fix: prune RPM metadata when a local file is evicted (#100)

Follow-up to #99.

## Why

Evicting or deleting a local RPM removed the \`local_files\` row but left its \`rpm_metadata\` behind. Since generated repodata is built from \`rpm_metadata\`, \`primary.xml\` kept advertising a package that no longer exists, producing 404s for clients that tried to fetch it.

## Changes

- Add \`PostDeleteHook\` and \`MetadataDeleter\` provider interfaces (symmetric to the existing \`PostUploadHook\`/\`MetadataStore\`), plus a \`DeleteRPMMetadata\` DB method.
- Implement \`AfterDelete\` in the RPM provider to drop the metadata row for the deleted file.
- Route both local delete paths — the new \`evictLocal\` and the existing files handler's \`remove\` — through a shared \`deleteLocalFile\` helper that removes the file then runs the provider's post-delete hook. Non-RPM providers have no hook, so nothing changes for them.
- Cover the cleanup with a dockerised test.

Reviewed-on: #100
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

internal/api/v2/local_evict_cleanup_test.go

@@ -0,0 +1,75 @@
+package v2
+
+import (
+	"context"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+
+	"git.unkin.net/unkin/artifactapi/internal/database"
+	"git.unkin.net/unkin/artifactapi/internal/provider"
+	_ "git.unkin.net/unkin/artifactapi/internal/provider/rpm" // register the rpm provider so its PostDeleteHook runs
+	"git.unkin.net/unkin/artifactapi/pkg/models"
+)
+
+// TestLocalEvictCleansRPMMetadata verifies that evicting an RPM from a local
+// repo also removes the derived rpm_metadata row, so generated repodata stops
+// listing the deleted package.
+func TestLocalEvictCleansRPMMetadata(t *testing.T) {
+	if testDSN == "" {
+		t.Skip("Docker unavailable")
+	}
+	ctx := context.Background()
+	db, err := database.New(testDSN)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	const repo = "rpm-evict-cleanup"
+	if err := db.CreateRemote(ctx, &models.Remote{Name: repo, PackageType: models.PackageRPM, RepoType: models.RepoTypeLocal}); err != nil {
+		t.Fatal(err)
+	}
+
+	const hash = "sha256:bb22"
+	const path = "Packages/example-0.1.0-1.x86_64.rpm"
+	if err := db.UpsertBlob(ctx, hash, "blobs/bb/22", 2048, "application/x-rpm"); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.CreateLocalFile(ctx, repo, path, hash); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.InsertRPMMetadata(ctx, &provider.RPMMetadata{
+		RepoName: repo, FilePath: path, ContentHash: hash,
+		Name: "example", Version: "0.1.0", Release: "1", Arch: "x86_64",
+		Requires: []provider.RPMDep{}, Provides: []provider.RPMDep{},
+		Files: []provider.RPMFile{}, Changelogs: []provider.RPMChangelog{},
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	h := NewObjectsHandler(db)
+	router := chi.NewRouter()
+	router.Route("/locals/{name}/objects", func(r chi.Router) {
+		r.Delete("/*", h.LocalRoutes().ServeHTTP)
+	})
+
+	del := httptest.NewRequest("DELETE", "/locals/"+repo+"/objects/"+path, nil)
+	dw := httptest.NewRecorder()
+	router.ServeHTTP(dw, del)
+	if dw.Code != 204 {
+		t.Fatalf("evict = %d, want 204", dw.Code)
+	}
+
+	if f, _ := db.GetLocalFile(ctx, repo, path); f != nil {
+		t.Fatalf("local file still present after evict: %+v", f)
+	}
+	entries, err := db.ListRPMMetadataEntries(ctx, repo)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(entries) != 0 {
+		t.Fatalf("rpm_metadata still present after evict: %+v", entries)
+	}
+}