docs(forms): adding forms strategy to washing machine workflow

[aramos-adobe]

Description

Adds contributor-facing documentation for the approved 2nd-gen forms strategy so the decisions are discoverable before form-field migration PRs are opened.

• New: CONTRIBUTOR-DOCS/03_project-planning/05_strategies/forms-strategy-rfc.md — the canonical forms strategy, mirroring the existing focus-management-strategy-rfc.md. Covers ElementInternals/FACE form participation (FieldAssociationController), where ARIA roles live (shadow DOM), the label/help/error IDREF model (LabellingController, same-root slots + cross-root element references), a naming table, and the axe-core policy for ElementInternals gaps.
• Updated: .../02_step-by-step/01_washing-machine-workflow.md — a new "Form participation (form fields only)" subsection in Phase 3 (API), label/help/error + cross-root IDREF guidance in Phase 4 (Accessibility), a Phase 4 axe/CI quality-gate item, a common-problems row, and a forms-strategy cross-link.
• Updated: .../03_components/README.md — routes form-field migrations to the canonical strategy.
• Regenerated breadcrumbs/TOC via the contributor-docs nav script; all links in the changed files validate.

Motivation and context

Form-field migration is about to scale, and the forms-strategy decisions previously lived only in a proof-of-concept repo and RFC discussion, not in the contributor docs. This surfaces them at the point migrators need them (Phase 3 and Phase 4 of the washing machine workflow) and gives every form field one canonical reference for form participation, role placement, cross-root labelling, and axe policy.

Content is sourced from the form-strategy proof-of-concept (nikkimk/web-component-form-strategy-demos). Controllers still under an open research decision (ButtonAssociationController, RadioGroupController) are explicitly marked pending research rather than presented as settled.

Related issue(s)

• fixes SWC-2055

Screenshots (if appropriate)

N/A — Markdown contributor documentation only.

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed the Accessibility Practices for this feature.
• I have added automated tests to cover my changes. — N/A, documentation only.
• I have included a well-written changeset if my change needs to be published. — N/A, CONTRIBUTOR-DOCS changes are not published to a package.
• I have included updated documentation if my change required it.

Reviewer's checklist

• Includes a Github Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features
• Automated tests cover all use cases and follow best practices for writing
• Validated on all supported browsers
• All VRTs are approved before the author can update Golden Hash

Manual review test cases

• New strategy doc and cross-links render correctly

  1. Check out this branch and open CONTRIBUTOR-DOCS/03_project-planning/05_strategies/forms-strategy-rfc.md.
  2. Confirm §3.1–§3.4, the naming table (§4), open questions, and appendix render with no TODO placeholders.
  3. Expect the pending research rows for button-like and grouped-selection fields to be clearly marked as provisional.

• Washing machine workflow additions

  1. Open .../02_step-by-step/01_washing-machine-workflow.md.
  2. Confirm the new Phase 3 "Form participation" subsection, the Phase 4 label/help/error step, the Phase 4 axe quality-gate item, and the common-problems row are present and read in context.
  3. Expect the phase framing to match this repo (a11y is Phase 4, styling is Phase 5).

• Links resolve

  1. From CONTRIBUTOR-DOCS/01_contributor-guides/07_authoring-contributor-docs, run node update-nav.js.
  2. Follow each forms-strategy link from the washing machine doc and the components README.
  3. Expect no new broken links introduced by this PR.

Device review

• Did it pass in Desktop?
• Did it pass in (emulated) Mobile?
• Did it pass in (emulated) iPad?

Accessibility testing checklist

This PR changes Markdown contributor documentation only. It adds no component, runtime behavior, or focusable UI, so there is no interactive surface to test with a keyboard or screen reader.

• Keyboard

  1. N/A — no component or focusable UI is added or modified; no interactive examples are introduced.

• Screen reader

  1. N/A — the docs describe accessibility patterns but ship no interactive UI. Rendered docs pages inherit the Storybook docs shell, which is unchanged by this PR.

[changeset-bot]

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[github-actions]

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[coveralls]

Coverage Report for CI Build 31039458154

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Coverage: 96.241%

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Coverage Stats

Relevant Lines:	39268
Covered Lines:	37993
Line Coverage:	96.75%
Relevant Branches:	6465
Covered Branches:	6021
Branch Coverage:	93.13%
Branches in Coverage %:	Yes
Coverage Strength:	460.61 hits per line

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[nikkimk]

Thanks for taking this on. I have just a few change listed.