compliance(media-buy): add proposal negotiation storyboard matrix

[bokelley]

Goal

Add a capability-gated proposal-negotiation storyboard matrix for AdCP 3.2 so implementors can test correctness, experiment with counteroffers, and compare their behavior with the public training seller.

Parent program: #6556
Related compact lifecycle suite: #6432
Protocol implementation: #6547

Required storyboard coverage

Capability and preflight

• Ask-only seller accepts ask revision.
• Explicitly unsupported typed dimension causes task-level UNSUPPORTED_FEATURE for the entire mixed batch with no mutation.
• Advertised max_alternatives violation causes task-level VALIDATION_ERROR with no mutation.
• Protocol boundaries: 10 alternatives accepted when the seller ceiling permits; 11 rejected; 25 refinements accepted; 26 rejected.

Typed revision outcomes

• Budget satisfied, absent, wrong currency, below/above bounds.
• Product include/omit satisfied and unsatisfied.
• Structured criteria replacement with omitted criteria inherited.
• Exact alternative count with unique terms_digest values.
• Fewer distinct alternatives reported as partial / alternatives_unavailable.
• Duplicate alternatives or false revised claims fail validation.
• Commercial refusal, uninterpreted ask, unsupported dimension when capabilities are unknown, and source unavailable.
• Ordered multi-source batch with a valid mix of revised, partial, and unable results.

Lifecycle, mutation, and retry

• Every successful revision creates a new immutable proposal and leaves the source unchanged.
• Exact replay returns the same outcome; changed payload under the same idempotency key conflicts.
• Finalize creates a committed proposal with expires_at and unchanged terms/digest.
• Multi-finalize is atomic on success and failure; no partial holds.
• Acceptance before and after expiry.
• Amendment and cancellation successors from an accepted proposal.

Experimentation support

• Provide a stable training-agent test kit/profile whose deterministic responses match the storyboard fixtures.
• Document how SDK maintainers run the matrix against local buyer/seller implementations.
• Capture identifiers and proposal lineage so a developer can inspect every transition.
• Include negative variants that intentionally violate one invariant and explain the expected failure.

Acceptance criteria

• Scenarios are gated by advertised 3.2 lifecycle/capability support and do not penalize legacy or ask-only sellers for undeclared typed behavior.
• Current /sales floors and required-clean assertions include the negotiation core.
• Storyboard lint, fixture-resolution, contradiction, context-entity, and 3.0 compatibility checks remain green.
• The same matrix runs against the public training seller and is consumable by official SDK integration tests.

Additional required coverage (contract hardening in #6547, efe48f522e)

New typed constraints

• cpm, impressions, and flight each satisfied and violated; violated drafts must appear as partial/unable with constraint_unsatisfiable and the failing key echoed in unsatisfied_constraints.
• Co-occurring failures (violated constraint + alternatives shortfall) must use constraint_unsatisfiable, with the shortfall visible only through proposals.length.

Rejection and error shapes

• Undeclared-dimension rejection is now a MUST: task-level UNSUPPORTED_FEATURE before any mutation, with details matching error-details/unsupported-refinement-dimension.json.
• Capability dimension name is product_changes (renamed from product_selection).

Holds

• Failing finalize entry returns unable/hold_unavailable; otherwise-eligible siblings return unable/batch_aborted; no partial finalize batches.
• Double-finalize of a held draft fails task-level with INVALID_STATE.

Integrity

• Every returned proposal carries parent_proposal_id equal to source_proposal_id.
• terms_digest recomputes from RFC 8785 JCS of commercial_terms; a tampered digest or duplicate-terms "alternatives" must fail validation.

[bokelley]

Triage

Classification: Feature request
Bucket(s): compliance-suite, spec-adjacent enablement
Status: deferred
Milestone: 3.2.0 (#already set)

Blocked-on: #6547 — resurfaces on merge. The storyboard scenarios and terms_digest fixtures can't be finalized until the protocol wire shape from that PR lands; writing them against a moving surface risks contradiction failures on merge.

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Triaged by Claude Code. Session: https://claude.ai/code/session_013RcvZa8FmxT3vdhLPLRFye

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Generated by Claude Code

[bokelley]

Alignment note with RFC #6287 (competence advertisement): the behavioral coverage in this matrix — counter-proposal on partial (drafts returned rather than bare unable), alternative distinctness beyond trivial deltas, honest uninterpreted vs commercially_declined selection — doubles as the evidence base a future competence layer would attest against. Prefer generative/randomized runs over fixed fixtures for these rows so they measure behavior rather than memorization; that keeps them reusable as competence attestation rather than teach-to-test artifacts.

🤖 Generated with Claude Code