STEP Import as: hierarchy / flat / union + progress

CHANGELOG.md

@@ -9,6 +9,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **STEP Import as**: the Import dialog replaces the **Union shapes** checkbox with an **Import as** combo (**Preserve hierarchy** default, **Flat solids**, **Union shapes**). Hierarchy keeps XCAF assembly groups and product/instance names; flat adds leaf solids at the document root; union fuses into one solid.
+
+- **STEP import progress**: on **Import into project**, an **Importing...** modal appears while transferring. Desktop shows stage/progress and Cancel (OCCT transfer on a background thread). Web shows a simple wait dialog (no Cancel; transfer runs on the main thread after the dialog paints). The Import dialog no longer shows a file metadata summary (opens immediately after file pick).
+
 - **Configurable hotkeys**: **Settings -> Keyboard shortcuts** remaps shape tools (Move/Rotate/Scale/Extrude/Chamfer/Fillet/Polar duplicate/Cross-section), sketch tools (inspection, from face, operation axis, node/line/multi-line/arc/square/rectangle/circle/slot, Dimension), boolean commands (Cut/Fuse/Common), Delete, New/Open/Save, and Undo/Redo. Bindings persist as **`gui.hotkeys`** (human-readable chords; missing keys use defaults). Toolbar tooltips follow remaps. **Delete** / **Backspace** stay fixed delete aliases; <kbd>Ctrl</kbd>+<kbd>Shift</kbd>+<kbd>Z</kbd> stays a fixed redo alias. Fixed, unsupported, and conflicting chords are rejected on assign with a status toast (and inline message); remaps accept letters, digits, and <kbd>Space</kbd> only (punctuation/numpad rejected); per-row **Reset** rejects when the factory chord is already bound elsewhere (same conflict message as assign); hotkey capture clears when Settings closes. A **?** at the top of the section opens the [Keyboard shortcuts](https://ezycad.readthedocs.io/en/latest/usage-settings.html#keyboard-shortcuts) settings guide.
 
 - **Extrude Twist**: Options **Twist** checkbox. Two-phase flow locks height first, then sets twist angle about the face centroid (mouse, or <kbd>Shift+Tab</kbd> for degrees). Height length dim is cleared on lock; a temporary angle annotation on the extruded front face shows degrees during twist. With **Both sides**, ends twist symmetrically by +/- half the angle. Geometry uses ruled thru-sections with compatibility off (keeps tooth pairing) and cuts twisted hole solids so face bores survive; straight prism when twist is zero. Dense-face **Extrude fast preview** also applies during Twist (face copies translate and rotate; finalize builds the solid).

docs/usage.md

@@ -127,7 +127,7 @@ Each row (left to right):
 - **Name** - Expandable tree row with an editable name. Click the row to select that solid (or all descendant solids for a group) and update the current group. **Ctrl+click** toggles multi-select. Drag to reparent (empty area below the list = document root).
 - **Right-click the name** - Solids: **Shape info...** / **Delete**. Groups: **Ungroup** (moves **all** direct children to the group's parent, then removes the group) / **Delete** (cascade-deletes the whole subtree).
 
-Boolean results stay under the shared parent of their inputs when all inputs share one parent; otherwise they are placed at the document root. **File -> Import** STEP assemblies preserve product/assembly groups in the tree (unless **Union shapes** is checked).
+Boolean results stay under the shared parent of their inputs when all inputs share one parent; otherwise they are placed at the document root. **File -> Import** STEP assemblies use **Import as** (default **Preserve hierarchy**) to keep product/assembly groups in the tree, import **Flat solids** at the root, or **Union shapes** into one solid.
 
 The **current group** and rows that match the **current 3D selection** use a highlighted full-row style. Hovering a visible solid row also highlights that shape in the 3D view (**Settings -> View presentation -> Element hover color**).
 
@@ -249,18 +249,13 @@ The typical modeling workflow in EzyCad follows these steps:
 
 ### Import dialog
 
-**File -> Import** opens an **Import** window for STEP or PLY. Review metadata, optionally enable **Union shapes** (STEP), then click **Import into project**. The window closes after a successful import.
-
-| Format                     | What the Import dialog shows                              |
-| -------------------------- | --------------------------------------------------------- |
-| **STEP** (`.step`, `.stp`) | Roots/shapes, import bodies, named bodies, topology, bbox |
-| **PLY** (`.ply`)           | Encoding, vertex and face counts from the header          |
+**File -> Import** opens an **Import** window for STEP or PLY. Choose how STEP assemblies land in the Shape List (**Import as**, default **Preserve hierarchy**), then click **Import into project**. STEP import shows an **Importing...** dialog while transferring (desktop also shows stage/progress and Cancel). The window closes after a successful import.
 
 **How to use:**
 1. Choose **File -> Import**
 2. Pick a `.step`, `.stp`, or `.ply` file
-3. Review the label/value table; for STEP, optionally enable **Union shapes**
-4. Click **Import into project**
+3. For STEP, choose **Import as** if needed
+4. Click **Import into project** (STEP may show a progress modal while transferring)
 
 For in-document topology of an already-loaded solid, use [Shape info](#shape-info) from the Shape List.
 
@@ -284,7 +279,7 @@ In addition to creating 3D shapes from sketches, EzyCad supports importing exist
 **How to import:**
 1. Use **File -> Import**
 2. Pick a `.step`, `.stp`, or `.ply` file
-3. Review metadata in the [Import dialog](#import-dialog); for STEP assemblies, optionally check **Union shapes**
+3. In the [Import dialog](#import-dialog), for STEP choose **Import as** if needed
 4. Click **Import into project** - geometry is added as 3D shape(s) in the document, scaled to project units (see below)
 5. You can move, rotate, scale, and use imported bodies in [boolean operations](#boolean-operations) like native solids where the geometry allows it
 
@@ -303,9 +298,11 @@ In addition to creating 3D shapes from sketches, EzyCad supports importing exist
 
 **STEP import notes:**
 - If the file cannot be read or contains no transferable geometry, a **message** explains the failure (invalid data, empty transfer, etc.).
-- Assemblies often arrive with XCAF product structure. Import builds Shape List **groups** for assemblies and leaf solids for bodies (unless **Union shapes** merges everything into one solid). The Import dialog **Import bodies** count shows how many leaf solids will be added.
-- When the STEP file includes product or part names, those names appear in the Shape List (duplicate names get `.001`, `.002`, ...). Unnamed bodies stay as `Shape`.
-- **Union shapes** (Import dialog) fuses those bodies into one solid before adding to the document. If union fails, the import is aborted and nothing is added.
+- Assemblies often arrive with XCAF product structure. The Import dialog **Import as** combo controls how they land in the Shape List:
+  - **Preserve hierarchy** (default) - builds Shape List **groups** for assemblies and leaf solids for bodies; group and part names come from product/instance names in the file when present.
+  - **Flat solids** - adds leaf solids only at the document root (no assembly groups); keeps per-body names from the file.
+  - **Union shapes** - fuses those bodies into one solid before adding to the document. If union fails, the import is aborted and nothing is added.
+- When the STEP file includes product or part names, those names appear in the Shape List (duplicate names get `.001`, `.002`, ...). Unnamed bodies stay as `Shape`; unnamed assemblies use `Assembly`.
 
 **Note:** **IGES** and **STL** are available for **export** only, not import.
 

src/doc/gui.md

@@ -13,7 +13,7 @@ Typical responsibilities:
 - ImGui frame: menu bar, dock space (passthrough central node for 3D input), toolbar, Sketch List, Shape List, Options, Settings, dist/angle popups.
 - Mode switching (`Mode` enum in [`mode.h`](../mode.h)) and parent-mode Esc behavior.
 - Persisted preferences (`ezycad_settings.json` via [`gui_settings.cpp`](../gui_settings.cpp)).
-- Project I/O (`.ezy` load/save, import/export dialogs; **File -> Import** shows metadata then loads STEP/PLY).
+- Project I/O (`.ezy` load/save, import/export dialogs; **File -> Import** confirms STEP/PLY with **Import as** for hierarchy / flat / union). STEP **Import into project** shows an Importing modal; desktop uses `Atomic_progress_indicator` + background Transfer + Cancel; WASM paints the modal for two frames then runs Transfer on the main thread (no Cancel).
 - CAD/mesh interchange scales about the origin: project display lengths follow **File -> Project units** (`Project_unit`; Inch or Millimeter). Model space stays inch-scaled (`model = inches * dimension_scale`). STEP import converts OCCT cascade **mm** into model space; PLY import treats coords as inches. **File -> Export** asks for **Inches** or **Millimeters** (STEP/IGES declare that unit; STL/PLY write unitless coords in that scale). `.ezy` persists `projectUnit`. **Settings -> New project defaults** stores `gui.default_project_unit` and inch-based default 2D framing for **File -> New**.
 - Contextual help links (`doc_urls` in `gui.h`).
 

src/doc/shape.md

@@ -35,7 +35,7 @@ Typical uses:
 - Each solid stores a `gp_Ax3` local frame. New geometry defaults to a world-aligned frame at its bounding-box center. Baked move/rotate/scale transforms update the frame; project JSON and shape undo records preserve it.
 - `Shp_ptr` is `opencascade::handle<Shp>`. New shapes are allocated with `new Shp(ctx(), topo_shape)` then registered through `Occt_view::add_shp_()`. Groups use `Shp::create_group` (empty compound, never displayed).
 - Hierarchy: `parent_id` (0 = root) + `sibling_order`. Organizational groups only (no transform inheritance). Helpers: `shape_children`, `shape_descendant_solids`, `group_shapes`, `ungroup_shape`, `reparent_shape`, `would_reparent_create_cycle`.
-- **Current group** (`Occt_view::current_group_id`, 0 = root): Shape List click sets it; empty groups are valid. Primitives / extrude / revolve / PLY / unioned STEP import call `add_shp_(..., use_current_group=true)` so new solids land under that group. Booleans keep `assign_result_parent_`.
+- **Current group** (`Occt_view::current_group_id`, 0 = root): Shape List click sets it; empty groups are valid. Primitives / extrude / revolve / PLY / unioned STEP import (`Step_import_mode::Union_shapes`) call `add_shp_(..., use_current_group=true)` so new solids land under that group. Hierarchical and flat STEP import place roots at document root (`parent_id` 0). STEP import may prepare geometry off-thread (`prepare_step_import`) then `commit_step_import` on the UI thread. Booleans keep `assign_result_parent_`.
 - `Shp_operation_base` is a **`friend` of `Occt_view`** so operations can call `add_shp_()`, read selection, and use pick helpers without exposing those on the public view API.
 - **`Occt_view&` must outlive** all `Shp_*` operation objects (they are member subobjects of the view).
 - Boolean/polar results call `assign_result_parent_` so the new solid shares the inputs' parent when all match; otherwise root (`parent_id` 0).

src/doc/utility.md

@@ -135,6 +135,8 @@ Used by **File -> Import**. Reads file bytes only until the user confirms import
 | `read_step_named_bodies`    | STEPCAF/XCAF bodies + product names (flat; falls back to plain reader)  |
 | `read_step_named_tree`      | STEPCAF/XCAF assembly tree as group/leaf `Named_node`s (falls back flat) |
 
+`Occt_view::import_step` takes `Step_import_mode` (`utl_types.h`): preserve hierarchy (default), flat root leaves, or union. Heavy work splits into `prepare_step_import` (thread-safe geometry) + `commit_step_import` (UI thread). STEP Transfer accepts optional `Atomic_progress_indicator` / `Message_ProgressRange` (`utl_occt_progress.h`). `collect` remains available for tooling but is not shown in the Import dialog.
+
 ## Logging and debug
 
 | Component                       | Role                                                    |