Docs: image cache keeps the levels drawn; canvas decodes in the background

ROADMAP.md

@@ -64,7 +64,7 @@ DesignCraft aims at full Adobe InDesign parity — and to be better: faster, ope
 - Document model: facing/non-facing spreads, parent pages with page-number markers, sections, layers, frames (text / graphic / unassigned), threaded stories, paragraph/character/object styles with based-on, swatches (process/spot/tints/gradients), corner options, text wrap, drop shadow, opacity/blend.
 - Text engine: Knuth–Plass paragraph composer and single-line composer, dictionary hyphenation (public-domain Moby list + our own trained Liang patterns), justification with word/letter/glyph-scaling ranges, keep options (keep with next, keep lines together, widows/orphans), balance ragged lines, optical margin alignment, hyphenation zone/limit, columns, threading across frames and spreads, tabs, bullets/numbering, rules, shading, baseline grid, first-baseline options, vertical justification, wrap exclusions, overset detection, caret/hit testing.
 - FID2: IDML underline/strikethrough Text Color resets survive style inheritance and roundtrip. Raster and PDF paint underlines behind glyphs, retain strikethrough above, and center rules on their offsets; synthetic overlap tests cover both backends.
-- Rendering: vello_cpu (SIMD, multithreaded) — pages, items, images with mip levels, gradients, composed text.
+- Rendering: vello_cpu (SIMD, multithreaded) — pages, items, images with mip levels (only the levels drawn are cached; the canvas decodes on background threads and shows a light box or another cached level meanwhile), gradients, composed text.
 - UI (egui): application bar + menus, Control panel (object and text modes), Tools panel with flyouts, document tabs, rulers, pasteboard, guides (margins, columns, bleed, baseline grid), frame edges, selection handles, text ports and threads, Properties / Pages / Layers dock, Swatches, Styles, Character, Paragraph, Stroke, Text Wrap panels, New Document and Preferences dialogs, Quick Apply (⌘Return), 4 brightness themes.
 - Pen tool, Direct Selection anchor/handle editing, rotate from corners, Rotate/Scale/Shear tools, Eyedropper, snapping & smart guides, Align/Distribute, Find/Change (text + GREP), Story Editor, Paragraph Style Options, Effects panel, hidden characters, native macOS menu bar, measured InDesign 2026 look (Medium Dark): Properties sections per selection state, 21 pt spinner fields with arithmetic, Contextual Task Bar, inverse (black) text selection, Pages panel with drag-and-drop reorder / parent apply, Layers panel with per-object rows.
 - Tools: Selection (click, marquee, move, Alt-duplicate, resize handles), Direct Selection, Type (draw frame, click caret, select, type), Rectangle/Ellipse/Polygon (+ frame variants), Line, Hand, Zoom.
@@ -394,6 +394,7 @@ list) · [roadmap.md](docs/roadmap.md) (milestones, plan) · [parity-checklist.m
 
 ## Progress log
 
+- **2026-11-14** · Photo books no longer freeze the canvas (#1411; based on #2051 by texjer). The image cache keeps only the mip level each image is drawn at, for every format and display quality: a TIFF, PNG, PSD or CMYK JPEG used to keep its full decode too (48 MB for a 12 MP photo), so after about a dozen photos each edit evicted and decoded them again on the render thread. The canvas no longer waits for decodes: an image not cached at its size shows a light box or another cached level and decodes on one of three background threads (within the same in-flight memory limit as the decodes ahead of a render), and finished decodes are drawn in batches, at most one canvas render every 250 ms. Zooming into an image decodes it at most twice. Thumbnails and exports still wait for every image. No readiness percentage change.
 - **2026-11-14** · Object › Text Frame Options shows the inset spacing (one Inset for a non-rectangular frame), the column width and gutter and the paragraph spacing limit in the document's ruler units, as the Properties panel does, instead of always in picas, and a bare number typed in any of its measure fields is in those units (#2739). No readiness percentage change.
 - **2026-11-12** · A render decodes the placed images in view that are not cached yet on several threads before it draws, instead of one after another while drawing. Page thumbnails, image exports and the first canvas frame of a page with six 24 MP photos take about 1.2 s instead of 2.8 s. No readiness percentage change.
 - **2026-11-12** · Properties › Text Frame shows the frame's inset spacing (Top, Bottom, Left and Right with a link that makes all four the same; one Inset for a non-rectangular frame) and four Vertical Justification buttons (Top, Center, Bottom, Justify), and the section also shows with the Type tool in a frame, where it changes the frame that shows the insertion point. No readiness percentage change.

docs/target-app-parity.md

@@ -273,7 +273,7 @@ It is evidence of breadth: each item exists. It is not a claim of InDesign-level
 - Document model: facing/non-facing spreads, parent pages with page-number markers, sections, layers, frames (text / graphic / unassigned), threaded stories, paragraph/character/object styles with based-on, swatches (process/spot/tints/gradients), corner options, text wrap, drop shadow, opacity/blend.
 - Text engine: Knuth–Plass paragraph composer and single-line composer, dictionary hyphenation (public-domain Moby list + our own trained Liang patterns), justification with word/letter/glyph-scaling ranges, keep options (keep with next, keep lines together — at start/end of paragraph by default, as in InDesign — widows/orphans), balance ragged lines, optical margin alignment, hyphenation zone/limit, columns, threading across frames and spreads, tabs, bullets/numbering, rules, shading, baseline grid, first-baseline options, vertical justification, wrap exclusions, overset detection, caret/hit testing.
 - FID2: IDML underline/strikethrough Text Color resets survive style inheritance and roundtrip. Raster and PDF paint underlines behind glyphs, retain strikethrough above, and center rules on their offsets; synthetic overlap tests cover both backends.
-- Rendering: vello_cpu (SIMD, multithreaded) — pages, items, images with mip levels, gradients, composed text.
+- Rendering: vello_cpu (SIMD, multithreaded) — pages, items, images with mip levels (only the levels drawn are cached; the canvas decodes on background threads and shows a light box or another cached level meanwhile), gradients, composed text.
 - UI (egui): application bar + menus, Control panel (object and text modes), Tools panel with flyouts and the Fill/Stroke proxy (D, X, Shift+X, / as `color.*` commands), document tabs, rulers, pasteboard, guides (margins, columns, bleed, baseline grid), document grid (View ▸ Grids & Guides, ⌘', on the snap positions, behind or in front of items), Lock Guides (⌥⌘;) and Lock Column Guides (View ▸ Grids & Guides; Lock Column Guides is saved with the document and in IDML), frame edges, selection handles, text ports and threads, Properties / Pages / Layers dock, Swatches (InDesign's header: Fill/Stroke proxy, Formatting Affects Container/Text, Tint, which reads 100 with nothing selected; a swatch goes to the fill or stroke in front; rows show InDesign's type columns: the crossed pencil on swatches that can't be edited, process or spot, and the colour mode; New Color Group / New Swatch / Delete Swatch row), Styles, Character, Paragraph, Stroke, Text Wrap panels, New Document and Preferences dialogs, Quick Apply (⌘Return), 4 brightness themes.
 - Pen tool, Direct Selection anchor/handle editing, rotate from corners, Rotate/Scale/Shear tools, Eyedropper, snapping & smart guides, Align/Distribute, Find/Change (text + GREP, with Find Format: text that has a character or paragraph style or character attributes; Change and Change/Find on the text Find Next found), Story Editor, Paragraph Style Options, Effects panel, hidden characters, native macOS menu bar, measured InDesign 2026 look (Medium Dark): Properties sections per selection state, 21 pt spinner fields with arithmetic, Contextual Task Bar, inverse (black) text selection, Pages panel with drag-and-drop reorder / parent apply, Layers panel with per-object rows, expandable groups and drag-and-drop reorder of layers and objects (the selection square moves the selection to another layer).
 - Tools: Selection (click, marquee, move, Alt-duplicate, resize handles), Direct Selection, Type (draw frame, click caret, select, type; Option/Alt+Left/Right kerns at the caret or tracks a selection by the Kerning/Tracking increment, ×5 with Cmd/Ctrl; words move with Cmd+Left/Right on macOS and Ctrl+Left/Right elsewhere), Rectangle/Ellipse/Polygon (+ frame variants), Line, Hand, Zoom.