[turinglambdaai]

Summary

• add raco rivet acceptance and a versioned, product-owned rivet-acceptance.rktd contract
• validate required kind/platform coverage before execution and launch argv directly without a shell
• bound suite duration/output, propagate failures, and require fresh generated evidence for native UI/package/release claims
• surface acceptance readiness through inspect, scaffold the initial contract, and document the CI/agent workflow
• record product acceptance as desktop closeout Gate D5

Why

A native host compiling on Windows, macOS, and Linux does not prove that product behavior or UI flows match. This adds one auditable definition of done while leaving assertions and platform-native accessibility drivers with the product.

Verification

• git diff --check passes
• new RackUnit coverage exercises scaffold defaults, platform filtering, failed-suite propagation, missing coverage, restricted evidence paths, mandatory UI evidence, and stale-evidence rejection
• local Racket execution is blocked on this Windows machine before Rivet code starts by Illegal System DLL Relocation; GitHub Actions is the runtime verification path for this PR

Taskly was intentionally not modified: its local checkout was behind the remote and could not be fast-forwarded from this environment.