Canvas: translucent art blends with the paper before the monitor profile

With Use Monitor Profile for Canvas converting, the art's raster was
converted on its own and then drawn over the separately converted
paper, so a translucent fill or an antialiased edge showed
blend(convert(art), convert(paper)) rather than the converted blend.

Each pixel with partial alpha over an artboard's paper, a colored
artboard, the transparency grid or Hide Artboards' paper now gets the
color that, drawn over the converted paper, shows the art blended with
the paper in sRGB and then converted. Its alpha is kept, so a grid
drawn in back still shows through. Opaque and empty pixels, art over
the pasteboard and Outline convert as before, and with no profile to
convert into nothing changes.

The frame rendered whole, the part an edit renders again, the render
worker's frame (and the pan fill), and the other windows' panes all
use the same rule. The paper is part of the canvas cache key, so
turning the grid on or hiding the artboards renders the art again.

docs/mcp.md

@@ -6010,8 +6010,9 @@ Color on (HDR or Automatic Color Management) and macOS windows are converted by
 again. In a Wayland session, and where no profile is set or the profile is not an RGB display profile of at most 1 MiB,
 the canvas stays sRGB. The app reads the display again every 10 seconds and when the window moves to another display.
 Exports, `ui.render`, the document, panels and thumbnails are not converted; with Proof Colors on, the proof is drawn
-first and then converted. The art is converted before it is drawn over the converted paper, so the blend of a
-translucent object or an antialiased edge with the paper can differ slightly from a conversion of the blended color.
+first and then converted. Translucent art and the antialiased edges of art over an artboard's paper or the
+transparency grid are blended with it in sRGB, and the blend is converted; over the pasteboard and in Outline the art
+is converted on its own.
 `ui.inspect` returns `displayProfile`: `{enabled, display, source, profile, from, applied, reason,
 osManaged}`, where `source` is `profile`, `srgbProfile` (a profile that shows sRGB unchanged), `system`, `none`,
 `pending` or `unsupported`, `applied` says whether the canvas is converted, and `reason` says why not.

docs/target-app-parity.md

@@ -732,6 +732,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 - **Document Setup modal handoff:** Document Setup → Edit Artboards applies valid settings, closes the dialog and activates the Artboard tool. Pointer-click tests cover successful handoff, invalid settings, OK, Cancel and Undo in `dialogs/document_setup.rs`.
 - **Document Setup › Color:** a Color tab shows the document color mode (RGB Color or CMYK Color), a Convert to CMYK or Convert to RGB box for a mode change (cleared: the colors keep their numbers), and the RGB and CMYK profiles assigned to the document, with a working-space entry for none. OK runs `edit.assignProfile` and then `file.documentColorMode` with the dialog's other changes in one `command.batch`, and the document's changes are one undo step. An unchanged Color tab adds no color commands, and Cancel, or OK with nothing changed, records no undo step. A Color tab field with a value of the wrong kind is an error, and the dialog stays open. The tab is VectorCraft's own layout; File › Document Color Mode and Edit › Assign Profile… stay as they are. Tests in `dialogs/document_setup.rs`.
 - **Canvas through the display's profile on Windows and X11:** Preferences › Performance › Use Monitor Profile for Canvas (on by default) converts the canvas's art, artboard paper and transparency grid from sRGB into the ICC profile of the display that shows most of the main window, after any proof, as the help page describes the monitor's profile translating the document's colors for the monitor ([the help page](https://help.adobe.com/archive/en_US/illustrator/cs4/illustrator_cs4_help.pdf#page=151)). Windows gives the display's default profile, and a display with Advanced Color on is left to Windows ([Microsoft Learn](https://learn.microsoft.com/en-us/windows/win32/wcs/advanced-color-icc-profiles)); X11 gives colord's profile for the output or the `_ICC_PROFILE` property. macOS converts the window itself, and a Wayland session stays sRGB. `ui.inspect` reports `displayProfile`. Tests in `color/src/cms/display.rs`, `ui-egui/src/display_profile.rs` and `canvas::tests::the_canvas_is_drawn_through_the_display_profile_while_the_preference_is_on`.
+- **Translucent art blended before the display profile:** with Use Monitor Profile for Canvas converting, translucent art and the anti-aliased edges of art over an artboard's paper, a colored artboard or the transparency grid are blended with it in sRGB and the blend is converted, so the monitor's profile translates the document's colors as they are composited ([the help page](https://help.adobe.com/archive/en_US/illustrator/cs4/illustrator_cs4_help.pdf#page=151)). The frame rendered whole, the part an edit renders again, the render worker's frame, the pan fill and the other windows' panes do the same; over the pasteboard and in Outline the art is converted on its own, and with no profile to convert into nothing changes. Tests `display_profile::tests::translucent_pixels_over_the_paper_are_blended_before_they_are_converted`, `the_transparency_grid_is_blended_cell_by_cell`, `the_backdrop_is_found_through_the_view` and `canvas::tests::translucent_art_over_the_paper_is_blended_before_the_display_profile`.
 - **Out-of-gamut warning after a profile change:** the out-of-gamut warning and its closest-color correction in the Color panel and Color Picker ([the help page](https://helpx.adobe.com/illustrator/using/adjusting-colors.html)) check the color against the document's assigned CMYK profile, else the working CMYK space, and update when Edit › Assign Profile… or Edit › Color Settings… changes that space or a loaded profile changes, without a change of color. Which CMYK space the warning uses is VectorCraft's own rule. Tests: `gamut_warning_follows_a_profile_change` and `gamut_warning_follows_a_profile_loaded_again` in `dialogs/color_picker/tests.rs`.
 - **Assign Profile and the working spaces:** Edit › Assign Profile… tags the document and leaves the working spaces of Edit › Color Settings… as they are, in Color Settings, the Separations panel and the settings saved for the next start. Colors show and convert through the profiles assigned; a change in Color Settings keeps the profiles the document in front is assigned in use, and removing an assigned profile in use puts the working space back in its place. The profiles in use follow the document in front: a new, opened or reverted document, a switch to another tab, a close, Undo and Redo of Assign Profile, a failed batch, each step of a batch, Export All Open and the update of placed documents put that document's profiles in use, and the working spaces where it is assigned none or no document is open. View › Proof Setup › Working CMYK simulates the working CMYK space of Color Settings in Proof Colors and Separations Preview, also in a document assigned another CMYK profile. Public references: [Changing the color profile for a document and About color working spaces](https://help.adobe.com/archive/en_US/illustrator/cs3/illustrator_cs3_help.pdf#page=150) and [Soft-proof presets](https://help.adobe.com/archive/en_US/illustrator/cs3/illustrator_cs3_help.pdf#page=134). Tests in `engine/tests/color_settings.rs`.
 - **New Document's More Settings and Save Preset:** More Settings opens a pop-up over New Document with only Number of Artboards, the artboard layout, Change to Right-to-Left Layout, Spacing and Columns; Done, Escape or a click outside closes it and keeps the values. Save Preset turns the top of Preset Details into a Save Document Preset heading with the preset's name, Cancel and Save, and hides the document's name, Close and Create until the preset is saved or canceled; nothing in that mode creates a document. Save Preset's default name is the first "Preset N" no saved preset has. VectorCraft's own layout. Harness tests in `dialogs/new_document.rs` cover both.