Add conversation, review, lifecycle, and merge writes using native GitCafe contracts. Keep the existing stack merge flow and handle credential continuation in the adapter.

Preserve reviewed revisions and durable operation identities across retries and uncertain responses. Keep operation outcomes intact through the RPC JSON codec.

Verified with focused tests and production browser acceptance in disposable repositories. Native restack reconciliation remains an upstream issue documented locally in the gc2 checkout.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0ac6e-37c6-7564-8ae6-06d08186b96e
Co-authored-by: Amp <amp@ampcode.com>