Support and compatibility

Contract	Current development support
Go	Exactly 1.26.5 for development and release verification
Spice provisional minimum	v0.0.0-20260805222830-a2ecd56df246
Spice current	v0.0.0-20260806053623-2ec6f862073f
Operating systems	Windows, Linux, and macOS; Linux integration evidence
Architectures	amd64 and arm64 compilation through the core public API
Transport security	Verified STARTTLS or implicit TLS; TLS 1.2 minimum
Authentication	SMTP AUTH PLAIN only after TLS
Real-system acceptance	Mailpit v1.30.0 image digest sha256:0059ef81e492a7192af3816281eed6859eb078bd7bdc58b76757c13e10e53a7d
Release renderer	github.com/spice-framework/development/cmd/spice-dev at v0.0.0-20260806132124-4c308d1b9fda
Release verifier tool	github.com/spice-framework/toolchain/cmd/spice-library-release-verify at v0.0.0-20260806133530-71211498297c
Release trust anchor	Configured at security/release/ed25519-public.pem; DER SHA-256 fingerprint fc7de5d2c7594c6e1871da5f2dc46969d29a9aa2d6a5babaca47fc1ae51b621e
Release secret contract	Only repository secret SPICE_LIBRARY_RELEASE_SIGNING_KEY is explicitly mapped to the protected reusable workflow; inheritance is forbidden

The first preview tag will define the first published minimum Spice version. Until then, the exact direct Spice requirement in go.mod is the provisional minimum development line. The machine-readable spice-compatibility.json also pins the current compatibility endpoint; that endpoint is a forward- compatibility signal, not an unbounded runtime dependency.

The compatibility runner resolves both versions through Go’s module tooling, uses isolated alternate modfiles, asserts the exact MVS selection, and then runs vet plus shuffled race tests over every product package with GOPROXY=off. It rejects any change to product Go files, go.mod, go.sum, or vendor. CI publishes parallel minimum/current jobs, while local make verify always proves both boundaries. A release may raise the minimum only through an intentional go.mod change, an updated compatibility manifest and table, and green minimum/current evidence. A moving branch name is never accepted as a compatibility version or written to release metadata.

net/smtp provides a deliberately bounded protocol subset. SMTPUTF8, DSN, custom SASL mechanisms, and connection pooling are not claimed. Applications that require those capabilities should use a separately reviewed transport behind the public mail.Sender interface.

The pinned central signer and independent verifier are the protected production path. Windows and Linux CI render the same inert central plan twice under vendor-only offline resolution and require byte-identical unsigned artifacts. The committed public trust anchor establishes the identity against which every published release must be independently verified.