feat: scroll viewport independently of the cursor

docs/editing.md

@@ -31,6 +31,7 @@ Indicators refresh asynchronously. Typing and undo/redo retain the last complete
 | Normal, Visual | `<line>g` jumps immediately to that one-based source line at first nonblank (`42g`); clamps at EOF and extends Visual selections |
 | Normal | Ctrl+o goes to an older jump location; Ctrl+i/Tab goes forward; counts select multiple locations |
 | Normal, Visual | Decimal prefixes repeat cursor/word/search motions: `5j`, `3k`, `2w`, `4e`, `2n`; Esc cancels a pending count |
+| Normal, Visual | Ctrl+u/Ctrl+d scroll half a viewport up/down without moving carets or selections; counts multiply the distance |
 | Normal | `J` (Shift+j) joins each targeted line with the next line |
 | Normal | `x`/Delete delete; `u` undo; `U` (Shift+u) redo; `:` enter command mode |
 | Normal | `yy` copies whole lines without moving; `dd` deletes them; `cc` changes them and enters Insert; counts work (`3yy`, `2dd`, `2cc`) |
@@ -64,6 +65,8 @@ On macOS, these modified Backspace defaults also edit prompt and filter queries,
 
 The terminal may deliver a native modifier or a conventional control sequence: Option may use legacy ESC+DEL, and Kitty CSI-u represents Command as **Super**, not Meta. Ghostty defaults to encoding Command+Backspace as Ctrl+u (`\x15`), which invokes the same backward line deletion without a Ghostty configuration override. Ctrl+u remains a separate, configurable binding; vamp cannot distinguish it from Command+Backspace when both send the same bytes. Vamp does not negotiate an enhanced keyboard protocol or support generic Command-modified character keys.
 
+Viewport scrolling uses screen rows, including wrapped continuations and diff display rows. It affects the focused text pane (both sides share the diff's vertical offset), and the caret may leave the screen. The next cursor motion or edit resumes caret following. Ctrl+e retains its clone-below binding; single-row scrolling is available through `config.core.scroll_up` / `config.core.scroll_down`. Insert, Command, Search, and picker Ctrl+u behavior is unchanged.
+
 ## Manual LSP completion
 
 With an enabled server that provides completion, Ctrl+n in Insert requests candidates at the **primary caret only**. The first candidate is inserted immediately and a small list appears near the caret; Ctrl+n or Ctrl+j cycles forward, Ctrl+k backward, with wraparound. There is no acceptance step. The **Original text** row restores the document and carets from before the result was shown, including any additional edits. Completion never broadcasts a candidate to secondary carets: they are preserved and translated through each chosen edit.