feat(spec): string-name escape hatch for tokens (Proposal 012)

[GarthDB]

Description

Implements Proposal 012: a formal escape hatch for tokens whose names cannot
be expressed using the structured name-object taxonomy.

Allows a token's name field to be a plain string (e.g.
"focus-ring-color-key-focus") instead of a name object. String-named tokens
are schema-valid but trigger SPEC-017 (severity: warning, category:
tech-debt), making the debt visible and trackable in conformance reports —
analogous to CSS !important.

Changes:

• token.schema.json — name field in both tokenWithValue and
  tokenWithRef becomes a oneOf [nameObject, string] union
• token-format.md — new "String-name escape hatch" section with NORMATIVE
  statements
• rules.yaml — SPEC-017 (string-name-tech-debt, severity: warning)
• sdk/core/src/validate/rules/spec017.rs — Rust validator with 3 unit tests
• Conformance fixtures: valid string-name token and invalid/SPEC-017/

Related Issue

Closes the formal gap for the 730+ tokens tracked in naming-exceptions.json.
Follows Proposals 009, 010 from the token spec gap analysis.

Motivation and Context

naming-exceptions.json already tracks 730+ tokens that don't roundtrip
through the name-object taxonomy. This proposal gives those tokens a formal,
spec-blessed path: they can be written with "name": "raw-string" and tooling
will surface them as tech debt rather than silently accepting them.

How Has This Been Tested?

• Rust SDK: 164 unit tests pass, 0 fail (cargo test in sdk/)
  — includes 3 new SPEC-017-specific tests
• cargo clippy -- -D warnings passes clean
• Conformance fixtures cover both the warning case and the no-warning case

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: acb6cd2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@adobe/design-data-spec	Minor

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Click here if you're a maintainer who wants to add another changeset to this PR

[GarthDB]

Run report for acb6cd28

Total time: 1m 54s | Comparison time: 5m 13s | Estimated savings: 3m 18s (63.3% faster)

	Action	Time	Status	Info
🟩	SyncWorkspace	7.6ms	Passed
🟩	SyncProject(designDataSpec)	0.3ms	Passed
🟩	SyncProject(sdk)	0.4ms	Passed
🟩	SyncProject(tokens)	0.3ms	Passed
🟩	SetupProto(0.51.4)	1.8s	Passed
⬛️	SetupToolchain(node:20.17.0)	2.4s	Skipped
🟩	SetupToolchain(rust:1.85.0)	17s	Passed
🟩	InstallWorkspaceDeps(rust:1.85.0, sdk)	1s	Passed
🟩	InstallProjectDeps(node:20.17.0, sdk)	17.1s	Passed
🟩	RunTask(sdk:codegen-check)	156.6ms	Passed
🟩	InstallWorkspaceDeps(node:20.17.0)	18.1s	Passed
🟩	RunTask(sdk:lint)	36.6s	Passed
🟩	RunTask(designDataSpec:check)	277ms	Passed
🟩	RunTask(sdk:build)	1m 22s	Passed
🟩	RunTask(tokens:verifyLegacyRoundtrip)	887.3ms	Passed
🟩	RunTask(tokens:verifyDesignDataSnapshot)	1.6s	Passed
🟩	RunTask(tokens:validateDesignData)	1.6s	Passed
🟩	RunTask(sdk:test)	1m 26s	Passed
🟩	RunTask(tokens:buildTokens)	1m 29s	Passed
🟩	RunTask(tokens:test)	3.4s	Passed

Touched files

.changeset/proposal-012-string-name-escape-hatch.md
docs/proposals/012-string-name-escape-hatch.md
packages/design-data-spec/conformance/invalid/SPEC-017/expected-errors.json
packages/design-data-spec/conformance/invalid/SPEC-017/tokens.tokens.json
packages/design-data-spec/conformance/valid/string-name-escape-hatch.json
packages/design-data-spec/rules/rules.yaml
packages/design-data-spec/schemas/token.schema.json
packages/design-data-spec/spec/token-format.md
sdk/core/src/validate/rules/mod.rs
sdk/core/src/validate/rules/spec017.rs