feat(media-buy): resolve seller acceptance-policy catalogs

[bokelley]

Summary

Add Python SDK parity for seller acceptance-policy catalog discovery from adcontextprotocol/adcp#6749 and adcontextprotocol/adcp#6794.

Required behavior

• Generate models for acceptance context, catalogs, profile references, profiles, requirements, and rules.
• Safely fetch the advertised HTTPS catalog with no credentials or redirects, public-address/DNS protections, and response/time bounds.
• Verify catalog_digest against exact response bytes before parsing and schema/model validation.
• Resolve seller-default and product profile IDs with cross-list uniqueness and exact policy/profile version and digest checks.
• Compose rules restrictively and preserve unknown for partial coverage, omissions, unavailable catalogs, and undisclosed seller policy.
• Expose an idiomatic buyer helper that explains likely allowed, prohibited, requires_disclosure, requires_setup, and requires_review outcomes while clearly marking discovery as advisory.
• Cache within the advertised capability lifetime and support capabilities-change invalidation.

Compatibility and tests

• valid reference-seller catalog and cross-SDK golden fixtures;
• exact-byte digest mismatch;
• redirects, URL credentials, private addresses, DNS rebinding, timeout, and oversized bodies;
• duplicate IDs and unresolved or digest-mismatched policy/profile pins;
• complete vs. partial coverage and restrictive default/product composition;
• stable, typed diagnostics for fetch, safety, digest, schema, and resolution failures.

Acceptance criteria

• Python buyers get the same normalized acceptance assessment as JavaScript buyers from identical capability, product, catalog, and context inputs.
• Missing or undisclosed information never becomes an implicit allow decision.
• Legacy sellers without the capability remain supported as unknown.

Upstream: adcontextprotocol/adcp#6749
Implementation: adcontextprotocol/adcp#6794

[bokelley]

Triage

Classification: Feature request
Bucket(s): client, validation, cross-repo (no matching repo labels exist for these buckets)
Status: ready-for-human

What the experts said:

• ad-tech-protocol-expert: BLOCKER — acceptance-policy schemas are absent from the bundled schema cache through 3.2.0-beta.5; SDK must not generate types until adcp#6749 and #6794 merge and publish. FLAG — catalog TTL anchor (HTTPS Cache-Control vs. capabilities.last_updated) needs spec clarification before the caching layer can be implemented correctly.
• security-reviewer: FLAGs — catalog fetcher must reuse the existing IP-pinned transport (_owned_pinned_client), not just DNS pre-flight checks, to close the TOCTOU rebinding window. Must use hmac.compare_digest() (not ==) for digest comparison. Must reject any URL where urllib.parse.urlparse().username or .password is non-None before opening a connection. Cache key must include catalog_digest alongside the URL to prevent stale-catalog serving after a digest rotation.
• code-reviewer: BLOCKER — adding new schemas to the codegen input set shifts the traversal-order numbering of all existing anonymous variant classes in generated_poc/, breaking the aliases.py layer (documented in CLAUDE.md). Implementation needs an explicit numbering-stability strategy before any PR can land cleanly.

My take: Two blockers gate implementation — spec PRs must land in the schema cache before models are generated, and a codegen plan must be in hand to protect aliases.py stability. The fetch surface also has enough security-sensitive detail (IP pinning, timing-safe comparison, URL credential rejection) that this warrants human sign-off before a branch starts.

Questions for @bokelley:

1. Are adcp#6749 and #6794 merge-imminent, or still actively evolving?
2. What digest algorithm does the spec mandate — SHA-256 over raw compressed bytes or the decoded body?
3. What anchors the catalog cache TTL — HTTPS Cache-Control, capabilities.last_updated, or a dedicated field in the capability declaration?

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Triaged by Claude Code. Session: https://claude.ai/code/session_01Y3fVeVeNbGmUquV3Bjn6Q2

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Generated by Claude Code