fix(backends,markdown): stream turn events live, no blank lines for tool blocks

src/beaver_gateway/frontends/markdown/renderer.py

@@ -33,7 +33,9 @@ __all__ = [
 # Empty ``### User:`` block appended after each assistant reply so the
 # human has an obvious place to type the next turn. Parser drops empty
 # user blocks, so this doesn't re-trigger dispatch on its own.
-USER_SCAFFOLD = "### User:\n"
+# Blank line after the header, like every rendered turn - the file stays
+# symmetric whether the human or the gateway wrote the marker.
+USER_SCAFFOLD = "### User:\n\n"
 
 
 # Default 4-backtick fence so tool results that contain literal ```` ``` ````
@@ -73,7 +75,12 @@ def render_assistant_message(message: Message) -> str:
     """
     parts: list[str] = ["### Assistant:", ""]
     for block in message.content:
-        parts.extend(_render_block(block))
+        lines = list(_render_block(block))
+        if not lines:
+            # Tool calls render to nothing - no separator for them either,
+            # or every tool leaves a blank line behind.
+            continue
+        parts.extend(lines)
         parts.append("")
     return "\n".join(parts).rstrip() + "\n"