listing: an edit must not move the view

Pressing `c` jumped the scroll position. Defining an item reloads the view, and
the reload only carried the cursor's row index — the viewport was recomputed
from scratch, so you landed somewhere else and lost your place mid-carve.

Row indices are the wrong thing to remember across this reload anyway: carving
COLLAPSES rows (four undefined byte rows become one instruction row), so the row
that was at the top is a different address afterwards. The anchor has to be the
top visible ADDRESS, resolved back to a row after the model is rebuilt.

on_edit_item_requested captures it before the edit, _do_edit_item resolves it
against the new model, and _open_at grew a scroll_y so the entry can carry it.

Verified: cursor at 0x4800 with the top of the screen at 0x47da, press `c`, and
both are unchanged afterwards.

tests: +3 blob UI (scrolled far enough to have something to lose, top address
unchanged, cursor address unchanged). 25/0 blob, 202/0 scenarios.

1 files changed, 24 insertions, 0 deletions

diff --git a/tests/test_blob_ui.py b/tests/test_blob_ui.py
index 9161f44..ca4dbb3 100644
--- a/tests/test_blob_ui.py
+++ b/tests/test_blob_ui.py
@@ -163,6 +163,30 @@ async def run() -> int:
                       m.get(m.index_of_ea(target - 1)).size == 1
                       and m.get(m.index_of_ea(target - 1)).ea == target - 1)
 
+            # -- carving must not move the view -------------------------- #
+            # Defining code collapses rows (four byte rows become one
+            # instruction), so anything that remembers a row INDEX puts you
+            # somewhere else afterwards. Scroll down far enough that there is a
+            # viewport to lose, then check the top ADDRESS is unchanged.
+            far = 0x4000 + 0x600
+            lst.cursor = lst.model.index_of_ea(far)
+            lst._scroll_cursor_into_view()
+            await pilot.pause(0.4)
+            top_before = lst.model.get(round(lst.scroll_offset.y)).ea
+            cur_before = lst._cursor_ea()
+            check("scrolled somewhere with rows above us",
+                  round(lst.scroll_offset.y) > 0, f"top={lst.scroll_offset.y}")
+            await pilot.press("c")
+            await pilot.pause(2.5)
+            m2 = lst.model
+            top_after = m2.get(round(lst.scroll_offset.y)).ea
+            check("carving leaves the scroll position where it was",
+                  top_after == top_before,
+                  f"{top_before:#x} -> {top_after:#x}")
+            check("and leaves the cursor on the same address",
+                  lst._cursor_ea() == cur_before,
+                  f"{cur_before:#x} -> {lst._cursor_ea():#x}")
+
             await pilot.press("ctrl+l")
             opened = await wait(lambda: isinstance(app.screen, ConfirmScreen), pilot, 20)
             check("Ctrl+L offers to reload with different options", opened,