Sardis v0.8.1: Protocol Conformance Hardening for AP2/TAP

v0.8.1 is a protocol-hardening release focused on correctness over breadth. We tightened AP2 payment semantics, strengthened TAP validation paths, and added a source-mapped conformance baseline so engineering decisions stay anchored to canonical AP2, TAP, UCP, and x402 references.

What Changed

• AP2 payment semantics hardened -- Payment mandates now include explicit ai_agent_presence and transaction_modality signals (human_present or human_not_present) and are enforced in verification.
• TAP header checks tightened -- Signature input validation now rejects unsupported message signature algorithms by default.
• Linked object signature hooks added -- agenticConsumer and agenticPaymentContainer validation supports canonical signature-base building and optional verification hooks.
• Conformance evidence improved -- New tests cover invalid alg, nonce mismatch, and signature-failure paths for TAP and modality guardrails for AP2.

Why This Release Matters

Before scaling integrations, protocol interpretation drift is one of the highest engineering risks. v0.8.1 reduces this risk by making protocol assumptions explicit in code and test gates.

• Lower interoperability risk across AP2/TAP counterparties
• Better auditability of policy and protocol decisions
• Stronger defaults for pre-prod design partner environments

Source Mapping and Governance

We now maintain a protocol source map that links canonical references to concrete enforcement points in code and tests. This keeps conformance work reviewable and repeatable over time.

See the Changelog and the release docs for implementation details.