Merge separate-core-ui: split business logic from the T/GUI layer.

Reorganises essim around a hard core/frontends boundary so multiple GUI/TUI engines can be built on the same business logic: - src/core/{domain,imports,app} — frontend-agnostic essim_core (no GUI toolkit); src/frontends/<name>/ — per-frontend UI. CMake selects one with -DESSIM_FRONTEND=<name> (default tui; "none" = core+tests, no FTXUI). - Application layer (core/app/): export / verify / connect / load extracted as System-in, result-struct-out operations; TUI commands and screens are thin wrappers. The analyze screen and dashboard now share app::verify instead of recomputing the passes (de-dup). - Frontend interface (frontends/frontend.hpp) + shared frontend_main: main.cpp is frontend-agnostic; a new frontend is a 4-line main plus a Frontend impl. - ImportBase hardened (read-only open, fail-fast on a missing file) and made leak-free (valgrind: no leaks, 0 errors). Tests: 78 core cases / 368 assertions + the TUI suite, all green. Binary stays ./build/essim; --batch/--commands-md/--help behaviour unchanged.
2026-06-03 20:37:35 +02:00
parent ac2edd90c4 3b6e626c8f
commit 091ef6fe4b
99 changed files with 1649 additions and 909 deletions
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,49 +11,60 @@ project(essim

 include(FetchContent)

-set(FTXUI_BUILD_DOCS OFF CACHE INTERNAL "")
-set(FTXUI_BUILD_EXAMPLES OFF CACHE INTERNAL "")
-set(FTXUI_BUILD_TESTS OFF CACHE INTERNAL "")
-set(FTXUI_ENABLE_INSTALL OFF CACHE INTERNAL "")
-
-FetchContent_Declare(ftxui
-  GIT_REPOSITORY https://github.com/ArthurSonzogni/FTXUI.git
-  GIT_TAG v6.1.9
-  GIT_SHALLOW TRUE
-)
-FetchContent_MakeAvailable(ftxui)
-
-find_package(libzip REQUIRED)
-find_package(pugixml REQUIRED)
-
-# libbsdl — standalone BSDL parser (LGPL-2.1), dynamically linked from essim
-# (EUPL-1.2, which the LGPL permits). Path overridable via -DBSDL_DIR=...;
-# its CLI and tests are not needed inside essim's build.
+# ----------------------------------------------------------------- core deps
+# libbsdl — standalone BSDL parser (LGPL-2.1), dynamically linked (EUPL-1.2,
+# which the LGPL permits). Override its path with -DBSDL_DIR=...
 set(BSDL_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../libbsdl" CACHE PATH "libbsdl source tree")
 set(BSDL_BUILD_CLI   OFF CACHE BOOL "" FORCE)
 set(BSDL_BUILD_TESTS OFF CACHE BOOL "" FORCE)
 add_subdirectory(${BSDL_DIR} ${CMAKE_BINARY_DIR}/libbsdl)

-# Library target = everything except main.cpp; reused by `essim` and `essim_tests`.
-file(GLOB_RECURSE LIB_SOURCES "src/*.cpp")
-list(REMOVE_ITEM LIB_SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/src/main.cpp")
+find_package(libzip REQUIRED)
+find_package(pugixml REQUIRED)

-add_library(essim_lib STATIC ${LIB_SOURCES})
-target_include_directories(essim_lib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/src)
-target_link_libraries(essim_lib
+# =============================================================== essim_core
+# All business logic — domain model, importers, application operations
+# (src/core/{domain,imports,app}). Frontend-agnostic: it links NO GUI/TUI
+# toolkit, so every frontend and the test suite share the exact same core.
+file(GLOB_RECURSE CORE_SOURCES "src/core/*.cpp")
+add_library(essim_core STATIC ${CORE_SOURCES})
+target_include_directories(essim_core PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/src)
+target_link_libraries(essim_core
  PUBLIC
-    ftxui::screen
-    ftxui::dom
-    ftxui::component
    libzip::zip
    pugixml::pugixml
    bsdl::bsdl
 )

-add_executable(essim src/main.cpp)
-target_link_libraries(essim PRIVATE essim_lib)
+# =============================================================== frontend(s)
+# Pick the GUI/TUI frontend to build the `essim` binary against. Each frontend
+# is a self-contained src/frontends/<name>/ (own CMakeLists, GUI toolkit, and
+# main.cpp) that links essim_core. "none" builds the core + tests only — no GUI
+# toolkit is fetched. To add a frontend (e.g. a Qt GUI), create
+# src/frontends/gui/ and configure with -DESSIM_FRONTEND=gui.
+set(ESSIM_FRONTEND "tui" CACHE STRING
+    "Frontend to build: a directory name under src/frontends/, or 'none'")
+set_property(CACHE ESSIM_FRONTEND PROPERTY STRINGS tui none)

-# Tests
+if(ESSIM_FRONTEND STREQUAL "none")
+  message(STATUS "essim: ESSIM_FRONTEND=none — core + tests only (no frontend, no GUI toolkit)")
+elseif(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/src/frontends/${ESSIM_FRONTEND}/CMakeLists.txt")
+  message(STATUS "essim: building frontend '${ESSIM_FRONTEND}'")
+  # Shared, GUI-toolkit-free frontend support: the abstract Frontend interface
+  # (header-only) and the frontend-agnostic launcher frontend_main(). Every
+  # frontend's main() links this and forwards argv to it.
+  add_library(essim_frontend STATIC
+    "${CMAKE_CURRENT_SOURCE_DIR}/src/frontends/frontend_main.cpp")
+  target_include_directories(essim_frontend PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/src)
+  add_subdirectory(src/frontends/${ESSIM_FRONTEND})
+else()
+  message(FATAL_ERROR
+    "Unknown ESSIM_FRONTEND '${ESSIM_FRONTEND}' — expected "
+    "src/frontends/${ESSIM_FRONTEND}/CMakeLists.txt, or 'none'.")
+endif()
+
+# =============================================================== tests (core)
+# The suite exercises essim_core only — no frontend, no GUI toolkit.
 include(CTest)
 if(BUILD_TESTING)
  set(CMAKE_POLICY_VERSION_MINIMUM 3.5)
@@ -65,20 +76,35 @@ if(BUILD_TESTING)
  FetchContent_MakeAvailable(doctest)
  unset(CMAKE_POLICY_VERSION_MINIMUM)

+  # Core tests — exercise essim_core only (tests/*.cpp, non-recursive, so the
+  # per-frontend tests under tests/<frontend>/ are not pulled in here).
  file(GLOB TEST_SOURCES "tests/*.cpp")
  if(TEST_SOURCES)
    add_executable(essim_tests ${TEST_SOURCES})
-    target_link_libraries(essim_tests PRIVATE essim_lib doctest::doctest)
+    target_link_libraries(essim_tests PRIVATE essim_core doctest::doctest)
    add_test(NAME essim_tests COMMAND essim_tests)
  endif()
+
+  # Per-frontend tests — tests/<frontend>/*.cpp, built and linked against that
+  # frontend's library only when the frontend itself is built.
+  if(TARGET essim_tui)
+    file(GLOB TUI_TEST_SOURCES "tests/tui/*.cpp")
+    if(TUI_TEST_SOURCES)
+      add_executable(essim_tui_tests
+        "${CMAKE_CURRENT_SOURCE_DIR}/tests/doctest_main.cpp" ${TUI_TEST_SOURCES})
+      target_link_libraries(essim_tui_tests PRIVATE essim_tui doctest::doctest)
+      add_test(NAME essim_tui_tests COMMAND essim_tui_tests)
+    endif()
+  endif()
 endif()

-# Documentation: Doxygen → XML → custom Python script → doc/api/ (Markdown rendered by gitea).
-# Optional — `doc` target is only created if Doxygen and Python 3 are present.
+# =============================================================== documentation
+# Doxygen → XML → gen_api_md.py → doc/api/, plus `essim --commands-md`. Needs the
+# `essim` binary, so it's only wired when a frontend that provides one is built.
 find_package(Doxygen COMPONENTS doxygen)
 find_package(Python3 COMPONENTS Interpreter)

-if(DOXYGEN_FOUND AND Python3_Interpreter_FOUND)
+if(TARGET essim AND DOXYGEN_FOUND AND Python3_Interpreter_FOUND)
  set(DOXYGEN_OUTPUT_DIR "${CMAKE_BINARY_DIR}/doc")
  file(MAKE_DIRECTORY "${DOXYGEN_OUTPUT_DIR}")
  configure_file(
@@ -103,11 +129,10 @@ if(DOXYGEN_FOUND AND Python3_Interpreter_FOUND)
    WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
    COMMENT "Generating documentation (doxygen → gen_api_md.py → doc/api/, essim --commands-md → doc/user/commands.md)"
    VERBATIM)
-elseif(NOT DOXYGEN_FOUND AND NOT Python3_Interpreter_FOUND)
-  message(STATUS "doc: Doxygen and Python 3 not found — `doc` target disabled.")
+elseif(NOT TARGET essim)
+  message(STATUS "doc: no `essim` binary (ESSIM_FRONTEND=none) — `doc` target disabled.")
 elseif(NOT DOXYGEN_FOUND)
-  message(STATUS "doc: Doxygen not found — `doc` target disabled "
-                 "(install via `pacman -S doxygen`).")
+  message(STATUS "doc: Doxygen not found — `doc` target disabled.")
 else()
  message(STATUS "doc: Python 3 interpreter not found — `doc` target disabled.")
 endif()
--- a/DESIGN.md
+++ b/DESIGN.md
@@ -10,72 +10,111 @@ cmake --build build -j
 ./build/essim
 ```

- CMake **3.14+** required (uses `FetchContent_MakeAvailable`).
- FTXUI is fetched at configure time from GitHub (`v6.1.9`, shallow clone). First configure pays ~20 s for the clone; subsequent ones are cached in `build/_deps/`.
- **System dependencies** (resolved via `find_package`): `libzip` (target `libzip::zip`) and `pugixml` (target `pugixml::pugixml`). Used by the ODS importer. Arch: `pacman -S libzip pugixml`; Debian/Ubuntu: `libzip-dev libpugixml-dev`.
- **`libbsdl`** (standalone BSDL parser, LGPL-2.1) is the sibling repo at `../libbsdl`, pulled in via `add_subdirectory` (path overridable with `-DBSDL_DIR=...`) and linked dynamically (`bsdl::bsdl`; an LGPL `.so` is fine from EUPL essim). Powers the BSDL ingest behind `attach-bsdl`.
- Sources are collected with `file(GLOB_RECURSE ALL_SOURCES "src/*.cpp")`. **After adding a new `.cpp`, re-run `cmake -S . -B build`** — CMake does not re-glob automatically and link will fail with "undefined reference".
+- CMake **3.14+** (uses `FetchContent_MakeAvailable`).
+- **Layered build** (see *Architecture* below). `essim_core` is the
+  frontend-agnostic business library; a frontend under `src/frontends/<name>/`
+  links it and produces the `essim` binary. Choose it with
+  `-DESSIM_FRONTEND=<name>` (default `tui`). **`-DESSIM_FRONTEND=none` builds the
+  core + tests only — no GUI toolkit is fetched.**
+- **Core system dependencies** (via `find_package`): `libzip` (`libzip::zip`)
+  and `pugixml` (`pugixml::pugixml`) for the ODS importer. Arch:
+  `pacman -S libzip pugixml`; Debian/Ubuntu: `libzip-dev libpugixml-dev`.
+- **`libbsdl`** (standalone BSDL parser, LGPL-2.1) — sibling repo at
+  `../libbsdl`, `add_subdirectory` (override `-DBSDL_DIR=...`), linked
+  dynamically **into the core** (`bsdl::bsdl`).
+- **FTXUI** is fetched by the **tui frontend only**
+  (`src/frontends/tui/CMakeLists.txt`), never by the core.
+- Sources are globbed per layer: `src/core/*.cpp` → `essim_core`,
+  `src/frontends/<fe>/*.cpp` → that frontend's lib + the `essim` binary.
+  **After adding a `.cpp`, re-run `cmake -S . -B build`** — CMake doesn't re-glob.
+- **Tests** are split: `essim_tests` links `essim_core` (no FTXUI) from
+  `tests/*.cpp`; per-frontend tests like `essim_tui_tests` link `essim_tui` from
+  `tests/<frontend>/*.cpp`.
 - **Headless / batch**: `essim --batch --source FILE` runs a script and prints its console output to stdout, then exits without the TUI (good for CI / capturing `verify`). Also `--restore FILE` and `--commands-md [FILE]`. `BootDispatch` runs `--restore`/`--source` synchronously before the event loop (`Source` takes its headless drain branch when no screen is attached), so the console buffer is complete by the time `--batch` dumps it (`Tui::DumpOutput`).

 ## Layout

 ```
 src/
-  main.cpp               -- launches Tui
-  system/                -- domain model
-    syselmts.hpp           SystemElement + SystemElementContainer<T> (templated, get/merge/iterate)
-    modules.{hpp,cpp}      Module, Modules
-    parts.{hpp,cpp}        Part (carries `kind` + `connector_type`), Parts
-    pins.{hpp,cpp}         Pin (carries PinSpec `spec`), Pins
-    signals.{hpp,cpp}      Signal, Signals
-    signal_type.hpp        SignalType + helpers
-    pin_spec.hpp           PinSpec (function/direction/pad/source) + SignalType mapping
-    component_kind.{hpp,cpp} ComponentKind enum + infer_component_kind(name)
-    pin_name.{hpp,cpp}     canonical_pin_name(s) — zero-pad digit suffix to 3
-    connect.{hpp,cpp}      Connection, Connections
-    transform.{hpp,cpp}    Transform / IdentityTransform / TransformRegistry +
-                           CheckIdentityCompatible + FillIdentityNCs
-    pin_role.{hpp,cpp}     pin_role(kind, name) → PinSpec, pin_layout(kind),
-                           FillPartFromLayout(part, kind)
-    pin_model.{hpp,cpp}    PinModel + apply_model(Part*, model) + ConnectorModel
-    bsdl_model.{hpp,cpp}   BsdlModel (libbsdl wrapper) + BsdlPinModel + apply_bsdl
-    bsdl_check.{hpp,cpp}   check_pin_specs / check_jtag_chain → vector<Anomaly>
-    nets.{hpp,cpp}         find_net / compute_all_nets / net_type_consistent
-    analysis.{hpp,cpp}     analyze_system → AnalysisReport (diff pairs, buses, anomalies)
-    persist.{hpp,cpp}      save / restore (tab-delimited)
-    system.{hpp,cpp}       System: owns Modules + Connections, exposes Load()
-  imports/               -- adapters that populate or emit the domain
-    import_base.hpp        ImportBase interface
-    import_mentor.{hpp,cpp} Mentor Graphics netlist parser
-    import_altium.{hpp,cpp} Altium netlist parser (`[ ]` parts, `( )` signals)
-    import_ods.{hpp,cpp}   ODS spreadsheet pinout (libzip + pugixml)
-    ods_writer.{hpp,cpp}   Minimal .ods writer (multi-sheet, string cells)
-  tui/                   -- FTXUI shell, split by responsibility
-    tui.{hpp,cpp}          Class Tui (state + Run() orchestrator + screen-mode event dispatcher)
-    tui_helpers.{hpp,cpp}  Free helpers: ToLower, NaturalLess, LongestCommonPrefix
-    shell.cpp              Print, Submit, Dispatch, Finalize, Tokenize, history persistence
-    completion.cpp         CompleteCommand, CompletePath, CompleteInline
-    commands.cpp           RegisterCommands (orchestrator + lifecycle / shell / topology commands)
-    commands_export.cpp    RegisterExportCommands (export → CSV / ODS, file-dialog hook)
-    screen_main.cpp        BuildMainScreen (visualisation area + bottom input)
-    screen_connect.cpp     BuildConnectScreen + shared RefreshFilteredPartList helper
-    screen_settype.cpp     BuildSettypeScreen
-    screen_explore.cpp     BuildExploreScreen (browse modules → parts/signals/connections → details; not scriptable)
-    screen_dashboard.cpp   BuildDashboardScreen (read-only system overview)
-    screen_analyze.cpp     BuildAnalyzeScreen (anomalies / groups / power decisions)
-    screen_palette.cpp     BuildPaletteModal (global Ctrl-P fuzzy launcher)
-    screen_filedialog.cpp  BuildFileDialog + OpenFileDialog (reusable file picker)
-    screen_error.cpp       BuildErrorModal + ShowError (centred error popup)
-    screen_help.cpp        BuildHelpScreen (topic-driven feature reference)
-    screen_sigtype_modal.cpp BuildSignalTypeModal (popup attached to explore via Modal())
-doc/classes.puml         -- PlantUML class diagram
+  core/                  -- business logic; NO GUI toolkit (builds libessim_core)
+    domain/              -- the model + read-only analyses
+      syselmts.hpp         SystemElement + SystemElementContainer<T> (get/merge/iterate)
+      modules.{hpp,cpp}    Module, Modules
+      parts.{hpp,cpp}      Part (kind, connector_type, bsdl_path; PinSpec per pin)
+      pins.{hpp,cpp}       Pin (carries PinSpec `spec`), Pins
+      signals.{hpp,cpp}    Signal, Signals
+      signal_type.hpp      SignalType + helpers
+      pin_spec.hpp         PinSpec (function/direction/pad/source), mappings, spec_source_rank
+      component_kind.{hpp,cpp}  ComponentKind + infer_component_kind(name)
+      pin_name.{hpp,cpp}   canonical_pin_name (zero-pad digit suffix to 3)
+      connect.{hpp,cpp}    Connection, Connections
+      transform*.{hpp,cpp} Transform / IdentityTransform / TransformRegistry, VPX transform
+      pin_role.{hpp,cpp}   pin_role(kind,name) -> PinSpec, pin_layout, FillPartFromLayout
+      pin_model.{hpp,cpp}  PinModel + apply_model(Part*, model) + ConnectorModel
+      bsdl_model.{hpp,cpp} BsdlModel (libbsdl wrapper) + BsdlPinModel + apply_bsdl
+      bsdl_check.{hpp,cpp} check_pin_specs / _jtag_chain / _source_conflicts / _bsdl_completeness
+      nets.{hpp,cpp}       find_net / compute_all_nets / net_type_consistent
+      analysis.{hpp,cpp}   analyze_system -> AnalysisReport (diff pairs, buses, anomalies)
+      persist.{hpp,cpp}    save / restore (tab-delimited; `B` tag = bsdl_path)
+      system.{hpp,cpp}     System: owns Modules + Connections, Load()
+    imports/             -- netlist / pinout adapters
+      import_base.hpp / import_{mentor,altium,ods}.{hpp,cpp} / ods_writer.{hpp,cpp}
+    app/                 -- application operations (UI-independent use cases)
+      export.{hpp,cpp}     export_connections(System*, path, format) -> ExportResult
+      verify.{hpp,cpp}     verify(System*) -> VerifyReport (the 7 verify passes)
+      connect.{hpp,cpp}    connect_parts(System*, m1,p1, m2,p2) -> ConnectResult
+      load.{hpp,cpp}       load_module(System*, name, path, ImportType) -> LoadResult
+  frontends/             -- one directory per GUI/TUI engine; each links essim_core
+    frontend.hpp         -- abstract Frontend interface (BootDispatch/Dump*/Run)
+    frontend_main.{hpp,cpp} -- frontend_main(argc,argv,Frontend&): argv + boot/batch/run
+    tui/                 -- FTXUI shell (builds libessim_tui + the `essim` binary)
+      CMakeLists.txt       fetches FTXUI; builds essim_tui + essim
+      main.cpp             entry point: construct Tui, call frontend_main
+      tui.{hpp,cpp}        class Tui (state + Run() + screen-mode event dispatch)
+      tui_helpers.{hpp,cpp}  ToLower, NaturalLess, RenderHelpPanel
+      shell.cpp            Print, Submit, Dispatch, Source / ProcessNextSourceLine
+      completion.cpp       CompleteCommand / CompletePath / CompleteInline
+      commands.cpp         RegisterCommands (thin: resolve args -> call core -> render)
+      commands_export.cpp  thin wrapper over app::export_connections
+      screen_*.cpp         dashboard, connect, settype, explore, analyze, help, main
+                           (console), palette, file dialog, error/confirm, sigtype modal
+tests/                   -- core tests (link essim_core)
+  tui/                   -- frontend tests (link essim_tui)
+doc/ , test/             -- docs; sample netlists + system.essim bring-up script
 ```

-`include/` and `lib/` are kept empty by design — FTXUI used to live there as precompiled `.a` + headers, now it comes through FetchContent.
+## Architecture — core vs frontends
+
+The hard rule: **`src/core/` never depends on a frontend** — no `#include
+"frontends/…"`, no GUI toolkit. Frontends depend on the core, never the reverse
+(`essim_core` links libzip / pugixml / bsdl only).
+
+- **Domain** (`core/domain/`) — the model and the read-only analyses
+  (`analyze_system`, the `check_*` passes, `compute_all_nets`).
+- **Application** (`core/app/`) — use-case operations a frontend invokes, e.g.
+  `export_connections(System*, path, format) -> ExportResult`. An operation
+  builds its artefact and returns data/stats; it **never** prints or opens a
+  dialog. (Anti-pattern being removed: the export command used to build the file
+  inside its lambda. The TUI command is now a thin wrapper — resolve args/dialog
+  → call the core op → render the result.)
+- **Frontends** (`frontends/<name>/`) — thin: map UI events to core calls and
+  render results. Each implements the **`Frontend`** interface
+  (`frontends/frontend.hpp`: `BootDispatch`, `DumpCommandsMd`, `DumpOutput`,
+  `Run`). The process entry is shared and frontend-agnostic:
+  `frontend_main(argc, argv, Frontend&)` (`frontends/frontend_main.cpp`, built
+  into the toolkit-free `essim_frontend` lib) parses the CLI flags and drives the
+  boot → batch/run flow through the interface; a frontend's `main()` is just
+  *construct the concrete Frontend, call `frontend_main`*. Add one by creating
+  `src/frontends/<name>/CMakeLists.txt` (build `essim_<name>` linking `essim_core`,
+  produce the `essim` binary linking `essim_frontend`) and configuring
+  `-DESSIM_FRONTEND=<name>`.
+
+Because the core links no toolkit, the suite links `essim_core` directly and
+`-DESSIM_FRONTEND=none` builds + tests the whole core with FTXUI never fetched.

 ## Domain conventions

- Everything in `system/` is **pointer-based** (commit `d8122d1`: "everything is pointer"). Containers store `T*`, ownership lives with the container.
+- Everything in `core/domain/` is **pointer-based** (commit `d8122d1`: "everything is pointer"). Containers store `T*`, ownership lives with the container.
 - `SystemElementContainer<T>::merge(name)` is the get-or-create primitive — call it instead of `add` when you don't know whether the element already exists. `add` throws on duplicate names or empty names.
 - `using namespace std;` is present in `syselmts.hpp` — pre-existing, don't add more `using namespace` in headers.
 - Include guards `_NAME_HPP_` *and* `#pragma once` are both used. Match the existing style.
@@ -110,11 +149,11 @@ Built-in commands: `new`, `set`, `load`, `duplicate`, `save`, `restore`, `source

 Pending prompts (from incomplete inline commands) are NOT considered interactive and are filled by subsequent script lines, the way you'd expect. Lines starting with `#` and blank lines are skipped; leading/trailing whitespace is trimmed; `~/` is expanded.

-`save` / `restore` (`src/system/persist.{hpp,cpp}`): tab-delimited line format, no extra deps. Tags: `M` (module), `P` (part with `connector_type`), `B` (part's attached BSDL `.bsd` path — re-parsed and re-applied on restore; the path is persisted, **not** the derived pin specs), `N` (pin → signal name; empty = NC; optional 4th field carries `nc_origin_tag()`: `U` = ImportedUnconnected, `D` = DroppedSingleton — omitted when the pin has a signal or when origin is `None`), `S` (signal → type override; only emitted for non-default), `C` (connection header with endpoints + `transform_name`), `W` (wire pair within the current connection). The 4th N field is backward-compatible: pre-existing snapshots without it restore with `nc_origin = None`.
+`save` / `restore` (`src/core/domain/persist.{hpp,cpp}`): tab-delimited line format, no extra deps. Tags: `M` (module), `P` (part with `connector_type`), `B` (part's attached BSDL `.bsd` path — re-parsed and re-applied on restore; the path is persisted, **not** the derived pin specs), `N` (pin → signal name; empty = NC; optional 4th field carries `nc_origin_tag()`: `U` = ImportedUnconnected, `D` = DroppedSingleton — omitted when the pin has a signal or when origin is `None`), `S` (signal → type override; only emitted for non-default), `C` (connection header with endpoints + `transform_name`), `W` (wire pair within the current connection). The 4th N field is backward-compatible: pre-existing snapshots without it restore with `nc_origin = None`.

 **Signals** carry a `type` (`SignalType::Power | GndShield | Other`). The `Signal` constructor **defaults to `Other`** — auto-inference no longer happens at construction. Types are set in three ways, in priority order:

-1. **`infer_signal_types(System*)`** (`src/system/analysis.{hpp,cpp}`) runs at the end of every `load` (after `drop_singleton_signals`). It assigns:
+1. **`infer_signal_types(System*)`** (`src/core/domain/analysis.{hpp,cpp}`) runs at the end of every `load` (after `drop_singleton_signals`). It assigns:
   - `GndShield` when the **name alone** is unambiguous (`GND`, `SHIELD`, `CHASSIS`, `EARTH`, …) — false-positive rate is essentially zero on these.
   - `Power` requires (a) the name heuristic (`infer_signal_type` says Power), (b) a **hard fan-out floor**: signals with fewer than `POWER_FANOUT_HARD_FLOOR = 3` pins are *always* refused, regardless of name or voltage pattern (a real rail physically cannot land on just 1-2 pads), and (c) at least one positive structural signal — fan-out ≥ `POWER_FANOUT_CONFIRM_MIN = 4` **or** a voltage pattern in the name (`3V3`, `5V`, `12V`, …; detector: a `V` adjacent to a digit). This catches `VSEL_*`, `PWR_OK`, `_VDD_SENSE` etc. which look like Power by name but aren't real rails. Both thresholds are exposed in `analysis.hpp` so the analyze screen can render the same reasoning without duplicating constants.
   - `Other` otherwise. The "name-said-Power-but-refuted-by-structure" count is reported by `load`.
@@ -123,17 +162,17 @@ Pending prompts (from incomplete inline commands) are NOT considered interactive

 The explore screen shows the type in the signal detail header.

-**Pin spec (expected attributes)**: every Pin carries a `PinSpec spec` (`src/system/pin_spec.hpp`) — the *expected* half of verification, set from a model: `function` (Power/Ground/Signal/Clock/NoConnect/Jtag*), `direction` (In/Out/Bidir/Passive/Power), `pad` (physical package terminal, e.g. a BSDL ball), and `source` (which model wrote it). `set-connector-type` populates it via `pin_role(connector_type, pin_name) → PinSpec`. `Pin::expected_signal_type()` is now a **derived accessor** — `to_signal_type(spec.function)` (Power→Power, Ground→GndShield, else Other) — not a stored field; the *observed* half stays `Pin::signal()` + the net + inference, and `verify` diffs the two. The VPX 3U connector lookup (`vpx_3u_role`) is still a stub returning Other, so connector-typed pins resolve to function Unknown until that table is filled. **`direction`/`function`/`pad` are populated from BSDL** via `attach-bsdl` (see below) and consumed by the model-driven checks (`check_pin_specs`: contention / undriven / NC-wired) and the JTAG chain check (`check_jtag_chain`), both run by `verify`.
+**Pin spec (expected attributes)**: every Pin carries a `PinSpec spec` (`src/core/domain/pin_spec.hpp`) — the *expected* half of verification, set from a model: `function` (Power/Ground/Signal/Clock/NoConnect/Jtag*), `direction` (In/Out/Bidir/Passive/Power), `pad` (physical package terminal, e.g. a BSDL ball), and `source` (which model wrote it). `set-connector-type` populates it via `pin_role(connector_type, pin_name) → PinSpec`. `Pin::expected_signal_type()` is now a **derived accessor** — `to_signal_type(spec.function)` (Power→Power, Ground→GndShield, else Other) — not a stored field; the *observed* half stays `Pin::signal()` + the net + inference, and `verify` diffs the two. The VPX 3U connector lookup (`vpx_3u_role`) is still a stub returning Other, so connector-typed pins resolve to function Unknown until that table is filled. **`direction`/`function`/`pad` are populated from BSDL** via `attach-bsdl` (see below) and consumed by the model-driven checks (`check_pin_specs`: contention / undriven / NC-wired) and the JTAG chain check (`check_jtag_chain`), both run by `verify`.

 **Connector pin layout (preparation)**: `pin_layout(connector_type)` returns the canonical full pin-name list for a known connector kind, and `FillPartFromLayout(part, kind)` materialises NC pins for any layout position absent from the imported netlist. `set-connector-type` calls it after setting `connector_type` (no-op today since `pin_layout` is a stub returning `{}` for everything — populate alongside `vpx_3u_role`). End-to-end chain in place: `set-connector-type → FillPartFromLayout → pin_role`.

-**BSDL models (`attach-bsdl`)**: `attach-bsdl <module> <part> <file.bsd>` parses a BSDL device through `libbsdl` (wrapped by `BsdlModel`, `src/system/bsdl_model.{hpp,cpp}`), then `apply_bsdl(part, model)` binds each port to a Pin **by port name first, then by physical pad** — so a netlist that names IC pins either by signal or by package ball both bind. Each bound pin gets its `spec` set: `direction` (BSDL in/out/inout/linkage), `function` (TAP role → Jtag\*, `linkage` → Power/Ground/NoConnect by name, else Signal), `pad` (PIN_MAP ball), `source = Bsdl`. The `.bsd` path is stored on `Part::bsdl_path`, persisted via the `B` tag and re-applied on `restore`. Real-world check: an `xcku15p` FPGA in a VPX system binds 1517/1517 ports.
+**BSDL models (`attach-bsdl`)**: `attach-bsdl <module> <part> <file.bsd>` parses a BSDL device through `libbsdl` (wrapped by `BsdlModel`, `src/core/domain/bsdl_model.{hpp,cpp}`), then `apply_bsdl(part, model)` binds each port to a Pin **by port name first, then by physical pad** — so a netlist that names IC pins either by signal or by package ball both bind. Each bound pin gets its `spec` set: `direction` (BSDL in/out/inout/linkage), `function` (TAP role → Jtag\*, `linkage` → Power/Ground/NoConnect by name, else Signal), `pad` (PIN_MAP ball), `source = Bsdl`. The `.bsd` path is stored on `Part::bsdl_path`, persisted via the `B` tag and re-applied on `restore`. Real-world check: an `xcku15p` FPGA in a VPX system binds 1517/1517 ports.

-**Unified application (`apply_model`)**: connector layout and BSDL are two implementations of one `PinModel` interface (`src/system/pin_model.{hpp,cpp}`: `spec_for(pin_name)`, `layout()`, `source()`). `ConnectorModel` wraps `pin_role`/`pin_layout`; `BsdlPinModel` wraps a parsed `BsdlModel`, indexed by both port name and physical pad. A single `apply_model(Part*, const PinModel&)` materialises the layout pins missing from the netlist, then sets each pin's `spec` **only where the model speaks** (`spec.source != None`). Sources are ranked (`spec_source_rank` in `pin_spec.hpp`: UserOverride > Bsdl > ConnectorModel > Inferred > Imported) and apply_model refuses to overwrite a spec owned by a higher-rank source — so one source never clobbers a more authoritative one, which is also the basis for `check_source_conflicts`. `set-connector-type` and `attach-bsdl` both funnel through it (the latter via the thin `apply_bsdl` adapter); `verify` stays agnostic of where a spec came from. A future SPICE/Modelica source would be a third `PinModel`.
+**Unified application (`apply_model`)**: connector layout and BSDL are two implementations of one `PinModel` interface (`src/core/domain/pin_model.{hpp,cpp}`: `spec_for(pin_name)`, `layout()`, `source()`). `ConnectorModel` wraps `pin_role`/`pin_layout`; `BsdlPinModel` wraps a parsed `BsdlModel`, indexed by both port name and physical pad. A single `apply_model(Part*, const PinModel&)` materialises the layout pins missing from the netlist, then sets each pin's `spec` **only where the model speaks** (`spec.source != None`). Sources are ranked (`spec_source_rank` in `pin_spec.hpp`: UserOverride > Bsdl > ConnectorModel > Inferred > Imported) and apply_model refuses to overwrite a spec owned by a higher-rank source — so one source never clobbers a more authoritative one, which is also the basis for `check_source_conflicts`. `set-connector-type` and `attach-bsdl` both funnel through it (the latter via the thin `apply_bsdl` adapter); `verify` stays agnostic of where a spec came from. A future SPICE/Modelica source would be a third `PinModel`.

 **`verify` (seven passes)**: (1) typed pins — local mismatch between each pin's `expected_signal_type()` (derived from its `PinSpec`) and the actual signal type; (2) bridged nets — Power↔GndShield inconsistencies; (3) orphan summary `N orphan pin(s) at import (X imported NC, Y dropped singleton)` (filters out pins bridged via any `Connection::pin_map` — typically `FillIdentityNCs`-materialised); (4) **model-driven pin checks** (`check_pin_specs`): `DriveContention` (≥2 push-pull `Out` on a net), `UndrivenNet` (a **fully-modelled** net with input(s) but no driver — nets with any Unknown-direction pin are skipped, so un-modelled drivers don't cause false positives), `NcWired` (a no-connect pin on a multi-pin net); (5) **JTAG chain** (`check_jtag_chain`): collects TAP pins by `spec.function`, maps each to its net, emits `JtagTapIncomplete` / `JtagBusUnbridged` (TMS or TCK not common to all TAP devices) / `JtagChainBreak` (dangling TDO/TDI, chain fan-out, or not a single head→tail daisy chain); (6) **source conflicts** (`check_source_conflicts`): a pin the BSDL declares power/ground (a must-connect rail) that the netlist leaves unconnected — a rail floated in the schematic (`SourceConflict`; the reverse, a BSDL no-connect that *is* wired, is the `NcWired` check); (7) **BSDL completeness** (`check_bsdl_completeness`): device power/ground ports (from the attached `.bsd`, re-parsed) with no matching pin on the netlist part — a rail the schematic symbol is missing (`BsdlPinMissing`, one aggregated finding per part). The BFS-reached `(module, signal)` set for any signal is shown live in `explore`'s detail pane when a signal entry is selected.

-**`analyze` (post-processing pass)**: `analyze_system(System*) → AnalysisReport` (`src/system/analysis.{hpp,cpp}`) is a stateless read-only pass that detects structural signal groups and anomalies. Per-module (signals are module-scoped):
+**`analyze` (post-processing pass)**: `analyze_system(System*) → AnalysisReport` (`src/core/domain/analysis.{hpp,cpp}`) is a stateless read-only pass that detects structural signal groups and anomalies. Per-module (signals are module-scoped):

 - **Diff pairs**: signal names ending `_P` / `_N` (case-insensitive) grouped by stem. Both halves present → candidate matched pair.
 - **Diff buses**: ≥ 2 matched diff pairs whose pair-stems share a common outer-stem after stripping a trailing integer (`MDI0` / `MDI1` / `MDI2` → outer `MDI` + indices). The strict `_` rule from plain buses does NOT apply to this trailing-index split: `_P`/`_N` was already stripped, so we know remaining digits are an index. Two index variants accepted: contiguous (`MDI0`) and underscore-separated (`PCIE_TX_0`). Emitted as `SignalGroup{kind=DiffBus, lo, hi}` with label `OUTER[lo..hi]_P/N`. Members include all 2·N constituent signals. A "bus" of size 1 falls back to `DiffPair` (single index does not a bus make).
@@ -145,13 +184,13 @@ Exposed as the `analyze` shell command which prints groups (sorted by module + l

 **Component classification**: every `Part` carries a `ComponentKind kind` (`Passive | Semiconductor | IntegratedCircuit | Connector | TestPoint | Switch | Crystal | Mechanical | Other`) inferred at construction by `infer_component_kind(name)` from the leading reference-designator letter(s) (longest-match: `LED/TP/SW/FB/MK/MP/MH/HS/RA/RN/RP/RV` first, then single-letter R/C/L/F/D/Q/U/J/P/Y/X/S). Recomputed on `restore` (no persistence tag). Not yet exposed in TUI commands — branchpoints will be `set-connector-type` guard, `explore` filter, and `explore` header.

-`SignalType` lives in its own header `src/system/signal_type.hpp` (extracted from signals to avoid a pins↔signals include cycle).
+`SignalType` lives in its own header `src/core/domain/signal_type.hpp` (extracted from signals to avoid a pins↔signals include cycle).

 **Pins** are either NC (`signal() == nullptr`) or connected to exactly one signal. The ODS importer creates a Pin for every row that has a non-empty pin name, even when the signal column is empty or `"NC"` — the pin stays in the Part as NC. `restore` replaces `Tui::sys` entirely (`unique_ptr::reset`). Names are stored as-is — must not contain TAB or newline (true for the EE netlists we ingest). Format is versioned by the `# essim system snapshot v1` header for future compatibility.

 **NC origin tag**: each `Pin` carries `NcOrigin nc_origin` (`None | ImportedUnconnected | DroppedSingleton`, default `None`). Set in three places: (a) Mentor importer when the signal field starts with `unconnected` → `ImportedUnconnected`; (b) `drop_singleton_signals(Signals*)` called at the end of `load` → `DroppedSingleton` on each detached pin (signals with exactly one pin are NC by definition — see commits motivating this); (c) `duplicate` propagates the tag. Pins materialised by `FillIdentityNCs` keep `None` — they have no local signal but are bridged via `pin_map` and shouldn't be counted as orphans. The tag is persisted (see `N` record), reported as a total in `verify`, and tested in `tests/test_nc_origin.cpp`.

-**Connector types & transforms**: every `Part` carries a `connector_type` string (default `""`, set via the `set-connector-type` command — inline `set-connector-type m p kind` or bare which opens a TUI screen with module menu, part filter+menu, type input, list of types already in use, and an Apply button). When `connect` validates a pair, it consults `TransformRegistry::lookup(p1->connector_type, p2->connector_type)` (defined in `src/system/transform.{hpp,cpp}`) — both directions of the pair are tried. If neither is registered, an `IdentityTransform` fallback wires each pin of A to the canonical-equivalent pin of B (when present). The resulting `(Pin*, Pin*)` list and the transform's name are stored on the `Connection` (`pin_map`, `transform_name`). To register a real transform: define a `Transform` subclass in `transform.cpp` and call `TransformRegistry::get().add("kindA", "kindB", new MyTransform())` at init — there's no startup hook for this yet, so a small `RegisterBuiltinTransforms()` helper is the natural place to add when more types appear.
+**Connector types & transforms**: every `Part` carries a `connector_type` string (default `""`, set via the `set-connector-type` command — inline `set-connector-type m p kind` or bare which opens a TUI screen with module menu, part filter+menu, type input, list of types already in use, and an Apply button). When `connect` validates a pair, it consults `TransformRegistry::lookup(p1->connector_type, p2->connector_type)` (defined in `src/core/domain/transform.{hpp,cpp}`) — both directions of the pair are tried. If neither is registered, an `IdentityTransform` fallback wires each pin of A to the canonical-equivalent pin of B (when present). The resulting `(Pin*, Pin*)` list and the transform's name are stored on the `Connection` (`pin_map`, `transform_name`). To register a real transform: define a `Transform` subclass in `transform.cpp` and call `TransformRegistry::get().add("kindA", "kindB", new MyTransform())` at init — there's no startup hook for this yet, so a small `RegisterBuiltinTransforms()` helper is the natural place to add when more types appear.

 **Identity wiring uses canonical names**: `IdentityTransform::apply` builds `unordered_map<canonical, Pin*>` for side B and looks up each side-A pin by its canonical form. So `A1` (one card) auto-pairs with `A001` (the other) thanks to `canonical_pin_name` (`pre + zero-padded(3) digit suffix`; mixed/non-numeric returns the original). Same canonicalisation in `CheckIdentityCompatible`. **`pin_role` doesn't need canonicalisation** because `parse_pin` extracts `(col, row)` via `stoi` which already strips leading zeros.

@@ -188,7 +227,7 @@ Today the only caller is `export` (`{"CSV", ".csv"}, {"ODS", ".ods"}` filters, k

 **Per-key path persistence** (`SaveLastUsed(key, dir, filename)` / `LoadLastUsed(key, &dir, &filename)` in `shell.cpp`): each key writes a tiny two-line file (`dir\nfilename\n`) under `UserDataDir() / <key>.last`. `UserDataDir()` is the cross-platform `XDG_DATA_HOME` / `LOCALAPPDATA` etc. helper also used by the command history file. Free functions, not Tui members, so any module (the file dialog today; could be the script-save buffer or the save command tomorrow) can use them with the same minimal API.

-**ODS writer** (`src/imports/ods_writer.{hpp,cpp}`): minimal OpenDocument Spreadsheet writer. Backed by libzip + pugixml (both already pulled in by the ODS importer). Class hierarchy is two structs:
+**ODS writer** (`src/core/imports/ods_writer.{hpp,cpp}`): minimal OpenDocument Spreadsheet writer. Backed by libzip + pugixml (both already pulled in by the ODS importer). Class hierarchy is two structs:

 - `OdsSheet` — sparse row-major grid of string cells (`set(row, col, value)`).
 - `OdsWriter` — owns the sheets, emits a valid `.ods` archive with `mimetype` (stored uncompressed, magic header), `META-INF/manifest.xml`, and `content.xml`.
@@ -248,9 +287,9 @@ Everything in this section is a precise description of how signals, pins, parts,

 Default: `Signal::type = SignalType::Other` (constructor does no inference).

-Type is set by `infer_signal_types(System*)` (`src/system/analysis.cpp`), called at the end of every `load` and after `duplicate`. The decision per signal:
+Type is set by `infer_signal_types(System*)` (`src/core/domain/analysis.cpp`), called at the end of every `load` and after `duplicate`. The decision per signal:

-1. Compute `named = infer_signal_type(name)` (`src/system/signals.cpp`):
+1. Compute `named = infer_signal_type(name)` (`src/core/domain/signals.cpp`):
   - `GndShield` if name matches **case-insensitively**: `GND`, `GROUND`, `EARTH`, `SHIELD`, `CHASSIS`, or starts with `GND_` / `GROUND_` / `EARTH_` / `SHIELD_` / `CHASSIS_`.
   - `Power` if the name contains any of `PWR`, `POWER`, `VCC`, `VDD`, `VEE`, `VSS`, `VBAT`, or starts with `VS_`, `VS3_`, `+`, `-` followed by a digit.
   - Else `Other`.
@@ -264,15 +303,15 @@ Type is set by `infer_signal_types(System*)` (`src/system/analysis.cpp`), called

 ### NC pin origin

-`Pin::nc_origin` (`src/system/pins.hpp`). Default `NcOrigin::None`. Set by:
+`Pin::nc_origin` (`src/core/domain/pins.hpp`). Default `NcOrigin::None`. Set by:

- **`NcOrigin::ImportedUnconnected`** — Mentor importer (`src/imports/import_mentor.cpp`): the signal field of an `Explicit Pin:` row starts case-insensitively with `unconnected` (e.g. `'unconnected'`, `'unconnected (by TERM)'`). The pin is kept on the part with no signal.
- **`NcOrigin::DroppedSingleton`** — `drop_singleton_signals(Signals*)` (`src/system/signals.cpp`) called at the end of `load`: any signal whose pin set has size exactly 1 is unconnected by definition. The pin is detached (`sig = nullptr`) and tagged; the `Signal` object is deleted.
+- **`NcOrigin::ImportedUnconnected`** — Mentor importer (`src/core/imports/import_mentor.cpp`): the signal field of an `Explicit Pin:` row starts case-insensitively with `unconnected` (e.g. `'unconnected'`, `'unconnected (by TERM)'`). The pin is kept on the part with no signal.
+- **`NcOrigin::DroppedSingleton`** — `drop_singleton_signals(Signals*)` (`src/core/domain/signals.cpp`) called at the end of `load`: any signal whose pin set has size exactly 1 is unconnected by definition. The pin is detached (`sig = nullptr`) and tagged; the `Signal` object is deleted.
 - **`NcOrigin::None` (no tag)** — pins materialised by `FillIdentityNCs` at `connect` time. These are unconnected locally but bridged to a real signal on the peer module via `Connection::pin_map`; they are explicitly excluded from the "orphan" count in `verify` and the analyze screen.

 ### Signal groups

-`analyze_system(System*)` (`src/system/analysis.cpp`) emits `SignalGroup`s **per module** (signals are module-scoped). Internal names (starting with `$` — Mentor's `$Nxxxx` convention) are skipped wholesale at every step.
+`analyze_system(System*)` (`src/core/domain/analysis.cpp`) emits `SignalGroup`s **per module** (signals are module-scoped). Internal names (starting with `$` — Mentor's `$Nxxxx` convention) are skipped wholesale at every step.

 **DiffPair** (`GroupKind::DiffPair`):
 - Signal name ends `_P` or `_N` (case-insensitive). The character before the suffix must be `_`.
@@ -303,7 +342,7 @@ The `verify` command (not the analyze screen, yet) also emits the **model-driven

 ### Component kind

-`Part::kind` is inferred at construction (`src/system/component_kind.cpp`) from the leading reference-designator letter(s) of the part name. **Longest-match wins**:
+`Part::kind` is inferred at construction (`src/core/domain/component_kind.cpp`) from the leading reference-designator letter(s) of the part name. **Longest-match wins**:

 - Two-letter prefixes (checked first, case-insensitive): `LED → Semiconductor`, `TP → TestPoint`, `SW → Switch`, `FB → Passive`, `MK / MP / MH → Mechanical`, `HS → Mechanical`, `RA / RN / RP / RV → Passive`.
 - Single-letter fallback: `R / C / L / F → Passive`, `D / Q → Semiconductor`, `U → IntegratedCircuit`, `J / P → Connector`, `Y / X → Crystal`, `S → Switch`.
@@ -315,7 +354,7 @@ Recomputed on `restore` (no persistence tag). Currently not used by any decision

 `connect` looks up a registered transform for `(p1->connector_type, p2->connector_type)` via `TransformRegistry::lookup`, tried in both directions. Fall-through is `IdentityTransform`:

- Compares pin sets by **canonical name** (`canonical_pin_name(s)`, `src/system/pin_name.cpp`): split into prefix + digit suffix; if the suffix is pure digits, zero-pad to width 3 (`A1` → `A001`, `A001` → `A001`, `A1B` → `A1B`, `VCC` → `VCC`).
+- Compares pin sets by **canonical name** (`canonical_pin_name(s)`, `src/core/domain/pin_name.cpp`): split into prefix + digit suffix; if the suffix is pure digits, zero-pad to width 3 (`A1` → `A001`, `A001` → `A001`, `A1B` → `A1B`, `VCC` → `VCC`).
 - `CheckIdentityCompatible(a, b)` accepts the **subset case** (one side's canonical set is a subset of the other's — typical because Altium drops NC, Mentor doesn't). Bidirectional mismatch (both sides have orphans) is refused.
 - After acceptance, `FillIdentityNCs(p1, p2)` **materialises** the missing canonical positions on the smaller side as new NC pins (`new Pin(other_side_name)`, no signal attached, `nc_origin = None`). Idempotent.

--- a/README.md
+++ b/README.md
@@ -15,6 +15,13 @@ cmake --build build -j
 ./build/essim
 ```

+The build is **layered**: `essim_core` is the frontend-agnostic business
+library (domain + importers + operations); the `essim` binary comes from a
+**frontend** under `src/frontends/<name>/` that links it. Select one with
+`-DESSIM_FRONTEND=<name>` (default `tui`); `-DESSIM_FRONTEND=none` builds the
+core + tests only, with no GUI toolkit fetched. Architecture in
+[`DESIGN.md`](DESIGN.md).
+
 Inside the shell, type `help` for the live command list — or read the
 auto-generated reference at [`doc/user/commands.md`](doc/user/commands.md).
 A worked bring-up script is at [`test/system.essim`](test/system.essim);
@@ -41,10 +48,14 @@ Step-by-step walkthroughs for both the batch and TUI workflows are in
  `../libbsdl`, pulled in via `add_subdirectory` and linked dynamically.
  Override its location with `-DBSDL_DIR=/path/to/libbsdl`. Powers the
  `attach-bsdl` command and the pin/JTAG checks.
- Fetched automatically at configure time via `FetchContent` (nothing to
-  install): **FTXUI** v6.1.9 and **doctest** v2.4.11.
+- Fetched automatically via `FetchContent` (nothing to install): **FTXUI**
+  v6.1.9 — only when building the **tui** frontend — and **doctest** v2.4.11
+  for the tests.
 - Optional, only for the `doc` target: **doxygen** and **python3**.

+libzip, pugixml and libbsdl are the **core** dependencies; FTXUI belongs to the
+tui frontend, so a `-DESSIM_FRONTEND=none` build needs none of it.
+
 ## Tests

 ```sh
@@ -53,6 +64,9 @@ Step-by-step walkthroughs for both the batch and TUI workflows are in
 ctest --test-dir build
 ```

+`ctest` runs `essim_tests` (core — links `essim_core`, no GUI toolkit) and
+`essim_tui_tests` (the FTXUI frontend's tests, under `tests/tui/`).
+
 Skip building tests entirely:

 ```sh
@@ -76,12 +90,17 @@ cmake --build build --target doc      # needs doxygen + python3
 ## Project layout

 ```
-src/system/   domain model (Module/Part/Pin/Signal, Connection, Transform, …)
-src/imports/  Mentor / Altium / ODS netlist importers
-src/tui/      FTXUI shell (commands, screens, completion, history)
-tests/        doctest suite
-doc/          api/ + user/ Markdown trees, Doxyfile.in, gen_api_md.py
-test/         sample netlists + system.essim bring-up script
+src/
+  core/                 business logic, NO GUI toolkit (→ libessim_core)
+    domain/             model (Module/Part/Pin/Signal, Connection, Transform…) + analyses
+    imports/            Mentor / Altium / ODS netlist importers + ODS writer
+    app/                use-case operations (export → CSV/ODS, …)
+  frontends/            one dir per GUI/TUI engine, each links essim_core
+    tui/                FTXUI shell + main.cpp (→ libessim_tui + the `essim` binary)
+tests/                  core tests (link essim_core)
+  tui/                  frontend tests (link essim_tui)
+doc/                    api/ + user/ Markdown, Doxyfile.in, gen_api_md.py
+test/                   sample netlists + system.essim bring-up script
 ```

 Full layout & rationale in [`DESIGN.md`](DESIGN.md).
--- a/src/core/app/connect.cpp
+++ b/src/core/app/connect.cpp
@@ -0,0 +1,67 @@
+#include "core/app/connect.hpp"
+
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/system.hpp"
+#include "core/domain/transform.hpp"
+
+#include <exception>
+#include <utility>
+
+namespace app {
+
+ConnectResult connect_parts(System *sys, Module *m1, Part *p1,
+                            Module *m2, Part *p2)
+{
+    ConnectResult r;
+
+    auto &reg = TransformRegistry::get();
+    Transform *t = reg.lookup(p1->connector_type, p2->connector_type);
+    bool both_empty = p1->connector_type.empty() && p2->connector_type.empty();
+
+    if (t == reg.identity()) {
+        if (!both_empty) {
+            r.refused = true;
+            r.error = "no transform for types '"
+                    + (p1->connector_type.empty() ? std::string("(none)")
+                                                   : p1->connector_type)
+                    + "' ↔ '"
+                    + (p2->connector_type.empty() ? std::string("(none)")
+                                                   : p2->connector_type)
+                    + "'. Set matching types via 'set-connector-type' first.";
+            return r;
+        }
+        std::string info;
+        std::string err = CheckIdentityCompatible(p1, p2, &info);
+        if (!err.empty()) {
+            r.refused = true;
+            r.error = err;
+            return r;
+        }
+        if (!info.empty()) {
+            r.identity_info = info;
+            r.nc_added = FillIdentityNCs(p1, p2);
+        }
+    }
+
+    auto pin_map = t->apply(p1, p2);
+
+    r.connection_name = m1->name + "/" + p1->name
+                      + " <-> " + m2->name + "/" + p2->name;
+    r.transform_name = t->name;
+    try {
+        Connection *c = new Connection(r.connection_name, m1, p1, m2, p2);
+        c->transform_name = t->name;
+        c->pin_map = std::move(pin_map);
+        sys->connections()->add(c);
+        r.wires = (int)c->pin_map.size();
+        r.ok = true;
+    } catch (const std::exception &e) {
+        r.error = e.what();
+    }
+
+    return r;
+}
+
+}  // namespace app
--- a/src/core/app/connect.hpp
+++ b/src/core/app/connect.hpp
@@ -0,0 +1,42 @@
+#ifndef _APP_CONNECT_HPP_
+#define _APP_CONNECT_HPP_
+
+#include <string>
+
+class System;
+class Module;
+class Part;
+
+// Application layer: UI-independent operations that any frontend (TUI, GUI, …)
+// can call. No console, no dialogs, no FTXUI — just System in, result out.
+namespace app {
+
+// Outcome of connecting two parts. The side effects (filling identity NC pins,
+// creating the Connection and adding it to the system) all happen in core; the
+// caller only renders the fields.
+struct ConnectResult {
+    bool ok = false;            ///< a Connection was created and added
+    bool refused = false;       ///< a business rule rejected it (vs. an exception)
+    std::string error;          ///< why refused/failed; empty when ok
+
+    std::string connection_name;
+    std::string transform_name;
+    int wires = 0;              ///< pin_map size of the created connection
+
+    // Identity-transform path only: the compatibility info line and how many NC
+    // pins were materialised so both sides match. Empty / 0 otherwise.
+    std::string identity_info;
+    int nc_added = 0;
+};
+
+// Wire part `p1` (in module `m1`) to part `p2` (in module `m2`): look up the
+// transform for their connector types, refuse on an unknown pairing or an
+// identity-incompatible layout, fill identity NC pins when needed, apply the
+// transform and create the Connection. Pure core — no resolution of names or
+// patterns (the frontend turns user input into the Module*/Part* it passes).
+ConnectResult connect_parts(System *sys, Module *m1, Part *p1,
+                            Module *m2, Part *p2);
+
+}  // namespace app
+
+#endif  // _APP_CONNECT_HPP_
--- a/src/core/app/export.cpp
+++ b/src/core/app/export.cpp
@@ -0,0 +1,190 @@
+#include "core/app/export.hpp"
+
+#include "core/imports/ods_writer.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signal_type.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
+
+#include <cctype>
+#include <fstream>
+#include <string>
+
+namespace app {
+
+namespace {
+
+std::string to_lower(std::string s)
+{
+    for (char &c : s) c = (char)std::tolower((unsigned char)c);
+    return s;
+}
+
+// Minimal CSV quoter — wraps in "…" and doubles internal quotes when the field
+// contains a comma, quote, or newline.
+std::string csv_quote(const std::string &s)
+{
+    if (s.find_first_of(",\"\n") == std::string::npos)
+        return s;
+    std::string out = "\"";
+    for (char c : s) { if (c == '"') out += '"'; out += c; }
+    out += '"';
+    return out;
+}
+
+// Flatten one pin into the string slots an export row uses.
+void pin_side(Pin *p, std::string &mod, std::string &part, std::string &pin,
+              std::string &sig, std::string &type, std::string &suspect)
+{
+    if (!p) { mod = part = pin = sig = type = suspect = ""; return; }
+    mod  = (p->prnt && p->prnt->prnt) ? p->prnt->prnt->name : "";
+    part = p->prnt ? p->prnt->name : "";
+    pin  = p->name;
+    Signal *s = p->signal();
+    if (!s) {
+        sig = ""; type = "(NC)"; suspect = "";
+    } else {
+        sig = s->name;
+        type = signal_type_name(s->type);
+        suspect = (infer_signal_type(s->name) == SignalType::Power
+                   && s->type == SignalType::Other) ? "yes" : "no";
+    }
+}
+
+// Excel rejects /\?*:[] in sheet names; ODS forbids < > & in raw table names.
+// Sanitise to underscores and clip to Excel's 31-char hard limit.
+std::string sanitise_sheet_name(std::string name)
+{
+    for (char &ch : name)
+        if (ch == '/' || ch == '\\' || ch == '?' || ch == '*' || ch == ':'
+            || ch == '[' || ch == ']' || ch == '<' || ch == '>' || ch == '&')
+            ch = '_';
+    if (name.size() > 31) name = name.substr(0, 31);
+    return name;
+}
+
+ExportResult write_ods(const System *sys, const std::string &path)
+{
+    ExportResult r;
+    OdsWriter w;
+    for (auto &ckv : *sys->connections()) {
+        Connection *c = ckv.second;
+        OdsSheet *s = w.add_sheet(sanitise_sheet_name(c->name));
+
+        std::string lmod = c->m1 ? c->m1->name : "";
+        std::string lprt = c->p1 ? c->p1->name : "";
+        std::string rmod = c->m2 ? c->m2->name : "";
+        std::string rprt = c->p2 ? c->p2->name : "";
+
+        // Meta header: label/value rows, a blank row, then the column headers.
+        auto meta = [&](int row, const std::string &k, const std::string &v) {
+            s->set(row, 0, k);
+            s->set(row, 1, v);
+        };
+        meta(0, "Connection", c->name);
+        meta(1, "Transform",  c->transform_name);
+        meta(2, "Left",       lmod + " / " + lprt);
+        meta(3, "Right",      rmod + " / " + rprt);
+        // Row 4 left blank by design.
+
+        const int HDR = 5;
+        s->set_header_row(HDR);
+        const char *hdr[] = {
+            "left_pin", "left_signal", "left_type", "left_suspect",
+            "right_pin", "right_signal", "right_type", "right_suspect",
+            "type_mismatch"};
+        for (int i = 0; i < 9; ++i) s->set(HDR, i, hdr[i]);
+
+        int row = HDR + 1;
+        for (auto &wp : c->pin_map) {
+            std::string lm, lp, ln, ls, lt, lsus;
+            std::string rm, rp, rn, rs, rt, rsus;
+            pin_side(wp.first,  lm, lp, ln, ls, lt, lsus);
+            pin_side(wp.second, rm, rp, rn, rs, rt, rsus);
+            std::string tm = (lt != "(NC)" && rt != "(NC)" && lt != rt) ? "yes" : "no";
+            s->set(row, 0, ln); s->set(row, 1, ls);
+            s->set(row, 2, lt); s->set(row, 3, lsus);
+            s->set(row, 4, rn); s->set(row, 5, rs);
+            s->set(row, 6, rt); s->set(row, 7, rsus);
+            s->set(row, 8, tm);
+            ++row; ++r.rows;
+        }
+    }
+
+    std::string err;
+    if (!w.save(path, err)) {
+        r.error = err;
+        return r;
+    }
+    r.ok = true;
+    r.sheets = (int)sys->connections()->size();
+    return r;
+}
+
+ExportResult write_csv(const System *sys, const std::string &path)
+{
+    ExportResult r;
+    std::ofstream f(path);
+    if (!f) {
+        r.error = "cannot open '" + path + "' for writing";
+        return r;
+    }
+
+    // One rectangular table: each row repeats the per-connection constants so
+    // the file stays parser-friendly (pandas / awk / spreadsheet).
+    f << "connection,transform,"
+         "left_module,left_part,"
+         "left_pin,left_signal,left_type,left_suspect,"
+         "right_module,right_part,"
+         "right_pin,right_signal,right_type,right_suspect,"
+         "type_mismatch\n";
+
+    for (auto &ckv : *sys->connections()) {
+        Connection *c = ckv.second;
+        for (auto &wp : c->pin_map) {
+            std::string lm, lp, ln, ls, lt, lsus;
+            std::string rm, rp, rn, rs, rt, rsus;
+            pin_side(wp.first,  lm, lp, ln, ls, lt, lsus);
+            pin_side(wp.second, rm, rp, rn, rs, rt, rsus);
+            std::string tm = (lt != "(NC)" && rt != "(NC)" && lt != rt) ? "yes" : "no";
+            f << csv_quote(c->name)           << ','
+              << csv_quote(c->transform_name) << ','
+              << csv_quote(lm) << ',' << csv_quote(lp) << ','
+              << csv_quote(ln) << ',' << csv_quote(ls) << ','
+              << csv_quote(lt) << ',' << csv_quote(lsus) << ','
+              << csv_quote(rm) << ',' << csv_quote(rp) << ','
+              << csv_quote(rn) << ',' << csv_quote(rs) << ','
+              << csv_quote(rt) << ',' << csv_quote(rsus) << ','
+              << tm << '\n';
+            ++r.rows;
+        }
+    }
+    r.ok = f.good();
+    if (!r.ok) r.error = "write error on '" + path + "'";
+    return r;
+}
+
+}  // namespace
+
+bool export_format_from_path(const std::string &path, ExportFormat &out)
+{
+    size_t dot = path.rfind('.');
+    std::string ext = (dot == std::string::npos) ? "" : to_lower(path.substr(dot));
+    if (ext == ".csv") { out = ExportFormat::Csv; return true; }
+    if (ext == ".ods") { out = ExportFormat::Ods; return true; }
+    return false;
+}
+
+ExportResult export_connections(const System *sys, const std::string &path,
+                                ExportFormat format)
+{
+    ExportResult r;
+    if (!sys) { r.error = "no system"; return r; }
+    return (format == ExportFormat::Ods) ? write_ods(sys, path)
+                                         : write_csv(sys, path);
+}
+
+}  // namespace app
--- a/src/core/app/export.hpp
+++ b/src/core/app/export.hpp
@@ -0,0 +1,34 @@
+#ifndef _APP_EXPORT_HPP_
+#define _APP_EXPORT_HPP_
+
+#include <string>
+
+class System;
+
+// Application layer: UI-independent operations that any frontend (TUI, GUI, …)
+// can call. No console, no dialogs, no FTXUI — just System in, result out.
+namespace app {
+
+enum class ExportFormat { Csv, Ods };
+
+// Outcome of an export. The only side effect is writing the target file; the
+// caller renders `error` / the stats however it likes.
+struct ExportResult {
+    bool ok = false;
+    std::string error;  ///< human-readable, set when !ok
+    int sheets = 0;     ///< ODS: number of sheets (one per connection); 0 for CSV
+    int rows = 0;       ///< wires written
+};
+
+// Map a filename extension (.csv / .ods, case-insensitive) to a format.
+// Returns false if the extension is neither.
+bool export_format_from_path(const std::string &path, ExportFormat &out);
+
+// Export the system's connections to `path` in `format`. Builds the file and
+// returns stats or an error. Pure core — safe to call from any frontend.
+ExportResult export_connections(const System *sys, const std::string &path,
+                                ExportFormat format);
+
+}  // namespace app
+
+#endif  // _APP_EXPORT_HPP_
--- a/src/core/app/load.cpp
+++ b/src/core/app/load.cpp
@@ -0,0 +1,46 @@
+#include "core/app/load.hpp"
+
+#include "core/domain/analysis.hpp"  // infer_signal_types, SignalTypeInferenceStats
+#include "core/domain/modules.hpp"
+#include "core/domain/signals.hpp"   // drop_singleton_signals
+#include "core/domain/system.hpp"
+
+#include <cctype>
+#include <exception>
+
+namespace app {
+
+bool import_type_from_name(const std::string &name, ImportType &out)
+{
+    std::string ls;
+    ls.reserve(name.size());
+    for (char c : name) ls += (char)std::tolower((unsigned char)c);
+    if (ls == "mentor") { out = ImportType::IMPORT_MENTOR; return true; }
+    if (ls == "altium") { out = ImportType::IMPORT_ALTIUM; return true; }
+    if (ls == "ods")    { out = ImportType::IMPORT_ODS;    return true; }
+    return false;
+}
+
+LoadResult load_module(System *sys, const std::string &module_name,
+                       const std::string &path, ImportType type)
+{
+    LoadResult r;
+    if (!sys) { r.error = "no system"; return r; }
+    try {
+        sys->Load(module_name, path, type);
+        Module *mod = sys->modules()->get(module_name);
+        r.dropped = drop_singleton_signals(mod->signals);
+        SignalTypeInferenceStats inf = infer_signal_types(sys);
+        r.parts      = (int)mod->size();
+        r.signals    = (int)mod->signals->size();
+        r.power      = inf.power;
+        r.gnd        = inf.gnd;
+        r.kept_other = inf.kept_other;
+        r.ok = true;
+    } catch (const std::exception &e) {
+        r.error = e.what();
+    }
+    return r;
+}
+
+}  // namespace app
--- a/src/core/app/load.hpp
+++ b/src/core/app/load.hpp
@@ -0,0 +1,36 @@
+#ifndef _APP_LOAD_HPP_
+#define _APP_LOAD_HPP_
+
+#include "core/domain/system.hpp"  // ImportType
+
+#include <string>
+
+// Application layer: UI-independent operations that any frontend (TUI, GUI, …)
+// can call. No console, no dialogs, no FTXUI — just System in, result out.
+namespace app {
+
+// Map an import-type name (mentor / altium / ods, case-insensitive) to an
+// ImportType. Returns false if the name is none of those.
+bool import_type_from_name(const std::string &name, ImportType &out);
+
+// Outcome of loading a module: the post-import counts the caller renders.
+struct LoadResult {
+    bool ok = false;
+    std::string error;   ///< human-readable, set when !ok
+    int parts = 0;
+    int signals = 0;
+    int dropped = 0;     ///< singleton/NC signals removed after import
+    int power = 0;       ///< signals inferred Power (name + structure)
+    int gnd = 0;         ///< signals inferred GndShield (name)
+    int kept_other = 0;  ///< name said Power but evidence too weak → kept Other
+};
+
+// Import a module from a netlist/pinout file into `sys`, drop singleton signals,
+// then infer signal types. Returns the counts or an error. Pure core — safe to
+// call from any frontend.
+LoadResult load_module(System *sys, const std::string &module_name,
+                       const std::string &path, ImportType type);
+
+}  // namespace app
+
+#endif  // _APP_LOAD_HPP_
--- a/src/core/app/verify.cpp
+++ b/src/core/app/verify.cpp
@@ -0,0 +1,105 @@
+#include "core/app/verify.hpp"
+
+#include "core/domain/bsdl_check.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/nets.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
+
+#include <unordered_set>
+#include <utility>
+#include <vector>
+
+namespace app {
+
+VerifyReport verify(System *sys)
+{
+    VerifyReport r;
+    if (!sys)
+        return r;
+
+    // Pass 1 — typed pins: expected (model) vs actual (net) signal type.
+    for (auto &mkv : *sys->modules()) {
+        Module *mod = mkv.second;
+        for (auto &pkv : *mod) {
+            Part *prt = pkv.second;
+            if (prt->connector_type.empty())
+                continue;
+            for (auto &nkv : *prt) {
+                Pin *pin = nkv.second;
+                ++r.typed_pins;
+                SignalType expected = pin->expected_signal_type();
+                if (expected == SignalType::Other)
+                    continue;
+                Signal *s = pin->signal();
+                SignalType actual = s ? s->type : SignalType::Other;
+                if (actual == expected)
+                    continue;
+                RoleMismatch m;
+                m.module = mod->name;
+                m.part = prt->name;
+                m.pin = pin->name;
+                m.signal = s ? s->name : std::string("(NC)");
+                m.expected = expected;
+                m.actual = actual;
+                r.role_mismatches.push_back(std::move(m));
+            }
+        }
+    }
+
+    // Pass 2 — bridged nets: flag Power/GndShield mixing. Compute the nets once
+    // here and reuse them for the model checks below.
+    std::vector<Net> nets = compute_all_nets(sys);
+    r.total_nets = (int)nets.size();
+    for (const Net &n : nets) {
+        if (n.members.size() < 2)
+            continue;
+        ++r.bridged_nets;
+        SignalType dom;
+        if (net_type_consistent(n, dom))
+            continue;
+        NetInconsistency ni;
+        for (const auto &mp : n.members)
+            ni.members.push_back({mp.first->name, mp.second->name, mp.second->type});
+        r.net_inconsistencies.push_back(std::move(ni));
+    }
+
+    // Pass 3 — orphans: pins with no signal and not bridged via a connection.
+    std::unordered_set<Pin *> bridged_pins;
+    for (auto &ckv : *sys->connections())
+        for (auto &wp : ckv.second->pin_map) {
+            if (wp.first)  bridged_pins.insert(wp.first);
+            if (wp.second) bridged_pins.insert(wp.second);
+        }
+    for (auto &mkv : *sys->modules())
+        for (auto &pkv : *mkv.second)
+            for (auto &nkv : *pkv.second) {
+                Pin *pin = nkv.second;
+                if (pin->signal() || bridged_pins.count(pin))
+                    continue;
+                bool dropped;
+                if (pin->nc_origin == NcOrigin::ImportedUnconnected) {
+                    ++r.orphan_imported;
+                    dropped = false;
+                } else if (pin->nc_origin == NcOrigin::DroppedSingleton) {
+                    ++r.orphan_dropped;
+                    dropped = true;
+                } else {
+                    continue;
+                }
+                r.orphans.push_back({mkv.first, pkv.first, nkv.first, dropped});
+            }
+
+    // Passes 4-7 — model-driven checks (reuse the nets from pass 2).
+    r.pin_anomalies          = check_pin_specs(sys, &nets);
+    r.jtag_anomalies         = check_jtag_chain(sys, &nets);
+    r.conflict_anomalies     = check_source_conflicts(sys);
+    r.completeness_anomalies = check_bsdl_completeness(sys);
+
+    return r;
+}
+
+}  // namespace app
--- a/src/core/app/verify.hpp
+++ b/src/core/app/verify.hpp
@@ -0,0 +1,69 @@
+#ifndef _APP_VERIFY_HPP_
+#define _APP_VERIFY_HPP_
+
+#include "core/domain/analysis.hpp"     // Anomaly
+#include "core/domain/signal_type.hpp"  // SignalType
+
+#include <string>
+#include <vector>
+
+class System;
+
+namespace app {
+
+// One typed-pin role mismatch: the connector/BSDL expectation disagrees with
+// the actual net type.
+struct RoleMismatch {
+    std::string module, part, pin;
+    std::string signal;        ///< signal name, or "(NC)"
+    SignalType expected = SignalType::Other;
+    SignalType actual   = SignalType::Other;
+};
+
+// One bridged net mixing Power and GndShield, with its members for display.
+struct NetInconsistency {
+    struct Member { std::string module, signal; SignalType type; };
+    std::vector<Member> members;
+};
+
+// One orphan pin: no signal and not bridged via a connection. `dropped` is true
+// for a dropped singleton (essim detached it), false for an import-time NC.
+struct OrphanPin {
+    std::string module, part, pin;
+    bool dropped = false;
+};
+
+// The full result of `verify`: structured data only — no strings beyond the
+// names, no formatting. Frontends (the verify command, the analyze screen, the
+// dashboard) render it however they like.
+struct VerifyReport {
+    int typed_pins = 0;                          ///< pins with a non-Other expectation considered
+    std::vector<RoleMismatch> role_mismatches;
+
+    int total_nets = 0;
+    int bridged_nets = 0;
+    std::vector<NetInconsistency> net_inconsistencies;
+
+    int orphan_imported = 0;
+    int orphan_dropped = 0;
+    std::vector<OrphanPin> orphans;              ///< per-pin detail (both origins)
+
+    std::vector<Anomaly> pin_anomalies;          ///< check_pin_specs
+    std::vector<Anomaly> jtag_anomalies;         ///< check_jtag_chain
+    std::vector<Anomaly> conflict_anomalies;     ///< check_source_conflicts
+    std::vector<Anomaly> completeness_anomalies; ///< check_bsdl_completeness
+
+    int orphan_total() const { return orphan_imported + orphan_dropped; }
+    int model_total() const {
+        return (int)(pin_anomalies.size() + jtag_anomalies.size()
+                     + conflict_anomalies.size() + completeness_anomalies.size());
+    }
+};
+
+// Run every verify pass over the system and return the findings. Pure core —
+// computes the nets once and feeds them to the net-based checks.
+VerifyReport verify(System *sys);
+
+}  // namespace app
+
+#endif  // _APP_VERIFY_HPP_
--- a/src/core/domain/analysis.cpp
+++ b/src/core/domain/analysis.cpp
--- a/src/core/domain/analysis.hpp
+++ b/src/core/domain/analysis.hpp
--- a/src/core/domain/bsdl_check.cpp
+++ b/src/core/domain/bsdl_check.cpp
--- a/src/core/domain/bsdl_check.hpp
+++ b/src/core/domain/bsdl_check.hpp
--- a/src/core/domain/bsdl_model.cpp
+++ b/src/core/domain/bsdl_model.cpp
--- a/src/core/domain/bsdl_model.hpp
+++ b/src/core/domain/bsdl_model.hpp
--- a/src/core/domain/component_kind.cpp
+++ b/src/core/domain/component_kind.cpp
@@ -1,4 +1,4 @@
-#include "system/component_kind.hpp"
+#include "core/domain/component_kind.hpp"

 #include <cctype>
 #include <string>
--- a/src/core/domain/component_kind.hpp
+++ b/src/core/domain/component_kind.hpp
--- a/src/core/domain/connect.cpp
+++ b/src/core/domain/connect.cpp
--- a/src/core/domain/connect.hpp
+++ b/src/core/domain/connect.hpp
--- a/src/core/domain/modules.cpp
+++ b/src/core/domain/modules.cpp
--- a/src/core/domain/modules.hpp
+++ b/src/core/domain/modules.hpp
--- a/src/core/domain/nets.cpp
+++ b/src/core/domain/nets.cpp
@@ -1,11 +1,11 @@
-#include "system/nets.hpp"
+#include "core/domain/nets.hpp"

-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <queue>
 #include <unordered_map>
--- a/src/core/domain/nets.hpp
+++ b/src/core/domain/nets.hpp
--- a/src/core/domain/parts.cpp
+++ b/src/core/domain/parts.cpp
--- a/src/core/domain/parts.hpp
+++ b/src/core/domain/parts.hpp
--- a/src/core/domain/persist.cpp
+++ b/src/core/domain/persist.cpp
--- a/src/core/domain/persist.hpp
+++ b/src/core/domain/persist.hpp
--- a/src/core/domain/pin_model.cpp
+++ b/src/core/domain/pin_model.cpp
--- a/src/core/domain/pin_model.hpp
+++ b/src/core/domain/pin_model.hpp
--- a/src/core/domain/pin_name.cpp
+++ b/src/core/domain/pin_name.cpp
@@ -1,4 +1,4 @@
-#include "system/pin_name.hpp"
+#include "core/domain/pin_name.hpp"

 #include <cstdio>
 #include <stdexcept>
--- a/src/core/domain/pin_name.hpp
+++ b/src/core/domain/pin_name.hpp
--- a/src/core/domain/pin_role.cpp
+++ b/src/core/domain/pin_role.cpp
--- a/src/core/domain/pin_role.hpp
+++ b/src/core/domain/pin_role.hpp
--- a/src/core/domain/pin_spec.hpp
+++ b/src/core/domain/pin_spec.hpp
--- a/src/core/domain/pins.cpp
+++ b/src/core/domain/pins.cpp
--- a/src/core/domain/pins.hpp
+++ b/src/core/domain/pins.hpp
--- a/src/core/domain/signal_type.hpp
+++ b/src/core/domain/signal_type.hpp
--- a/src/core/domain/signals.cpp
+++ b/src/core/domain/signals.cpp
--- a/src/core/domain/signals.hpp
+++ b/src/core/domain/signals.hpp
--- a/src/core/domain/syselmts.hpp
+++ b/src/core/domain/syselmts.hpp
--- a/src/core/domain/system.cpp
+++ b/src/core/domain/system.cpp
@@ -0,0 +1,56 @@
+
+#include "system.hpp"
+
+#include "connect.hpp"
+#include "modules.hpp"
+#include "core/imports/import_altium.hpp"
+#include "core/imports/import_mentor.hpp"
+#include "core/imports/import_ods.hpp"
+
+System::System() : mods(nullptr), conns(nullptr)
+{
+    mods = new Modules();
+    conns = new Connections();
+}
+
+System::~System()
+{
+    delete mods;
+    delete conns;
+}
+
+void System::Load(std::string module_name, std::string file_name, ImportType type)
+{
+    // Build the importer first, based on the import type.
+    ImportBase *imp;
+    if (type == ImportType::IMPORT_MENTOR)
+    {
+        imp = new ImportMentor(file_name);
+    } else if (type == ImportType::IMPORT_ALTIUM)
+    {
+        imp = new ImportAltium(file_name);
+    } else if (type == ImportType::IMPORT_ODS)
+    {
+        imp = new ImportOds(file_name);
+    }
+    else
+    {
+        throw std::runtime_error("Unknown import type");
+    }
+
+    // Fail fast on a missing/unreadable file, before touching the module table,
+    // so a failed load never leaves behind an empty module.
+    if (!imp->is_open())
+    {
+        delete imp;
+        throw std::runtime_error("cannot open file: " + file_name);
+    }
+
+    // Creation or retrieval of the module, then parse into it. add() copies the
+    // Part pointers into the module, which takes ownership; deleting the
+    // importer then frees the (now drained) Parts container, not the parts.
+    Module *mod = mods->merge(module_name);
+    imp->parse(mod->signals);
+    mod->add(imp->parts());
+    delete imp;
+}
--- a/src/core/domain/system.hpp
+++ b/src/core/domain/system.hpp
@@ -1,7 +1,7 @@
 #ifndef _SYSTEM_HPP_
 #define _SYSTEM_HPP_

-#include "imports/import_base.hpp"
+#include "core/imports/import_base.hpp"

 #pragma once
 class Modules; ///< Forward declaration of the Modules class.
--- a/src/core/domain/transform.cpp
+++ b/src/core/domain/transform.cpp
--- a/src/core/domain/transform.hpp
+++ b/src/core/domain/transform.hpp
--- a/src/core/domain/transform_vpx.cpp
+++ b/src/core/domain/transform_vpx.cpp
--- a/src/core/domain/transform_vpx.hpp
+++ b/src/core/domain/transform_vpx.hpp
--- a/src/core/imports/import_altium.cpp
+++ b/src/core/imports/import_altium.cpp
@@ -1,8 +1,8 @@
 #include "import_altium.hpp"

-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"

 #include <cctype>
 #include <string>
--- a/src/core/imports/import_altium.hpp
+++ b/src/core/imports/import_altium.hpp
--- a/src/core/imports/import_base.hpp
+++ b/src/core/imports/import_base.hpp
@@ -4,8 +4,8 @@
 #include <string>
 #include <fstream>

-#include "system/parts.hpp"
-#include "system/signals.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/signals.hpp"

 /**
 * @brief Base class for importing data from a file.
@@ -27,11 +27,22 @@ public:
     *
     * @param file_name Name of the file to be imported.
     */
-    ImportBase(std::string file_name) : file_lines(std::fstream(file_name))
+    ImportBase(std::string file_name) : file_lines(file_name, std::ios::in)
    {
        prts = new Parts();
    };

+    /**
+     * @brief Whether the input file was opened successfully.
+     *
+     * Opened read-only, so this is false only when the file is genuinely
+     * missing or unreadable (a read-only but present file still opens).
+     * System::Load checks it to fail fast instead of producing an empty module.
+     *
+     * @return true if the file stream is open.
+     */
+    bool is_open() const { return file_lines.is_open(); }
+
    /**
     * @brief Pure virtual method for parsing the file.
     *
@@ -53,9 +64,13 @@ public:
    /**
     * @brief Virtual destructor for ImportBase.
     *
-     * Ensures proper cleanup of derived classes.
+     * Frees the Parts container object. Only the container is deleted, not the
+     * Part objects it holds: by the time the importer is destroyed those have
+     * been transferred to a Module (SystemElementContainer::add copies the
+     * pointers), which owns and deletes them. The default ~Parts frees the map
+     * without touching the elements, so there is no double free.
     */
-    virtual ~ImportBase() = default;
+    virtual ~ImportBase() { delete prts; }
 };

 #endif // _IMPORT_BASE_HPP_
--- a/src/core/imports/import_mentor.cpp
+++ b/src/core/imports/import_mentor.cpp
@@ -1,6 +1,6 @@
 #include "import_mentor.hpp"
-#include "system/pins.hpp"
-#include "system/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/parts.hpp"

 #include <cctype>
 #include <vector>
@@ -43,16 +43,6 @@ enum class State
 */
 ImportMentor::ImportMentor(string filename) : ImportBase(filename) {}

-/**
- * @brief Destructor for ImportMentor.
- *
- * Ensures proper cleanup by calling the base class destructor.
- */
-ImportMentor::~ImportMentor()
-{
-    ImportBase::~ImportBase();
-}
-
 /**
 * @brief Parses the file to extract parts, pins, and signals.
 *
--- a/src/core/imports/import_mentor.hpp
+++ b/src/core/imports/import_mentor.hpp
@@ -10,7 +10,6 @@ class ImportMentor : public ImportBase
 public:
    ImportMentor(std::string filename);
    void parse(Signals *signals) override;
-    ~ImportMentor();
 };

 #endif // _IMPORT_MENTOR_HPP_
--- a/src/core/imports/import_ods.cpp
+++ b/src/core/imports/import_ods.cpp
@@ -1,8 +1,8 @@
 #include "import_ods.hpp"

-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"

 #include <pugixml.hpp>
 #include <zip.h>
--- a/src/core/imports/import_ods.hpp
+++ b/src/core/imports/import_ods.hpp
--- a/src/core/imports/ods_writer.cpp
+++ b/src/core/imports/ods_writer.cpp
--- a/src/core/imports/ods_writer.hpp
+++ b/src/core/imports/ods_writer.hpp
--- a/src/frontends/frontend.hpp
+++ b/src/frontends/frontend.hpp
@@ -0,0 +1,30 @@
+#ifndef _FRONTEND_HPP_
+#define _FRONTEND_HPP_
+
+#include <iosfwd>
+#include <string>
+
+// Abstract entry-point interface every frontend (TUI, GUI, …) implements, so
+// one shared launcher (frontend_main) can drive any of them: parse argv, run
+// boot commands, optionally dump output (batch / docs) and enter the event
+// loop. Lives in the frontends layer — essim_core never depends on it.
+class Frontend {
+public:
+    virtual ~Frontend() = default;
+
+    // Dispatch one command synchronously, exactly as if the user typed it
+    // (e.g. "restore foo.essim" or "source bring-up.essim"), before the event
+    // loop starts — used to seed the system at boot.
+    virtual void BootDispatch(const std::string &raw) = 0;
+
+    // Write the command registry as Markdown (used for doc generation).
+    virtual void DumpCommandsMd(std::ostream &out) const = 0;
+
+    // Write the accumulated console output (batch mode: no event loop).
+    virtual void DumpOutput(std::ostream &out) const = 0;
+
+    // Enter the interactive event loop.
+    virtual void Run() = 0;
+};
+
+#endif  // _FRONTEND_HPP_
--- a/src/frontends/frontend_main.cpp
+++ b/src/frontends/frontend_main.cpp
@@ -1,4 +1,6 @@
-#include "tui/tui.hpp"
+#include "frontends/frontend_main.hpp"
+
+#include "frontends/frontend.hpp"

 #include <fstream>
 #include <iostream>
@@ -11,16 +13,17 @@ void print_usage(const char *prog) {
        "usage: " << prog << " [--batch] [--source FILE] [--restore FILE]\n"
        "       " << prog << " --commands-md [FILE]\n"
        "       " << prog << " --help\n"
-        "  (no args)             launch the TUI on an empty system.\n"
+        "  (no args)             launch the interface on an empty system.\n"
        "  --source FILE         after boot, run FILE as an essim script\n"
        "                        (one command per line; same as the `source`\n"
-        "                        command). Output is in the console screen.\n"
+        "                        command). Output goes to the console.\n"
        "  --restore FILE        after boot, restore the system snapshot in\n"
        "                        FILE (same as the `restore` command).\n"
        "                        Combine with --source to layer a script on\n"
        "                        top of a restored snapshot.\n"
        "  --batch               run --restore/--source, print the console\n"
-        "                        output to stdout, and exit without the TUI.\n"
+        "                        output to stdout, and exit without launching\n"
+        "                        the interface.\n"
        "  --commands-md [FILE]  dump the command registry as Markdown.\n"
        "                        With FILE: write there. Without: stdout.\n"
        "                        (Used by `cmake --build build --target doc`.)\n"
@@ -29,7 +32,7 @@ void print_usage(const char *prog) {

 }  // namespace

-int main(int argc, char **argv) {
+int frontend_main(int argc, char **argv, Frontend &fe) {
    std::string boot_restore;
    std::string boot_source;
    bool batch = false;
@@ -37,16 +40,15 @@ int main(int argc, char **argv) {
    for (int i = 1; i < argc; ++i) {
        std::string a = argv[i];
        if (a == "--commands-md") {
-            Tui tui;
            if (i + 1 < argc) {
                std::ofstream f(argv[++i]);
                if (!f) {
                    std::cerr << "essim: cannot open " << argv[i] << " for writing\n";
                    return 1;
                }
-                tui.DumpCommandsMd(f);
+                fe.DumpCommandsMd(f);
            } else {
-                tui.DumpCommandsMd(std::cout);
+                fe.DumpCommandsMd(std::cout);
            }
            return 0;
        }
@@ -79,20 +81,19 @@ int main(int argc, char **argv) {
        return 2;
    }

-    Tui tui;
    // Order matters: a `--restore` brings up a snapshot, then `--source`
    // can layer additional commands on top of it (useful e.g. for "load
    // snapshot, then re-run a small script that adds a new card").
-    if (!boot_restore.empty()) tui.BootDispatch("restore " + boot_restore);
-    if (!boot_source.empty())  tui.BootDispatch("source "  + boot_source);
+    if (!boot_restore.empty()) fe.BootDispatch("restore " + boot_restore);
+    if (!boot_source.empty())  fe.BootDispatch("source "  + boot_source);

-    // Batch mode: the boot dispatch already ran synchronously (no screen yet),
-    // so the console output is complete. Print it and exit without the TUI.
+    // Batch mode: the boot dispatch already ran synchronously (no event loop
+    // yet), so the console output is complete. Print it and exit.
    if (batch) {
-        tui.DumpOutput(std::cout);
+        fe.DumpOutput(std::cout);
        return 0;
    }

-    tui.Run();
+    fe.Run();
    return 0;
 }
--- a/src/frontends/frontend_main.hpp
+++ b/src/frontends/frontend_main.hpp
@@ -0,0 +1,13 @@
+#ifndef _FRONTEND_MAIN_HPP_
+#define _FRONTEND_MAIN_HPP_
+
+class Frontend;
+
+// Shared process entry point, frontend-agnostic. Parses argv
+// (--source / --restore / --batch / --commands-md / --help), drives `fe`
+// through the boot commands and then either dumps output (batch) or enters its
+// event loop, and returns the process exit code. Each frontend's main() just
+// constructs its concrete Frontend and forwards to this.
+int frontend_main(int argc, char **argv, Frontend &fe);
+
+#endif  // _FRONTEND_MAIN_HPP_
--- a/src/frontends/tui/CMakeLists.txt
+++ b/src/frontends/tui/CMakeLists.txt
@@ -0,0 +1,39 @@
+# TUI frontend (FTXUI). Builds the `essim` executable against essim_core.
+#
+# A frontend is self-contained here: it pulls its own GUI toolkit, compiles its
+# sources into a library that links essim_core, and produces the `essim` binary
+# from its own entry point (main.cpp). To add another frontend, create a sibling
+# src/frontends/<name>/ with the same shape and select it with
+# -DESSIM_FRONTEND=<name>.
+
+set(FTXUI_BUILD_DOCS OFF CACHE INTERNAL "")
+set(FTXUI_BUILD_EXAMPLES OFF CACHE INTERNAL "")
+set(FTXUI_BUILD_TESTS OFF CACHE INTERNAL "")
+set(FTXUI_ENABLE_INSTALL OFF CACHE INTERNAL "")
+
+FetchContent_Declare(ftxui
+  GIT_REPOSITORY https://github.com/ArthurSonzogni/FTXUI.git
+  GIT_TAG v6.1.9
+  GIT_SHALLOW TRUE
+)
+FetchContent_MakeAvailable(ftxui)
+
+# Frontend library = every .cpp here except the entry point.
+file(GLOB TUI_SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/*.cpp")
+list(REMOVE_ITEM TUI_SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/main.cpp")
+
+add_library(essim_tui STATIC ${TUI_SOURCES})
+target_link_libraries(essim_tui
+  PUBLIC
+    essim_core
+    ftxui::screen
+    ftxui::dom
+    ftxui::component
+)
+
+add_executable(essim "${CMAKE_CURRENT_SOURCE_DIR}/main.cpp")
+target_link_libraries(essim PRIVATE essim_tui essim_frontend)
+
+# Keep the binary at the top of the build tree (./build/essim), regardless of
+# which frontend subdir produced it.
+set_target_properties(essim PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}")
--- a/src/frontends/tui/commands.cpp
+++ b/src/frontends/tui/commands.cpp
@@ -1,28 +1,28 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/analysis.hpp"
-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/nets.hpp"
-#include "system/parts.hpp"
-#include "system/persist.hpp"
-#include "system/pin_role.hpp"
-#include "system/pin_model.hpp"
-#include "system/bsdl_model.hpp"
-#include "system/bsdl_check.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
-#include "system/transform.hpp"
-#include "system/transform_vpx.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/persist.hpp"
+#include "core/domain/pin_role.hpp"
+#include "core/domain/pin_model.hpp"
+#include "core/domain/bsdl_model.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
+
+#include "core/app/connect.hpp"
+#include "core/app/load.hpp"
+#include "core/app/verify.hpp"
+#include "core/domain/transform_vpx.hpp"  // ValidatePartForKind

 #include <algorithm>
 #include <cctype>
 #include <cstdlib>
 #include <exception>
 #include <fstream>
-#include <unordered_set>
 #include <utility>

 void Tui::RegisterCommands() {
@@ -138,29 +138,23 @@ void Tui::RegisterCommands() {
         {"import type [mentor|altium|ods]", Completion::None}},
        [this](const std::vector<std::string> &args) {
            if (!sys) { Print("no system: run 'new' first."); return; }
-            std::string ls = ToLower(args[2]);
            ImportType t;
-            if      (ls == "mentor") t = ImportType::IMPORT_MENTOR;
-            else if (ls == "altium") t = ImportType::IMPORT_ALTIUM;
-            else if (ls == "ods")    t = ImportType::IMPORT_ODS;
-            else { Print("unknown import type: " + args[2]); return; }
-            try {
-                sys->Load(args[0], args[1], t);
-                Module *mod = sys->modules()->get(args[0]);
-                int dropped = drop_singleton_signals(mod->signals);
-                auto inf = infer_signal_types(sys.get());
-                Print("loaded '" + args[0] + "' from " + args[1]);
-                Print("  parts:   " + std::to_string(mod->size()));
-                Print("  signals: " + std::to_string(mod->signals->size())
-                      + (dropped ? " (dropped " + std::to_string(dropped)
-                                   + " singleton/NC signal(s))" : ""));
-                Print("  types:   " + std::to_string(inf.power) + " power, "
-                      + std::to_string(inf.gnd)   + " gnd, "
-                      + std::to_string(inf.kept_other)
-                      + " suspect Power (name only — kept as Other)");
-            } catch (const std::exception &e) {
-                Print(std::string("load failed: ") + e.what());
+            if (!app::import_type_from_name(args[2], t)) {
+                Print("unknown import type: " + args[2]); return;
            }
+            // Import + drop-singletons + infer-types is one core op; the command
+            // only parses the type and renders the counts.
+            app::LoadResult r = app::load_module(sys.get(), args[0], args[1], t);
+            if (!r.ok) { Print(std::string("load failed: ") + r.error); return; }
+            Print("loaded '" + args[0] + "' from " + args[1]);
+            Print("  parts:   " + std::to_string(r.parts));
+            Print("  signals: " + std::to_string(r.signals)
+                  + (r.dropped ? " (dropped " + std::to_string(r.dropped)
+                               + " singleton/NC signal(s))" : ""));
+            Print("  types:   " + std::to_string(r.power) + " power, "
+                  + std::to_string(r.gnd)   + " gnd, "
+                  + std::to_string(r.kept_other)
+                  + " suspect Power (name only — kept as Other)");
        },
        /*prompt_for_missing=*/ true,
        "load a module from a netlist / pinout file (mentor, altium, ods)",
@@ -228,104 +222,43 @@ void Tui::RegisterCommands() {

    commands["verify"] = { {}, [this](auto &) {
        if (!sys) { Print("no system: run 'new' first."); return; }
-        int checked = 0;
-        int mismatches = 0;
-        for (auto &mkv : *sys->modules()) {
-            Module *mod = mkv.second;
-            for (auto &pkv : *mod) {
-                Part *prt = pkv.second;
-                if (prt->connector_type.empty()) continue;
-                for (auto &nkv : *prt) {
-                    Pin *pin = nkv.second;
-                    ++checked;
-                    SignalType expected = pin->expected_signal_type();
-                    if (expected == SignalType::Other) continue;
-                    Signal *s = pin->signal();
-                    SignalType actual = s ? s->type : SignalType::Other;
-                    if (actual == expected) continue;
-                    ++mismatches;
-                    std::string sig_label = s ? s->name : std::string("(NC)");
-                    Print("  " + mod->name + "/" + prt->name + "/" + pin->name
-                          + ": expected " + signal_type_name(expected)
-                          + ", got " + signal_type_name(actual)
-                          + " (signal: " + sig_label + ")");
-                }
-            }
-        }
-        Print("verify: " + std::to_string(mismatches) + " local mismatch(es) over "
-              + std::to_string(checked) + " typed pin(s).");
+        app::VerifyReport r = app::verify(sys.get());

-        auto nets = compute_all_nets(sys.get());
-        int bridged = 0, inconsistent = 0;
-        for (const auto &n : nets) {
-            if (n.members.size() < 2) continue;
-            ++bridged;
-            SignalType dom;
-            if (net_type_consistent(n, dom)) continue;
-            ++inconsistent;
+        for (const auto &m : r.role_mismatches)
+            Print("  " + m.module + "/" + m.part + "/" + m.pin
+                  + ": expected " + signal_type_name(m.expected)
+                  + ", got " + signal_type_name(m.actual)
+                  + " (signal: " + m.signal + ")");
+        Print("verify: " + std::to_string(r.role_mismatches.size())
+              + " local mismatch(es) over " + std::to_string(r.typed_pins)
+              + " typed pin(s).");
+
+        for (const auto &ni : r.net_inconsistencies) {
            std::string line = "  net mixes Power and GndShield:";
-            for (const auto &mp : n.members) {
-                line += " " + mp.first->name + "/" + mp.second->name
-                      + "(" + signal_type_name(mp.second->type) + ")";
-            }
+            for (const auto &mem : ni.members)
+                line += " " + mem.module + "/" + mem.signal
+                      + "(" + signal_type_name(mem.type) + ")";
            Print(line);
        }
-        Print("verify: " + std::to_string(inconsistent) + " inconsistent net(s) over "
-              + std::to_string(bridged) + " bridged net(s) ("
-              + std::to_string(nets.size()) + " total).");
+        Print("verify: " + std::to_string(r.net_inconsistencies.size())
+              + " inconsistent net(s) over " + std::to_string(r.bridged_nets)
+              + " bridged net(s) (" + std::to_string(r.total_nets) + " total).");

-        // Orphan pin report. A pin is "orphan" if it came out of import (or
-        // post-import drop) with no signal, and is still not bridged to a
-        // real signal via any Connection::pin_map. Use `nc-export` for the
-        // per-pin list.
-        std::unordered_set<Pin *> bridged_pins;
-        for (auto &ckv : *sys->connections())
-            for (auto &wp : ckv.second->pin_map) {
-                if (wp.first)  bridged_pins.insert(wp.first);
-                if (wp.second) bridged_pins.insert(wp.second);
-            }
-        int orph_imported = 0, orph_dropped = 0;
-        for (auto &mkv : *sys->modules())
-            for (auto &pkv : *mkv.second)
-                for (auto &nkv : *pkv.second) {
-                    Pin *pin = nkv.second;
-                    if (pin->signal() || bridged_pins.count(pin)) continue;
-                    if (pin->nc_origin == NcOrigin::ImportedUnconnected) ++orph_imported;
-                    else if (pin->nc_origin == NcOrigin::DroppedSingleton) ++orph_dropped;
-                }
-        Print("verify: " + std::to_string(orph_imported + orph_dropped)
-              + " orphan pin(s) at import ("
-              + std::to_string(orph_imported) + " imported NC, "
-              + std::to_string(orph_dropped)  + " dropped singleton).");
+        Print("verify: " + std::to_string(r.orphan_total())
+              + " orphan pin(s) at import (" + std::to_string(r.orphan_imported)
+              + " imported NC, " + std::to_string(r.orphan_dropped)
+              + " dropped singleton).");

-        // Model-driven pin checks (drive contention / undriven net / NC-wired)
-        // from the PinSpec direction/function populated by connector/BSDL models.
-        auto pin_anoms = check_pin_specs(sys.get(), &nets);
-        for (const auto &a : pin_anoms)
-            Print("  [" + std::string(anomaly_kind_name(a.kind)) + "] " + a.message);
-        Print("verify: " + std::to_string(pin_anoms.size())
-              + " model-driven pin anomaly(ies).");
-
-        // JTAG boundary-scan chain integrity (TAP pins → nets).
-        auto jtag_anoms = check_jtag_chain(sys.get(), &nets);
-        for (const auto &a : jtag_anoms)
-            Print("  [" + std::string(anomaly_kind_name(a.kind)) + "] " + a.message);
-        Print("verify: " + std::to_string(jtag_anoms.size())
-              + " JTAG chain anomaly(ies).");
-
-        // Model-vs-netlist conflicts (e.g. a BSDL power pin left unconnected).
-        auto conflict_anoms = check_source_conflicts(sys.get());
-        for (const auto &a : conflict_anoms)
-            Print("  [" + std::string(anomaly_kind_name(a.kind)) + "] " + a.message);
-        Print("verify: " + std::to_string(conflict_anoms.size())
-              + " source-conflict(s).");
-
-        // BSDL completeness: device power/ground pins missing from the netlist.
-        auto missing_anoms = check_bsdl_completeness(sys.get());
-        for (const auto &a : missing_anoms)
-            Print("  [" + std::string(anomaly_kind_name(a.kind)) + "] " + a.message);
-        Print("verify: " + std::to_string(missing_anoms.size())
-              + " BSDL completeness issue(s).");
+        // Each model-driven group: per-finding lines + a one-line summary.
+        auto render = [this](const std::vector<Anomaly> &v, const char *tail) {
+            for (const auto &a : v)
+                Print("  [" + std::string(anomaly_kind_name(a.kind)) + "] " + a.message);
+            Print("verify: " + std::to_string(v.size()) + tail);
+        };
+        render(r.pin_anomalies,          " model-driven pin anomaly(ies).");
+        render(r.jtag_anomalies,         " JTAG chain anomaly(ies).");
+        render(r.conflict_anomalies,     " source-conflict(s).");
+        render(r.completeness_anomalies, " BSDL completeness issue(s).");
    }, true,
       "check pin roles, power/gnd net consistency, and (with BSDL) pin and JTAG checks" };

@@ -622,47 +555,23 @@ void Tui::RegisterCommands() {
            auto [p2, p2_alts] = resolve_part(m2, args[3]);
            if (!p2) { report_ambiguous("part in " + m2->name, args[3], p2_alts); return; }

-            auto &reg = TransformRegistry::get();
-            Transform *t = reg.lookup(p1->connector_type, p2->connector_type);
-            bool both_empty = p1->connector_type.empty() && p2->connector_type.empty();
-            if (t == reg.identity()) {
-                if (!both_empty) {
-                    Print("connect refused: no transform for types '"
-                          + (p1->connector_type.empty() ? "(none)" : p1->connector_type)
-                          + "' ↔ '"
-                          + (p2->connector_type.empty() ? "(none)" : p2->connector_type)
-                          + "'. Set matching types via 'set-connector-type' first.");
-                    return;
-                }
-                std::string info;
-                std::string err = CheckIdentityCompatible(p1, p2, &info);
-                if (!err.empty()) {
-                    Print("connect refused: " + err);
-                    return;
-                }
-                if (!info.empty()) {
-                    int added = FillIdentityNCs(p1, p2);
-                    Print("connect: " + info);
-                    if (added > 0)
-                        Print("connect: added " + std::to_string(added)
-                              + " NC pin(s) so both sides match");
-                }
-            }
-            auto pin_map = t->apply(p1, p2);
-
-            std::string conn_name = m1->name + "/" + p1->name
-                                  + " <-> " + m2->name + "/" + p2->name;
-            try {
-                Connection *c = new Connection(conn_name, m1, p1, m2, p2);
-                c->transform_name = t->name;
-                c->pin_map = std::move(pin_map);
-                sys->connections()->add(c);
-                Print("connected: " + conn_name
-                      + "  via " + t->name
-                      + " (" + std::to_string(c->pin_map.size()) + " wires)");
-            } catch (const std::exception &e) {
-                Print(std::string("connect failed: ") + e.what());
+            // Resolution above is arg-parsing (user text → objects); the wiring
+            // itself — transform lookup, identity NC fill, Connection creation —
+            // is app::connect_parts.
+            app::ConnectResult cr = app::connect_parts(sys.get(), m1, p1, m2, p2);
+            if (cr.refused) { Print("connect refused: " + cr.error); return; }
+            if (!cr.identity_info.empty()) {
+                Print("connect: " + cr.identity_info);
+                if (cr.nc_added > 0)
+                    Print("connect: added " + std::to_string(cr.nc_added)
+                          + " NC pin(s) so both sides match");
            }
+            if (cr.ok)
+                Print("connected: " + cr.connection_name
+                      + "  via " + cr.transform_name
+                      + " (" + std::to_string(cr.wires) + " wires)");
+            else
+                Print(std::string("connect failed: ") + cr.error);
        },
        /*prompt_for_missing=*/ false,
        "connect a part across two modules (interactive screen if no args)",
--- a/src/frontends/tui/commands_export.cpp
+++ b/src/frontends/tui/commands_export.cpp
@@ -0,0 +1,70 @@
+#include "frontends/tui/tui.hpp"
+
+#include "core/app/export.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/system.hpp"
+
+#include <string>
+#include <vector>
+
+// Thin UI wrapper around app::export_connections — this file only resolves
+// arguments / the file dialog and renders the result. All the actual export
+// (CSV / ODS building, file writing) lives in src/app/export.cpp.
+void Tui::RegisterExportCommands() {
+    commands["export"] = {
+        {{"kind [connections]", Completion::None},
+         {"filename (.csv)",    Completion::Path}},
+        [this](const std::vector<std::string> &args) {
+            if (!sys) { Print("no system: run 'new' first."); return; }
+
+            if (args.empty()) {
+                // Bare → the generic file dialog. The CSV/ODS filter rewrites
+                // the extension; the action below dispatches on it.
+                OpenFileDialog(
+                    "Export — connections",
+                    "export.connections",
+                    "connections.csv",
+                    {{"CSV", ".csv"}, {"ODS", ".ods"}},
+                    [this](const std::string &path) {
+                        Dispatch("export connections " + path);
+                    });
+                return;
+            }
+            if (args.size() != 2) {
+                Print("usage: export <kind> <file>   (or no args for the dialog)");
+                return;
+            }
+            const std::string &kind = args[0];
+            const std::string &path = args[1];
+
+            if (kind != "connections") {
+                ShowError("export: unknown kind '" + kind + "'\n"
+                          "Known kinds: connections");
+                return;
+            }
+
+            app::ExportFormat fmt;
+            if (!app::export_format_from_path(path, fmt)) {
+                ShowError("export: unknown extension — accepted: .csv, .ods");
+                return;
+            }
+
+            app::ExportResult r = app::export_connections(sys.get(), path, fmt);
+            if (!r.ok) {
+                ShowError("export failed:\n" + r.error);
+                return;
+            }
+
+            const bool ods = (fmt == app::ExportFormat::Ods);
+            std::string msg = ods ? "export connections (.ods): "
+                                  : "export connections (.csv): ";
+            if (ods) msg += std::to_string(r.sheets) + " sheet(s), ";
+            Print(msg + std::to_string(r.rows) + " wire(s) → " + path);
+        },
+        /*prompt_for_missing=*/ false,
+        "export structured data to CSV / ODS (kinds: connections; "
+        "bare form opens the file-picker dialog)",
+        /*scriptable=*/ true,
+        /*interactive=*/ true,
+    };
+}
--- a/src/frontends/tui/completion.cpp
+++ b/src/frontends/tui/completion.cpp
@@ -1,5 +1,5 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

 #include <cctype>
 #include <cstdlib>
--- a/src/frontends/tui/main.cpp
+++ b/src/frontends/tui/main.cpp
@@ -0,0 +1,11 @@
+#include "frontends/frontend_main.hpp"
+#include "frontends/tui/tui.hpp"
+
+// The TUI frontend's entry point: construct the concrete Frontend (Tui) and
+// hand off to the shared, frontend-agnostic launcher. All argv parsing and the
+// boot/batch/run flow live in frontend_main(); a second frontend's main() looks
+// exactly like this with its own Frontend type.
+int main(int argc, char **argv) {
+    Tui tui;
+    return frontend_main(argc, argv, tui);
+}
--- a/src/frontends/tui/screen_analyze.cpp
+++ b/src/frontends/tui/screen_analyze.cpp
@@ -1,15 +1,11 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/analysis.hpp"
-#include "system/bsdl_check.hpp"
-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/nets.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/app/verify.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
@@ -17,7 +13,6 @@

 #include <algorithm>
 #include <array>
-#include <unordered_set>

 using namespace ftxui;

@@ -57,41 +52,23 @@ Component Tui::BuildAnalyzeScreen() {
        // connection), then structural anomalies from the analysis pass.
        analyze_issues.clear();

-        int n_role_mismatches = 0, n_typed_pins = 0;
-        for (auto &mkv : *sys->modules())
-            for (auto &pkv : *mkv.second) {
-                Part *prt = pkv.second;
-                if (prt->connector_type.empty()) continue;
-                for (auto &nkv : *prt) {
-                    Pin *pin = nkv.second;
-                    ++n_typed_pins;
-                    SignalType expected = pin->expected_signal_type();
-                    if (expected == SignalType::Other) continue;
-                    Signal *s = pin->signal();
-                    SignalType actual = s ? s->type : SignalType::Other;
-                    if (actual == expected) continue;
-                    ++n_role_mismatches;
-                    std::string sig_label = s ? s->name : std::string("(NC)");
-                    analyze_issues.push_back(
-                        "[pin-role] " + mkv.first + "/" + prt->name + "/"
-                        + pin->name + ": expected " + signal_type_name(expected)
-                        + ", got " + signal_type_name(actual)
-                        + " (signal: " + sig_label + ")");
-                }
-            }
+        // verify + structural anomalies. The verify passes (pin-role, net-mix,
+        // orphans, model checks) come from the shared core op; the structural
+        // anomalies (diff-pair/bus) come from analyze_system above.
+        app::VerifyReport vr = app::verify(sys.get());

-        auto nets = compute_all_nets(sys.get());
-        int n_bridged = 0, n_inconsistent = 0;
-        for (const auto &n : nets) {
-            if (n.members.size() < 2) continue;
-            ++n_bridged;
-            SignalType dom;
-            if (net_type_consistent(n, dom)) continue;
-            ++n_inconsistent;
+        for (const auto &m : vr.role_mismatches)
+            analyze_issues.push_back(
+                "[pin-role] " + m.module + "/" + m.part + "/" + m.pin
+                + ": expected " + signal_type_name(m.expected)
+                + ", got " + signal_type_name(m.actual)
+                + " (signal: " + m.signal + ")");
+
+        for (const auto &ni : vr.net_inconsistencies) {
            std::string line = "[net-mix] mixes Power and Gnd:";
-            for (const auto &mp : n.members)
-                line += " " + mp.first->name + "/" + mp.second->name
-                      + "(" + signal_type_name(mp.second->type) + ")";
+            for (const auto &mem : ni.members)
+                line += " " + mem.module + "/" + mem.signal
+                      + "(" + signal_type_name(mem.type) + ")";
            analyze_issues.push_back(std::move(line));
        }

@@ -100,28 +77,25 @@ Component Tui::BuildAnalyzeScreen() {
                                     + anomaly_kind_name(a.kind) + "] "
                                     + a.message);

-        // Model-driven checks (same as `verify`), reusing the nets above.
-        std::vector<Anomaly> model_anoms;
-        {
-            auto a1 = check_pin_specs(sys.get(), &nets);
-            auto a2 = check_jtag_chain(sys.get(), &nets);
-            auto a3 = check_source_conflicts(sys.get());
-            auto a4 = check_bsdl_completeness(sys.get());
-            model_anoms.insert(model_anoms.end(), a1.begin(), a1.end());
-            model_anoms.insert(model_anoms.end(), a2.begin(), a2.end());
-            model_anoms.insert(model_anoms.end(), a3.begin(), a3.end());
-            model_anoms.insert(model_anoms.end(), a4.begin(), a4.end());
-        }
-        for (const auto &a : model_anoms)
-            analyze_issues.push_back(std::string("[")
-                                     + anomaly_kind_name(a.kind) + "] "
-                                     + a.message);
-        int n_model = (int)model_anoms.size();
+        // Model-driven checks (pin / JTAG / source-conflict / completeness).
+        auto push_anoms = [this](const std::vector<Anomaly> &v) {
+            for (const auto &a : v)
+                analyze_issues.push_back(std::string("[")
+                                         + anomaly_kind_name(a.kind) + "] "
+                                         + a.message);
+        };
+        push_anoms(vr.pin_anomalies);
+        push_anoms(vr.jtag_anomalies);
+        push_anoms(vr.conflict_anomalies);
+        push_anoms(vr.completeness_anomalies);
+        int n_model = vr.model_total();

        if (analyze_issues.empty()) analyze_issues.push_back("(no issue found)");
        if (analyze_issue_idx >= (int)analyze_issues.size())
            analyze_issue_idx = (int)analyze_issues.size() - 1;

+        int n_role_mismatches = (int)vr.role_mismatches.size();
+        int n_inconsistent    = (int)vr.net_inconsistencies.size();
        std::string issues_header = "Issues ("
            + std::to_string(n_role_mismatches + n_inconsistent
                             + (int)rep.anomalies.size() + n_model)
@@ -215,26 +189,11 @@ Component Tui::BuildAnalyzeScreen() {
                std::string(tag) + r.mod + "/" + r.sig + "  —  " + reason);
        }

-        // NC orphan rollup — same filter as the verify pass.
-        std::unordered_set<Pin *> bridged_pins;
-        for (auto &ckv : *sys->connections())
-            for (auto &wp : ckv.second->pin_map) {
-                if (wp.first)  bridged_pins.insert(wp.first);
-                if (wp.second) bridged_pins.insert(wp.second);
-            }
-        int orph_imported = 0, orph_dropped = 0;
-        for (auto &mkv : *sys->modules())
-            for (auto &pkv : *mkv.second)
-                for (auto &nkv : *pkv.second) {
-                    Pin *pin = nkv.second;
-                    if (pin->signal() || bridged_pins.count(pin)) continue;
-                    if (pin->nc_origin == NcOrigin::ImportedUnconnected) ++orph_imported;
-                    else if (pin->nc_origin == NcOrigin::DroppedSingleton) ++orph_dropped;
-                }
+        // NC orphan rollup — from the shared verify report.
        analyze_types.push_back(
-            "[NC] orphan pin(s): " + std::to_string(orph_imported + orph_dropped)
-            + " (" + std::to_string(orph_imported) + " imported, "
-            + std::to_string(orph_dropped) + " dropped)");
+            "[NC] orphan pin(s): " + std::to_string(vr.orphan_total())
+            + " (" + std::to_string(vr.orphan_imported) + " imported, "
+            + std::to_string(vr.orphan_dropped) + " dropped)");

        if (analyze_type_idx >= (int)analyze_types.size())
            analyze_type_idx = (int)analyze_types.size() - 1;
--- a/src/frontends/tui/screen_confirm.cpp
+++ b/src/frontends/tui/screen_confirm.cpp
@@ -1,4 +1,4 @@
-#include "tui/tui.hpp"
+#include "frontends/tui/tui.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/event.hpp>
--- a/src/frontends/tui/screen_connect.cpp
+++ b/src/frontends/tui/screen_connect.cpp
@@ -1,11 +1,10 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/system.hpp"
-#include "system/transform.hpp"
+#include "core/app/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/system.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
@@ -67,37 +66,24 @@ Component Tui::BuildConnectScreen() {
            Part *p1 = m1->get(connect_p1_list[connect_p1_idx]);
            Part *p2 = m2->get(connect_p2_list[connect_p2_idx]);

-            auto &reg = TransformRegistry::get();
-            Transform *t = reg.lookup(p1->connector_type, p2->connector_type);
-            bool both_empty = p1->connector_type.empty() && p2->connector_type.empty();
-            if (t == reg.identity()) {
-                if (!both_empty) {
-                    Print("connect refused: no transform for types '"
-                          + (p1->connector_type.empty() ? "(none)" : p1->connector_type)
-                          + "' ↔ '"
-                          + (p2->connector_type.empty() ? "(none)" : p2->connector_type)
-                          + "'. Set matching types via 'set-connector-type' first.");
-                    screen_idx = 0;
-                    return;
-                }
-                std::string err = CheckIdentityCompatible(p1, p2);
-                if (!err.empty()) {
-                    Print("connect refused: " + err);
-                    screen_idx = 0;
-                    return;
+            // Same wiring op as the `connect` command — see app::connect_parts.
+            app::ConnectResult cr = app::connect_parts(sys.get(), m1, p1, m2, p2);
+            if (cr.refused) {
+                Print("connect refused: " + cr.error);
+            } else {
+                if (!cr.identity_info.empty()) {
+                    Print("connect: " + cr.identity_info);
+                    if (cr.nc_added > 0)
+                        Print("connect: added " + std::to_string(cr.nc_added)
+                              + " NC pin(s) so both sides match");
                }
+                if (cr.ok)
+                    Print("connected: " + cr.connection_name
+                          + "  via " + cr.transform_name
+                          + " (" + std::to_string(cr.wires) + " wires)");
+                else
+                    Print(std::string("connect failed: ") + cr.error);
            }
-            auto pin_map = t->apply(p1, p2);
-
-            std::string conn_name = m1->name + "/" + p1->name
-                                  + " <-> " + m2->name + "/" + p2->name;
-            Connection *c = new Connection(conn_name, m1, p1, m2, p2);
-            c->transform_name = t->name;
-            c->pin_map = std::move(pin_map);
-            sys->connections()->add(c);
-            Print("connected: " + conn_name
-                  + "  via " + t->name
-                  + " (" + std::to_string(c->pin_map.size()) + " wires)");
        } catch (const std::exception &e) {
            Print(std::string("connect failed: ") + e.what());
        }
--- a/src/frontends/tui/screen_dashboard.cpp
+++ b/src/frontends/tui/screen_dashboard.cpp
@@ -1,22 +1,19 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/analysis.hpp"
-#include "system/bsdl_check.hpp"
-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/nets.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/app/verify.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/dom/elements.hpp>

 #include <algorithm>
 #include <map>
-#include <unordered_set>
 #include <vector>

 using namespace ftxui;
@@ -77,58 +74,23 @@ Component Tui::BuildDashboardScreen() {
      }
      int n_conn = (int)sys->connections()->size();

-      // ---- verify-style health (recomputed; cheap on realistic sizes) ----
-      int n_role_mismatches = 0, n_typed_pins = 0;
-      for (auto &mkv : *sys->modules())
-          for (auto &pkv : *mkv.second) {
-              Part *prt = pkv.second;
-              if (prt->connector_type.empty()) continue;
-              for (auto &nkv : *prt) {
-                  Pin *pin = nkv.second;
-                  ++n_typed_pins;
-                  SignalType expected = pin->expected_signal_type();
-                  if (expected == SignalType::Other) continue;
-                  Signal *s = pin->signal();
-                  SignalType actual = s ? s->type : SignalType::Other;
-                  if (actual != expected) ++n_role_mismatches;
-              }
-          }
+      // ---- verify-style health (shared core op; cheap on realistic sizes) ----
+      app::VerifyReport vr = app::verify(sys.get());
+      int n_role_mismatches = (int)vr.role_mismatches.size();
+      int n_typed_pins      = vr.typed_pins;
+      int n_inconsistent    = (int)vr.net_inconsistencies.size();
+      int n_bridged         = vr.bridged_nets;
+      int orph_imported     = vr.orphan_imported;
+      int orph_dropped      = vr.orphan_dropped;

-      auto nets = compute_all_nets(sys.get());
-      int n_bridged = 0, n_inconsistent = 0;
-      for (const auto &n : nets) {
-          if (n.members.size() < 2) continue;
-          ++n_bridged;
-          SignalType dom;
-          if (!net_type_consistent(n, dom)) ++n_inconsistent;
-      }
-
-      // ---- NC orphan summary (matches verify pass 3) ----
-      std::unordered_set<Pin *> bridged_pins;
-      for (auto &ckv : *sys->connections())
-          for (auto &wp : ckv.second->pin_map) {
-              if (wp.first)  bridged_pins.insert(wp.first);
-              if (wp.second) bridged_pins.insert(wp.second);
-          }
-      int orph_imported = 0, orph_dropped = 0;
      // Per-module list of dropped-singleton pins, for the detail rows below
      // the NC health line. The signal name is gone (the Signal object was
      // deleted by `drop_singleton_signals`), but the pin's full path is
      // enough to locate it in `explore`.
      std::map<std::string, std::vector<std::string>> dropped_by_module;
-      for (auto &mkv : *sys->modules())
-          for (auto &pkv : *mkv.second)
-              for (auto &nkv : *pkv.second) {
-                  Pin *pin = nkv.second;
-                  if (pin->signal() || bridged_pins.count(pin)) continue;
-                  if (pin->nc_origin == NcOrigin::ImportedUnconnected) {
-                      ++orph_imported;
-                  } else if (pin->nc_origin == NcOrigin::DroppedSingleton) {
-                      ++orph_dropped;
-                      dropped_by_module[mkv.first].push_back(
-                          pkv.first + "/" + nkv.first);
-                  }
-              }
+      for (const auto &o : vr.orphans)
+          if (o.dropped)
+              dropped_by_module[o.module].push_back(o.part + "/" + o.pin);

      auto health_line = [](bool ok, const std::string &s) {
          return hbox({
@@ -144,7 +106,7 @@ Component Tui::BuildDashboardScreen() {
          + " typed pin(s)"));
      health_rows.push_back(health_line(n_inconsistent == 0,
          "nets:    " + std::to_string(n_inconsistent) + " inconsistent over "
-          + std::to_string(n_bridged) + " bridged (" + std::to_string(nets.size())
+          + std::to_string(n_bridged) + " bridged (" + std::to_string(vr.total_nets)
          + " total)"));
      int orph_total = orph_imported + orph_dropped;
      health_rows.push_back(health_line(orph_total == 0,
@@ -172,12 +134,9 @@ Component Tui::BuildDashboardScreen() {
          }
      }

-      // Model-driven checks (BSDL pin specs, JTAG chain, source conflicts),
-      // reusing the nets computed above.
-      int n_model = (int)(check_pin_specs(sys.get(), &nets).size()
-                          + check_jtag_chain(sys.get(), &nets).size()
-                          + check_source_conflicts(sys.get()).size()
-                          + check_bsdl_completeness(sys.get()).size());
+      // Model-driven checks (BSDL pin specs, JTAG chain, source conflicts,
+      // completeness) — from the shared verify report.
+      int n_model = vr.model_total();
      health_rows.push_back(health_line(n_model == 0,
          "model:   " + std::to_string(n_model) + " BSDL/JTAG anomaly(ies)"));

--- a/src/frontends/tui/screen_error.cpp
+++ b/src/frontends/tui/screen_error.cpp
@@ -1,4 +1,4 @@
-#include "tui/tui.hpp"
+#include "frontends/tui/tui.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/event.hpp>
--- a/src/frontends/tui/screen_explore.cpp
+++ b/src/frontends/tui/screen_explore.cpp
@@ -1,13 +1,13 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/nets.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/nets.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
--- a/src/frontends/tui/screen_filedialog.cpp
+++ b/src/frontends/tui/screen_filedialog.cpp
@@ -1,5 +1,5 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
--- a/src/frontends/tui/screen_help.cpp
+++ b/src/frontends/tui/screen_help.cpp
@@ -1,5 +1,5 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
--- a/src/frontends/tui/screen_main.cpp
+++ b/src/frontends/tui/screen_main.cpp
@@ -1,5 +1,5 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
--- a/src/frontends/tui/screen_palette.cpp
+++ b/src/frontends/tui/screen_palette.cpp
@@ -1,9 +1,9 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/modules.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
--- a/src/frontends/tui/screen_settype.cpp
+++ b/src/frontends/tui/screen_settype.cpp
@@ -1,13 +1,13 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pin_model.hpp"
-#include "system/pin_role.hpp"
-#include "system/pins.hpp"
-#include "system/system.hpp"
-#include "system/transform_vpx.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pin_model.hpp"
+#include "core/domain/pin_role.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/system.hpp"
+#include "core/domain/transform_vpx.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
--- a/src/frontends/tui/screen_sigtype_modal.cpp
+++ b/src/frontends/tui/screen_sigtype_modal.cpp
@@ -1,8 +1,8 @@
-#include "tui/tui.hpp"
+#include "frontends/tui/tui.hpp"

-#include "system/modules.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/component_options.hpp>
--- a/src/frontends/tui/shell.cpp
+++ b/src/frontends/tui/shell.cpp
@@ -1,9 +1,9 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui.hpp"
+#include "frontends/tui/tui_helpers.hpp"

-#include "system/modules.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <cctype>
 #include <chrono>
--- a/src/frontends/tui/tui.cpp
+++ b/src/frontends/tui/tui.cpp
@@ -1,6 +1,6 @@
-#include "tui/tui.hpp"
+#include "frontends/tui/tui.hpp"

-#include "system/system.hpp"
+#include "core/domain/system.hpp"

 #include <ftxui/component/component.hpp>
 #include <ftxui/component/event.hpp>
--- a/src/frontends/tui/tui.hpp
+++ b/src/frontends/tui/tui.hpp
@@ -13,9 +13,11 @@
 #include <ftxui/component/component.hpp>
 #include <ftxui/component/screen_interactive.hpp>

+#include "frontends/frontend.hpp"
+
 class System;

-class Tui {
+class Tui : public Frontend {
    enum class Completion { None, Path, Command };

    struct Prompt {
@@ -198,16 +200,16 @@ private:
 public:
    Tui();
    ~Tui();
-    void Run();
-    void DumpCommandsMd(std::ostream &out) const;
+    void Run() override;
+    void DumpCommandsMd(std::ostream &out) const override;
    // Write the accumulated console output to `out`. Used by batch mode to
    // surface a script's output without starting the TUI.
-    void DumpOutput(std::ostream &out) const;
+    void DumpOutput(std::ostream &out) const override;

    // Boot-time hook: dispatch a single command exactly as if the user
    // typed it (e.g. `restore foo.essim` or `source bring-up.essim`).
    // Call before `Run()` to seed the system before the event loop starts.
-    void BootDispatch(const std::string &raw);
+    void BootDispatch(const std::string &raw) override;

 private:
    // Lifecycle (commands.cpp)
--- a/src/frontends/tui/tui_helpers.cpp
+++ b/src/frontends/tui/tui_helpers.cpp
@@ -1,4 +1,4 @@
-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui_helpers.hpp"

 #include <ftxui/dom/elements.hpp>

--- a/src/frontends/tui/tui_helpers.hpp
+++ b/src/frontends/tui/tui_helpers.hpp
--- a/src/system/system.cpp
+++ b/src/system/system.cpp
@@ -1,49 +0,0 @@
-
-#include "system.hpp"
-
-#include "connect.hpp"
-#include "modules.hpp"
-#include "imports/import_altium.hpp"
-#include "imports/import_mentor.hpp"
-#include "imports/import_ods.hpp"
-
-System::System() : mods(nullptr), conns(nullptr)
-{
-    mods = new Modules();
-    conns = new Connections();
-}
-
-System::~System()
-{
-    delete mods;
-    delete conns;
-}
-
-void System::Load(std::string module_name, std::string file_name, ImportType type)
-{
-    ImportBase *imp;
-    Module *mod = nullptr;
-    Parts *prts = nullptr;
-
-    // Creation or retrieval of the module.
-    mod = mods->merge(module_name);
-
-    // Parsing of the file based on the import type.
-    if (type == ImportType::IMPORT_MENTOR)
-    {
-        imp = new ImportMentor(file_name);
-    } else if (type == ImportType::IMPORT_ALTIUM)
-    {
-        imp = new ImportAltium(file_name);
-    } else if (type == ImportType::IMPORT_ODS)
-    {
-        imp = new ImportOds(file_name);
-    }
-    else
-    {
-        throw std::runtime_error("Unknown import type");
-    }
-    imp->parse(mod->signals);
-    prts = imp->parts();
-    mod->add(prts);
-}
--- a/src/tui/commands_export.cpp
+++ b/src/tui/commands_export.cpp
@@ -1,235 +0,0 @@
-#include "tui/tui.hpp"
-#include "tui/tui_helpers.hpp"
-
-#include "imports/ods_writer.hpp"
-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signal_type.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
-
-#include <fstream>
-#include <string>
-#include <vector>
-
-namespace {
-
-// Minimal CSV quoter — wraps in `"…"` and doubles internal quotes when
-// the field contains a comma, quote, or newline. Local to this file.
-std::string csv_quote(const std::string &s) {
-    bool needs = s.find_first_of(",\"\n") != std::string::npos;
-    if (!needs) return s;
-    std::string out = "\"";
-    for (char c : s) { if (c == '"') out += '"'; out += c; }
-    out += '"';
-    return out;
-}
-
-// Flatten one pin into the 6 string slots the export row uses.
-void pin_side(Pin *p, std::string &mod, std::string &part,
-              std::string &pin, std::string &sig,
-              std::string &type, std::string &suspect) {
-    if (!p) { mod = part = pin = sig = type = suspect = ""; return; }
-    mod  = (p->prnt && p->prnt->prnt) ? p->prnt->prnt->name : "";
-    part = p->prnt ? p->prnt->name : "";
-    pin  = p->name;
-    Signal *s = p->signal();
-    if (!s) {
-        sig = ""; type = "(NC)"; suspect = "";
-    } else {
-        sig = s->name;
-        type = signal_type_name(s->type);
-        suspect = (infer_signal_type(s->name) == SignalType::Power
-                   && s->type == SignalType::Other) ? "yes" : "no";
-    }
-}
-
-}  // namespace
-
-void Tui::RegisterExportCommands() {
-    commands["export"] = {
-        {{"kind [connections]", Completion::None},
-         {"filename (.csv)",    Completion::Path}},
-        [this](const std::vector<std::string> &args) {
-            if (!sys) { Print("no system: run 'new' first."); return; }
-            if (args.empty()) {
-                // Bare → reuse the generic file dialog. Filters give a
-                // one-keystroke CSV/ODS toggle; picking either rewrites
-                // the filename's extension, and the action below
-                // dispatches on that extension.
-                OpenFileDialog(
-                    "Export — connections",
-                    "export.connections",
-                    "connections.csv",
-                    {{"CSV", ".csv"}, {"ODS", ".ods"}},
-                    [this](const std::string &path) {
-                        Dispatch("export connections " + path);
-                    });
-                return;
-            }
-            if (args.size() != 2) {
-                Print("usage: export <kind> <file>   (or no args for the dialog)");
-                return;
-            }
-            const std::string &kind = args[0];
-            const std::string &path = args[1];
-
-            if (kind == "connections") {
-                // Accepted extensions: `.csv` (flat file) and `.ods`
-                // (one sheet per connection). Anything else is an error.
-                std::string ext;
-                {
-                    size_t dot = path.rfind('.');
-                    if (dot != std::string::npos) ext = ToLower(path.substr(dot));
-                }
-                bool ods = (ext == ".ods");
-                bool csv = (ext == ".csv");
-                if (!ods && !csv) {
-                    ShowError("export: unknown extension '"
-                              + (ext.empty() ? std::string("(none)") : ext)
-                              + "'\nAccepted: .csv, .ods");
-                    return;
-                }
-
-                if (ods) {
-                    OdsWriter w;
-                    int total = 0;
-                    for (auto &ckv : *sys->connections()) {
-                        Connection *c = ckv.second;
-                        // Sheet names: Excel rejects /\?*:[] characters,
-                        // ODS forbids < > & in raw cell/table names.
-                        // Sanitise to underscores; clip to 31 chars
-                        // (Excel's hard limit).
-                        std::string sname = c->name;
-                        for (char &ch : sname)
-                            if (ch == '/' || ch == '\\' || ch == '?' || ch == '*'
-                                || ch == ':' || ch == '[' || ch == ']'
-                                || ch == '<' || ch == '>' || ch == '&') ch = '_';
-                        if (sname.size() > 31) sname = sname.substr(0, 31);
-                        OdsSheet *s = w.add_sheet(sname);
-
-                        // Pull the constants for this connection once.
-                        // `transform`, the left module/part, and the
-                        // right module/part don't vary across the wires
-                        // of a single connection — putting them in
-                        // every row was repetitive.
-                        std::string lmod, lprt;
-                        std::string rmod, rprt;
-                        if (c->m1) lmod = c->m1->name;
-                        if (c->p1) lprt = c->p1->name;
-                        if (c->m2) rmod = c->m2->name;
-                        if (c->p2) rprt = c->p2->name;
-
-                        // Meta header above the table: 5 rows of label /
-                        // value, then a blank, then the column headers
-                        // on row 6 (index 5).
-                        auto meta = [&](int r, const std::string &k,
-                                         const std::string &v) {
-                            s->set(r, 0, k);
-                            s->set(r, 1, v);
-                        };
-                        meta(0, "Connection", c->name);
-                        meta(1, "Transform",  c->transform_name);
-                        meta(2, "Left",       lmod + " / " + lprt);
-                        meta(3, "Right",      rmod + " / " + rprt);
-                        // Row 4 left blank by design.
-
-                        const int HDR = 5;
-                        s->set_header_row(HDR);
-                        const char *hdr[] = {
-                            "left_pin", "left_signal", "left_type", "left_suspect",
-                            "right_pin", "right_signal", "right_type", "right_suspect",
-                            "type_mismatch"};
-                        for (int i = 0; i < 9; ++i) s->set(HDR, i, hdr[i]);
-
-                        int row = HDR + 1;
-                        for (auto &wp : c->pin_map) {
-                            std::string lm, lp, ln, ls, lt, lsus;
-                            std::string rm, rp, rn, rs, rt, rsus;
-                            pin_side(wp.first,  lm, lp, ln, ls, lt, lsus);
-                            pin_side(wp.second, rm, rp, rn, rs, rt, rsus);
-                            // `type_mismatch = yes` when both sides have a
-                            // real signal AND their types disagree (e.g.
-                            // Power ↔ Gnd, or Power ↔ Other).
-                            std::string tm = (lt != "(NC)" && rt != "(NC)" && lt != rt)
-                                            ? "yes" : "no";
-                            s->set(row, 0, ln); s->set(row, 1, ls);
-                            s->set(row, 2, lt); s->set(row, 3, lsus);
-                            s->set(row, 4, rn); s->set(row, 5, rs);
-                            s->set(row, 6, rt); s->set(row, 7, rsus);
-                            s->set(row, 8, tm);
-                            ++row; ++total;
-                        }
-                    }
-                    std::string err;
-                    if (!w.save(path, err)) {
-                        ShowError("export (.ods) failed:\n" + err);
-                        return;
-                    }
-                    Print("export connections (.ods): "
-                          + std::to_string(sys->connections()->size())
-                          + " sheet(s), " + std::to_string(total)
-                          + " wire(s) → " + path);
-                    return;
-                }
-
-                // Classic flat CSV: a single rectangular table — one
-                // header line, N data rows, every row carries the per-
-                // connection constants too. The 9 right-most column
-                // names match the ODS sheet headers exactly; the 5
-                // leading ones (connection, transform, left_module,
-                // left_part, right_module, right_part) correspond to
-                // the ODS meta block (Connection, Transform, Left,
-                // Right). Repeating the constants per row keeps the
-                // file parser-friendly (pandas / awk / spreadsheet).
-                std::ofstream f(path);
-                if (!f) {
-                    ShowError("export: cannot open '" + path + "' for writing");
-                    return;
-                }
-                f << "connection,transform,"
-                     "left_module,left_part,"
-                     "left_pin,left_signal,left_type,left_suspect,"
-                     "right_module,right_part,"
-                     "right_pin,right_signal,right_type,right_suspect,"
-                     "type_mismatch\n";
-
-                int rows = 0;
-                for (auto &ckv : *sys->connections()) {
-                    Connection *c = ckv.second;
-                    for (auto &wp : c->pin_map) {
-                        std::string lm, lp, ln, ls, lt, lsus;
-                        std::string rm, rp, rn, rs, rt, rsus;
-                        pin_side(wp.first,  lm, lp, ln, ls, lt, lsus);
-                        pin_side(wp.second, rm, rp, rn, rs, rt, rsus);
-                        std::string tm = "no";
-                        if (lt != "(NC)" && rt != "(NC)" && lt != rt) tm = "yes";
-                        f << csv_quote(c->name)           << ','
-                          << csv_quote(c->transform_name) << ','
-                          << csv_quote(lm) << ',' << csv_quote(lp) << ','
-                          << csv_quote(ln) << ',' << csv_quote(ls) << ','
-                          << csv_quote(lt) << ',' << csv_quote(lsus) << ','
-                          << csv_quote(rm) << ',' << csv_quote(rp) << ','
-                          << csv_quote(rn) << ',' << csv_quote(rs) << ','
-                          << csv_quote(rt) << ',' << csv_quote(rsus) << ','
-                          << tm << '\n';
-                        ++rows;
-                    }
-                }
-                Print("export connections (.csv): " + std::to_string(rows)
-                      + " wire(s) → " + path);
-                return;
-            }
-
-            ShowError("export: unknown kind '" + kind + "'\n"
-                      "Known kinds: connections");
-        },
-        /*prompt_for_missing=*/ false,
-        "export structured data to CSV / ODS (kinds: connections; "
-        "bare form opens the file-picker dialog)",
-        /*scriptable=*/ true,
-        /*interactive=*/ true,
-    };
-}
--- a/tests/test_analysis.cpp
+++ b/tests/test_analysis.cpp
@@ -1,11 +1,11 @@
 #include <doctest/doctest.h>

-#include "system/analysis.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <memory>
 #include <string>
--- a/tests/test_bsdl_apply.cpp
+++ b/tests/test_bsdl_apply.cpp
@@ -1,14 +1,14 @@
 #include <doctest/doctest.h>

-#include "system/analysis.hpp"
-#include "system/bsdl_check.hpp"
-#include "system/bsdl_model.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/pin_spec.hpp"
-#include "system/system.hpp"
-#include "system/modules.hpp"
-#include "system/persist.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/bsdl_check.hpp"
+#include "core/domain/bsdl_model.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/pin_spec.hpp"
+#include "core/domain/system.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/persist.hpp"

 #include <cstdio>
 #include <fstream>
--- a/tests/test_bsdl_check.cpp
+++ b/tests/test_bsdl_check.cpp
@@ -1,13 +1,13 @@
 #include <doctest/doctest.h>

-#include "system/analysis.hpp"
-#include "system/bsdl_check.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pin_spec.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/analysis.hpp"
+#include "core/domain/bsdl_check.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pin_spec.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <algorithm>
 #include <vector>
--- a/tests/test_component_kind.cpp
+++ b/tests/test_component_kind.cpp
@@ -1,7 +1,7 @@
 #include <doctest/doctest.h>

-#include "system/component_kind.hpp"
-#include "system/parts.hpp"
+#include "core/domain/component_kind.hpp"
+#include "core/domain/parts.hpp"

 #include <memory>

--- a/tests/test_connect.cpp
+++ b/tests/test_connect.cpp
@@ -0,0 +1,79 @@
+#include <doctest/doctest.h>
+
+#include "core/app/connect.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/system.hpp"
+
+// app::connect_parts is pure core: given two already-resolved parts it looks up
+// the transform, fills identity NC pins, creates the Connection and returns a
+// ConnectResult. No Print/dialog/FTXUI. These tests drive it directly.
+
+namespace {
+
+// A part with the given pin names, attached to a fresh module.
+Part *make_part(System &sys, const std::string &mod, const std::string &part,
+                std::initializer_list<const char *> pins,
+                const std::string &type = "")
+{
+    Module *m = sys.modules()->merge(mod);
+    Part *p = new Part(part);
+    p->connector_type = type;
+    m->add(p);
+    for (const char *pn : pins) p->add(new Pin(pn));
+    return p;
+}
+
+}  // namespace
+
+TEST_CASE("connect_parts wires an identity-compatible pair") {
+    System sys;
+    Module *a = sys.modules()->merge("A");
+    Module *b = sys.modules()->merge("B");
+    Part *p1 = make_part(sys, "A", "J1", {"1", "2"});
+    Part *p2 = make_part(sys, "B", "P1", {"1", "2"});
+
+    app::ConnectResult r = app::connect_parts(&sys, a, p1, b, p2);
+
+    CHECK(r.ok);
+    CHECK_FALSE(r.refused);
+    CHECK(r.transform_name == "identity");
+    CHECK(r.wires == 2);
+    CHECK(r.identity_info.empty());   // identical sets → no NC fill, no warning
+    CHECK(r.nc_added == 0);
+    CHECK(r.connection_name == "A/J1 <-> B/P1");
+    CHECK(sys.connections()->size() == 1);
+}
+
+TEST_CASE("connect_parts refuses an unknown connector-type pairing") {
+    System sys;
+    Module *a = sys.modules()->merge("A");
+    Module *b = sys.modules()->merge("B");
+    Part *p1 = make_part(sys, "A", "J1", {"1"}, "foo");
+    Part *p2 = make_part(sys, "B", "P1", {"1"}, "bar");
+
+    app::ConnectResult r = app::connect_parts(&sys, a, p1, b, p2);
+
+    CHECK_FALSE(r.ok);
+    CHECK(r.refused);
+    CHECK(r.error.find("no transform") != std::string::npos);
+    CHECK(sys.connections()->size() == 0);   // nothing created
+}
+
+TEST_CASE("connect_parts fills NC pins on the subset side and reports it") {
+    System sys;
+    Module *a = sys.modules()->merge("A");
+    Module *b = sys.modules()->merge("B");
+    Part *p1 = make_part(sys, "A", "J1", {"1", "2", "3"});  // larger side
+    Part *p2 = make_part(sys, "B", "P1", {"1", "2"});       // missing "3"
+
+    app::ConnectResult r = app::connect_parts(&sys, a, p1, b, p2);
+
+    CHECK(r.ok);
+    CHECK_FALSE(r.identity_info.empty());   // subset path surfaces a warning
+    CHECK(r.nc_added == 1);                  // pin "3" materialised on B
+    CHECK(r.wires == 3);                     // all three now wired
+    CHECK(p2->size() == 3);                  // the NC pin really got added
+}
--- a/tests/test_export.cpp
+++ b/tests/test_export.cpp
@@ -0,0 +1,76 @@
+#include <doctest/doctest.h>
+
+#include "core/app/export.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
+
+#include <cstdio>
+#include <fstream>
+#include <sstream>
+#include <string>
+
+namespace {
+
+std::string slurp(const std::string &path)
+{
+    std::ifstream f(path);
+    std::stringstream ss;
+    ss << f.rdbuf();
+    return ss.str();
+}
+
+}  // namespace
+
+TEST_CASE("export_format_from_path maps extensions") {
+    app::ExportFormat f;
+    CHECK(app::export_format_from_path("a.csv", f));
+    CHECK(f == app::ExportFormat::Csv);
+    CHECK(app::export_format_from_path("a.ODS", f));
+    CHECK(f == app::ExportFormat::Ods);
+    CHECK_FALSE(app::export_format_from_path("a.txt", f));
+    CHECK_FALSE(app::export_format_from_path("noext", f));
+}
+
+TEST_CASE("export_connections writes a flat CSV (no UI needed)") {
+    // Two cards, one wired pin pair via a connection.
+    System sys;
+    Module *a = sys.modules()->merge("A");
+    Module *b = sys.modules()->merge("B");
+    Part *ja = new Part("J1"); a->add(ja);
+    Part *jb = new Part("P1"); b->add(jb);
+    Pin *pa = new Pin("1"); ja->add(pa);
+    Pin *pb = new Pin("1"); jb->add(pb);
+    Signal *sa = a->signals->merge("NETA"); sa->add(pa); pa->connect(sa);
+    Signal *sb = b->signals->merge("NETB"); sb->add(pb); pb->connect(sb);
+
+    Connection *c = new Connection("A.J1<->B.P1", a, ja, b, jb);
+    c->transform_name = "identity";
+    c->pin_map.emplace_back(pa, pb);
+    sys.connections()->add(c);
+
+    const char *path = "test_export_out.csv";
+    app::ExportResult r = app::export_connections(&sys, path, app::ExportFormat::Csv);
+    CHECK(r.ok);
+    CHECK(r.rows == 1);
+
+    std::string out = slurp(path);
+    CHECK(out.find("connection,transform,") == 0);           // header present
+    CHECK(out.find("A.J1<->B.P1") != std::string::npos);     // connection name
+    CHECK(out.find("identity") != std::string::npos);        // transform
+    CHECK(out.find("NETA") != std::string::npos);            // left signal
+    CHECK(out.find("NETB") != std::string::npos);            // right signal
+
+    std::remove(path);
+}
+
+TEST_CASE("export_connections reports a bad path instead of crashing") {
+    System sys;
+    app::ExportResult r = app::export_connections(
+        &sys, "/nonexistent-dir-xyz/out.csv", app::ExportFormat::Csv);
+    CHECK_FALSE(r.ok);
+    CHECK_FALSE(r.error.empty());
+}
--- a/tests/test_load.cpp
+++ b/tests/test_load.cpp
@@ -0,0 +1,63 @@
+#include <doctest/doctest.h>
+
+#include "core/app/load.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/system.hpp"
+
+#include <cstdio>
+#include <fstream>
+#include <string>
+
+// app::load_module is pure core: import a module, drop singleton signals, infer
+// signal types, return counts or an error — no Print/dialog/FTXUI. The parse
+// helper import_type_from_name is likewise UI-free.
+
+TEST_CASE("import_type_from_name maps names case-insensitively") {
+    ImportType t;
+    CHECK(app::import_type_from_name("mentor", t));
+    CHECK(t == ImportType::IMPORT_MENTOR);
+    CHECK(app::import_type_from_name("ALTIUM", t));
+    CHECK(t == ImportType::IMPORT_ALTIUM);
+    CHECK(app::import_type_from_name("Ods", t));
+    CHECK(t == ImportType::IMPORT_ODS);
+    CHECK_FALSE(app::import_type_from_name("kicad", t));
+    CHECK_FALSE(app::import_type_from_name("", t));
+}
+
+TEST_CASE("load_module imports, drops singletons and reports counts") {
+    // Minimal Mentor netlist: two parts; NETA/NETB span both parts (2 pins
+    // each, kept), LONELY sits on one pin only (dropped as a singleton).
+    const char *path = "test_load_in.net";
+    {
+        std::ofstream f(path);
+        f << "COMP: 'C1' 'J1'\n"
+             " Explicit Pin: '1' 'x' 'NETA'\n"
+             " Explicit Pin: '2' 'x' 'NETB'\n"
+             " Explicit Pin: '3' 'x' 'LONELY'\n"
+             "COMP: 'C2' 'J2'\n"
+             " Explicit Pin: '1' 'x' 'NETA'\n"
+             " Explicit Pin: '2' 'x' 'NETB'\n";
+    }
+
+    System sys;
+    app::LoadResult r = app::load_module(&sys, "M", path, ImportType::IMPORT_MENTOR);
+
+    CHECK(r.ok);
+    CHECK(r.error.empty());
+    CHECK(r.parts == 2);
+    CHECK(r.signals == 2);   // NETA, NETB — LONELY dropped
+    CHECK(r.dropped == 1);   // LONELY
+
+    std::remove(path);
+}
+
+TEST_CASE("load_module fails cleanly on a missing file") {
+    // ImportBase opens read-only and System::Load checks is_open(), so a missing
+    // file is a clean error — and no empty module is left in the system.
+    System sys;
+    app::LoadResult r = app::load_module(
+        &sys, "M", "/nonexistent-dir-xyz/nope.net", ImportType::IMPORT_MENTOR);
+    CHECK_FALSE(r.ok);
+    CHECK(r.error.find("cannot open") != std::string::npos);
+    CHECK(sys.modules()->size() == 0);
+}
--- a/tests/test_nc_origin.cpp
+++ b/tests/test_nc_origin.cpp
@@ -1,11 +1,11 @@
 #include <doctest/doctest.h>

-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/persist.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/persist.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <filesystem>
 #include <memory>
--- a/tests/test_persist.cpp
+++ b/tests/test_persist.cpp
@@ -1,12 +1,12 @@
 #include <doctest/doctest.h>

-#include "system/connect.hpp"
-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/persist.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/persist.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"

 #include <filesystem>
 #include <memory>
--- a/tests/test_pin_model.cpp
+++ b/tests/test_pin_model.cpp
@@ -1,9 +1,9 @@
 #include <doctest/doctest.h>

-#include "system/parts.hpp"
-#include "system/pin_model.hpp"
-#include "system/pin_spec.hpp"
-#include "system/pins.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pin_model.hpp"
+#include "core/domain/pin_spec.hpp"
+#include "core/domain/pins.hpp"

 #include <string>
 #include <vector>
--- a/tests/test_pin_name.cpp
+++ b/tests/test_pin_name.cpp
@@ -1,9 +1,9 @@
 #include <doctest/doctest.h>

-#include "system/parts.hpp"
-#include "system/pin_name.hpp"
-#include "system/pins.hpp"
-#include "system/transform.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pin_name.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/transform.hpp"

 #include <memory>

--- a/tests/test_signal_type.cpp
+++ b/tests/test_signal_type.cpp
@@ -1,6 +1,6 @@
 #include <doctest/doctest.h>

-#include "system/signal_type.hpp"
+#include "core/domain/signal_type.hpp"

 TEST_CASE("signal_type_name round-trips with from_name") {
    SignalType t;
--- a/tests/test_verify.cpp
+++ b/tests/test_verify.cpp
@@ -0,0 +1,95 @@
+#include <doctest/doctest.h>
+
+#include "core/app/verify.hpp"
+#include "core/domain/connect.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
+
+// app::verify is pure core: it takes a System* and returns a VerifyReport of
+// structured findings, with no Print/dialog/FTXUI. These tests build small
+// systems by hand and assert the report — no UI involved.
+
+TEST_CASE("verify on a null or empty system reports nothing") {
+    app::VerifyReport none = app::verify(nullptr);
+    CHECK(none.typed_pins == 0);
+    CHECK(none.total_nets == 0);
+    CHECK(none.role_mismatches.empty());
+
+    System sys;
+    app::VerifyReport r = app::verify(&sys);
+    CHECK(r.typed_pins == 0);
+    CHECK(r.total_nets == 0);
+    CHECK(r.bridged_nets == 0);
+    CHECK(r.net_inconsistencies.empty());
+    CHECK(r.orphan_total() == 0);
+    CHECK(r.model_total() == 0);
+}
+
+TEST_CASE("verify flags a bridged net that mixes Power and GndShield") {
+    // Two cards, one wired pin pair: A.NETA (Power) <-> B.NETB (GndShield).
+    System sys;
+    Module *a = sys.modules()->merge("A");
+    Module *b = sys.modules()->merge("B");
+    Part *ja = new Part("J1"); a->add(ja);
+    Part *jb = new Part("P1"); b->add(jb);
+    Pin *pa = new Pin("1"); ja->add(pa);
+    Pin *pb = new Pin("1"); jb->add(pb);
+    Signal *sa = a->signals->merge("NETA"); sa->type = SignalType::Power;
+    Signal *sb = b->signals->merge("NETB"); sb->type = SignalType::GndShield;
+    sa->add(pa); pa->connect(sa);
+    sb->add(pb); pb->connect(sb);
+
+    Connection *c = new Connection("A.J1<->B.P1", a, ja, b, jb);
+    c->transform_name = "identity";
+    c->pin_map.emplace_back(pa, pb);
+    sys.connections()->add(c);
+
+    app::VerifyReport r = app::verify(&sys);
+
+    CHECK(r.total_nets == 1);
+    CHECK(r.bridged_nets == 1);
+    REQUIRE(r.net_inconsistencies.size() == 1);
+    CHECK(r.net_inconsistencies[0].members.size() == 2);
+    // Both endpoints are present with their declared types.
+    bool seen_power = false, seen_gnd = false;
+    for (const auto &m : r.net_inconsistencies[0].members) {
+        if (m.type == SignalType::Power)     seen_power = true;
+        if (m.type == SignalType::GndShield) seen_gnd = true;
+    }
+    CHECK(seen_power);
+    CHECK(seen_gnd);
+}
+
+TEST_CASE("verify counts orphan pins by their import origin") {
+    System sys;
+    Module *m = sys.modules()->merge("M");
+    Part *p = new Part("J1"); m->add(p);
+    Pin *imp = new Pin("1"); imp->nc_origin = NcOrigin::ImportedUnconnected; p->add(imp);
+    Pin *drp = new Pin("2"); drp->nc_origin = NcOrigin::DroppedSingleton;    p->add(drp);
+    Pin *wired = new Pin("3"); p->add(wired);
+    Signal *s = m->signals->merge("NET"); s->add(wired); wired->connect(s);
+
+    app::VerifyReport r = app::verify(&sys);
+
+    CHECK(r.orphan_imported == 1);
+    CHECK(r.orphan_dropped == 1);
+    CHECK(r.orphan_total() == 2);
+
+    // Per-pin detail carries the path and origin (the dashboard lists the
+    // dropped ones under the NC health row).
+    REQUIRE(r.orphans.size() == 2);
+    int n_dropped = 0;
+    bool dropped_path_ok = false;
+    for (const auto &o : r.orphans) {
+        if (o.dropped) {
+            ++n_dropped;
+            if (o.module == "M" && o.part == "J1" && o.pin == "2")
+                dropped_path_ok = true;
+        }
+    }
+    CHECK(n_dropped == 1);
+    CHECK(dropped_path_ok);
+}
--- a/tests/test_vpx_transform.cpp
+++ b/tests/test_vpx_transform.cpp
@@ -1,12 +1,12 @@
 #include <doctest/doctest.h>

-#include "system/modules.hpp"
-#include "system/parts.hpp"
-#include "system/pins.hpp"
-#include "system/signals.hpp"
-#include "system/system.hpp"
-#include "system/transform.hpp"
-#include "system/transform_vpx.hpp"
+#include "core/domain/modules.hpp"
+#include "core/domain/parts.hpp"
+#include "core/domain/pins.hpp"
+#include "core/domain/signals.hpp"
+#include "core/domain/system.hpp"
+#include "core/domain/transform.hpp"
+#include "core/domain/transform_vpx.hpp"

 #include <map>
 #include <memory>
--- a/tests/tui/test_helpers.cpp
+++ b/tests/tui/test_helpers.cpp
@@ -1,6 +1,6 @@
 #include <doctest/doctest.h>

-#include "tui/tui_helpers.hpp"
+#include "frontends/tui/tui_helpers.hpp"

 #include <algorithm>
 #include <vector>