fix: check MkdirAll errors, add gopls to toolchain

- serve.go/cmdAPIDownload: check MkdirAll error, use absolute path
- main.go/cmdDownload,cmdExtract: check MkdirAll errors
- check-toolchain.sh: verify gopls installation
- mise.toml: add gopls install task
- AGENTS.md: document gopls as dev dependency

AGENTS.md

@@ -5,6 +5,7 @@
 ```bash
 mise trust        # trust the mise.toml config (first time only)
 mise install      # installs go 1.26, node 22
+mise run gopls    # install gopls (Go LSP) — one-time dev setup
 ```
 
 All build/run tasks are defined in `mise.toml`:

main.go

@@ -250,7 +250,9 @@ func cmdDownload(args []string) {
 	jobs := fs.Int("jobs", 2, "concurrent downloads")
 	_ = fs.Parse(args)
 
-	os.MkdirAll(*outDir, 0755)
+	if err := os.MkdirAll(*outDir, 0755); err != nil {
+		fatal("create %s: %v", *outDir, err)
+	}
 
 	var identifiers []string
 	if *identifier != "" {
@@ -383,7 +385,9 @@ func cmdExtract(args []string) {
 	jobs := fs.Int("jobs", 2, "concurrent extractions")
 	_ = fs.Parse(args)
 
-	os.MkdirAll(*outDir, 0755)
+	if err := os.MkdirAll(*outDir, 0755); err != nil {
+		fatal("create %s: %v", *outDir, err)
+	}
 
 	entries, err := os.ReadDir(*isoDir)
 	if err != nil {

mise.toml

@@ -20,3 +20,4 @@ docker-build = "docker build -t akai-fetch ."
 check-toolchain = "bash scripts/check-toolchain.sh"
 check-docker-toolchain = "bash scripts/check-docker-toolchain.sh"
 check-all = { run = "bash scripts/check-toolchain.sh && echo '' && bash scripts/check-docker-toolchain.sh" }
+gopls = "go install golang.org/x/tools/gopls@latest"

scripts/check-toolchain.sh

@@ -98,6 +98,19 @@ fi
 
 echo ""
 
+# ─── gopls (Go LSP) ────────────────────────────────────────────────────
+echo "gopls (Go language server):"
+if command -v gopls &>/dev/null; then
+    gopls_ver=$(gopls version 2>/dev/null)
+    ok "gopls found: $gopls_ver"
+else
+    warn "gopls not found (recommended for IDE support)"
+    echo "    Install: go install golang.org/x/tools/gopls@latest"
+    echo "    (ensure $(go env GOPATH)/bin is in PATH)"
+fi
+
+echo ""
+
 # ─── Node ──────────────────────────────────────────────────────────────
 echo "Node:"
 if command -v node &>/dev/null; then

serve.go

@@ -158,7 +158,13 @@ func handleAPIDownload(w http.ResponseWriter, r *http.Request) {
 		outDir = "."
 	}
 
-	os.MkdirAll(outDir, 0755)
+	if abs, err := filepath.Abs(outDir); err == nil {
+		outDir = abs
+	}
+	if err := os.MkdirAll(outDir, 0755); err != nil {
+		writeJSON(w, map[string]any{"error": fmt.Sprintf("create %s: %v", outDir, err)})
+		return
+	}
 
 	files := getItemFiles(identifier)
 	if len(files) == 0 {
@@ -287,8 +293,6 @@ func handleAPIExtract(w http.ResponseWriter, r *http.Request) {
 		outDir = "./wavs"
 	}
 
-	os.MkdirAll(outDir, 0755)
-
 	entries, err := os.ReadDir(isoDir)
 	if err != nil {
 		writeJSON(w, map[string]any{"error": err.Error()})