[freshtonic]

Layer 8 of the CIP-5203 stack. Implements CIP-5311 (ADR-0014).

• The encrypt guest links stack-kms-vendor and the four vendor crates. A vendor request is a step of the step loop: the guest pauses with the signed request, and the host performs it, as it does for ZeroKMS. A credential is a step too. The host supplies short-lived credentials only: AWS temporary credentials, or an OAuth or Vault token. There is no RSA in the guest; the GCP service-account login is behind a default feature.
• Go API: WithKeyVendor, WithKeysetRecords, WithDefaultKeyset, WithRootKeyTTL, ErrNoZeroKMS. The vendor types are AWSKMS, GoogleCloudKMS, AzureKeyVault, VaultTransit and StaticKey. Credential seams are added; no vendor SDK is added to go.mod.
• A vendor-only client needs no CipherStash credentials.
• One guest with all backends.
• Tests: hermetic Go tests with the static key, and with AWS through a fake RoundTripper that checks SigV4 and call counts.

Decisions are in docs/plans/2026-11-05-key-vendor-backends-decisions.md (CIP-5311 section).

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[github-actions]

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

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[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 guest drops the per-settle and v2 paths and the ForeignBackend status. Folded in: #1560, #1561 and the Go part of #1563. The Go docs state the index key gap. The CLI PR #1533 is not in this stack: it is a separate PR on #1531, because a stack is linear and the Go and CLI work do not depend on each other.

[freshtonic]

Replaced by #1630, 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.