feat: reimplement WAV extraction in Go (replaces extract_wavs.sh)

extract.go replaces the bash script with idiomatic Go:
- akaiutil process communication via stdin/stdout pipes
- partition enumeration (df output parsing)
- volume enumeration (dir output parsing per partition)
- sample2wavall per volume with WAV count aggregation

runAkaiutil is a package-level var — tests stub it with canned
output to verify parsing without a real akaiutil binary or ISO.

Removed: findScript(), -tool flag on extract, os/exec from main.go
Kept: extract_wavs.sh as a standalone utility (no longer called)

extract.go

@@ -0,0 +1,202 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func findAkaiutil() (string, error) {
+	if env := os.Getenv("AKAIUTIL"); env != "" {
+		if fi, err := os.Stat(env); err == nil && !fi.IsDir() {
+			return env, nil
+		}
+	}
+
+	candidates := []string{
+		filepath.Join(filepath.Dir(os.Args[0]), "akaiutil"),
+		filepath.Join(filepath.Dir(os.Args[0]), "third_party", "akaiutil", "akaiutil"),
+		filepath.Join("third_party", "akaiutil", "akaiutil"),
+		"akaiutil",
+	}
+	for _, p := range candidates {
+		if fi, err := os.Stat(p); err == nil && !fi.IsDir() {
+			return p, nil
+		}
+	}
+	return "", fmt.Errorf("akaiutil not found — set AKAIUTIL env var or run: make akaiutil")
+}
+
+var runAkaiutil = func(isoPath, commands string) (string, error) {
+	bin, err := findAkaiutil()
+	if err != nil {
+		return "", err
+	}
+
+	cmd := exec.Command(bin, "-r", isoPath)
+	cmd.Stderr = nil
+
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return "", fmt.Errorf("stdin pipe: %w", err)
+	}
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return "", fmt.Errorf("stdout pipe: %w", err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return "", fmt.Errorf("start akaiutil: %w", err)
+	}
+
+	stdin.Write([]byte(commands))
+	stdin.Close()
+
+	output, _ := io.ReadAll(stdout)
+	cmd.Wait()
+
+	return string(output), nil
+}
+
+type volInfo struct {
+	Part string
+	Name string
+}
+
+func listPartitions(isoPath string) ([]string, error) {
+	out, err := runAkaiutil(isoPath, "df\nq\n")
+	if err != nil {
+		return nil, err
+	}
+
+	re := regexp.MustCompile(`^\s+([A-Z])\s+`)
+	var parts []string
+	for _, line := range strings.Split(out, "\n") {
+		if m := re.FindStringSubmatch(line); m != nil {
+			parts = append(parts, m[1])
+		}
+	}
+	if len(parts) == 0 {
+		return []string{"A"}, nil
+	}
+	return parts, nil
+}
+
+func listVolumes(isoPath string, partitions []string) ([]volInfo, error) {
+	var cmds strings.Builder
+	for _, p := range partitions {
+		fmt.Fprintf(&cmds, "cd /disk0/%s\n", p)
+		fmt.Fprintf(&cmds, "dir\n")
+	}
+	cmds.WriteString("q\n")
+
+	out, err := runAkaiutil(isoPath, cmds.String())
+	if err != nil {
+		return nil, err
+	}
+
+	rePrompt := regexp.MustCompile(`/disk0/([A-Z])\s*>`)
+	reEntry := regexp.MustCompile(`^\s+\d+\s+(.+?)\s+-\s+`)
+
+	var vols []volInfo
+	currentPart := ""
+
+	for _, line := range strings.Split(out, "\n") {
+		if m := rePrompt.FindStringSubmatch(line); m != nil {
+			currentPart = m[1]
+			continue
+		}
+		if m := reEntry.FindStringSubmatch(line); m != nil {
+			name := strings.TrimRight(m[1], " ")
+			if currentPart != "" && name != "" {
+				vols = append(vols, volInfo{Part: currentPart, Name: name})
+			}
+		}
+	}
+	return vols, nil
+}
+
+func runExtraction(isoPath, baseDir string, vols []volInfo) (int, error) {
+	var cmds strings.Builder
+	for _, v := range vols {
+		safe := sanitiseISOName(v.Name)
+		if safe == "" {
+			safe = "volume"
+		}
+		volDir := filepath.Join(baseDir, safe)
+		os.MkdirAll(volDir, 0755)
+
+		nav := strings.ReplaceAll(v.Name, " ", "_")
+		fmt.Fprintf(&cmds, "lcd %s\n", volDir)
+		fmt.Fprintf(&cmds, "cd /disk0/%s/%s\n", v.Part, nav)
+		fmt.Fprintf(&cmds, "sample2wavall\n")
+	}
+	fmt.Fprintf(&cmds, "lcd /\nq\n")
+
+	out, err := runAkaiutil(isoPath, cmds.String())
+	if err != nil {
+		return 0, err
+	}
+
+	re := regexp.MustCompile(`exported\s+(\d+)\s+file`)
+	total := 0
+	for _, line := range strings.Split(out, "\n") {
+		if m := re.FindStringSubmatch(line); m != nil {
+			n, _ := strconv.Atoi(m[1])
+			total += n
+		}
+	}
+	return total, nil
+}
+
+func extractWAVs(isoPath, outDir string) (int, error) {
+	parts, err := listPartitions(isoPath)
+	if err != nil {
+		return 0, fmt.Errorf("enumerate partitions: %w", err)
+	}
+
+	vols, err := listVolumes(isoPath, parts)
+	if err != nil {
+		return 0, fmt.Errorf("enumerate volumes: %w", err)
+	}
+	if len(vols) == 0 {
+		return 0, nil
+	}
+
+	isoBase := sanitiseISOName(filepath.Base(isoPath))
+	baseDir := filepath.Join(outDir, isoBase)
+	os.MkdirAll(baseDir, 0755)
+
+	return runExtraction(isoPath, baseDir, vols)
+}
+
+func extractISO(isoPath, outDir string) (string, error) {
+	isoOutDir := filepath.Join(outDir, sanitiseISOName(filepath.Base(isoPath)))
+
+	if fi, err := os.Stat(isoOutDir); err == nil && fi.IsDir() {
+		var wavCount int
+		filepath.WalkDir(isoOutDir, func(p string, d os.DirEntry, err error) error {
+			if err == nil && !d.IsDir() && strings.HasSuffix(strings.ToLower(d.Name()), ".wav") {
+				wavCount++
+			}
+			return nil
+		})
+		if wavCount > 0 {
+			return fmt.Sprintf("skipped (%d WAVs exist)", wavCount), nil
+		}
+	}
+
+	start := time.Now()
+	total, err := extractWAVs(isoPath, outDir)
+	elapsed := time.Since(start).Round(time.Second)
+	if err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("Total WAV files: %d (%s)", total, elapsed), nil
+}