Halt a running glide before a landing that finds the pane already in place

fnd/tui/match_navigator.py

@@ -883,6 +883,8 @@ def _go(self, *, forward: bool) -> None:
     def _scroll_to_stop(self, pane: VerticalScroll, top_y: int, vh: int) -> None:
         from textual.geometry import Region
 
+        from fnd.tui.preview_scrollbar import MatchAwareScroll
+
         # The anchor IS the view's top: views tile by exactly one viewport, so a
         # hop covers a screenful and the border's count of screenfuls and of
         # presses are the same number. Offsetting the match down the viewport
@@ -899,6 +901,8 @@ def _scroll_to_stop(self, pane: VerticalScroll, top_y: int, vh: int) -> None:
         if preview is not None:
             preview.begin_reconcile_scroll()
         try:
+            if isinstance(pane, MatchAwareScroll):
+                pane.halt_glide()
             pane.scroll_to_region(region, top=True, animate=False, immediate=True)
             self._app._diag_log(f"scroll site=nb_stop top_y={top_y}")
         finally:

fnd/tui/preview_scroll.py

@@ -850,6 +850,8 @@ def _scroll_pane_to_match_region(
             region = Region(
                 region.x, max(0, region.y - margin), region.width, region.height + margin
             )
+        if isinstance(pane, MatchAwareScroll):
+            pane.halt_glide()
         start = int(pane.scroll_offset.y)
         delta = pane.scroll_to_region(region, top=True, animate=animate, immediate=not animate)
         self._host.diag_log(f"scroll site=match region_y={region.y} animate={animate}")

fnd/tui/preview_scrollbar.py

@@ -415,6 +415,15 @@ def action_scroll_up(self) -> None:
             return
         super().action_scroll_up()
 
+    def halt_glide(self) -> None:
+        """Stop a scroll animation where it is. A scroll that finds the pane in
+        place issues nothing, so a glide to an earlier target would carry on;
+        animating to the current value drops it without ``force_stop``'s jump."""
+        if not self.app.animator.is_being_animated(self, "scroll_y"):
+            return
+        self.animate("scroll_y", self.scroll_y, duration=0)
+        self.scroll_target_y = self.scroll_y
+
     #: ``(widget, virtual_y)`` for a chunk just below content being revealed
     #: ABOVE the viewport. Every layout that pushes that widget further down is
     #: the prepend landing, and the pane scrolls by exactly that so the document

tests/test_match_nav_integration.py

@@ -24,7 +24,7 @@
 from fnd.config import Config, load
 from fnd.index import build_index
 from fnd.tui import FNDApp
-from tests._pilot_wait import safe_press, settle, wait_until
+from tests._pilot_wait import safe_press, settle, wait_stable, wait_until
 
 
 def _write(p: Path, body: str) -> None:
@@ -550,6 +550,54 @@ async def test_a_hand_over_onto_the_row_the_cursor_already_holds_still_lands(
         )
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("site", ["landing", "nb_stop"])
+async def test_a_scroll_to_where_the_pane_already_is_still_ends_a_glide(
+    cfg: Config, flashcards_index: Path, site: str
+) -> None:
+    """A scroll that finds the pane already in place still supersedes a glide elsewhere."""
+    from textual.geometry import Region
+
+    app = FNDApp(index_dir=flashcards_index, config=cfg, collection="notes", initial_query="CRC")
+    async with app.run_test(size=(110, 24)) as pilot:
+        pane = app.query_one("#preview_pane", VerticalScroll)
+        await wait_until(
+            pilot,
+            lambda: (
+                _focus_seq(app) is not None
+                and not app._preview_scroll.is_settling
+                and not app.animator.is_being_animated(pane, "scroll_y")
+            ),
+            timeout=30.0,
+            message="the preview never landed",
+        )
+        await wait_stable(
+            pilot,
+            lambda: (pane.scroll_y, app._preview_scroll.is_settling),
+            rounds=6,
+            message="the landing never held still",
+        )
+        here = int(pane.scroll_y)
+        assert here > 0, "the landing must leave room to glide towards the top"
+        pane.scroll_to(y=0, animate=True, duration=0.3, immediate=True)
+        assert app.animator.is_being_animated(pane, "scroll_y")
+
+        if site == "landing":
+            app._preview_scroll_structural._scroll_pane_to_match_region(
+                pane, Region(0, here, 1, 1), 0, animate=True
+            )
+        else:
+            app._match_nav._scroll_to_stop(pane, here, pane.scrollable_content_region.height)
+
+        await wait_until(
+            pilot,
+            lambda: not app.animator.is_being_animated(pane, "scroll_y"),
+            timeout=5.0,
+            message="the glide never ended",
+        )
+        assert int(pane.scroll_y) == here
+
+
 @pytest.fixture
 def three_section_index(tmp_path: Path, tmp_index_dir: Path) -> Path:
     """A long middle section, so the last section's final stop sits on the