fix: unblock the underside, make the cross-section real and movable, replace the selection heart (#8)

[PouyanJay]

Fixes #8. Thanks @Phantom-VK — all three reports were valid, and two of them turned out to be covering deeper bugs.

1. The view-blocking platform

Removed. The opaque plinth walled off the bottom of every specimen, so a full 360° orbit was impossible.

Three things leaned on it, so this wasn't a one-line delete:

• The contact shadow that grounded the organ stays, but is now anchored to each organ's own bounding box (organs are fitted by their longest axis, so a fixed height left flat organs' shadows adrift) and fades by camera elevation, reaching zero before the camera crosses its plane. It can never sit between you and the specimen.
• HOME_CAMERA.y drops 1.05 → 0.3, since nothing needs to be seen at an angle any more.
• Isolate was literally defined as "fade the plinth". It now dims the remaining staging — shadow, particles, accent glow.

2. "Layers" doesn't cut the object

Correct, and the tool that does cut — Cross-section — was broken in four ways that would have hidden it even if found:

• the sweep started fully clipped, so the organ blinked out before wiping back in
• turning it off dropped the clipping planes before the reverse tween, so it popped
• side = FrontSide meant the cut read as a hole through to the background rather than exposing anything
• the plane was fixed in world space, so from half of all orbit positions it removed the half you couldn't see — the tool looked like it had done nothing

All four fixed, and Layers is now Wireframe, so no button promises something it doesn't do. The layered metaphor moved onto the tool that actually opens the organ up.

The cut is also now movable, which it wasn't before at all:

• Sagittal / coronal / axial presets, plus Free (squares up to the current view). The plane lives in the organ's own space and is carried to world space through the pivot each frame, which is what makes a named plane stay named while the specimen is turned.
• A depth slider whose travel is measured against each organ's own box projected onto the plane normal — so the same position means "halfway through" for an eyeball and for a pair of lungs. This also fixes a case where a plane pinned to the origin removed an entire kidney instead of sectioning one.
• Flip, so both faces are reachable without orbiting around.
• The plane itself is drawn in the scene: a translucent, accent-tinted pane with an outlined rim, posed at the exact cut in the organ's own space — so its orientation and depth are readable at a glance, and it rides the specimen through orbit, axis changes, depth drags, flips and the open/close sweep. A Plane checkbox in the section controls hides it for a clean look at the cut face; Reset restores it.
• Markers on the discarded half fade out with it instead of floating in the gap.

Known limit, stated plainly

The models are single closed surface shells with no interior geometry (meshCount: 1). So the cut reveals whatever a given model actually contains — which is genuinely good for skin, eye, lungs and heart, and empty for brain and kidneys. No rendering technique can section anatomy that isn't in the file.

I prototyped a stencil-buffer cap that fills the cut face, and removed it: with shell geometry the parity test reports "solid" across the whole silhouette, so it painted a heart as a solid block of myocardium and hid the real modelled atria underneath. For a teaching tool that's worse than an honest hollow. Proper interiors need segmented assets (per-structure closed meshes); that's tracked separately.

3. The heart icon

Replaced with a check mark. The heart read as "favourited", a meaning the Bookmark control in the panel heading already owns. The list also carries role="radiogroup" / aria-checked now — selection previously had no programmatic representation at all, only a CSS class.

Also fixed along the way

The toolbar tracked a single activeTool: string | null while Isolate, Cross-section and Wireframe are independent toggles — so two could be on with only one lit, and Reset cleared the highlight while leaving the cut applied in the viewer. Tool state is now a record, and reset() clears the viewer as well as the buttons.

Verification

Driven in a real browser with Playwright, not just typechecked:

• full 360° orbit incl. directly underneath, all 9 organs
• cut across all 9 organs × 4 plane orientations, full depth sweep on each
• cut carried across organ switches, including 4 rapid switches mid-fade
• Isolate + Wireframe simultaneously; Reset clears both
• mobile (390×844) — panel clears the caption, auto-rotate pill and tool bar; slider and flip reachable
• prefers-reduced-motion
• tsc --noEmit and eslint app clean

Note: npm test is already failing on main — tests/rendered-html.test.mjs still asserts the deleted starter skeleton (app/_sites-preview/, react-loading-skeleton, title: "Starter Project"). Pre-existing, untouched here.

[vercel]

@PouyanJay is attempting to deploy a commit to the thebuggeddev-9222's projects Team on Vercel.

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[Phantom-VK]

@PouyanJay thank you for picking up the issue, can you please add screenshots of how the UI/UX looking now, after the changes?

[PouyanJay]

@Phantom-VK

[Phantom-VK]

@Phantom-VK

Looking good!

[PouyanJay]

@thebuggeddev just a reminder about this PR :)