## What problem does this PR solve?
Go test files are never compiled in CI — only production binaries via
`go build`. This allowed a missing `"sort"` import in
`metadata_filter_test.go` to be merged without detection.
## Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
## Changes
- Add `go test -count=1 ./internal/...` step after Go build in CI
workflow
- Fix missing `"sort"` import in `metadata_filter_test.go` (pre-existing
compile error)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
### Description
This PR syncs the `documentServiceIface` interface and introduces
handler methods for document preview, artifact fetching, and downloading
in the Go API. It also ensures that strict dataset alignment and access
checks are enforced when retrieving or downloading documents.
Furthermore, this PR introduces comprehensive unit tests for both the
newly added Handler and Service methods to ensure robustness and prevent
future regressions.
### Key Changes
* **Router & Handler Integration**:
* Added and wired new API endpoints in `internal/router/router.go`.
* Synchronized the `documentServiceIface` with `GetDocumentArtifact`,
`GetDocumentPreview`, and `DownloadDocument`.
* Implemented handlers for these endpoints in
`internal/handler/document.go`.
* **Access & Validation Enforcement**:
* Refactored `internal/service/document.go` to strictly check if a
document belongs to the requested dataset before allowing downloads or
previews.
* Added robust artifact file sanitization (`sanitizeArtifactFilename`)
and attachment handling (`shouldForceArtifactAttachment`).
* **Comprehensive Unit Testing**:
* **Handler Layer (`internal/handler/document_test.go`)**: Added mock
service implementations and Gin router tests covering success,
not-found, and internal error states for all 3 new endpoints.
* **Service Layer (`internal/service/document_test.go`)**: Added
extensive business logic tests including dataset mismatch checks,
non-existent document checks, and artifact file validation.
