Embed LDH's RDF-defined blocks as atomic RDFa islands

[namedgraph]

Summary

Blocks defined purely in RDF — ldh:View, ldh:ResultSetChart, ldh:Object — can now be embedded wherever the content model admits a block, per the LDH v6 document format: a div[@about][@typeof] element with its definition triples as span[@property] children (objects via @resource, literals as span text). No wrappers, no rdf:_N sequences, no document→block containment edges — extraction yields the block descriptions, containment is implicit in the content.

The editor treats such a block as an atomic island:

• never a text host — the placeholder and its spans are locked, tabindex="-1" makes it a focusable navigation island (shared doctrine with block images: arrow-key selection, Backspace/Delete removes it whole, undo/redo chords work while it's focused);
• a hard boundary for Backspace merges (local:merge-host-in gains a tail-island guard) and for the cross-host delete machine (local:clamped-range moves boundaries out of islands, so a selection takes them whole or not at all);
• byte-identical round-trip: the visual rendering is injected into an ephemeral div[data-role=rendering] child by the overridable mode="local:render-island" hook and stripped at canonicalization; the extractor skips it.

Core / extension split

• src/blocks.xsl (core, zero LDH knowledge): $object-block-types param (default empty), the local:island() predicate, the render hook + neutral card, and extension stubs for dialogs / toolbar buttons / slash-menu items.
• src/ldh-blocks.xsl + entry src/ldh-editor.xsl (xsl:import layering, higher import precedence): the LDH class list, async renderers — ixsl:promise/ixsl:http-request chains fetching the referenced documents by content negotiation on clean trailing-slash URIs (no file extensions anywhere) — and the "Block…" insert dialog wired into the slash menu and toolbar. In production LinkedDataHub, client.xsl plays this module's role, bridging the hook into its block rendering (v6 ldh:Block / v5 ldh:RenderRow — MIGRATION.md §12).

Build & deployment

Two SEFs: the core dist/index.xsl.sef.json is what GitHub Pages deploys (Pages can't content-negotiate); the LDH-extended dist/ldh-editor.xsl.sef.json powers the local /demo/ showcase and the browser fixtures. make up now serves via node serve.mjs, which negotiates application/rdf+xml / application/sparql-results+xml representations of document URIs.

Test plan

• make test — 50 headless PASS, incl. new extractor/canonical/lint fixtures for the storage form
• make test-browser — all 14 suites green, incl. new blocks.mjs (43 assertions: hydration, view-source round-trip, island navigation/deletion/boundaries, dialog insertion top-level and nested in a list item, stage-2/sweep delete atomicity, canonical copy, undo + invariants after every mutation)
• fixture-nesting.html runs the extended SEF, so every existing suite doubles as proof the extension layers without disturbing core behavior
• Manual: make up → /demo/ hydrates a chart and a nested object block over conneg; Source shows the clean v6 placeholder; Extract RDF shows the block descriptions

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