The first-run installers (install.sh, install.ps1) downloaded and
extracted the bsk release archive with no integrity check, even though
the in-app `bsk update` path treats a sha256 checksum as mandatory
(update.rs bails with "does not include a sha256 checksum; cannot
safely auto-update"). The release version.json already carries a
per-asset sha256 (render-version-json.mjs renders with --dist), so the
installers can verify the same way.
Both installers now fetch version.json once (pinned and latest), read
`assets[<platform>].sha256`, and verify the downloaded archive's sha256
before extracting:
- install.sh: POSIX sed to parse the field (no jq dependency), and
sha256sum/shasum to compute the digest.
- install.ps1: Invoke-RestMethod + Get-FileHash.
A checksum mismatch is fatal (fail-closed, matching `bsk update`). A
missing manifest/checksum, or the absence of a sha256 tool, only skips
verification with a warning, so the first-run bootstrap still works on
minimal/offline machines.
Validation: `sh -n` / `bash -n`; functional test of the sed extraction
against a realistic version.json and of compute_sha256 against
sha256sum. The installers are not exercised by CI (no shell harness).
Co-authored-by: Claude <noreply@anthropic.com>
