refactor: Implement fixed frame rate and precise timing for the scrolling animation loop.

mainline.py

@@ -491,6 +491,7 @@ def _save_cache(items):
 
 # ─── STREAM ───────────────────────────────────────────────
 _SCROLL_DUR = 3.75  # seconds per headline
+_FRAME_DT = 0.05    # 50ms base frame rate (20 FPS)
 FIREHOSE_H = 12     # firehose zone height (terminal rows)
 _mic_db = -99.0     # current mic level, written by background thread
 _mic_stream = None
@@ -766,13 +767,14 @@ def stream(items):
     fh = FIREHOSE_H if FIREHOSE else 0
     sh = h - fh                    # scroll zone height
     GAP = 3            # blank rows between headlines
-    dt = _SCROLL_DUR / (sh + 15) * (4 if FIREHOSE else 2)
+    scroll_interval = _SCROLL_DUR / (sh + 15) * 2
 
     # active blocks: (content_rows, color, canvas_y, meta_idx)
     active = []
     cam = 0            # viewport top in virtual canvas coords
     next_y = sh        # canvas-y where next block starts (off-screen bottom)
     noise_cache = {}
+    scroll_accum = 0.0
 
     def _noise_at(cy):
         if cy not in noise_cache:
@@ -780,17 +782,31 @@ def stream(items):
         return noise_cache[cy]
 
     while queued < HEADLINE_LIMIT or active:
+        t0 = time.monotonic()
         w, h = tw(), th()
         fh = FIREHOSE_H if FIREHOSE else 0
         sh = h - fh
 
-        # Enqueue new headlines when room at the bottom
-        while next_y < cam + sh + 10 and queued < HEADLINE_LIMIT:
-            t, src, ts = _next_headline(pool, items, seen)
-            content, hc, midx = _make_block(t, src, ts, w)
-            active.append((content, hc, next_y, midx))
-            next_y += len(content) + GAP
-            queued += 1
+        # Advance scroll on schedule
+        scroll_accum += _FRAME_DT
+        while scroll_accum >= scroll_interval:
+            scroll_accum -= scroll_interval
+            cam += 1
+
+            # Enqueue new headlines when room at the bottom
+            while next_y < cam + sh + 10 and queued < HEADLINE_LIMIT:
+                t, src, ts = _next_headline(pool, items, seen)
+                content, hc, midx = _make_block(t, src, ts, w)
+                active.append((content, hc, next_y, midx))
+                next_y += len(content) + GAP
+                queued += 1
+
+            # Prune off-screen blocks and stale noise
+            active = [(c, hc, by, mi) for c, hc, by, mi in active
+                      if by + len(c) > cam]
+            for k in list(noise_cache):
+                if k < cam:
+                    del noise_cache[k]
 
         # Draw scroll zone
         top_zone = max(1, int(sh * 0.25))
@@ -841,19 +857,12 @@ def stream(items):
                 gi = random.randint(0, g_limit - 1)
                 buf[gi] = f"\033[{gi+1};1H{glitch_bar(w)}"
 
-        sys.stdout.write("".join(buf))
+        sys.stdout.buffer.write("".join(buf).encode())
         sys.stdout.flush()
-        time.sleep(dt)
 
-        # Advance viewport
-        cam += 1
-
-        # Prune off-screen blocks and stale noise
-        active = [(c, hc, by, mi) for c, hc, by, mi in active
-                  if by + len(c) > cam]
-        for k in list(noise_cache):
-            if k < cam:
-                del noise_cache[k]
+        # Precise frame timing
+        elapsed = time.monotonic() - t0
+        time.sleep(max(0, _FRAME_DT - elapsed))
 
     sys.stdout.write(CLR)
     sys.stdout.flush()