feat(backend): Implement multi-take sequence differencing and text formatting utility

src/synthesis_formatter.py

@@ -0,0 +1,42 @@
+def format_takes_diff(takes: dict[str, list[dict]]) -> str:
+ if not takes:
+  return ""
+ 
+ histories = list(takes.values())
+ if not histories:
+  return ""
+
+ min_len = min(len(h) for h in histories)
+ common_prefix_len = 0
+ for i in range(min_len):
+  first_msg = histories[0][i]
+  if all(h[i] == first_msg for h in histories):
+   common_prefix_len += 1
+  else:
+   break
+
+ shared_lines = []
+ for i in range(common_prefix_len):
+  msg = histories[0][i]
+  shared_lines.append(f"{msg.get('role', 'unknown')}: {msg.get('content', '')}")
+ 
+ shared_text = "=== Shared History ==="
+ if shared_lines:
+  shared_text += "\n" + "\n".join(shared_lines)
+
+ variation_lines = []
+ if len(takes) > 1:
+  for take_name, history in takes.items():
+   if len(history) > common_prefix_len:
+    variation_lines.append(f"[{take_name}]")
+    for i in range(common_prefix_len, len(history)):
+     msg = history[i]
+     variation_lines.append(f"{msg.get('role', 'unknown')}: {msg.get('content', '')}")
+    variation_lines.append("")
+ else:
+  # Single take case
+  pass
+
+ variations_text = "=== Variations ===\n" + "\n".join(variation_lines)
+
+ return shared_text + "\n\n" + variations_text