[dotCooCoo]

What and why

This change follows up #3305 (hidden edges). Select a face of a Live Paint group with the Live Paint Selection tool
and choose Object › Hide. On main the hidden face is still highlighted under the pointer, Live Paint Selection
selects it again, and the Live Paint Bucket fills it. Where it lies over another Live Paint group's face, neither tool
can highlight or pick the face behind it.

live_paint_at and lp_part_at in crates/tools/src/builder.rs now take the front-most face that is not hidden
(visible_face_at). A point on a hidden face falls through to the visible face of a group behind it. Where no visible
face lies under it, an edge pick takes the nearest visible edge as it does outside the faces. livePaint.fill also
skips hidden faces. With group, a point on a hidden face returns "no Live Paint face at that point". With ids, it
fills the face there of another Live Paint group among the objects, or else returns that error and does not merge the
group. docs/mcp.md describes the change.

How it was tested

• builder::tests::live_paint_tools_skip_hidden_faces: of two groups whose faces overlap, the front one's face is
  hidden. Both tools highlight and pick the back face where they overlap and pick no face over the hidden one alone,
  and Alt-click inside it selects the back group's nearest side.
• tests_build::live_paint_fill_skips_hidden_faces: livePaint.fill on a hidden face fails with group and with
  ids without filling or rebuilding the group, and with ids naming a second group it fills that group's face.

Each test fails with main's code.

On Windows 11 (x86-64) with rustc 1.99.0, on top of main at cb0a7d9:

• CRAFT_FONTS_DIR=<craft-fonts checkout> cargo xtask ci passes its 10 steps: 8,791 tests passed, 0 failed, 13 ignored.

git merge-tree reports no conflicts with main at ff02191. #3275, #3255, #3238, #2526, #1849, #1838 and #1281
also change crates/tools/src/builder.rs, crates/engine/src/cmd/buildcmds.rs or crates/engine/src/tests_build.rs,
and this branch adds no conflict with any of them.

Checklist

• cargo xtask ci passes (fmt, clippy, tests, assets, brands, layers, wasm).
• No panics in shipped code: no unwrap(), expect(), panic!, unreachable!, todo! or
  unimplemented! outside tests, and no unchecked indexing on data from files, parameters or
  messages. Errors are returned as Result and shown to the user
  (why and how).
• Clean-room: nothing copied from Adobe products or GPL/AGPL code (AGENTS.md).
• Every new asset has a row in ASSETS.md.

Summary by CodeRabbit

• Bug Fixes

  • Live Paint filling and hit testing now skip hidden faces.
  • Attempts to fill hidden faces return an error without modifying or merging groups.
  • Visible faces and edges remain selectable, including when overlapping hidden regions.

• Documentation

  • Updated Live Paint fill documentation to clarify hidden-face behavior.

• Tests

  • Added coverage for hidden faces, overlapping groups, hidden-only regions, and edge selection.

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📒 Files selected for processing: 2

• crates/engine/src/cmd/buildcmds.rs
• docs/mcp.md

+-------------------------------------+
| I don't chase bugs; they surrender. |
+-------------------------------------+
  \
   \     /)/)
        ( '')
        /  |
      o(___)

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📥 Commits

Reviewing files that changed from the base of the PR and between 44104b6 and 1728bc8.

📒 Files selected for processing: 4

• crates/engine/src/cmd/buildcmds.rs
• crates/engine/src/tests_build.rs
• crates/tools/src/builder.rs
• docs/mcp.md

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📝 Walkthrough

Live Paint hit testing and filling now skip hidden faces. A fill on a hidden face returns an error without merging objects. When another Live Paint group has a visible face at that point, filling can use that group instead.

Changes: Live Paint hidden-face handling

Layer / File(s)	Summary
Visible-face hit testing crates/tools/src/builder.rs	Face lookup can filter hidden faces. Live Paint group and in-group lookups use visible faces, while visible-edge lookup remains available. Tests cover overlapping groups, hidden-only regions, and nearby visible edges.
Fill visible faces crates/engine/src/cmd/buildcmds.rs, crates/engine/src/tests_build.rs, docs/mcp.md	lp_fill searches for visible faces and errors on a hidden-face target before merging objects. It reuses a group with a visible face at the point, or creates a group when no face matches. Tests and documentation describe these cases.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix

Suggested reviewers: echelon

Merge Risk: ⚪ Minimal · up to 1728b

The change skips hidden Live Paint faces while retaining visible-face and edge behavior. No actionable merge risk is identified beyond normal checks.

Architecture risk: 🟡 Medium · up to 1728b

The change affects 2 systems.

Changed systems: crates, docs

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — crates (service) was modified; 3 changed files map to changed impact.
• observed — docs (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in crates/engine/src/cmd/buildcmds.rs: Updated the livePaint.fill command description to document that hidden faces are skipped.
• observed — Modified behavior in crates/engine/src/cmd/buildcmds.rs: lp_fill now searches for visible faces rather than any face. Points on hidden faces return an error before objects are merged; visible-face matches reuse their group, and unmatched points still create a Live Paint group. Final face lookup also requires visibility.
• observed — Modified behavior in crates/engine/src/tests_build.rs: Added coverage for hidden-face selection during Live Paint filling, including unchanged group state on errors and fallback to another visible group at the same point.
• observed — Modified behavior in crates/tools/src/builder.rs: Added shared face hit-testing through front_face, retained face_at for all faces, and added visible_face_at to search only visible faces.

Reliability and maintainability

• inferred — Risk-relevant change factors for crates: blast_radius_1; blast_radius_2; direct_dependents_1; direct_dependents_2

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: Live Paint tools and livePaint.fill now skip hidden faces.
Description check		The description includes the required What and why, How it was tested, and Checklist sections. It explains the behavior changes, identifies added tests, reports CI results, and marks all checklist ite…
Docstring Coverage		Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 3 files. (1 skipped: 1 …
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description includes the required What and why, How it was tested, and Checklist sections. It explains the behavior changes, identifies added tests, reports CI results, and marks all checklist items complete.

Full details: Docstring Coverage

Explanation

Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 3 files. (1 skipped: 1 unsupported.)

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