Prerelease upgrade notes (rc.1 → rc.2)

If you adopted 3.0.0-rc.1, review these changes before upgrading to rc.2. If you are migrating from v2, see the main migration guide.

Potentially breaking for rc.1 adopters

Area	rc.1	rc.2	What to do
Account auth model	`account_resolution` capability	Removed — `require_operator_auth` now determines account model	Update capability parsing and auth/account branching logic
Creative library task boundary	`list_creatives` / `sync_creatives` documented under Media Buy	Creative library operations live in the Creative Protocol	Route library reads/writes through Creative Protocol assumptions, even when a sales agent implements both protocols
Sandbox capability discovery	`media_buy.features.sandbox`	`account.sandbox`	Read sandbox support from the account capability block
DOOH flat rate parameters	`flat_rate.parameters` without discriminator	`flat_rate.parameters.type: "dooh"` required when parameters are present	Add the discriminator in request builders and validators
Deprecated governance task docs	`delete_content_standards`, `get_property_features` documented	Removed	Use `update_content_standards`, property lists, and `get_adcp_capabilities` instead

Creative generation and preview — build_creative adds include_preview, preview_inputs, preview_quality, preview_output_format, quality, item_limit, and multi-format target_format_ids. Buyers can now preview inline, choose draft vs production generation, and request multiple output formats in one call.
Creative library retrieval — build_creative also supports library retrieval using creative_id, optional concept_id, media_buy_id, package_id, and macro_values, so ad servers and creative platforms can resolve stored creatives into delivery-ready manifests.
Creative capability discovery — Creative agents can declare supports_generation, supports_transformation, and has_creative_library. list_creatives now uses library-oriented fields like include_snapshot, has_served, and items.
Product discovery and planning — get_products adds exclusivity, preferred_delivery_types, and time_budget, with incomplete in the response. Products may omit delivery_measurement, and packages can now carry per-package start_time / end_time.
Compliance and governance — Creative disclosures add persistence semantics, and campaign governance introduces sync_plans, check_governance, report_plan_outcome, and get_plan_audit_logs.
Accounts and sandbox ergonomics — sync_accounts adds payment_terms, and sandbox now participates in the natural account key for implicit account references.