feat: add output-rate override and stronger offline wav tests

cmd/offline/main.go

@@ -14,12 +14,16 @@ func main() {
     configPath := flag.String("config", "", "path to JSON config")
     out := flag.String("output", "", "output IQ file path")
     duration := flag.Duration("duration", 2*time.Second, "generation duration")
+    outputRate := flag.Int("output-rate", 0, "override composite output sample rate")
     flag.Parse()
 
     cfg, err := cfgpkg.Load(*configPath)
     if err != nil {
         log.Fatalf("load config: %v", err)
     }
+    if *outputRate > 0 {
+        cfg.FM.CompositeRateHz = *outputRate
+    }
 
     gen := offpkg.NewGenerator(cfg)
     if err := gen.WriteFile(*out, *duration); err != nil {

internal/audio/wav_test.go

@@ -10,6 +10,9 @@ func TestPCM16ToSample(t *testing.T) {
     if pcm16ToSample(32767) <= 0 {
         t.Fatal("expected positive sample")
     }
+    if pcm16ToSample(-32768) < -1.0 {
+        t.Fatal("expected clamped lower bound")
+    }
 }
 
 func TestLoadWAVSource(t *testing.T) {
@@ -36,3 +39,14 @@ func TestLoadWAVSource(t *testing.T) {
     }
     _ = src.NextFrame()
 }
+
+func TestRejectInvalidWAV(t *testing.T) {
+    dir := t.TempDir()
+    path := filepath.Join(dir, "bad.wav")
+    if err := os.WriteFile(path, []byte("nope"), 0o644); err != nil {
+        t.Fatalf("write wav: %v", err)
+    }
+    if _, err := LoadWAVSource(path); err == nil {
+        t.Fatal("expected wav load error")
+    }
+}

internal/offline/generator_test.go

@@ -3,6 +3,7 @@ package offline
 import (
     "os"
     "path/filepath"
+    "strings"
     "testing"
     "time"
 
@@ -36,3 +37,13 @@ func TestWriteFile(t *testing.T) {
         t.Fatal("expected non-empty file")
     }
 }
+
+func TestSummaryUsesToneFallback(t *testing.T) {
+    cfg := cfgpkg.Default()
+    cfg.Audio.InputPath = ""
+    g := NewGenerator(cfg)
+    summary := g.Summary(10 * time.Millisecond)
+    if !strings.Contains(summary, "source=tones") {
+        t.Fatalf("unexpected summary: %s", summary)
+    }
+}