[freshtonic]

Layer 5 of the CIP-5203 stack. Implements CIP-5310.

• New crate stack-kms-vault: a hand-written Transit client (encrypt, decrypt, rewrap).
• stack_kms_vendor::bound binds the AAD into the wrapped key itself. Vault ignores context on a key that is not derived, and Azure (CIP-5309) needs the same mechanism.
• Auth: token, AppRole, and Kubernetes (native only).
• Tests: recorded fixtures, the contract suite, and a vault server -dev CI job.
• The crate is staged in the stack-kms-vendor release group.

Decisions are in docs/plans/2026-11-05-key-vendor-backends-decisions.md (CIP-5310 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: the one-item batch_input wire format stays, and the multi-item batches and VaultConfig::batch_size are gone. The fixtures were recorded again from vault server -dev 1.20.4. The dev-server tests passed locally.

[freshtonic]

Replaced by #1627, 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.