Resolve per-type graph styles via data() mappers, not per-type selectors

[kmcginnes]

Description

The Schema View locked up and never rendered on databases with very large label sets (~10k node types + ~10k edge types). Root cause: createGraphStyles emitted one Cytoscape selector per type (node[type="…"], edge[type="…"]), so Cytoscape resolved every element's style by scanning ~20k selectors — O(elements × contexts) ≈ 4×10⁸, pinning the main thread. A trace attributed ~88% of self-time to the Cytoscape style engine; layout was never reached.

This moves per-type styling off the stylesheet and onto element data: each element's resolved style values are precomputed onto ele.data() as ge_* fields, and a single static node rule + single edge rule read them back through data(…) mappers (plus two gated selectors for the optional cases, node[__iconUrl] and edge[ge_lineDashPattern]). Style-context count drops from ~20k to O(1) in the number of types. The type→style mapping now happens once per element at build time instead of per element × per selector at style time — the same pattern the pre-existing node[__iconUrl] mapper already used, generalized.

Both surfaces that share useGraphStyles are covered: the explorer graph (renderedEntities.ts) and the Schema View (useSchemaGraphData.ts). The Schema View merges its label into the base node/edge rules rather than replacing them, so the ge_* mappers survive. Supporting change: useBackgroundImageMap moves into core/icons so the element-enrichment seam consumes it without a core → modules import.

How to read

1. graphElementStyleData.ts — start here; the new pure vertexStyleData / edgeStyleData producers that own the per-element precompute (isDark label color, dotted→dashed remap + dash pattern, border-opacity)
2. useGraphStyles.ts — the collapsed static stylesheet: one node rule + one edge rule of data(ge_*) mappers, replacing createGraphStyles
3. renderedEntities.ts & useSchemaGraphData.ts — the two element-enrichment seams that write ge_* onto element data
4. useSchemaGraphStyles.ts — merges the schema label into the base rules (must not clobber the ge_* mappers)
5. useBackgroundImageMap.ts — relocated to core/icons (file move + import repoint)

docs/adr/20260813-element-data-style-mappers.md records the decision, the O(1) rationale, and the two lockstep constraints (producer/consumer must move together; a stylesheet consumer must merge into — not replace — the base rules).

Validation

• pnpm checks passes (types + lint + format); pnpm test passes (222 files, 2672 tests).
• New coverage: pure producer tests for graphElementStyleData, O(1) style-context-count guards on both the explorer and schema stylesheets, a guard that the schema label-merge retains the ge_* mappers, and an empty-labelColor crash guard.
• Verified live against a real 10k-label Neptune sync: the Schema View renders (previously locked up), no console errors, and Cytoscape style self-time drops from ~88% to ~0% in a fresh trace.

Related Issues

• Closes Schema view lockup from per-type Cytoscape style selectors in useGraphStyles #2104
• Related to Scale gracefully to very large label sets #2091
• Related to Push node background-color to Cytoscape ele.data() with styled type atoms #1725
• Related to Spike: Resolve per-type graph styling off both selectors and element data #2111

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.