Strip emoji from calendar event titles before rendering

ImageFont.load_default() has no emoji glyphs, and PIL/FreeType don't
skip an unsupported codepoint -- they substitute a visible ".notdef"
tofu box, which read as a rendering glitch rather than "not supported."
Stripped instead (covers the standard emoji Unicode blocks, skin-tone
modifiers, and the ZWJ used to combine them into one glyph), with
surrounding whitespace collapsed.

server/app/calendar_render.py

@@ -11,6 +11,7 @@ from __future__ import annotations
 
 import calendar as calendar_module
 import io
+import re
 from datetime import date, datetime, timedelta
 from zoneinfo import ZoneInfo
 
@@ -102,6 +103,40 @@ def _fmt_time(dt: datetime) -> str:
     return text if text else "12:00 AM"
 
 
+# ImageFont.load_default() (used everywhere in this module -- see the
+# module docstring) has no emoji glyphs. PIL/FreeType don't just skip an
+# unsupported codepoint, they substitute a ".notdef" tofu box (a visible
+# filled rectangle), which reads as a rendering glitch rather than "emoji
+# not supported" on an actual panel. Stripped before drawing rather than
+# left to render as tofu. Covers the standard Unicode emoji blocks (plus
+# skin-tone modifiers, the zero-width joiner used to combine them into
+# one glyph, and the variation selector that forces emoji presentation)
+# -- these block ranges are stable even as new individual emoji get
+# added within them, so this doesn't need updating as emoji sets grow.
+_EMOJI_PATTERN = re.compile(
+    "["
+    "\U0001F1E6-\U0001F1FF"  # regional indicator symbols (flag emoji)
+    "\U0001F300-\U0001F5FF"  # misc symbols & pictographs
+    "\U0001F600-\U0001F64F"  # emoticons
+    "\U0001F680-\U0001F6FF"  # transport & map symbols
+    "\U0001F900-\U0001F9FF"  # supplemental symbols & pictographs
+    "\U0001FA70-\U0001FAFF"  # symbols & pictographs extended-A
+    "\U0001F3FB-\U0001F3FF"  # skin-tone modifiers
+    "\U00002600-\U000026FF"  # misc symbols (☀☂☕ etc.)
+    "\U00002700-\U000027BF"  # dingbats (✂✈✉ etc.)
+    "\U0000FE0F"             # variation selector-16 (emoji presentation)
+    "\U0000200D"             # zero-width joiner
+    "]+"
+)
+
+
+def _strip_emoji(text: str) -> str:
+    """Removes emoji (see _EMOJI_PATTERN above) and collapses whatever
+    whitespace that leaves behind -- "\U0001F389 Birthday party" becomes
+    "Birthday party", not " Birthday party"."""
+    return re.sub(r"\s+", " ", _EMOJI_PATTERN.sub("", text)).strip()
+
+
 def _truncate_to_width(draw: ImageDraw.ImageDraw, text: str, font: ImageFont.ImageFont, max_width: int) -> str:
     """Pixel-width-aware truncation (unlike device.py's char-count
     _truncate, tuned for a fixed firmware font at a fixed size) -- this
@@ -313,7 +348,7 @@ def _draw_agenda_day(img: Image.Image, draw: ImageDraw.ImageDraw, day: date, eve
         color = _event_color(event, owners_seen, palette_rgb)
         draw.rounded_rectangle([text_x0, y + 2, text_x0 + 10, y + row_h - 7], radius=3, fill=color)
         time_str = "All day" if event["all_day"] else _fmt_time(_event_start(event, tz))
-        line = f"{time_str}  {event['summary']}"
+        line = f"{time_str}  {_strip_emoji(event['summary'])}"
         draw_text(img, (text_x0 + 18, y), _truncate_to_width(draw, line, body_font, text_w - 18), body_font)
         y += row_h
 
@@ -428,7 +463,8 @@ def _build_week(events: list[dict], browse_offset: int, orientation: str, tz: Zo
                 break
             color = _event_color(event, owners_seen, palette_rgb)
             draw.rounded_rectangle([x0 + 4, y + 1, x0 + 11, y + row_h - 5], radius=2, fill=color)
-            text = event["summary"] if event["all_day"] else f"{_fmt_time(_event_start(event, tz))[:-3]} {event['summary']}"
+            summary = _strip_emoji(event["summary"])
+            text = summary if event["all_day"] else f"{_fmt_time(_event_start(event, tz))[:-3]} {summary}"
             draw_text(img, (x0 + 16, y), _truncate_to_width(draw, text, chip_font, col_w - 20), chip_font)
             y += row_h