test: add comprehensive test suite - 5 test files, 65% coverage

- cli_test.go: 10 tests for list/search/extract/download commands
- serve_test.go: 11 tests for HTTP handlers and SSE progress
- http_test.go: 5 subtests for archive.org API
- download_test.go: 10 tests for download logic
- util_test.go: 7 tests for string/util helpers

Error paths covered: server errors, empty results, download failures,
extract failures, missing identifiers, ReadDir errors.

golangci-lint: 0 issues, go vet: clean

main.go

@@ -16,10 +16,10 @@ import (
 	"time"
 )
 
-const (
+var (
+	userAgent   = "akai-fetch/1.0"
 	iaSearchURL = "https://archive.org/advancedsearch.php"
 	iaBaseURL   = "https://archive.org"
-	userAgent   = "akai-fetch/1.0"
 )
 
 type SearchResult struct {
@@ -121,6 +121,15 @@ Serve flags:
 // ─── Search ────────────────────────────────────────────────────────────
 
 func cmdSearch(args []string) {
+	defer func() {
+		if e := recover(); e != nil {
+			if fe, ok := e.(fatalErr); ok {
+				osExit(fe.code)
+				return
+			}
+			panic(e)
+		}
+	}()
 	fs := flag.NewFlagSet("search", flag.ExitOnError)
 	query := fs.String("query", "subject:akai AND subject:sampler", "search query")
 	filter := fs.String("filter", "", "extra term AND-ed onto the query")
@@ -167,7 +176,7 @@ func searchArchive(query string, limit int) []SearchDoc {
 	if err != nil {
 		fatal("search request: %v", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
@@ -184,6 +193,15 @@ func searchArchive(query string, limit int) []SearchDoc {
 // ─── List ──────────────────────────────────────────────────────────────
 
 func cmdList(args []string) {
+	defer func() {
+		if e := recover(); e != nil {
+			if fe, ok := e.(fatalErr); ok {
+				osExit(fe.code)
+				return
+			}
+			panic(e)
+		}
+	}()
 	if len(args) < 1 {
 		fatal("usage: akai-fetch list <identifier>")
 	}
@@ -200,7 +218,7 @@ func cmdList(args []string) {
 	}
 }
 
-func getItemFiles(identifier string) []MetadataFile {
+var getItemFiles = func(identifier string) []MetadataFile {
 	u := fmt.Sprintf("%s/metadata/%s", iaBaseURL, url.PathEscape(identifier))
 	client := &http.Client{Timeout: 30 * time.Second}
 	req, _ := http.NewRequest("GET", u, nil)
@@ -209,7 +227,7 @@ func getItemFiles(identifier string) []MetadataFile {
 	if err != nil {
 		fatal("metadata request: %v", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
@@ -243,6 +261,15 @@ type downloadJob struct {
 }
 
 func cmdDownload(args []string) {
+	defer func() {
+		if e := recover(); e != nil {
+			if fe, ok := e.(fatalErr); ok {
+				osExit(fe.code)
+				return
+			}
+			panic(e)
+		}
+	}()
 	fs := flag.NewFlagSet("download", flag.ExitOnError)
 	identifier := fs.String("i", "", "archive.org item identifier")
 	idFile := fs.String("f", "", "file with identifiers (one per line)")
@@ -329,8 +356,10 @@ func cmdDownload(args []string) {
 	fmt.Printf("\nDownloaded %s total\n", humanSize(totalDownloaded))
 }
 
-func downloadFile(job downloadJob) (int64, error) {
-	os.MkdirAll(filepath.Dir(job.OutPath), 0755)
+var downloadFile = func(job downloadJob) (int64, error) {
+	if err := os.MkdirAll(filepath.Dir(job.OutPath), 0755); err != nil {
+		return 0, fmt.Errorf("mkdir: %w", err)
+	}
 
 	// Check if file already exists and has the expected size
 	if fi, err := os.Stat(job.OutPath); err == nil {
@@ -359,7 +388,7 @@ func downloadFile(job downloadJob) (int64, error) {
 	if err != nil {
 		return 0, fmt.Errorf("get: %w", err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 
 	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
 		return 0, fmt.Errorf("HTTP %d", resp.StatusCode)
@@ -369,7 +398,7 @@ func downloadFile(job downloadJob) (int64, error) {
 	if err != nil {
 		return 0, fmt.Errorf("open: %w", err)
 	}
-	defer outFile.Close()
+	defer func() { _ = outFile.Close() }()
 
 	written, err := io.Copy(outFile, resp.Body)
 	if err != nil {
@@ -381,6 +410,15 @@ func downloadFile(job downloadJob) (int64, error) {
 // ─── Extract ───────────────────────────────────────────────────────────
 
 func cmdExtract(args []string) {
+	defer func() {
+		if e := recover(); e != nil {
+			if fe, ok := e.(fatalErr); ok {
+				osExit(fe.code)
+				return
+			}
+			panic(e)
+		}
+	}()
 	fs := flag.NewFlagSet("extract", flag.ExitOnError)
 	isoDir := fs.String("dir", ".", "directory with ISO files")
 	outDir := fs.String("out", "./wavs", "output directory for WAVs")
@@ -462,6 +500,15 @@ func sanitiseISOName(path string) string {
 // ─── Pipeline ──────────────────────────────────────────────────────────
 
 func cmdPipeline(args []string) {
+	defer func() {
+		if e := recover(); e != nil {
+			if fe, ok := e.(fatalErr); ok {
+				osExit(fe.code)
+				return
+			}
+			panic(e)
+		}
+	}()
 	fs := flag.NewFlagSet("pipeline", flag.ExitOnError)
 	query := fs.String("query", "subject:akai AND subject:sampler", "search query")
 	filter := fs.String("filter", "", "extra term AND-ed onto the query")
@@ -527,9 +574,17 @@ func cmdPipeline(args []string) {
 
 // ─── Helpers ───────────────────────────────────────────────────────────
 
+var osExit = os.Exit
+
+type fatalErr struct {
+	code    int
+	message string
+}
+
 func fatal(format string, args ...any) {
-	fmt.Fprintf(os.Stderr, "error: "+format+"\n", args...)
-	os.Exit(1)
+	msg := fmt.Sprintf("error: "+format+"\n", args...)
+	fmt.Fprintf(os.Stderr, msg, args...)
+	panic(fatalErr{code: 1, message: msg})
 }
 
 func truncate(s string, n int) string {
@@ -556,6 +611,8 @@ func humanSize(bytes int64) string {
 }
 
 func init() {
-	// Ensure we can parse flags even with -count or other test flags
-	flag.CommandLine.Parse([]string{})
+	if err := flag.CommandLine.Parse([]string{}); err != nil {
+		// In init context, best we can do is note the issue
+		fmt.Fprintf(os.Stderr, "flag init: %v\n", err)
+	}
 }