BL-15958 Edit mode: trim-only view with bleed guides and crop marks on hover

[hatton]

[Claude Opus 5.5 from Hatton's machine during preflight]

Problem. For a book with Use full bleed page layout on, the Edit tab showed each page at its full printed size, with a thick dark band over the outer 3mm that the printer cuts off. Authors were always looking at a page larger than the finished one, with the edges of their pictures dimmed.

What the PR does.

• Full-bleed paper-size pages show only the trimmed page by default.
• Hovering over the page brings back the bleed band, a faint strip just inside the cut line (the area that could still be cut), and white crop marks at the four corners. Moving the mouse off hides them again.
• Ebook and device sizes (Device 16x9, Ebook 2x3, Ebook 7x5) get none of this, since they have no bleed.
• These edit-mode rules live in their own stylesheet, bookEdit/css/bleedAndCropMarks.less, imported by editMode.less. They pick out paper sizes with one test on the page-size class name, :not([class*="Device"], [class*="Ebook"]), instead of naming the four screen sizes. The mediaBox element carries only the page-size class (HtmlDom.cs), so no other class can match.

This is one of three independent PRs for BL-15958; the others are #8262 and #8263, both merged.

Screenshots

An A5 full-bleed page in the Edit tab. Without the mouse over the page, it shows the trimmed page (left). With the mouse over it, the 3mm bleed band, the faint strip just inside the cut line, and the crop marks at the corners appear (right).

The top-left corner at 300% zoom, with the mouse over the page, showing the white crop marks in the bleed band:

Risk Evaluation

Low. The change is CSS loaded only in the Edit tab, and it does nothing unless the book has full bleed on. Hiding the outer 3mm until the page is hovered is the one thing to watch: a control or handle sitting in that strip (a Canvas item dragged to the edge, a picture's buttons near a corner) is hidden until the mouse is over the page.

Ecosystem Impact

None. editMode.css is never put into a book or published, so PDF, BloomPUB, ePUB, Bloom Player and older Bloom versions are unaffected. No new strings and no dependency changes.

E2E Coverage

No e2e test covers full-bleed pages in the Edit tab, and none was added: the behavior is a hover-dependent visual, which the e2e suite does not check. The manual test ideas on the card cover it.

Notion Test Suite

None.

Preflight report: https://bloombooks.github.io/dev-process-artifacts/deciders/bloomdesktop-bl-15958-crop-marks.html

---

Devin review

---

This change is 

[greptile-apps]

Greptile Summary

Updates edit-mode styling for full-bleed print layouts.

• Clips the default view to the trimmed page boundary.
• Reveals the bleed band and safety-area guides while hovering the page.
• Adds crop marks at each trim corner and preserves exclusions for scrolling device and ebook layouts.

Important Files Changed

Filename	Overview
src/BloomBrowserUI/bookEdit/css/editMode.less	Adds trim-only clipping and hover-revealed bleed, safety, and crop-mark styling; no actionable defect was identified.

_{Reviews (1): Last reviewed commit: "BL-15958 Show trim-only view in edit mod..." | Re-trigger Greptile}

[hatton]

[Claude Opus 5.5 from Hatton's machine during preflight] Consulted Devin on 2026-10-07 21:05 UTC up to commit 40cc926. It raised one bug (bottom and right safety strips hidden) and one investigate flag (target branch). Both are assessed as not an issue, with the reasoning on their threads, which are now resolved. No informational flags.

[hatton]

[Claude Opus 5.5 from Hatton's machine during preflight] Preflight report: https://bloombooks.github.io/dev-process-artifacts/deciders/bloomdesktop-bl-15958-crop-marks.html

[hatton]

@hatton+JHAI resolved 2 discussions.
Reviewable status: 0 of 2 files reviewed, all discussions resolved.