Backport supports_proposals capability flag to 3.0.x

[estofko-scope3]

Summary

Request backport of #3844 / #3865 to the 3.0.x release line. The media_buy.supports_proposals capability flag is currently 3.1-only; sellers on 3.0.x cannot opt out of the proposal_finalize storyboard even when they don't generate proposals, which is causing false-negative compliance failures.

Background

PR #3865 (merged 2026-05-02) added media_buy.supports_proposals: boolean to get-adcp-capabilities-response.json and gated proposal_finalize.yaml with requires_capability: { path: media_buy.supports_proposals, equals: true }. This lets sellers without a proposal engine cleanly skip the scenario via capability_unsupported.

The fix is present in compliance/cache/3.1.0-rc.2/ but absent from compliance/cache/3.0.x/. The 3.0.x storyboard fires for any seller declaring supported_buying_modes: ["brief"] (or similar) and has no opt-out path.

Current behavior on 3.0.x

Verified against @adcp/sdk@7.11.1 bundled caches:

• compliance/cache/3.1.0-rc.2/domains/media-buy/scenarios/proposal_finalize.yaml → has requires_capability: media_buy.supports_proposals
• compliance/cache/3.0.12/domains/media-buy/scenarios/proposal_finalize.yaml → no gating
• schemas/cache/3.0.x/.../get-adcp-capabilities-response.json → no supports_proposals field

Affected adopters

InMobi seller agent (https://adcp-nonprod.exchange.inmobi.com/mcp) — currently testing against AdCP 3.0.12. Their capabilities declare supported_buying_modes: ["brief", "wholesale", "refine"] but they don't generate proposals, so get_products_brief returns null for /proposals and the storyboard fails. With supports_proposals: false declared (or omitted) on 3.0.x, the scenario would correctly skip.

Why this is patch-eligible

Same shape as #5042 / #5175 (Basic auth backport):

• Additive schema field — supports_proposals is optional; omission is the default and existing 3.0.x agents continue to behave as before
• Additive storyboard gate — requires_capability adds a skip path; agents that previously failed because they couldn't opt out now skip cleanly; agents that were passing continue to pass
• No wire breakage — no required field added, no enum value changed, no shape modified
• Already debated and resolved by the WG — semantics agreed in Add supports_proposals capability flag to media_buy block in get_adcp_capabilities #3844 (commitment about the conformance brief, not generic feature inventory)

Proposed change

Cherry-pick the relevant pieces of PR #3865 onto the 3.0.x line:

1. Add media_buy.supports_proposals: boolean (optional) to static/schemas/source/protocol/get-adcp-capabilities-response.json with the commitment-flavored description from Add supports_proposals capability flag to media_buy block in get_adcp_capabilities #3844
2. Add requires_capability: { path: media_buy.supports_proposals, equals: true } to static/compliance/source/domains/media-buy/scenarios/proposal_finalize.yaml
3. Cut a 3.0.x patch release

References

• Add supports_proposals capability flag to media_buy block in get_adcp_capabilities #3844 — original issue (closed/completed)
• feat(media-buy): supports_proposals capability flag — closes #3844 #3865 — implementation PR (merged 3.1)
• security_baseline should accept HTTP Basic auth as a sanctioned mechanism #5042 / [codex] Backport Basic auth compliance baseline to 3.0.x #5175 — precedent (Basic auth backport)

[bokelley]

Triage

Thanks for filing!

Classification: Conformance failure
Bucket(s): compliance-suite, media-buy
Status: ready-to-implement
Milestone: Spec Backlog

What the experts said:

• ad-tech-protocol-expert: Storyboard-only backport (Option A) is protocol-sound and patch-eligible; adding media_buy.supports_proposals to the 3.0.x stable schema (Option B) is blocked — get-adcp-capabilities-response.json is on the known-divergent-file list and the stable-schemas rule prohibits new fields in patches.
• adtech-product-expert: Option A fully resolves InMobi's false-negative; schema addition adds only speculative audit-trail benefit for 3.0.x and should remain 3.1-only.

My take: The storyboard-gate-only path fixes the adopter symptom without touching a stable schema. When supports_proposals is absent, requires_capability: { equals: true } correctly causes the runner to skip via capability_unsupported — no schema field needed for the fix.

Implementation (3.0.x branch only):

• Edit static/compliance/source/…/media-buy/scenarios/proposal_finalize.yaml — add (identical to main):

requires_capability:
  path: media_buy.supports_proposals
  equals: true

• Optional: add inline comment # field defined in 3.1 schema; absent on 3.0.x treated as false to avoid reader confusion.
• Do not add media_buy.supports_proposals to get-adcp-capabilities-response.json on 3.0.x — not patch-eligible.
• Changeset: patch. Run npm run build:compliance before pushing.
• Non-breaking: adds a skip path only; previously-passing storyboards unaffected.

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Triaged by Claude Code. Session: https://claude.ai/code/session_01VujVwuZnRNHpLoMzTue7RK

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Generated by Claude Code

[bokelley]

Closed by the merged 3.0.x backport PR #5496. GitHub did not auto-close this because the PR targeted the non-default 3.0.x branch.