feat: follow forward working-checkout changes in diffs

docs/configuration.md

@@ -21,6 +21,7 @@ Vamp.configure do |config|
   config.diff_expand_lines = 15
   config.diff_view_mode = "split" # or "unified"
   config.diff_split_orientation = "vertical" # or "horizontal"
+  config.diff_follow_working_copy = true
   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"
@@ -51,6 +52,8 @@ Plugin paths resolve relative to the config file, not the shell's working direct
 
 `config.diff_view_mode` selects the initial view for each new comparison: `"split"` (default) or `"unified"`. `config.diff_split_orientation` selects `"vertical"` (left/right, default) or `"horizontal"` (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.
 
+`config.diff_follow_working_copy` defaults to `true`. A Working-checkout After follows descendant checkouts automatically, including in inactive tabs; `false` disables endpoint following without disabling ordinary live-buffer editing or reload. Only literal booleans are accepted. Historical After endpoints never follow. See [repository diff](editing.md#repository-diff) for ancestry and refresh behavior.
+
 ```ruby
 config.bind "ctrl+b", config.core.diff.mode.toggle
 config.bind "leader v", config.core.diff.view.toggle

docs/editing.md

@@ -349,6 +349,10 @@ 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 Failed file loads can be retried by selecting the file again; cancelled or superseded results cannot replace the current selection. Working-checkout comparisons still capture working bytes and the historical content needed to identify changes, preserving the frozen Before snapshot and unsaved After buffers.
 
+**Working checkout After follows forward checkouts automatically**, checked asynchronously once per second, including inactive tabs. A descendant jj change or Git HEAD rebuilds the changed-file catalog and captures current working bytes plus eligible unsaved buffers, while keeping the original Before frozen. jj tracking uses change IDs, so snapshot/description rewrites of the same change do not advance the endpoint or prevent following its later descendants. Same, backward, and unrelated checkouts do not rebuild the catalog; live-buffer editing and external reload still work normally. Historical After never follows. Set `config.diff_follow_working_copy = false` to disable following.
+
+Refresh retains the selected path when still present, explorer query/view/visibility, logical text-side focus, and split/unified/orientation/wrap choices; it clears review marks for the new endpoint. Removed selections fall back to the first changed file. Failed refreshes keep the previous comparison visible. Superseded file loads and LSP navigation cannot apply to the new comparison; snapshots still displayed in other panes or tabs remain read-only.
+
 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, vertical (left/right)** view by default. In Normal mode, **Space v** cycles split/unified; **Space s** switches a split between vertical (left/right) and horizontal (above/below, Before above After). 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 = "vertical"` or `"horizontal"`. Current choices survive file and tab switches; closing and reopening uses the configured defaults. Orientation stays unchanged while unified is active.