feat(schema): add native creative localization contract

[bokelley]

Why

AdCP has no typed way to request or read back provider-native creative localization. Implementations must either reject localization or accept unvalidated provider extensions, which loses locale, asset, review, and variant identity across sync_creatives and list_creatives. This blocks adcp-client#2370 and downstream Meta exact-readback work.

What Changed

• Added a provider-neutral, sync-only localization write contract. sync_creatives.creatives[].localization uses explicit typed oneOf arms for buyer-supplied and provider-generated targets; inline creatives on media-buy create/update reject localization.
• Added creative.localization capability discovery with the current supported locale set, translation modes, variant ceiling, and review scope.
• Added typed source/buyer/provider readback arms and exact request → sync → list verifier constraints for source ID/locale and target ID/locale/mode.
• Made top-level platform_id the single provider creative identity; localization retains only per-variant provider IDs.
• Required complete status/platform/localization evidence for accepted localized sync results and excluded localization from failed/deleted results.
• Enforced status/launch compatibility, machine-readable blockers, deterministic aggregate status, and whole-creative archive atomicity.
• Made localized-source upserts fail closed: omitting localization can preserve topology only when source assets are exactly unchanged; source changes require a full topology or explicit removal.
• Kept locale_variant_id separate from both build_variant_id and delivery variant_id.
• Updated normative docs, schema-extension guidance, composed conformance coverage, and the minor changeset.

Exact implementation head: 8ca0b9f1bc597b42c715cdfb7372abea572fc4e4.

Test Plan

• npm run build:schemas — pass (651 source schemas; 89 bundled schemas)
• npm run test:schemas — pass (19/19)
• npm run test:composed — pass (172/172, including standalone bundled compilation)
• npm run test:json-schema — pass (285 schema-backed documentation examples)
• npm run test:platform-agnostic — pass
• npm run test:oneof-discriminators — pass (no new undiscriminated unions)
• npm run test:schema-utf8 — pass
• npm run lint:schema-links — pass
• npm run typecheck — pass
• Push gates — pass (version sync, changeset policy, schema-link convention, Mintlify broken links)

The full local suite also exposed two pre-existing environment/baseline failures unrelated to this diff: released 3.1.3 is correctly marked withdrawn while dist-schema-version-ids still expects every semver release to be stable, and nine C2PA tests cannot load the cloned native Mach-O slice on this host. This PR changes neither area; Linux CI remains authoritative for those checks.

Unblocks adcontextprotocol/adcp-client#2370; that issue remains open until a generated client release consumes this schema.

[aao-secretariat]

Argus is not auto-reviewing this PR because it modifies protected paths that require human review (.changeset/add-native-creative-localization-contract.md, static/schemas/source/core/creative-asset.json, static/schemas/source/core/creative-localization-readback.json, static/schemas/source/core/creative-localization.json, static/schemas/source/core/locale-tag.json, static/schemas/source/core/x-entity-types.json, static/schemas/source/creative/list-creatives-request.json, static/schemas/source/creative/list-creatives-response.json, static/schemas/source/creative/sync-creatives-response.json, static/schemas/source/index.json, static/schemas/source/protocol/get-adcp-capabilities-response.json). A human reviewer should review and merge this PR; Argus will resume on subsequent PRs once these changes land on main.

[bokelley]

Independent exact-head contract audit found five substantive blockers despite 31/31 CI: generated union narrowing, request→sync→list equality, status/launch and whole-creative archive invariants, source-update semantics, and accidental inline-trafficking scope. I moved this PR back to draft while those are corrected; please hold human review until a new exact head is posted. The provider-neutral identity/mode model remains the right direction, but downstream Meta must not claim exact localization against an underconstrained contract.

[bokelley]

The five HOLD findings are addressed at exact head 8ca0b9f1bc597b42c715cdfb7372abea572fc4e4:

1. Request and readback variants are explicit typed oneOf arms with required string const discriminators.
2. Machine-readable verifiers and tests enforce exact request → sync → list identity, accepted/failed action boundaries, and one top-level provider creative ID.
3. Status/launch pairs, blockers, aggregate status, and whole-creative archive atomicity are enforced.
4. Localized source upserts reject ambiguous source changes when localization is omitted.
5. Localization writes are scoped to sync_creatives; inline create/update package creatives reject the field.

The rebuilt schema, composed (172/172), documentation JSON, oneOf, platform-agnostic, UTF-8, schema-link, TypeScript, changeset-policy, and Mintlify push gates pass. I am leaving the PR draft for CI and protected-path human review.