Blank edge style colors are not dropped at the read boundary

[kmcginnes]

An edge style stored with an empty color renders as no color at all. The equivalent defect for vertex styles was fixed in #2102; edges were left because they need a transform that does not exist yet.

Why it happens

stylingParser.ts validates every color as a bare optional string, so a styling file carrying "lineColor": "" is stored verbatim. resolveEdgeStyle (core/StateProvider/graphStyles.ts) then plain-spreads the user entry over the defaults:

return { type, ...appDefaultEdgeStyle, ...user } as const;

A spread only skips absent keys, so "" overrides the default. Consumers read the value directly — useGraphStyles passes lineColor to cytoscape line-color and labelColor to text-background-color — and an empty string is not a color, so the edge or its label badge renders without one.

Three fields are exposed, all from EdgeVisualStyle / LabelVisualStyle:

• lineColor (default #b3b3b3)
• labelColor (default #17457b)
• labelBorderColor (default #17457b)

Fix

Mirror what #2102 did for vertices. That fix lives in transformVertexStyles, a read-time transform wired onto user-vertex-styles — the home the read-time-transform-for-persisted-values ADR assigns to intra-key value normalization, and the point where persisted storage and file import converge.

user-edge-styles has no transform today, so this needs:

1. A new core/StateProvider/edgeStylesTransform.ts exporting transformEdgeStyles, dropping the three color fields when blank (use .trim() so whitespace-only counts).
2. Wiring in storageAtoms.ts, alongside the existing reconcile for that key.
3. Tests in the describe("backward compatibility: ...") form the vertex transform test uses.

Drop the field rather than substituting a default, so "no user value" stays the representation and the style keeps following the app default if it ever changes. Follow the vertex version, which names the color fields explicitly rather than cleaning all strings — for edges there is no iconUrl equivalent, but being explicit keeps the two transforms symmetrical.

Notes

Pre-existing; not introduced by #2102. Reachable through a hand-edited or third-party styling file, or storage written by an older build — the color picker in the UI cannot produce an empty value.

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Important

Internal only — this issue is maintained by the core team and is not accepting external contributions.