feat: resolve alias_of in cache pipeline

Packages with alias_of in releases.conf (e.g. dashd → dashcore,
golang → go) now get symlinked cache files so they resolve to the
same JSON as their target. 13 aliases total.

Added AliasOf as a proper field in installerconf.Conf, LinkAlias
method to fsstore, and alias handling in webicached's Run loop.

cmd/webicached/main.go

@@ -132,8 +132,10 @@ func (wc *WebiCache) Run(filterPkgs []string) {
 	log.Printf("refreshing %d packages", len(packages))
 	runStart := time.Now()
 
+	var aliases []pkgConf
 	for _, pkg := range packages {
-		if alias := pkg.conf.Extra["alias_of"]; alias != "" {
+		if pkg.conf.AliasOf != "" {
+			aliases = append(aliases, pkg)
 			continue
 		}
 
@@ -142,6 +144,13 @@ func (wc *WebiCache) Run(filterPkgs []string) {
 		}
 	}
 
+	// Create symlinks for aliases after all targets are written.
+	for _, pkg := range aliases {
+		if err := wc.Store.LinkAlias(pkg.name, pkg.conf.AliasOf); err != nil {
+			log.Printf("  ERROR alias %s → %s: %v", pkg.name, pkg.conf.AliasOf, err)
+		}
+	}
+
 	log.Printf("refreshed %d packages in %s", len(packages), time.Since(runStart))
 }
 

internal/installerconf/installerconf.go

@@ -98,6 +98,11 @@ type Conf struct {
 	// variant detection logic lives in Go code per-package.
 	Variants []string
 
+	// AliasOf names another package that this one mirrors.
+	// When set, the package has no releases of its own — it shares
+	// the cache output of the named target (e.g. dashd → dashcore).
+	AliasOf string
+
 	// Extra holds any unrecognized keys for forward compatibility.
 	Extra map[string]string
 }
@@ -153,6 +158,7 @@ func Read(path string) (*Conf, error) {
 	}
 
 	c.AssetFilter = raw["asset_filter"]
+	c.AliasOf = raw["alias_of"]
 
 	if v := raw["variants"]; v != "" {
 		c.Variants = strings.Fields(v)
@@ -164,7 +170,7 @@ func Read(path string) (*Conf, error) {
 		"base_url": true, "url": true,
 		"tag_prefix": true, "version_prefix": true, "version_prefixes": true,
 		"exclude": true, "asset_exclude": true, "asset_filter": true,
-		"variants": true,
+		"variants": true, "alias_of": true,
 	}
 	for k, v := range raw {
 		if !known[k] {

internal/storage/fsstore/fsstore.go

@@ -143,6 +143,27 @@ func atomicWrite(path string, data []byte) error {
 	return nil
 }
 
+// LinkAlias creates symlinks so that alias resolves to the same cache
+// files as target: alias.json → target.json, alias.updated.txt → target.updated.txt.
+func (s *Store) LinkAlias(alias, target string) error {
+	dir := filepath.Join(s.root, monthDir(time.Now()))
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("fsstore: mkdir: %w", err)
+	}
+
+	for _, ext := range []string{".json", ".updated.txt"} {
+		link := filepath.Join(dir, alias+ext)
+		dest := target + ext // relative symlink within same dir
+
+		// Remove existing link/file so we can recreate it.
+		os.Remove(link)
+		if err := os.Symlink(dest, link); err != nil {
+			return fmt.Errorf("fsstore: symlink %s → %s: %w", alias+ext, dest, err)
+		}
+	}
+	return nil
+}
+
 // parseTimestamp parses the "seconds.millis" format from .updated.txt files.
 func parseTimestamp(s string) time.Time {
 	f, err := strconv.ParseFloat(s, 64)