[freshtonic]

Layer 4 of the CIP-5203 stack. Implements CIP-5307 (ADR-0014).

• New crate stack-kms-aws: a hand-written AWS KMS JSON client with in-crate SigV4 (no aws-sdk). It wraps the root key with Encrypt and unwraps it with Decrypt. The AAD is bound through EncryptionContext.
• Credentials: static and environment, IRSA, the ECS container endpoint, and IMDSv2 (native only), cached and refreshed before expiry.
• HttpVendorTransport (native, in stack-kms-vendor).
• Tests: SigV4 vectors, recorded fixtures, the contract suite, and a LocalStack job that runs on PRs.
• The crate is staged for crates.io, with release = false.

Decisions are in docs/plans/2026-11-05-key-vendor-backends-decisions.md (CIP-5307 sections).

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[github-actions]

Mutation testing (cargo-mutants, --in-diff, stack-auth + stack-encrypt)

No mutants were generated for the changed lines.

[freshtonic]

Scope reduced (2026-11-12). This branch was rebuilt from one final tree by path, and the follow-up PRs #1555 to #1563 were folded in. The plan is docs/plans/2026-11-12-key-vendor-backends-scope-reduction.md; the decision log's "Scope reduction" section records each change. Decisions: no stack-encrypt change, no v2 leaf, and the wrapped data key mode deferred.

In this PR: no GenerateDataKey, and no cipherstash:descriptor in the encryption context. The fixtures were brought up to date with the record AAD. The LocalStack test passed locally.

[freshtonic]

Replaced by #1626, in the new stack #1633. The code is the same, rebased onto the latest next. The ADRs are now ADR-0013 and ADR-0014, and the text about the wrapped data key mode is removed.