSING_CASE) — python_gil_abi_changed covers the free-threaded/no-GIL build split and python_stable_abi_violation covers reaching into a non-guaranteed field, but no case exercises either, and CPython's own object-layout evolution across interpreter versions has no fixture.
• ecosystem-specific.sycl-device-binary-format-change (MISSING_CASE) — The SYCL plugin/runtime detectors exist, but the two SYCL cases in the catalog are host-side (an overload set and a device-impl pointer field); no case changes the packaged device-binary format or target list.
• ecosystem-specific.kernel-btf-type-id-change (PARTIALLY_COVERED) — abicheck reads BTF and reports the underlying struct layout change (case121), which is the cause. It does not model BTF type IDs, the type graph's own shape, or which CO-RE relocations a BPF program would have to be re-relocated for -- the effect this leaf names has no detector.