compliance(media-buy): base media_buy_seller flow should be runnable by sales-non-guaranteed-only sellers

[fgranata]

Problem

The base media_buy_seller flow (static/compliance/source/protocols/media-buy/index.yaml) is unrunnable by a seller that declares only specialisms: ["sales-non-guaranteed"].

• Its fixtures.products are guaranteed-only (sports_preroll_q2, lifestyle_display_q2, both delivery_type: guaranteed), and
• its create_buy step hardcodes a guaranteed buy (those products + cpm_guaranteed).

A non-guaranteed-only seller correctly rejects a guaranteed buy (per enums/delivery-type.json + enums/specialism.json, sales-non-guaranteed = "Non-guaranteed auction-based media buys") with a terminal DELIVERY_MODE_NOT_SUPPORTED. So create_buy fails and the dependent creative_sync / delivery_monitoring steps cascade as prerequisite_failed — the base lifecycle is unrunnable for that entire seller class, even though the lifecycle it tests (discover → create → deliver) is delivery-type-agnostic.

Change

Switch the base lifecycle to the universal non_guaranteed (auction) path: the fixtures + the create_buy packages now use delivery_type: non_guaranteed with floor-priced pricing options. Non-guaranteed is the lowest-common-denominator delivery type; the guaranteed lifecycle (human IO approval, proposal_finalize) is already covered by the sales-guaranteed specialism bundle, which carries its own guaranteed fixtures.

This is consistent with the existing pattern in specialisms/sales-guaranteed/index.yaml, whose fixtures already seed non-guaranteed products first for the shared seller scenarios, with the note that "a fixture set that contains only guaranteed products will fail those four shared scenarios." This PR applies the same reasoning to the base protocol flow.

Reproduction

Against any live sales-non-guaranteed seller: get_adcp_capabilities → specialisms includes sales-non-guaranteed; running the base media_buy_seller flow → create_buy returns DELIVERY_MODE_NOT_SUPPORTED (terminal) and creative_sync / delivery_monitoring cascade.

For maintainer review

• Guaranteed-only sellers: if a strictly guaranteed-only seller relies on the base flow exercising a guaranteed create, this changes that. The intent here is that the base flow is the universal lifecycle and delivery-type-specific behavior lives in the specialism bundles — but flagging it explicitly for your call. Happy to instead gate fixture provisioning on the seller's declared specialism in the runner if you prefer that shape.
• Packaged cache: dist/compliance/ is generated from this source; I wasn't able to run the workspace build standalone, so the cache regen is left for your build/CI.

Only the source YAML + a changeset are touched.

[aao-release-bot]

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[bokelley]

Reviewed for triage cleanup: green, scoped, and no 3.2-triggering changeset.