fix(core): correct TUI sidebar viewport height off-by-one

[comp615]

This PR description was generated by Amp.

Current Behavior

The TUI task sidebar appears scrolled down by one entry on render, hiding the first continuous task from view.

Here you can see that watch-deps is running in addition to dev.

Expected Behavior

All continuous tasks should be visible in the sidebar without any initial scroll offset.

Related Issue(s)

N/A (discovered via visual inspection)

Details

The viewport height calculation in tasks_list.rs subtracted 4 rows for header overhead, but the actual overhead is only 3 rows:

1. top_margin (1 row)
2. Header content (1 row)
3. Spacing row (1 row)

This off-by-one caused the viewport to be 1 row too small, making the task list appear scrolled down by one entry on initial render.

Changes

1. Unified overhead constant: Introduced TABLE_HEADER_OVERHEAD_ROWS = 3 and SCROLLBAR_Y_OFFSET = 2, replacing scattered hardcoded values. The scrollbar y-offset is 2 (not 3) because the scrollbar visually spans from the spacing row downward, while the viewport only counts content rows.

2. Stale scroll correction: Added logic in set_viewport_height to reset scroll_offset to 0 when the viewport grows from a small placeholder size (≤ 5) to the real terminal size, provided the selected item is still visible from the top. This prevents stale scroll positions set during initialization from hiding top items.

3. Regression tests: Added test_viewport_growth_resets_stale_scroll_offset and test_viewport_growth_preserves_scroll_when_selection_not_visible to cover the stale scroll correction.

4. Snapshot updates: 14 snapshot files updated to reflect one additional visible row.

History

The 4 originated in commit 6541751a (James Henry, Apr 2025) with the comment "Reserve space for pagination and borders." However, the table had no borders (Block::default() without Borders), and pagination lived in its own layout chunk. The 4 was a rough estimate that was never precisely derived from the actual header structure. When scrolling replaced pagination in commit 1782e8c7 (Leosvel Perez Espinola, Sep 2025), the value was carried forward unchanged. The same commit also introduced a separate header_and_spacing_rows = 2 for the scrollbar y-offset, confirming these values were set independently without unified accounting.

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---

☁️ Nx Cloud last updated this comment at 2026-03-04 22:49:28 UTC

[nx-cloud]

Important

At least one additional CI pipeline execution has run since the conclusion below was written and it may no longer be applicable.

Nx Cloud is proposing a fix for your failed CI:

These changes fix the nx:format-native failure by reformatting the assert_eq! macro in the newly added viewport growth test to comply with Rust's cargo fmt standards. The multi-line assertion was condensed to a single line, which is the expected format for this macro signature, ensuring the code passes formatting validation without altering the test's behavior or the PR's core viewport fix.

Tip

✅ We verified this fix by re-running nx:format-native.

diff --git a/packages/nx/src/native/tui/components/task_selection_manager.rs b/packages/nx/src/native/tui/components/task_selection_manager.rs
index 0606acc26a..f30175effe 100644
--- a/packages/nx/src/native/tui/components/task_selection_manager.rs
+++ b/packages/nx/src/native/tui/components/task_selection_manager.rs
@@ -928,8 +928,7 @@ mod tests {
 
         // scroll_offset should reset to 0 because task-1 (selected, index 0) fits
         assert_eq!(
-            manager.scroll_offset,
-            0,
+            manager.scroll_offset, 0,
             "scroll_offset should reset to 0 when viewport grows from placeholder"
         );
 

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