Add detailed debugging for lm_gen.step() returning None

v1.4.8 - Debug text generation failure:
- Added detailed logging for lm_gen.step() calls
- Check if step() returns None vs actual tensor data
- Log tensor shapes and types at each step
- Will reveal why 'NoneType' object is not subscriptable
- Progress: Audio encoding ✅, C++ compiler ✅, debugging step API

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app.py

@@ -21,7 +21,7 @@ from fastapi.responses import JSONResponse, HTMLResponse
 import uvicorn
 
 # Version tracking
-VERSION = "1.4.7"
+VERSION = "1.4.8"
 COMMIT_SHA = "TBD"
 
 # Configure logging
@@ -182,11 +182,21 @@ def transcribe_audio_moshi(audio_data: np.ndarray, sample_rate: int = 24000) ->
                             for i in range(audio_tokens.shape[-1]):
                                 # Extract single timestep tokens
                                 code_step = audio_tokens[:, :, i:i+1]  # [B, 8, 1]
+                                logger.info(f"🔍 Step {i}: code_step shape: {code_step.shape}")
+                                
                                 # Generate tokens using step method
                                 tokens_out = lm_gen.step(code_step)  # [B, 1 + 8, 1]
-                                # Extract text token (index 1)
-                                text_token = tokens_out[:, 1:2, :]  # [B, 1, 1]
-                                text_tokens.append(text_token)
+                                logger.info(f"🔍 Step {i}: tokens_out type: {type(tokens_out)}, value: {tokens_out}")
+                                
+                                if tokens_out is not None:
+                                    logger.info(f"🔍 Step {i}: tokens_out shape: {tokens_out.shape}")
+                                    # Extract text token (index 1)
+                                    text_token = tokens_out[:, 1:2, :]  # [B, 1, 1]
+                                    text_tokens.append(text_token)
+                                    logger.info(f"✅ Step {i}: Added text token shape: {text_token.shape}")
+                                else:
+                                    logger.error(f"❌ Step {i}: lm_gen.step() returned None!")
+                                    break
                                 
                             # Concatenate all text tokens
                             if text_tokens: