feat: add configurable diff modes and split orientation

docs/architecture.md

@@ -73,6 +73,8 @@ The TUI allocates a flexible buffer viewport and optional one-row top/bottom bar
 
 Comparison views reserve no separate metadata header or native-buffer help footer. Revision labels render bottom-left in pane borders (combined on single-pane views), with per-side editability top-right and focus indicated by border styling. Dock and document geometry use the reclaimed workspace rows; conditional loading/error/file notices remain separate from the border metadata.
 
+Each comparison owns its split/unified mode and split axis; startup defaults apply only when opening a comparison. Source alignment and file-side availability stay independent of presentation. Unified display rows carry a side projection: equal context maps both sources, changed runs emit Before rows followed by After rows, and folds retain aligned coordinates. Native navigation/editing continues to bind source buffers rather than a synthetic unified document. The TUI reuses side-specific syntax/wrap/overlay pipelines in one unified region or the existing axis-based split geometry, exposing only the active logical side for unified hit-testing and directional focus.
+
 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.
 
 Already-ready mouse reports share a redraw: at most 64 reports are applied in their original order before painting, without dropping or summing away wheel steps. Readiness checks do not wait. The first non-mouse event is retained for the next iteration after rendering, so keys, paste, and resizes cannot reuse geometry from before their layout changes. The batch bound keeps continuous mouse input from starving drawing or background polling.

docs/configuration.md

@@ -18,6 +18,8 @@ Vamp.configure do |config|
   config.file_picker_view = "tree"
   config.diff_context_lines = 10
   config.diff_expand_lines = 15
+  config.diff_view_mode = "split" # or "unified"
+  config.diff_split_orientation = "left_right" # or "above_below"
   config.bind "ctrl+h", config.core.left, mode: config.modes.tree
   config.bind "ctrl+l", config.core.right, mode: config.modes.tree
   config.plugin "plugins/greeting.rb"
@@ -44,6 +46,13 @@ Plugin paths resolve relative to the config file, not the shell's working direct
 
 `config.diff_context_lines = 10` sets how many unchanged aligned lines appear above and below each diff change; it defaults to `10` and accepts nonnegative integers, including `0` for changes only. `config.diff_expand_lines = 15` sets how many additional lines each directional expansion reveals per keypress; it defaults to `15` and accepts positive integers. Both are bounded by the platform's Rust `usize` maximum (`18446744073709551615` on 64-bit systems). Floats, strings, booleans, negative or oversized values, and a zero expansion step reject the whole Ruby configuration.
 
+`config.diff_view_mode` selects the initial view for each new comparison: `"split"` (default) or `"unified"`. `config.diff_split_orientation` selects `"left_right"` (default) or `"above_below"` for split views. Invalid values reject the configuration. Normal-mode **Space v** cycles split/unified; **Space s** flips split orientation. These controls affect the current comparison, not startup defaults, and retain their choices across file switches and tabs. Orientation changes apply only in split view.
+
+```ruby
+config.bind "leader v", config.core.diff.view.toggle
+config.bind "leader s", config.core.diff.orientation.toggle
+```
+
 ### Top and bottom bars
 
 `config.bar.top` and `config.bar.bottom` each accept ordered `left`, `center`, and `right` arrays of segment names. Both bars accept every builtin and custom segment, with the same anchors, title templates, padding, styled edges, and collision handling. Left and right groups anchor to their respective edges; the center group is centered on the whole row, not on the gap remaining between the other groups. Array order is display order within each group. Omitted groups and segment options retain that bar's defaults; an empty array removes that group.
@@ -151,7 +160,7 @@ Normal `dd` and `cc` delete/change complete rows, with leading counts. Bind `con
 | Normal | `save`, `force_save`, `quit`, `force_quit`, `restart`, `force_restart`, `save_and_quit`, `force_save_and_quit`, `plugins` |
 | Normal | `edit`, `buffers`, `buffer`, `buffer_next`, `buffer_previous`, `buffer_delete`, `buffer_force_delete` |
 | Normal | `follow_link` |
-| Normal | `diff` |
+| Normal | `diff`, `diff.view.toggle`, `diff.orientation.toggle` |
 | Normal, Insert, Visual, Command, Search | `diff.close` |
 | Normal, Insert, Visual, Command, Search | `word_wrap.toggle` |
 | Normal | `pane.split_horizontal`, `pane.split_vertical`, `pane.focus_left`, `pane.focus_down`, `pane.focus_up`, `pane.focus_right`, `pane.close`, `pane.force_close` |
@@ -228,7 +237,7 @@ config.bind "ctrl+h", nil, mode: config.modes.tree
 
 The diff's changed-file explorer and floating picker use these same tree and selection contexts, including remaps and disabled keys. Enter opens the selected file's comparison; Working checkout After reuses its editable buffer. The catalog contains only changed paths, with A/M/D/R status markers, rather than a disk scan.
 
-Ordinary `config.core.file_picker` and `config.core.file_explorer` bindings work inside comparisons. Ctrl+w closes a focused picker/explorer, retaining its query, selection, and expansion state; the panes use the reclaimed width. Ctrl+e has no reserved diff behavior. Escape closes the revision selector in either stage, but an opened comparison still closes explicitly through `:diff.close`, its palette action, or the generated action value below. `config.core.diff` remains the opening action and also exposes its immutable `close` child.
+Ordinary `config.core.file_picker` and `config.core.file_explorer` bindings work inside comparisons. Ctrl+w closes a focused picker/explorer, retaining its query, selection, and expansion state; the panes use the reclaimed width. Ctrl+e has no reserved diff behavior. Escape closes the revision selector in either stage, but an opened comparison still closes explicitly through `:diff.close`, its palette action, or the generated action value below. `config.core.diff` remains the opening action and exposes immutable `close`, `view.toggle`, and `orientation.toggle` children.
 
 `config.core.pane.close` and `config.core.pane.force_close` close a focused **docked** file list instead of its editor pane, without discarding buffers or exiting the comparison. A floating picker does not intercept these actions: normal close still protects underlying dirty buffers, while force-close retains its existing discard semantics. For example, bind `config.bind "ctrl+x", config.core.pane.close`; focused tree/selection overrides and printable filter input retain priority. Palette-originated close actions retain the originating dock target through force confirmation.
 

docs/editing.md

@@ -327,7 +327,11 @@ The selector initially lists local revisions and known tracking refs **without c
 
 Comparison discovery builds the changed-path/status catalog first. File text, notices, and hunks load asynchronously when a file is selected and remain cached for that comparison. Failed file loads can be retried by selecting the file again; cancelled or superseded results cannot replace the current selection. Working-checkout comparisons still capture working bytes and the historical content needed to identify changes, preserving the frozen Before snapshot and unsaved After buffers.
 
-The changed-file explorer is **docked on the right**. Modified files show Before on the left and After on the right. Added files show only After, using the full text workspace; deleted files show only Before. Rename-only files show one empty pane, with the old and new paths in the explorer; renames with text or final-newline changes retain the split view. Before and historical/remote After snapshots are read-only. Selecting **Working checkout** as After binds eligible regular UTF-8 files to normal editor buffers, reusing already-open dirty buffers and their undo history. Editable After supports native edits, completion, undo/redo, and `:w`. Removed files, rename-only files, binary files, symlinks, and submodules remain read-only. Closing the diff keeps its buffers and unsaved edits.
+The changed-file explorer is **docked on the right**. In the default split layout, modified files show Before on the left and After on the right. Added files show only After, using the full text workspace; deleted files show only Before. Rename-only files show one empty pane, with the old and new paths in the explorer; renames with text or final-newline changes retain both source sides. Before and historical/remote After snapshots are read-only. Selecting **Working checkout** as After binds eligible regular UTF-8 files to normal editor buffers, reusing already-open dirty buffers and their undo history. Editable After supports native edits, completion, undo/redo, and `:w`. Removed files, rename-only files, binary files, symlinks, and submodules remain read-only. Closing the diff keeps its buffers and unsaved edits.
+
+Comparisons start in **split, left/right** view by default. In Normal mode, **Space v** cycles split/unified; **Space s** switches a split between left/right and above/below (Before above, After below). Canonical commands are `:diff.view.toggle` and `:diff.orientation.toggle`; both are available in the palette and as remappable `config.core.diff.view.toggle` / `config.core.diff.orientation.toggle` actions. Configure new-comparison defaults with `config.diff_view_mode = "split"` or `"unified"` and `config.diff_split_orientation = "left_right"` or `"above_below"`. Current choices survive file and tab switches; closing and reopening uses the configured defaults. Orientation stays unchanged while unified is active.
+
+**Unified** uses one full-width text pane with both original line-number columns: context appears once, then each changed run shows removed (`-`) lines followed by added (`+`) lines, without alignment holes. Tab/Shift+Tab still switches logical Before/After focus, preserving native source coordinates, read-only protection, and Working After editing. The border shows the combined revisions and the focused side's editability. Word wrap, syntax/semantic and character highlighting, search, selections, excerpt expansion, and wheel scrolling work in either view.
 
 Diff metadata lives in the text-pane borders instead of a separate info row: split panes show their own Before/After revision labels at the bottom-left; a single visible pane shows the combined `before → after` label there. Each pane shows its read-only/editable state at the top-right, independently of keyboard focus. Before is always read-only; After is editable only for an eligible Working-checkout file. The changed-file explorer and panes start directly below configured chrome, and there is no native-buffer help footer. Loading/error/file notices remain visible when applicable. Narrow borders prioritize state and clip titles without painting over the gutter or source text.