Elements: Type VirtualList's item template as an element

[moersoy]

Part of #70 (item 1).

Problem

@geastack/elements VirtualList does not compile to C++. VirtualListItemTemplate returns any, and each slot renders {itemTemplate(...)} (VirtualList.tsx:79-82). An any result lowers to gea::Value, which gea::jsx::child has no rule for, so the C++ build stops:

gea_runtime.h:47048: static assertion failed due to requirement 'detail::always_false_v<gea::Value>':
gea::jsx::child: no append/text rule installed for this child value's C++ type

No app or test imports the component, so nothing caught it.

Fix

Type the template's result as GeaJsxElement, the type core uses for a component's returned element, in VirtualList.tsx and VirtualList.d.ts. The result now lowers to an element handle, which gea::jsx::child appends. The .d.ts says to wrap plain text in an element.

GeaJsxElement is an empty interface, so TypeScript still accepts a template that returns a string. geatsc then refuses it at compile time with "no runtime conversion is installed from string to native-handle(jsx-element)", instead of the C++ static_assert. Under any, no template compiled at all.

Tests

• Added run-gea-elements-virtual-list-pipeline.sh with the fixture packages/core/test/fixtures/gea-elements-virtual-list, so the test does not depend on geastack/examples. The fixture uses the component the way the README shows. test_gea_elements_virtual_list_main.cpp checks:
  • the list takes its height from the class (the rows are absolutely positioned);
  • its 16 slots show rows 0..15 once each.
• The test passes with the fix. With the template typed any again, the C++ build fails with the static_assert above.
• With vlIndexForSlot shifted by one, the test fails with "expected rows 0..15 once each, got 16 labels: 1 2 ... 16".
• The fixture and the README snippet type-check with tsc 5.9.3 (strict).
• Full core suite, test by test on macOS: 153/155, the same as main apart from the new test. The two failures fail on main too: run-ui-memory-census.sh needs a reference engine, and test_gea_vite_module_graph_assets.mjs is fixed by Point the module-graph asset test's compiler at this checkout's Core #66. run-gea-virtual-list-pipeline.sh (the raw tag) still passes.

Not covered

Scrolling is not tested. onScroll does not fire until geastack/compiler#4 lands, and even then a scrollTop change re-renders VirtualList and replaces its <virtual-list> node, which resets the scroll offset. Both are described in #70. Target scope: native harness tested; other targets source-only.

[coderabbitai]

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[moersoy]

Pushed a6771b7: components/index.ts now exports VirtualListProps and VirtualListItemTemplate too. A native build resolves value imports of @geastack/elements to index.ts, so import { VirtualList, type VirtualListItemTemplate } from '@geastack/elements' type-checked but failed in geatsc with "has no exported member". Checked with a scratch app built through run-gea-native-app-pipeline.sh: it fails before the change and builds and renders its rows after it. run-gea-elements-virtual-list-pipeline.sh still passes. CameraViewProps has the same gap and is left for a separate change.