Add an optional TV-static overlay during track start/end

Shows a brief static effect (sparse noise specks, bundled as a small
animated GIF) over the album art during the first/last 5 seconds of a
track, as a transition cue. Implemented via render.Stack compositing a
bundled images/static.gif over the zoomed art -- pixlet has no per-frame
procedural drawing hook, so the noise is pre-baked with Pillow rather
than generated at render time; render.Image plays animated GIFs back
natively, independent of the zoom's own animation timeline.

Tuned the GIF's frame count/density/flicker speed down after an initial
version pushed total payload within a few percent of the 460KB device
limit on some album art -- more, faster-changing frames give WebP less
opportunity to dedupe near-identical frames, which compounds with the
zoom animation's own dedupe needs. Final version adds ~50KB regardless of
art complexity, verified via a pinned-cover test harness for reliable
before/after comparison (the live station's currently-playing track kept
changing between test runs otherwise).

Added a "Static overlay" On/Off schema toggle (default On) per request.

subwave_nowplaying.star

@@ -11,6 +11,7 @@ load("http.star", "http")
 load("cache.star", "cache")
 load("time.star", "time")
 load("animation.star", "animation")
+load("images/static.gif", STATIC_ASSET = "file")
 
 DEFAULT_STATION_URL = ""
 NOWPLAYING_TTL = 20
@@ -90,6 +91,13 @@ COLOR_SCHEMES = {
 }
 DEFAULT_COLOR_SCHEME = "cyberpunk"  # matches the station's own site theme
 
+# How many seconds into a track's start, or before its end, the "static"
+# overlay shows over the album art (a bundled animated GIF of sparse noise
+# specks over a transparent background -- images/static.gif). Only used
+# when the "Static overlay" schema field is enabled.
+STATIC_OVERLAY_SECONDS = 5
+DEFAULT_STATIC_OVERLAY = "on"
+
 # How far in the album art zoom goes, relative to its fully-zoomed-out rest
 # state (see _art_widget below for why scale never goes below 1.0).
 ZOOM_LEVELS = {
@@ -150,6 +158,7 @@ def main(config):
     colors = COLOR_SCHEMES.get(config.get("color_scheme", DEFAULT_COLOR_SCHEME), COLOR_SCHEMES[DEFAULT_COLOR_SCHEME])
     zoom_scale = ZOOM_LEVELS.get(config.get("zoom_level", DEFAULT_ZOOM_LEVEL), ZOOM_LEVELS[DEFAULT_ZOOM_LEVEL])
     zoom_position = config.get("zoom_position", DEFAULT_ZOOM_POSITION)
+    static_overlay_enabled = config.get("static_overlay", DEFAULT_STATIC_OVERLAY) == "on"
 
     if not station_url:
         return render.Root(child = _with_background(_message_screen(["Set station URL", "in app settings"], colors), colors))
@@ -164,6 +173,16 @@ def main(config):
     art = _fetch_cover(station_url, now["subsonic_id"])
     progress = _track_progress(now["subsonic_id"], now["duration"])
 
+    # Only meaningful once _track_progress has real elapsed/remaining data
+    # (i.e. on a long-lived server -- see its own comment below for why a
+    # one-shot `pixlet render` CLI call always sees elapsed=0). On a local
+    # render this will always show the "starting" static, never "ending".
+    show_static = (
+        static_overlay_enabled and
+        progress != None and
+        (progress["elapsed"] < STATIC_OVERLAY_SECONDS or progress["remaining"] < STATIC_OVERLAY_SECONDS)
+    )
+
     # The show/host and time/temp rows always render, even when empty, so
     # they hold a fixed vertical position regardless of which fields a given
     # track/moment actually has data for -- rather than the layout shifting
@@ -196,7 +215,7 @@ def main(config):
     )
 
     if art:
-        content = render.Row(children = [_art_widget(art, zoom_scale, zoom_position, now["subsonic_id"]), text_column])
+        content = render.Row(children = [_art_widget(art, zoom_scale, zoom_position, now["subsonic_id"], show_static), text_column])
     else:
         content = render.Column(
             main_align = "center",
@@ -254,7 +273,7 @@ ART_SIZE = 36
 ART_SLOT = 32
 ART_ZOOM_DURATION = 200  # 10s round-trip (5s in, 5s out) at the default 50ms/tick
 
-def _art_widget(art_bytes, zoom_scale, zoom_position, subsonic_id):
+def _art_widget(art_bytes, zoom_scale, zoom_position, subsonic_id, show_static):
     art = render.Image(src = art_bytes, width = ART_SIZE, height = ART_SIZE)
 
     # Always route through animation.Transformation, even when zoom is off
@@ -301,7 +320,21 @@ def _art_widget(art_bytes, zoom_scale, zoom_position, subsonic_id):
             ),
         ],
     )
-    return render.Box(width = ART_SLOT, height = ART_SLOT, child = zoom)
+    cropped = render.Box(width = ART_SLOT, height = ART_SLOT, child = zoom)
+
+    if not show_static:
+        return cropped
+
+    # images/static.gif is a bundled, pre-baked animated GIF (sparse noise
+    # specks over a transparent background) -- not something generated at
+    # render time. pixlet's Starlark sandbox has no per-frame procedural
+    # drawing hook; animated widgets work by either interpolating
+    # animation.Transformation keyframes (no good way to get true random
+    # noise out of that) or, as here, by playing back a real animated
+    # image asset, which render.Image supports natively for GIFs. The GIF
+    # loops independently of ART_ZOOM_DURATION at its own frame rate.
+    static = render.Image(src = STATIC_ASSET.readall(), width = ART_SLOT, height = ART_SLOT)
+    return render.Stack(children = [cropped, static])
 
 def _message_screen(lines, colors):
     return render.Column(
@@ -449,5 +482,16 @@ def get_schema():
                     schema.Option(display = "Random", value = "random"),
                 ],
             ),
+            schema.Dropdown(
+                id = "static_overlay",
+                name = "Static overlay",
+                desc = "Show a brief TV-static effect over the album art as a track starts and ends.",
+                icon = "tv",
+                default = DEFAULT_STATIC_OVERLAY,
+                options = [
+                    schema.Option(display = "On", value = "on"),
+                    schema.Option(display = "Off", value = "off"),
+                ],
+            ),
         ],
     )