D1022 — Releases carry keyless build provenance and SBOMs, and the installer never skips the manifest

Decision. release.yml attests what it publishes with actions/attest-build-provenance (GitHub artifact attestations, Sigstore, keyless through the job's OIDC identity): the goreleaser job attests every asset listed in sha256sums.txt and the file itself, the docker job attests the image digest and pushes the attestation to ghcr. The image is built with provenance: mode=max and sbom: true; GoReleaser publishes one SPDX SBOM per platform binary (sboms:, syft installed at a pinned version and archive sha256). install.sh fails when sha256sums.txt cannot be downloaded, as install.ps1 already did.

Why. sha256sums.txt is published by the same job as the binaries: whoever can replace an asset can replace the manifest with it, so it proves integrity, not origin. An attestation ties a file to this repository's workflow and commit, and needs no long-lived signing key to guard. In install.sh a failed manifest request installed unverified, so dropping that one request was enough to skip verification; the premise that older tags have no manifest is false (every release since v0.1.0 ships one), so there is no boundary to keep and no reason to tolerate its absence.

Alternatives rejected. - A long-lived signing key (cosign key pair, GPG): a secret to store, rotate and lose. - Making the installers verify attestations: requires gh on every machine that installs; the checksum stays the installers' contract and attestation is for whoever has gh. - A version boundary below which a missing manifest is tolerated: no such release exists. - Cataloging the archives (artifacts: archive) for the SBOMs: it skips the raw darwin/linux assets, which are not archives. - Attesting the image in preview.yml: previews are not releases and nothing verifies them.

Consequences. New release assets (cartographer_<version>_<os>_<arch>.sbom.json) and attestations in the repository's attestation store; no existing asset is renamed (test/install/goreleaser_guard.sh pins the names and that the SBOMs exist). The jobs that attest hold id-token: write and attestations: write, so a new step in them is reviewed as one that can mint an identity for this repository. A bump of syft is an edit of its version and sha256. docs/deployment.md §Verifying a release carries the commands.