Vegas mode: end cycles before the wrap, keep the width budget honest

Three fixes, the first a regression from lead_in_width defaulting to 0.

get_visible_portion wraps: once scroll_position + display_width passes the end
of the strip it fills the right of the frame from the *head* of the same strip.
So the final display_width of travel showed the cycle's first plugin re-entering
on the right while its last plugin exited on the left, and the recompose that
followed replaced both at once. On a 512px panel at 50px/s that was 10.2s of
two plugins on screen at once, ending in a hard cut — reported as the ticker
"switching mid-scroll" from F1 to news.

That used to be invisible because the strip began with a full display_width of
blank, so the wrapped-in region was black. Removing that blank (it was 10s of
dead panel per cycle) exposed the wrap. Cycles now end one display width
earlier, before any wrapped content appears, clamped for strips no wider than
the display so they don't complete instantly and spin the recompose loop.

Verified on hardware: a 3936px strip now completes at 68.5s, exactly
(3936 - 512) / 50.

Second, auto_trim=False also skipped the width budget, which is an unrelated
concern — turning off margin cropping should not let one plugin hold the panel
for minutes. Seen in the field: the F1 scoreboard contributed 116 images and
14,848px untouched, giving a 33,821px cycle (11 minutes of content). The budget
now applies regardless of trimming; with it restored that cycle is 6,362px.

Third, the budget accounted for row gaps using the flat intra_plugin_gap while
the compositor had moved to measured separation, so it under-counted by up to
(min_content_separation - intra_plugin_gap) per row and a many-row plugin
overran its cap. Both now use the same separation_gap() rule, and a test
asserts the composed block fits the budget end to end rather than trusting the
two paths to agree.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

src/vegas_mode/render_pipeline.py

@@ -265,21 +265,29 @@ class RenderPipeline:
 
             # Determine if the cycle is done.
             #
-            # scroll_helper considers a cycle complete only after
-            # total_distance_scrolled >= total_scroll_width + display_width.
-            # That extra display_width of travel causes a "wrap-around" phase
-            # where scroll_position resets to ~0 and the first plugin's content
-            # re-enters from the right — the user sees this 2-3 s of re-entry
-            # as "a plugin partially displaying before the next one starts."
+            # get_visible_portion wraps: once scroll_position + display_width
+            # passes the end of the strip it fills the right-hand side of the
+            # frame from the *head* of the same strip. So the last
+            # display_width of travel shows the cycle's first plugin re-entering
+            # on the right while its last plugin exits on the left, and the
+            # recompose that follows then replaces both at once. That reads as
+            # the ticker "switching mid-scroll".
             #
-            # We end the cycle as soon as total_distance_scrolled reaches
-            # total_scroll_width (the wrap-around point), before any second-pass
-            # content becomes visible.  The scroll_helper's own is_scroll_complete()
-            # check is kept as a fallback for any edge-cases where that threshold
-            # is never hit.
+            # This used to be hidden because the strip began with a full
+            # display_width of blank, so the wrapped-in region was black.
+            # lead_in_width now defaults to 0 (that blank was 10s of dead panel
+            # at 50px/s), which exposed the wrap — so the cycle has to end
+            # before it, one display width earlier.
+            #
+            # A strip no wider than the display never wraps, and subtracting
+            # would make the cycle complete instantly, so clamp in that case.
+            wrap_point = self.scroll_helper.total_scroll_width
+            if wrap_point > self.display_width:
+                wrap_point -= self.display_width
+
             at_wrap_point = (
                 not self._cycle_complete and
-                self.scroll_helper.total_distance_scrolled >= self.scroll_helper.total_scroll_width
+                self.scroll_helper.total_distance_scrolled >= wrap_point
             )
 
             if at_wrap_point or self.scroll_helper.is_scroll_complete():