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

tests/test_markdown_renderer.py

@@ -0,0 +1,45 @@
+from anthropic.types import Message, TextBlock, ThinkingBlock, ToolUseBlock, Usage
+
+from beaver_gateway.frontends.markdown import renderer
+
+
+def _message(*blocks: object) -> Message:
+    return Message(
+        id="m",
+        type="message",
+        role="assistant",
+        model="x",
+        content=list(blocks),  # type: ignore[arg-type]
+        stop_reason="end_turn",
+        stop_sequence=None,
+        usage=Usage(input_tokens=1, output_tokens=1),
+    )
+
+
+def test_tool_calls_leave_no_blank_lines() -> None:
+    message = _message(
+        TextBlock(type="text", text="first"),
+        ToolUseBlock(type="tool_use", id="t1", name="Bash", input={"command": "ls"}),
+        ToolUseBlock(type="tool_use", id="t2", name="Read", input={"file_path": "x"}),
+        ToolUseBlock(type="tool_use", id="t3", name="Grep", input={"pattern": "y"}),
+        TextBlock(type="text", text="second"),
+    )
+    assert renderer.render_assistant_message(message) == (
+        "### Assistant:\n\nfirst\n\nsecond\n"
+    )
+
+
+def test_thinking_renders_as_collapsed_callout() -> None:
+    message = _message(
+        ThinkingBlock(type="thinking", thinking="a\nb", signature="s"),
+        TextBlock(type="text", text="answer"),
+    )
+    assert renderer.render_assistant_message(message) == (
+        "### Assistant:\n\n> [!thinking]-\n> a\n> b\n\nanswer\n"
+    )
+
+
+def test_user_scaffold_matches_rendered_user_turn_shape() -> None:
+    body = renderer.append_to_body("### Assistant:\n\nhi\n", renderer.USER_SCAFFOLD)
+    assert body.endswith("\n\n---\n\n### User:\n\n")
+    assert renderer.render_user_text("q").startswith("### User:\n\n")