fix(binds): route preview scroll as DIRECT for fzf previewers

Preview scroll actions (preview-half-page-down, preview-page-down,
etc.) in keymap.builtin go through the transform handler which calls
win.lua functions operating on the neovim preview buffer. With fzf
previewers (bat, git status/commits), the preview is in fzf pane so
these functions are no-ops and scrolling does nothing.

Fix: in classify_bind, when a preview action matches a whitelist of
valid fzf preview action names and the previewer is fzf-native, set
entry.fzf_action and return DIRECT so fzf processes it natively.

Detect fzf previewer via opts.previewer (set for explicit previewer
like "bat") or opts.preview (set by providers like git_commits when
the preview command is a fzf --preview string). Only when BOTH are
nil is the previewer the neovim builtin overlay.

Whitelist prevents invalid fzf action names (preview-reset,
preview-ts-ctx-*, etc.) from being routed as DIRECT which would
cause fzf to error.

Author: ibhagwan

lua/fzf-lua/binds.lua

@@ -271,7 +271,39 @@ local function classify_bind(key, entry, opts)
   end
 
   -- Builtin action → transform
+  -- Preview scroll actions with fzf previewer should be DIRECT so fzf
+  -- can scroll its own preview pane (the neovim-side functions only
+  -- work for the builtin previewer). Only route actions that are valid
+  -- fzf action names; neovim-only preview actions (preview-reset,
+  -- preview-ts-ctx-*, etc.) must stay as TRANSFORM.
   if entry.builtin then
+    if entry.builtin:match("^preview%-") then
+      local p = opts.previewer
+      -- Detect fzf previewer when opts.previewer is not yet resolved:
+      --   opts.previewer is set → check directly (string/function/table = fzf)
+      --   opts.previewer is nil → check opts.preview (fzf --preview command)
+      --     if opts.preview is a string → fzf previewer (e.g. git show)
+      --     if opts.preview is nil → builtin previewer
+      local is_builtin = (p == nil or p == true
+          or p == "hidden" or p == "nohidden")
+          and not opts.preview
+      -- Whitelist of preview actions valid in fzf
+      local fzf_preview_action = ({
+        ["preview-up"]             = true,
+        ["preview-down"]           = true,
+        ["preview-page-up"]        = true,
+        ["preview-page-down"]      = true,
+        ["preview-half-page-up"]   = true,
+        ["preview-half-page-down"] = true,
+        ["preview-top"]            = true,
+        ["preview-bottom"]         = true,
+        ["focus-preview"]          = true,
+      })[entry.builtin]
+      if not is_builtin and fzf_preview_action then
+        entry.fzf_action = entry.builtin
+        return M.DIRECT
+      end
+    end
     return M.TRANSFORM
   end