ci: reduce repeated integration test compilation in platform gates

.github/workflows/ci.yml

@@ -25,6 +25,8 @@ jobs:
       craft-fonts-ref: aced4137c022f1f587624d48e81ec77e1914a9cc
       os: '["ubuntu-24.04","windows-latest"]'
       toolchain: "1.96.0"
+      # xtask ci runs cargo test (including doctests), not cargo nextest.
+      tools: ""
       packages: >-
         libxkbcommon-dev libwayland-dev libx11-dev libxrandr-dev libxi-dev libgl1-mesa-dev
         libgtk-3-dev

crates/engine/tests/it/main.rs

@@ -0,0 +1,24 @@
+//! One integration-test executable avoids linking the same dependencies for every feature.
+//! Keep feature tests in their own modules; the standalone session.rs target remains available.
+
+mod bake;
+mod bake_resolution;
+mod bake_settings;
+mod bake_tiles;
+mod content_effects;
+mod export_colour_space;
+mod filter_swap;
+mod filters;
+mod instances;
+mod materialcraft_link;
+mod materialx;
+mod materialx_import;
+mod painter_gaps;
+mod path_tool;
+mod perf;
+mod polygon_fill;
+mod project_recovery;
+mod sample;
+mod tools;
+mod udim;
+mod uv_strokes;

crates/ui-egui/tests/it/main.rs

@@ -0,0 +1,27 @@
+//! One integration-test executable avoids linking the same dependencies for every feature.
+//! Keep feature tests in their own modules; the standalone ui_snapshots.rs target remains available.
+
+mod bake_mode;
+mod brush_drag;
+mod close_unsaved;
+mod color_picker;
+mod curvature_generator;
+mod effect_rows;
+mod effect_sliders;
+mod fill_channel_image;
+mod fill_projection_section;
+mod filter_picker;
+mod history_panel;
+mod layer_clipboard;
+mod layer_rename;
+mod path_list;
+mod pen_pressure;
+mod polygon_fill;
+mod properties_popup;
+mod shelf_drop;
+mod shelf_hover_preview;
+mod shift_lines_2d;
+mod skew_paint;
+mod split_divider;
+mod start_window;
+mod toolbar;

docs/testing-ci.md

@@ -0,0 +1,24 @@
+# Integration tests and CI
+
+The engine and UI integration tests share one `it` executable per crate. This
+avoids compiling and linking the same crate dependencies into a separate
+executable for every feature. Feature modules keep their own helpers and tests.
+When adding a file under `tests/it/`, register it with `mod name;` in that
+folder's `main.rs` so Cargo runs it.
+
+Run a feature module with a test-name filter, for example:
+
+```sh
+cargo test -p texturecraft-engine --test it bake::
+```
+
+The standalone engine `session` target and UI `ui_snapshots` target remain
+available for the commands in `AGENTS.md`. Existing ignore attributes are
+unchanged. Tests in the shared executable can run concurrently across modules;
+keep temporary paths unique and avoid changing process-wide state.
+
+CI continues to use the shared gate workflow and `cargo xtask ci` on Ubuntu and
+Windows: formatting, Clippy, workspace tests (including doctests), layering and
+isolated per-package WebAssembly checks. The caller disables the shared
+workflow's optional tool installation because this gate uses `cargo test` and
+does not use nextest.