refactor: name configurable viewport scroll steps accurately

docs/architecture.md

@@ -84,7 +84,7 @@ Resolution exposes its projected comparison through the same active DiffState an
 
 `Editor::scroll_distance()` supplies the session-wide optional edge margin. The TUI applies it to document/diff visual rows and unwrapped text columns, and retains independent picker offsets across navigation frames. Picker windows exclude their fixed chrome and align whole multi-row entries. File projections carry a monotonic viewport revision, so catalog/filter/expansion changes invalidate picker identity without hashing the entire catalog on every redraw. Metadata-only status changes do not move the viewport. Explicit LSP/wrap-toggle anchors and detached wheel views retain precedence.
 
-Keyboard viewport actions queue per-view row and half-page counts without moving carets. `Editor::take_viewport_scroll(height)` resolves half-page counts using the session-wide `scroll_half_page_lines` preference, or half the focused viewport when unset, and saturates multiplication before the frontend clamps movement to content bounds. Ordinary, diff, and conflict-history rendering share this resolution.
+Keyboard viewport actions queue per-view row and configured-step counts without moving carets. `Editor::take_viewport_scroll(height)` resolves step counts using the session-wide `scroll_step_lines` preference, or half the focused viewport when unset, and saturates multiplication before the frontend clamps movement to content bounds. Ordinary, diff, and conflict-history rendering share this resolution.
 
 Mouse wheel input uses the last rendered document/panel rectangles for hit-testing. Document offsets and explorer scroll state remain frontend-owned; three-row wheel steps never become document cursor motions. Manual document views persist until logical caret-reveal, caret/selection, mode, revision, or buffer changes; offscreen primary and browsing-selection cursors are not placed. Hover wheel input reuses the existing editor-owned popup scrolling.
 

docs/configuration.md

@@ -16,7 +16,7 @@ Vamp.configure do |config|
   config.git_blame = true # false disables current-line attribution
   config.git_gutter = "bar" # or "symbols", "line_numbers", "none"
   config.scroll_distance = 0 # nonnegative edge distance, or nil to center
-  config.scroll_half_page_lines = nil # Ctrl+u/d: half viewport, or a positive screen-row count
+  config.scroll_step_lines = nil # Ctrl+u/d: half viewport, or a positive screen-row count
   config.highlight_trailing_whitespace = false # true marks line-end whitespace in red
   config.whitespace_characters = {} # opt in: { " " => "·", "\t" => "→", "\n" => "↵" }
   config.whitespace_scope = "all" # or "leading" for indentation only
@@ -58,7 +58,7 @@ Plugin paths resolve relative to the config file, not the shell's working direct
 
 The setting applies to ordinary and historical buffers, split/unified diff panes, file pickers and explorers, command/buffer palettes, completion lists, and revision selectors. Wrapped text measures visual rows, not source lines; picker distances use result rows, excluding borders, search fields, and help. Manual mouse-wheel scrolling remains detached until keyboard navigation resumes. Only `nil` or integers from `0` through the platform's Rust `usize` maximum (`18446744073709551615` on 64-bit systems) are accepted; other values reject the configuration.
 
-`config.scroll_half_page_lines` controls Normal/Visual Ctrl+u/Ctrl+d (`core.scroll_half_up` / `core.scroll_half_down`). The default `nil` scrolls half the focused text viewport, rounded down with a minimum of one screen row. A positive integer, such as `config.scroll_half_page_lines = 3`, fixes the distance in screen rows, including wrapped continuations and diff display rows. Counts multiply that distance; `2` then Ctrl+d scrolls six rows with this example. This session-wide setting applies to ordinary, historical, diff, and conflict text panes without moving carets or selections. It does not change the cursor-edge margin, one-row scroll actions, mouse wheel, or picker navigation. Only `nil` or integers from `1` through the platform's Rust `usize` maximum are accepted; other values reject the configuration. Distances and count multiplication saturate at Rust's `isize` limit before the viewport clamps to content bounds.
+`config.scroll_step_lines` controls Normal/Visual Ctrl+u/Ctrl+d (`core.scroll_step_up` / `core.scroll_step_down`). The default `nil` scrolls half the focused text viewport, rounded down with a minimum of one screen row. A positive integer, such as `config.scroll_step_lines = 3`, fixes the distance in screen rows, including wrapped continuations and diff display rows. Counts multiply that distance; `2` then Ctrl+d scrolls six rows with this example. This session-wide setting applies to ordinary, historical, diff, and conflict text panes without moving carets or selections. It does not change the cursor-edge margin, one-row scroll actions, mouse wheel, or picker navigation. Only `nil` or integers from `1` through the platform's Rust `usize` maximum are accepted; other values reject the configuration. Distances and count multiplication saturate at Rust's `isize` limit before the viewport clamps to content bounds.
 
 `config.highlight_trailing_whitespace` defaults to `false`. Set it to `true` to give trailing whitespace a red background in ordinary and historical buffers and both sides of split/unified diffs, including wrapped and horizontally scrolled text. Spaces, expanded tab cells, and Unicode whitespace at the end of a source line are highlighted; whitespace-only lines are included, but empty lines and padding beyond the text are not. Wrapping does not make interior whitespace trailing. Search, selections, and secondary carets retain their background precedence; diagnostic underlines remain visible. This changes display only, not file contents. Only literal Ruby booleans are accepted; other values reject the configuration.
 
@@ -211,7 +211,7 @@ Normal `C` / `D` / `Y` change/delete/copy the cursor-to-line-end suffix through
 
 `f<char>` / `F<char>` seeks forward/backward on the current line in Normal and Visual, with counts such as `2fx`. Rebind `config.core.seek_forward` / `config.core.seek_backward` to a single key or leader sequence; the action then waits for a literal target character. For example, `config.bind "s", config.core.seek_forward` makes `2sx` seek the second following `x`. Pass `mode: config.modes.visual` to install a Visual route. These native-only actions do not have Ex commands.
 
-Normal and Visual Ctrl+u/Ctrl+d invoke `config.core.scroll_half_up` / `config.core.scroll_half_down` without moving carets or selection endpoints. Counts multiply the configured `scroll_half_page_lines` distance (half a viewport by default). Bind `config.core.scroll_up` / `config.core.scroll_down` for one screen row per count, for example `config.bind "ctrl+e", config.core.scroll_down` to replace clone-below in Normal. Pass `mode: config.modes.visual` to rebind Visual too. These actions work in ordinary and diff text panes, use wrapped screen rows, and have no Ex commands. Cursor navigation or editing resumes caret following.
+Normal and Visual Ctrl+u/Ctrl+d invoke `config.core.scroll_step_up` / `config.core.scroll_step_down` without moving carets or selection endpoints. Counts multiply the configured `scroll_step_lines` distance (half a viewport by default). Bind `config.core.scroll_up` / `config.core.scroll_down` for one screen row per count, for example `config.bind "ctrl+e", config.core.scroll_down` to replace clone-below in Normal. Pass `mode: config.modes.visual` to rebind Visual too. These actions work in ordinary and diff text panes, use wrapped screen rows, and have no Ex commands. Cursor navigation or editing resumes caret following.
 
 ## Action reference
 
@@ -243,7 +243,7 @@ Normal and Visual Ctrl+u/Ctrl+d invoke `config.core.scroll_half_up` / `config.co
 | Normal, Visual | `file_picker`, `file_explorer` |
 | Normal, Visual | `document_start`, `document_end`, `go_to_line` |
 | Normal, Visual | `seek_forward`, `seek_backward` |
-| Normal, Visual | `scroll_up`, `scroll_down`, `scroll_half_up`, `scroll_half_down` |
+| Normal, Visual | `scroll_up`, `scroll_down`, `scroll_step_up`, `scroll_step_down` |
 | Normal, Insert, Visual | `line_start`, `line_end` |
 | Normal, Insert, Visual, Tree | `left`, `right` |
 | Normal, Insert, Visual, Selection, Tree | `down`, `up` |

docs/development.md

@@ -76,7 +76,7 @@ Diff styling checks cover independent snapshot language/shebang/injection detect
 
 - Undo uses full-buffer snapshots and movement scans the current line. This favors straightforward correctness over large-file performance.
 - Rapid-wheel verification must replay bursts against the running editor and measure arrival at the final viewport after input stops, not just individual frame duration. Cheap frames can still accumulate a visible backlog if each queued report requires its own redraw.
-- Keyboard viewport scrolling coalesces up to 64 consecutive inputs for the same resolved scroll action into one redraw. Reversals, changes between row/half-page scrolling, and cursor motions end the batch so boundary clamping and caret reveal happen before the next action. Burst checks must include direction changes at the start/end of the buffer, not just throughput.
+- Keyboard viewport scrolling coalesces up to 64 consecutive inputs for the same resolved scroll action into one redraw. Reversals, changes between row/configured-step scrolling, and cursor motions end the batch so boundary clamping and caret reveal happen before the next action. Burst checks must include direction changes at the start/end of the buffer, not just throughput.
 - PTY throughput alone cannot prove terminal presentation stays smooth: capture the editor and terminal while the user reproduces a pause. Synchronized-output commands must not reach the terminal during frame computation, even when individual frames and queued-input catch-up appear fast.
 - Annotation coordinate validation fast-paths ASCII grapheme lengths using byte lengths with CRLF pair accounting, retaining Unicode segmentation for non-ASCII text. Validation remains atomic and still checks every token; large Unicode buffers or diagnostic batches can require foreground work.
 - Legacy synchronous plugin invocation may pause input for up to 500 ms before a host timeout. Async plugins opt into background replies; pending requests and transport queues are bounded. Config/plugin startup has a 2-second deadline per host. Buffer context/document snapshots must fit within a 4 MiB JSON frame; a too-large frame disables that plugin, not editing.

docs/editing.md

@@ -31,7 +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 up/down without moving carets or selections; half a viewport by default, configurable with `config.scroll_half_page_lines`; counts multiply the distance |
+| Normal, Visual | Ctrl+u/Ctrl+d scroll up/down without moving carets or selections; half a viewport by default, configurable with `config.scroll_step_lines`; 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`) |