feat: report active offline source and fallback state

docs/README.md

@@ -16,6 +16,7 @@ Current no-hardware sources:
 - generated stereo tones via config
 - 16-bit PCM WAV file input via `audio.inputPath`
 - basic sample-rate adaptation for WAV sources into the composite generation path
+- transparent tone fallback if the configured WAV source cannot be loaded
 
 ### Tone configuration
 
@@ -67,6 +68,7 @@ This is the current closest no-hardware stand-in for the future transmit pipelin
 
 `cmd/offline` generates a deterministic no-hardware IQ/composite-style file using the repository's output backend path.
 This is still an MVP path, but it is a more realistic offline artifact than the JSON-only dry-run.
+The generator summary now reports whether the active source is tones, wav, or tone-fallback.
 
 ## Release posture
 

internal/offline/generator.go

@@ -20,6 +20,12 @@ type frameSource interface {
     NextFrame() audio.Frame
 }
 
+type SourceInfo struct {
+    Kind       string
+    SampleRate float64
+    Detail     string
+}
+
 type Generator struct {
     cfg cfgpkg.Config
 }
@@ -28,13 +34,14 @@ func NewGenerator(cfg cfgpkg.Config) *Generator {
     return &Generator{cfg: cfg}
 }
 
-func (g *Generator) sourceFor(sampleRate float64) frameSource {
+func (g *Generator) sourceFor(sampleRate float64) (frameSource, SourceInfo) {
     if g.cfg.Audio.InputPath != "" {
         if src, err := audio.LoadWAVSource(g.cfg.Audio.InputPath); err == nil {
-            return audio.NewResampledSource(src, sampleRate)
+            return audio.NewResampledSource(src, sampleRate), SourceInfo{Kind: "wav", SampleRate: float64(src.SampleRate), Detail: g.cfg.Audio.InputPath}
         }
+        return audio.NewConfiguredToneSource(sampleRate, g.cfg.Audio.ToneLeftHz, g.cfg.Audio.ToneRightHz, g.cfg.Audio.ToneAmplitude), SourceInfo{Kind: "tone-fallback", SampleRate: sampleRate, Detail: g.cfg.Audio.InputPath}
     }
-    return audio.NewConfiguredToneSource(sampleRate, g.cfg.Audio.ToneLeftHz, g.cfg.Audio.ToneRightHz, g.cfg.Audio.ToneAmplitude)
+    return audio.NewConfiguredToneSource(sampleRate, g.cfg.Audio.ToneLeftHz, g.cfg.Audio.ToneRightHz, g.cfg.Audio.ToneAmplitude), SourceInfo{Kind: "tones", SampleRate: sampleRate, Detail: "generated"}
 }
 
 func (g *Generator) GenerateFrame(duration time.Duration) *output.CompositeFrame {
@@ -68,7 +75,7 @@ func (g *Generator) GenerateFrame(duration time.Duration) *output.CompositeFrame
     })
     rdsSamples := rdsEnc.Generate(samples)
 
-    source := g.sourceFor(sampleRate)
+    source, _ := g.sourceFor(sampleRate)
 
     for i := 0; i < samples; i++ {
         t := float64(i) / sampleRate
@@ -121,9 +128,10 @@ func (g *Generator) WriteFile(path string, duration time.Duration) error {
 }
 
 func (g *Generator) Summary(duration time.Duration) string {
-    source := "tones"
-    if g.cfg.Audio.InputPath != "" {
-        source = g.cfg.Audio.InputPath
+    sampleRate := float64(g.cfg.FM.CompositeRateHz)
+    if sampleRate <= 0 {
+        sampleRate = 228000
     }
-    return fmt.Sprintf("offline frame: freq=%.1fMHz sampleRate=%d duration=%s outputDrive=%.2f stereo=%t rds=%t source=%s", g.cfg.FM.FrequencyMHz, g.cfg.FM.CompositeRateHz, duration.String(), g.cfg.FM.OutputDrive, g.cfg.FM.StereoEnabled, g.cfg.RDS.Enabled, source)
+    _, info := g.sourceFor(sampleRate)
+    return fmt.Sprintf("offline frame: freq=%.1fMHz sampleRate=%d duration=%s outputDrive=%.2f stereo=%t rds=%t source=%s detail=%s", g.cfg.FM.FrequencyMHz, g.cfg.FM.CompositeRateHz, duration.String(), g.cfg.FM.OutputDrive, g.cfg.FM.StereoEnabled, g.cfg.RDS.Enabled, info.Kind, info.Detail)
 }

internal/offline/generator_test.go

@@ -47,3 +47,13 @@ func TestSummaryUsesToneFallback(t *testing.T) {
         t.Fatalf("unexpected summary: %s", summary)
     }
 }
+
+func TestSummaryUsesFallbackLabelOnBadWAV(t *testing.T) {
+    cfg := cfgpkg.Default()
+    cfg.Audio.InputPath = "missing.wav"
+    g := NewGenerator(cfg)
+    summary := g.Summary(10 * time.Millisecond)
+    if !strings.Contains(summary, "source=tone-fallback") {
+        t.Fatalf("unexpected summary: %s", summary)
+    }
+}