feat(schemas): regen for AdCP 3.0 GA — custom pricing + experimental_features

[bokelley]

Closes #204. Regenerates Pydantic models from the upstream AdCP 3.0 GA protocol bundle (adcontextprotocol/adcp#2422).

Summary

• New custom variant in vendor pricing discriminated union (VendorPricing, VendorPricingOption). Requires description and metadata (non-empty), optional currency. Consumers dispatching on .root.model should add a "custom" branch — recommended default is operator review, not auto-select.
• per_unit pricing variant (added in an earlier 3.0 rc) is now in the generated models alongside custom.
• New optional experimental_features: list[str] | None on GetAdcpCapabilitiesResponse. Dot-namespaced ids (brand.rights_lifecycle, governance.campaign, trusted_match.core) declared by sellers that implement experimental surfaces.
• x-status: experimental annotations on Brand Rights, Campaign Governance, and TMP — metadata only; datamodel-code-generator ignores unknown x-* extensions, so type output is unchanged.
• Idempotency now carries a required supported: bool (pulled in via the latest bundle). Four test fixtures updated to pass supported=True.

Wire format

No breaks. All changes are additive.

Test plan

• make regenerate-schemas succeeds
• ruff check src/ passes
• mypy src/adcp/ passes (671 source files)
• pytest tests/ passes (1696 passed, 14 skipped)
• Verified VendorPricing5/VendorPricingOption11 carry model: Literal["custom"] with required description + metadata
• Verified experimental_features field on GetAdcpCapabilitiesResponse in both protocol/ and bundled/protocol/

🤖 Generated with Claude Code

[bokelley]

Expert review follow-up

Ran the PR past three expert reviewers. Summary of findings and actions:

Addressed in 9ff08c9 (follow-up commit)

[must-fix from code-reviewer] _ensure_idempotency_capability in src/adcp/client.py ignored the new required supported field. A seller declaring supported=false, replay_ttl_seconds=86400 (contradictory but type-valid) passed the strict gate silently. Fixed to raise IdempotencyUnsupportedError on any of:

• adcp.idempotency missing entirely
• supported=false (seller does not dedupe — naive retry double-processes)
• supported=true but replay_ttl_seconds is None (seller is spec-incomplete)

Updated IdempotencyUnsupportedError to carry a reason string so logs show which mode tripped. Added three tests covering each failure mode plus the happy path.

Not addressed (acknowledged, scoped out of this PR)

• Metadata.minProperties: 1 not enforced on custom pricing (ad-tech-protocol-expert, python-expert). The JSON Schema says the metadata object on custom-pricing variants must be non-empty, but datamodel-codegen flattens additionalProperties: true + optional summary_for_operator to a model that accepts {}. This is a codegen limitation, not something this regen introduced. Worth a follow-up as a post_generate_fixes.py hook or a hand-written model_validator that survives regen.
• Idempotency conditional if supported then require ttl not enforced at the model level (ad-tech-protocol-expert). Same class of codegen gap (draft-07 if/then isn't emitted). The client-side gate fix above compensates for the buyer path; a seller building capabilities responses should still own spec conformance.
• VendorPricing / VendorPricingOption / ExperimentalFeature / capability-response Idempotency not re-exported via adcp.types public API (python-expert). Tests in test_capabilities.py reach into adcp.types.generated_poc.protocol.get_adcp_capabilities_response directly — this pre-existed this PR. Adding public re-exports + semantic aliases (CustomPricing, etc.) is worth doing but is a distinct DX improvement, not a regen correctness fix.

Confirmed correct / no action needed

• Custom-variant fields match spec: model, description (min_length=1), metadata required; currency (ISO-4217 pattern) and ext optional. extra="allow" preserves escape-hatch semantics for vendor-specific metadata keys.
• experimental_features field correctly propagates the dot-namespace pattern and is optional (matches wire contract — seller absence = "implements none").
• Making Idempotency.supported required matches the spec posture ("clients MUST NOT assume a default").
• Multiple-inheritance subclasses on VendorPricingOption7..11 dispatch deterministically via the model Literal discriminant under Pydantic v2. No MRO pitfall.
• No SDK-internal dispatch on pricing .model exists (verified via grep) — consumers are responsible for adding a custom branch per the issue's guidance.
• aliases.py intentionally omits per-variant signal-pricing aliases (see existing comment at lines 1062-1067); adding CustomPricing here alone would be inconsistent with the established pattern.