## Why
`github_alpine` is the Alpine/apk analog of the existing `github_deb`/`github_rpm` metadata-only remotes. It lets a plain GitHub-releases repo of `.apk` files be consumed as a real apk repository without artifactapi ever precaching the packages: it scans the repo's releases, derives each package's `.PKGINFO` from a ranged prefix fetch, synthesizes a per-arch `APKINDEX.tar.gz` from the cached metadata, and redirects the actual `.apk` downloads to a backend `releases_remote`. It stacks on the apk-local branch, reusing that work's alpine APKINDEX generator, `.apk`/`.PKGINFO` parser, Q1 pull-checksum, and `AlpineMetadata` store.
## How
- **`pkg/models`**: add `PackageGitHubAlpine` to the enum + validators (and test).
- **`internal/provider/alpine/github.go`**: the `github_alpine` provider. `ServeRemote` serves per-arch `<arch>/APKINDEX.tar.gz` (reusing `generateAPKIndex` over arch-filtered `AlpineMetadata` rows, `normalizeIndexPath` for apk's `./` dot-segment), 302-redirects `*.apk` to `{proxyBaseURL}/api/v1/remote/{releases_remote}/{path}`, and cold-starts with a 503 + `Retry-After`. `scanWithState` lists releases with ETag/If-None-Match and incrementally derives/prunes. `deriveAsset` does a **ranged GET of just the front of the `.apk`** — the control gzip stream carrying `.PKGINFO` sits near the front — doubling the range on truncation; it parses `.PKGINFO` and computes the `C:` Q1 checksum (`Q1`+base64(sha1(control stream))). `FilePath` = the github-relative asset path so the redirect resolves.
- **`internal/provider/alpine/syncer.go`**: a parallel background `Syncer` (own worker pool, shared rate limiter, deduped queue, DB lease), separate from the deb/rpm syncers.
- **`internal/database/alpine_github_sync.go`** + `github_alpine_sync_state` table: `ListGitHubAlpineRemotes` + Claim/Release per-remote sync lease, kept separate from the deb/rpm tables.
- **`internal/server/server.go`**: construct + `Run` the alpine syncer alongside deb/rpm and register it in the `PackageType→Primer` map (priming on create then flows through the existing generic `remotes.go` path).
The rpm/deb providers, syncers, and tables are untouched — this adds parallel alpine equivalents and reuses shared helpers already present in the alpine package.
## Tests
Mirror the deb github tests: scan derives `.PKGINFO`/Q1 from a ranged prefix of a `testsupport.MinimalApk` served over an httptest range server (no full download); diff/prune; pattern filter; per-arch `ServeRemote` routing (index served per-arch and grouped, dot-segment collapse, `.apk` → 302, cold-start 503, warm 200, canceled-request-serves-cache); DB lease prevents a second replica; prime bypasses the recency window. `go build`/`go vet`/`go mod tidy` clean, `make test` (-race) green, pre-commit green.
Reviewed-on: #115
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>
unkin-agent
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