Define chart scaffold gray ladder and neutral roles

Problem

Capture the chart scaffold gray research, lock the M1 neutral role model for titles, labels, guides, and surfaces, and record the implementation that rolled those neutrals into chart themes and defaults.

Context

• Recent M1 chart work converged on a clear principle: chart scaffold should use a stepped neutral hierarchy rather than a single gray for every non-data element.
• The source token base is the Fivetran gray spectrum, with chart roles mapped onto a compressed ladder for titles, labels, guides, rules, surfaces, and no-data fills.
• The key durable references are:
• tasks/workstreams/graph-library/tasks/m1-pilot-chart-batch.md
• docs/docs/guides/chart-design-notes.md
• dataface/core/compile/chart_themes/light.yml
• dataface/core/compile/chart_defaults.yml
• Relevant implementation landed incrementally across the March 24-25 color work, including the tonal-foundation rollout and later scaffold-gray centralization.
• This task is retrospective documentation for work that is effectively done, not a new execution request.

Possible Solutions

• Keep chart scaffold mostly implicit inside mixed theme defaults. Trade-offs: low documentation overhead, but the role model stays hard to explain and easy to regress.
• Recommended: capture the scaffold-gray ladder explicitly as an M1 chart task, record the role mapping that was chosen, and point to the landed theme implementation that now uses it. Trade-offs: some retrospective cleanup work now, but much better milestone clarity and less rediscovery later.
• Re-open the neutral system as unresolved design work. Trade-offs: inaccurate given the work already landed, and it would make the milestone view look less complete than reality.

Plan

1. Capture the research and decision context that produced the scaffold ladder.
2. Record the chosen M1 role model for chart neutrals.
3. Point back to the landed implementation and docs so this work is visible in the milestone inventory.
4. Mark the task complete as retrospective roadmap cleanup.

Implementation Progress

• 2026-03-24: M1 planning locked the first scaffold role model around the Fivetran gray scale, with explicit roles for strongest anchors, supporting text, rules, grids, and subtle surfaces.
• 2026-03-24: Implement tonal foundations for Dataface neutrals shipped the first neutral-system implementation in PR #763, replacing earlier ad hoc dark/light defaults with the Fivetran-aligned tonal base.
• 2026-03-24: The broader theme-color rollout landed the chart-library-owned color surfaces needed for neutrals and categorical color to behave as one coherent system.
• 2026-03-25: Centralize scaffold gray ladder further consolidated the gray ladder so scaffold roles are defined in one place instead of drifting across theme files and render defaults.
• 2026-03-25: Closed this task as complete because the research, definition, documentation trail, and implementation all now exist. Follow-on work, if any, should build on this ladder rather than re-deciding whether it exists.

QA Exploration

• [x] QA exploration completed (or N/A for non-UI tasks)
• N/A for retrospective task capture; the implementation shipped through the existing reviewed PRs listed above.

Review Feedback

• [x] Review cleared
• Covered by the landed review/PR flow for the neutral and scaffold work.