gui_toolkit 0.29.0

Fixes found by the review of render and draw (branch fix/render-draw). 0.30.0 is the font / ui / platform review branch. Each fix has a test that failed before it (tests/lifecycle is new).

Fixed

• Plane pieces with more than 6 cuts (draw/bsp.odin): a piece bounded by more than MAX_PLANE_CUTS cuts had the extra ones thrown away, so it was drawn over its siblings' region at its own rank and covered planes that had to be in front. It is now divided by a chord between two of its corners into convex halves (the chord is one more cut for each), as often as needed: no cut is lost, no limit. Hidden (skip) items no longer take part in the crossing tests.
• draw.app_shader keeps AppIn.pos, size and px in local units under a uniform scale plus translation (DPI, zoom) as docs/shaders.md says (they were pixels: a scale was baked into the rectangle); any scale now goes through a transform entry. It returns false for a shader that is not render.app_shader_ready.
• Device loss with several windows (Direct3D 11): a Surface set aside by surface_use kept its swap chain, views and capture copy from the old device (undefined behaviour, then a loop of recoveries); and set_blend_space gave the new view format to the current window only. The window state carries the device generation and the blend space it was made in, and surface_use remakes a stale one (render.Renderer.swap_gen, swap_space, space_epoch; Surface.gen, space_epoch). d3d_recover flushes the old context after releasing its objects (the old HWND swap chain used to keep the window, and CreateSwapChainForHwnd crashed). An offscreen renderer notices a device loss at frame_end.
• Captures belong to their window (Capture_State is exchanged with the Surface: the next frame_end of that window takes it, not whichever window ends a frame first); the staging copy of an old device is released at recovery (a pending copy becomes Failed) instead of being used on the new device.
• wgpu_destroy read the texture table after freeing it. wgpu_recover without a device (adapter gone) returns false at once instead of creating textures on a null device and dropping the textures and shaders for good. A refused app pipeline on wgpu (the module passed, the pipeline did not) gives the shader up instead of invalidating every frame.
• App shaders that cannot be remade after a device loss keep their handle (and name) until destroy_app_shader; the handle used to be given to the next shader. render.app_shader_ready(r, s) says whether one can be drawn.
• Kept layers and planes (cache_id) follow set_text_rendering, set_corner_smoothing and the font atlas settings (they are in the key now), and a result drawn while a color glyph was still pending (Settings.color_async) is not kept (the glyph never came in). A masked layer that lost a target is not kept as the masked result.
• push_plane inside a recorded picture records nothing (it recorded the content flat, unprojected); current_clip is not empty while recording.
• Slug text, when the device refuses the Slug shaders, is not drawn (it was one solid rounded rect per glyph); d3d_update_texture_r8 checks the handle, the block and the pixels like the other uploads.

Docs

• docs/webgpu.md lists the functions the WebGPU backend does not have; docs/draw.md no longer says 3D is unsupported (planes are); docs/shaders.md: app_shader and app_shader_ready.

Not fixed (reported)

• bsp still splits the whole context when one pair crosses, with no limit on the number of pieces, and Plane_Item.geom is the texel-aligned rectangle (faces that touch look crossing; Wren works around it); a backdrop of a cut plane is captured once per piece; the hash of an app shader does not cover APP_BINDINGS (changing it makes every precompiled blob stale: to be done with the applications' blobs); Surface release on a thread, the DirectComposition Panel lifetime, canvas source textures never zeroed (to check).