smoother scroll restore on jump-back; non-degenerate test

The restored scroll was correct in the final state but load() zeroed
virtual_size (snapping scroll to 0) and only a deferred call_after_refresh
jumped to the target -> a visible flash to the top before settling. Now: don't
zero virtual_size on load, and apply the target scroll synchronously in
_on_primed (plus the deferred call as a fallback for un-sized regions).

Also hardened the scroll test to use a MID-viewport cursor (rel>0). The prior
test had the cursor at the viewport top (rel=0), where scroll-into-view derives
the same scroll -> it would have passed even if scroll restore were broken.
pilot suite 52/52.

1 files changed, 15 insertions, 4 deletions

diff --git a/tests/test_tui.py b/tests/test_tui.py
index 18194bf..51c9f57 100644
--- a/tests/test_tui.py
+++ b/tests/test_tui.py
@@ -495,16 +495,27 @@ async def run(db):
         for _ in range(4):
             await pilot.press("ctrl+d")
         await pilot.pause(0.2)
+        # Put the cursor in the MIDDLE of the viewport so the test is
+        # non-degenerate: with rel>0, restoring only the cursor (scroll-into-view)
+        # would derive a different scroll, so this actually checks scroll restore.
+        base = round(dis.scroll_offset.y)
+        mid = base + min(dis.size.height // 2, max(dis.total - base - 1, 0))
+        dis.cursor, dis.cursor_x = mid, 0
+        dis.refresh()
+        dis._after_cursor_move()
+        await pilot.pause(0.1)
         want_sy, want_cur = round(dis.scroll_offset.y), dis.cursor
+        want_rel = want_cur - want_sy
         await goto_name(fb.name)
         await wait_until(pilot, lambda: app._cur.ea == fb.addr, timeout=20)
         await pilot.press("escape")
         await wait_until(pilot, lambda: app._cur.ea == fa.addr, timeout=20)
         await wait_until(pilot, lambda: dis.total > 40, timeout=20)
-        await pilot.pause(0.4)
-        check("disasm scroll + cursor restored on back",
-              round(dis.scroll_offset.y) == want_sy and dis.cursor == want_cur,
-              f"scroll={round(dis.scroll_offset.y)} (want {want_sy}) cursor={dis.cursor}")
+        await pilot.pause(0.5)
+        check("disasm scroll + cursor restored on back (mid-viewport)",
+              round(dis.scroll_offset.y) == want_sy and dis.cursor == want_cur and want_rel > 0,
+              f"scroll={round(dis.scroll_offset.y)} (want {want_sy}) "
+              f"cursor={dis.cursor} (want {want_cur}) rel_before={want_rel}")
 
         # PageUp/Down keep the cursor at the same viewport-relative row.
         await goto_name(fa.name)