omit netrw from saved sessions

LOG.md

@@ -220,6 +220,7 @@ Record every decision here with a short rationale. Append new entries; do not re
 - 2026-10-28: Made netrw file previews intentionally plain after CSS and HTML exposed residual colour. The remaining decoration was Vim regex syntax plus indent-blankline extmarks, not diagnostics or Tree-sitter. Preview buffers now clear `syntax` and disable their buffer-local indent guides, then restore both recorded states on real edit.
 - 2026-10-28: Added buffer-local netrw `<M-j>` / `<M-k>` mappings to scroll the current preview with native `<C-e>` / `<C-y>` behavior while focus remains in the tree. The mappings accept Vim counts and quietly do nothing when no preview exists.
 - 2026-10-28: Hardened preview scrolling after an interactive over-scroll surfaced a window-local error that did not reproduce headlessly. The temporary preview-window call is now protected, so stale-window and boundary failures are treated like native top/bottom clamping instead of reaching the command line.
+- 2026-10-28: Excluded netrw from automatic session persistence after `:mksession` serialized its generated `NetrwTreeListing` name and restored an empty explorer buffer. Before the existing exit-time save, preview windows and netrw windows are removed; a netrw-only tab is dropped, while the sole remaining netrw window is replaced with an ordinary file buffer or a blank fallback. Netrw is intentionally not rebuilt on load.
 
 ## Project-Local Configuration
 

MIGRATION_PLAN.md

@@ -500,6 +500,7 @@ Source of truth for the step-by-step rebuild. Keep this concise and up to date.
 ## Phase 12.6 — Final polish
 - [x] Review all keymaps and ensure they're documented (README.md + :KeymapsGuide)
 - [x] Update LOG.md with final architecture and usage
+- [x] Omit transient netrw and preview windows from automatic session saves
 - [ ] Clean up any remaining debug code or temporary comments
 
 ## Phase 13 — Controlled Neovim 0.12 Upgrade

README.md

@@ -16,6 +16,7 @@ Session support is automatic but user-controlled:
 **Auto-load/save** (via `lua/autocmds.lua`):
 - On startup: auto-loads `Session.vim` if it exists (unless files specified on command line)
 - On exit: auto-saves to `Session.vim` if it already exists
+- Netrw and its preview windows are omitted from the saved layout; generated `NetrwTreeListing` buffers are not restorable
 - Sessions are per-directory and opt-in (just create one to start using)
 
 **Stop using a session**:

lua/autocmds.lua

@@ -137,6 +137,78 @@ vim.api.nvim_create_autocmd("SessionLoadPost", {
 	end,
 })
 
+local function is_netrw_session_buffer(buf)
+	return vim.api.nvim_buf_is_valid(buf)
+		and (vim.bo[buf].filetype == "netrw" or vim.api.nvim_buf_get_name(buf):match("NetrwTreeListing$") ~= nil)
+end
+
+local function session_fallback_buffer()
+	for _, buf in ipairs(vim.api.nvim_list_bufs()) do
+		if
+			vim.api.nvim_buf_is_valid(buf)
+			and vim.bo[buf].buflisted
+			and vim.bo[buf].buftype == ""
+			and vim.api.nvim_buf_get_name(buf) ~= ""
+			and not is_netrw_session_buffer(buf)
+		then
+			return buf
+		end
+	end
+
+	return vim.api.nvim_create_buf(true, false)
+end
+
+local function close_session_tab(tab)
+	if vim.api.nvim_tabpage_close then
+		pcall(vim.api.nvim_tabpage_close, tab, true)
+		return
+	end
+
+	pcall(function()
+		vim.api.nvim_set_current_tabpage(tab)
+		vim.cmd("tabclose!")
+	end)
+end
+
+local function omit_netrw_from_session()
+	local tabs_with_netrw = {}
+	for _, tab in ipairs(vim.api.nvim_list_tabpages()) do
+		for _, win in ipairs(vim.api.nvim_tabpage_list_wins(tab)) do
+			if is_netrw_session_buffer(vim.api.nvim_win_get_buf(win)) then
+				tabs_with_netrw[tab] = true
+				break
+			end
+		end
+	end
+
+	for tab in pairs(tabs_with_netrw) do
+		if vim.api.nvim_tabpage_is_valid(tab) then
+			for _, win in ipairs(vim.api.nvim_tabpage_list_wins(tab)) do
+				if vim.api.nvim_win_is_valid(win) and vim.wo[win].previewwindow then
+					pcall(vim.api.nvim_win_close, win, true)
+				end
+			end
+
+			if vim.api.nvim_tabpage_is_valid(tab) then
+				for _, win in ipairs(vim.api.nvim_tabpage_list_wins(tab)) do
+					if
+						vim.api.nvim_win_is_valid(win)
+						and is_netrw_session_buffer(vim.api.nvim_win_get_buf(win))
+					then
+						if #vim.api.nvim_tabpage_list_wins(tab) > 1 then
+							pcall(vim.api.nvim_win_close, win, true)
+						elseif #vim.api.nvim_list_tabpages() > 1 then
+							close_session_tab(tab)
+						else
+							vim.api.nvim_win_set_buf(win, session_fallback_buffer())
+						end
+					end
+				end
+			end
+		end
+	end
+end
+
 -- Auto-save session on exit, but ONLY if Session.vim already exists
 vim.api.nvim_create_autocmd("VimLeavePre", {
 	group = session_aug,
@@ -144,6 +216,7 @@ vim.api.nvim_create_autocmd("VimLeavePre", {
 	callback = function()
 		-- Only save if Session.vim exists (user manually created it)
 		if vim.fn.filereadable("Session.vim") == 1 then
+			omit_netrw_from_session()
 			vim.cmd("mksession! Session.vim")
 		end
 	end,