add Variants []string to Asset and Dist, keep Extra for version info

Extra is for version-related sort metadata (build numbers, etc.).
Variants captures build qualifiers like "rocm", "jetpack5",
"fxdependent", "installer" — things the resolver should skip by
default unless explicitly requested.

Also update format classification docs: most formats (.pkg, .deb,
.dmg, .msi) are extractable — only .exe is ambiguous and needs
the "installer" variant tag when it's not the actual binary.

GO_WEBI.md

@@ -364,8 +364,9 @@ type Asset struct {
     Libc     string  // "musl"
     Format   string  // ".tar.gz"
     Channel  string  // "stable"
-    Extra    string  // "" (base) or "rocm", "jetpack5", "fxdependent"
-    Download string  // full URL
+    Extra    string    // extra version info for sorting
+    Variants []string  // ["rocm"], ["installer"], ["fxdependent"], etc.
+    Download string    // full URL
     ...
 }
 ```
@@ -378,10 +379,9 @@ hardware or runtime configuration beyond OS/arch/libc:
 - `fxdependent`, `fxdependentWinDesktop` — .NET framework-dependent (pwsh)
 - `profile` — debug profiling build (bun)
 - `source` — source archive, not a binary
-- `installer` — non-extractable installer format (.pkg, .msi, .deb, .rpm,
-  .dmg, .msixbundle, .AppImage, .exe-installer)
+- `installer` — `.exe` that is a GUI installer, not the actual tool binary
 
-The resolver **deprioritizes** assets with non-empty `Extra` — they're only
+The resolver **deprioritizes** assets with non-empty `Variants` — they're only
 selected when the user explicitly requests that variant (e.g., `?variant=rocm`).
 The full API still serves them for broader use cases.
 
@@ -392,20 +392,23 @@ selection naturally.
 
 ### Format Classification
 
-All assets are stored — nothing is dropped at classification time. Installer
-formats are tagged with `Extra = "installer"` so the resolver skips them by
-default while the full API can still serve them:
+All assets are stored — nothing is dropped at classification time.
 
-- `.pkg` (macOS installer)
-- `.msi` (Windows installer)
-- `.deb`, `.rpm` (Linux package managers)
-- `.dmg` (macOS disk image)
-- `.sh` (self-extracting installer scripts)
-- `.msixbundle`, `.AppImage`
-- `.exe` when it's an installer, not the actual binary
+Most formats are extractable and need no special tagging — the file extension
+is enough signal for the install scripts:
 
-Webi's default install path uses **extractable archives** (tar.gz, tar.xz, zip,
-7z) and **bare binaries** only.
+- `.tar.gz`, `.tar.xz`, `.tar.zst`, `.zip`, `.7z` — standard archives
+- `.pkg` — macOS: extractable via `pkgutil --expand-full` (flat files, no install)
+  See: https://coolaj86.com/articles/how-to-extract-pkg-files-and-payload/
+- `.deb` — extractable via `ar x` + `tar xf data.tar.*`
+- `.dmg` — mountable via `hdiutil attach`
+- `.msi` — extractable via `msiexec /a` or `lessmsi`
+- `.AppImage` — self-contained, chmod +x and run
+
+The one ambiguous format is `.exe` — it could be a bare binary (the actual tool)
+or a GUI installer (which can't be automated). Assets where `.exe` is an installer
+(not the tool itself) get `Variants: ["installer"]` so the resolver skips them
+by default.
 
 ### Legacy Export Filtering
 
@@ -464,8 +467,9 @@ behavior must be preserved for backward compatibility.
 
 - **Shell out to `node releases.js`?** No — all source types are implemented in
   Go. The Go pipeline fetches and classifies everything directly.
-- **Asset.Extra vs new Variant type?** `Extra` (string) serves the purpose.
-  The resolver already deprioritizes non-empty Extra. Keep it simple.
+- **Asset.Extra vs Variants?** `Extra` stays as version-related sort info.
+  New `Variants []string` field captures build qualifiers (rocm, installer,
+  fxdependent). Resolver deprioritizes assets with any variants.
 
 ## Current Node.js Architecture (Reference)
 

internal/resolve/resolve.go

@@ -27,17 +27,19 @@ type Dist struct {
 	Size     int64
 	LTS      bool
 	Date     string
-	Extra    string
+	Extra    string   // extra version info for sorting
+	Variants []string // build qualifiers: "installer", "rocm", "fxdependent", etc.
 }
 
 // Query describes what the caller wants.
 type Query struct {
-	OS      buildmeta.OS
-	Arch    buildmeta.Arch
-	Libc    buildmeta.Libc
-	Formats []string // acceptable formats (e.g. ".tar.gz", ".zip"), in preference order
-	Channel string   // "stable" (default), "beta", etc.
-	Version string   // version prefix constraint ("24", "24.14", ""), empty = latest
+	OS       buildmeta.OS
+	Arch     buildmeta.Arch
+	Libc     buildmeta.Libc
+	Formats  []string // acceptable formats (e.g. ".tar.gz", ".zip"), in preference order
+	Channel  string   // "stable" (default), "beta", etc.
+	Version  string   // version prefix constraint ("24", "24.14", ""), empty = latest
+	Variants []string // if non-empty, only match assets with these variants
 }
 
 // Match is the resolved release.
@@ -134,7 +136,7 @@ func Best(dists []Dist, q Query) *Match {
 			ver:        ver,
 			archRank:   aRank,
 			formatRank: fRank,
-			hasExtra:   d.Extra != "",
+			hasVariants: len(d.Variants) > 0,
 		}
 
 		if best == nil || c.betterThan(best) {
@@ -219,7 +221,7 @@ type candidate struct {
 	ver        lexver.Version
 	archRank   int
 	formatRank int
-	hasExtra   bool // true if dist.Extra is non-empty (GPU variant, etc.)
+	hasVariants bool // true if dist has variant qualifiers (GPU, installer, etc.)
 }
 
 // betterThan returns true if c is a better match than other.
@@ -229,9 +231,9 @@ func (c *candidate) betterThan(other *candidate) bool {
 	if cmp != 0 {
 		return cmp > 0
 	}
-	// Prefer base variant over GPU/special variants (rocm, jetpack, etc.)
-	if c.hasExtra != other.hasExtra {
-		return !c.hasExtra
+	// Prefer base build over variant builds (rocm, installer, etc.)
+	if c.hasVariants != other.hasVariants {
+		return !c.hasVariants
 	}
 	if c.archRank != other.archRank {
 		return c.archRank < other.archRank

internal/storage/storage.go

@@ -29,7 +29,8 @@ type Asset struct {
 	Libc     string
 	Format   string
 	Download string
-	Extra    string
+	Extra    string   // extra version info for sorting (e.g. build metadata)
+	Variants []string // build qualifiers: "installer", "rocm", "jetpack5", "fxdependent", etc.
 }
 
 // PackageData is the full set of assets for a package, plus metadata.