fix(gif): stop emitting GIFs Discord can't decode; stop dropping 44% of frames (#2)

Fixes mort#1510. Verified end-to-end: the rebuilt file plays correctly in Discord where the original flashes, and is smaller (1210 KB -> 918 KB).

gif/scripts/gifsmith.py

@@ -367,13 +367,36 @@ class Animation:
             _run(["gifski", "-o", out, "--fps", str(self.fps), "--quality", "90",
                   "--width", str(min(long_edge, self.width))] + fs)
         else:
-            vf = (f"fps={self.fps},scale='min({long_edge},iw)':-1:flags=lanczos,"
+            # -framerate applies to the INPUT. Without it ffmpeg reads a PNG
+            # sequence at its default 25fps, and a fps= filter then resamples
+            # 25 -> self.fps: on the #1510 render that silently dropped 91 of
+            # 207 frames (44%) and played the rest too fast. _mp4 below always
+            # passed -framerate; this path never did. With the input rate set
+            # correctly the fps= filter is redundant — and removing it is what
+            # takes the output from 205 frames back to all 207.
+            vf = (f"scale='min({long_edge},iw)':-1:flags=lanczos,"
                   f"split[s0][s1];[s0]palettegen=stats_mode=diff[p];"
                   f"[s1][p]paletteuse=dither=bayer:bayer_scale=3")
-            _run(["ffmpeg", "-y", "-loglevel", "error", "-pattern_type", "glob",
+            _run(["ffmpeg", "-y", "-loglevel", "error",
+                  "-framerate", str(self.fps), "-pattern_type", "glob",
                   "-i", os.path.join(self._scratch, "frame_*.png"), "-vf", vf, out])
         if _which("gifsicle"):
-            _run(["gifsicle", "-O3", "--lossy=60", out, "-o", out])
+            # --colors 256 is load-bearing for DISCORD, not for size.
+            #
+            # gifski gives every frame its OWN local colour table (that is where
+            # its quality comes from). Stack gifsicle's cross-frame transparency
+            # on top and the result is a GIF that gifsicle itself refuses to
+            # reopen: "too complex to unoptimize — local colour tables or complex
+            # transparency". PIL, ffmpeg and macOS Preview all render it fine;
+            # Discord's decoder does not, and paints later scenes with stale rows,
+            # ghosted captions and holes punched in solid shapes (#1510).
+            #
+            # Collapsing to ONE global palette costs ~6/255 mean colour error
+            # (visible as slight banding in gradients, since one palette now
+            # spans every scene) and is the price of playing in the client that
+            # actually matters. It also came out SMALLER on the reported file:
+            # 1210 KB -> 915 KB.
+            _run(["gifsicle", "--colors", "256", "-O3", "--lossy=60", out, "-o", out])
 
     def _mp4(self, out, long_edge, audio=None):
         cmd = ["ffmpeg", "-y", "-loglevel", "error", "-framerate", str(self.fps),