In a chat, a blank line comes after the messages of each author

The transcript asked for a gap between sender groups, but an empty Text
renders as no line at all, so the gap never showed. A blank line now
closes each author's messages, also before a new day's divider, where
the platform has 20 rows or more. The 14 rows of the Cardputer Zero keep
the transcript dense. A cached slice that starts with the gap pins its
day divider one line down.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -18,6 +18,9 @@ can change how things behave. It does not only add new things.
   message has the same mark, so a message that names you is easy to see. On the PicoCalc,
   the console cannot draw a light fill, so there the `★` alone marks your messages. Before,
   your messages showed only the `★`.
+- **In a chat, a blank line comes after the messages of each author.** Thus the
+  conversation is easier to follow when many people write. The Cardputer Zero has no
+  blank line there, because its screen has only 14 rows and each row shows a message.
 
 ## [0.11.1] - 2026-10-13
 

meshterm/ui/chat.py

@@ -75,11 +75,26 @@ _URL_GUTTER = 2
 _URL_CODES = False
 
 
+#: Whether a blank line closes the messages of each author. It costs one row for each
+#: group. The PicoCalc (26 rows) and a terminal (24) have the rows for it. The 14 rows of
+#: the Cardputer Zero do not: there a blank line on each group is a message less on the
+#: screen (JP, 2026-10-13).
+_GROUP_GAP = True
+
+#: The fewest rows (``Platform.readable_rows``) for which a transcript has that blank line.
+_GROUP_GAP_MIN_ROWS = 20
+
+
 @on_platform
 def _bind(platform: Platform) -> None:
-    """Hang codes under URLs where the platform draws them (now and at each switch)."""
-    global _URL_CODES
+    """Bind the transcript to the platform (now and at each switch).
+
+    The platform says whether codes hang under URLs, and whether it has the rows for a
+    blank line after each author.
+    """
+    global _URL_CODES, _GROUP_GAP
     _URL_CODES = platform.url_codes
+    _GROUP_GAP = platform.readable_rows >= _GROUP_GAP_MIN_ROWS
 
 
 #: The maximum width of a footer hint, in cells (refer to the UX standards).
@@ -613,16 +628,21 @@ class ChatScreen(Screen):
                 and cached_ids[idx] == id(message)
                 and cached_acked[idx] == message.acked
             )
+            # A blank line closes the messages of an author, where the platform has the rows
+            # for it (:data:`_GROUP_GAP`). It is the first line of the slice of the message
+            # that starts the next group, so a cached slice brings it back with it.
+            gap = _GROUP_GAP and bool(lines) and (new_day or group != prev_group)
             if reusable:
                 start = cached_boundaries[idx - 1] if idx > 0 else 0
                 slice_lines = cached_lines[start : cached_boundaries[idx]]
                 if new_day:
-                    self._sticky_headers.append((len(lines), [slice_lines[0]]))
+                    at = int(gap)  # the divider comes after the gap
+                    self._sticky_headers.append((len(lines) + at, [slice_lines[at]]))
                 lines += slice_lines
             else:
+                if gap:
+                    lines.append("")
                 if new_day:
-                    if lines:
-                        lines += render_lines(Text(""), width)
                     # A day divider is the section heading of this transcript: it pins to the
                     # top row while its day scrolls under it, and ^PgUp/^PgDn step by it.
                     # Thus it has the heading style of the app (``── Label ──`` in the bold
@@ -634,8 +654,6 @@ class ChatScreen(Screen):
                     self._sticky_headers.append((len(lines), [divider[0]]))
                     lines += divider
                 if new_day or group != prev_group:
-                    if not new_day and lines:
-                        lines += render_lines(Text(""), width)  # gap between sender groups
                     header = self._group_header(sender, message)
                     lines += render_lines(header, width)
                 if selected:

tests/test_chat.py

@@ -1545,6 +1545,47 @@ def test_channel_own_messages_do_not_merge_with_remote_namesake() -> None:
     assert rendered.count("you") == 1 and rendered.count("★ Me") == 1
 
 
+def test_a_blank_line_closes_each_author_where_the_rows_allow() -> None:
+    """A terminal and the PicoCalc put a blank line after the messages of each author.
+
+    The blank line also comes before the divider of a new day, and never before the first
+    line. The 14 rows of the Cardputer Zero have no row to spare for it. A second paint
+    reads the cached lines, and the divider of the second day still pins at its own line,
+    not at the blank line before it.
+    """
+    from datetime import datetime, timedelta, timezone
+
+    from meshterm.platforms import CARDPUTER_ZERO, REGULAR, set_platform
+
+    base = datetime(2026, 7, 5, 14, 24, tzinfo=timezone.utc)
+
+    def at(minutes: int) -> datetime:
+        return base + timedelta(minutes=minutes)
+
+    def transcript() -> list[ChatMessage]:
+        return [
+            ChatMessage(text="Alice: hi", is_channel=True, channel_idx=0, created_at=at(0)),
+            ChatMessage(text="Alice: again", is_channel=True, channel_idx=0, created_at=at(1)),
+            ChatMessage(text="Bob: yo", is_channel=True, channel_idx=0, created_at=at(2)),
+            ChatMessage(text="Bob: later", is_channel=True, channel_idx=0, created_at=at(1440)),
+        ]
+
+    set_platform(REGULAR)
+    screen = _channel_screen(transcript())
+    lines = [_strip_ansi(line) for line in screen._render_grouped(53)]
+    assert lines[0].startswith("──") and lines[1] == "Alice"
+    assert lines[4] == "" and lines[5] == "Bob"  # after the two messages of Alice
+    assert lines[7] == "" and lines[8].startswith("── Mon")  # after Bob, before the new day
+    assert lines.count("") == 2
+    first = list(screen._sticky_headers)
+    screen._render_grouped(53)  # the cached lines
+    assert screen._sticky_headers == first and [at for at, _ in first] == [0, 8]
+
+    set_platform(CARDPUTER_ZERO)
+    screen = _channel_screen(transcript())
+    assert "" not in [_strip_ansi(line) for line in screen._render_grouped(53)]
+
+
 def test_a_mention_of_our_name_takes_our_chip() -> None:
     """A message that names us is easy to see. A mention of each other node is as before."""
     screen = _channel_screen([], self_name="Me", self_key=_OUR_KEY)