fix: make the Steam patch survive Steam's own file check

Steam's autoscroll worked, except when it didn't. Every report of that came
down to the same thing: Steam started in a way that carried no -noverifyfiles,
noticed the patched web helper script, put its own copy back, and spent the
session without the flag. There is no way to make every possible way of
starting Steam carry an argument - a game launcher, a shortcut, a terminal,
another program calling `steam steam://` - so the patch stops depending on it.

The check is on size and timestamp, not on content, so the patch is now written
to look untouched: the bytes the flag costs come back out of the script's own
comments, and the timestamp of the untouched copy is restored afterwards. The
file Steam finds is exactly as long and exactly as old as the one it wrote. A
client that verifies its files finds nothing to repair. -noverifyfiles stays as
the fallback for a script with no comments left to pay for the flag.

Two things fall out of that. A patch that keeps the size no longer has to wait
for Steam to close, because there is no size mismatch for the client to chase;
only the growing one still defers. And an installation patched by the earlier
version is quietly redone at the original size on the next apply, so the fix
arrives without anyone having to know about it.

Then the launch paths that were never covered:

- Shortcuts on the desktop itself. Nothing in the XDG search path looks at
  that folder, so nothing had ever seen them - and Steam writes one there for
  every game somebody asks for a shortcut to. Its name is translated, so it is
  read from user-dirs.dirs and handed to the watcher in a drop-in.
- Steam as a Flatpak was never recognised as Steam, so its entry got nothing
  while its script got patched - the worst of both. The switch goes after the
  application id there, where flatpak passes it on rather than reading it.
- steam-native and steam-jupiter, which are ordinary Steam starts under
  another name, and Flatpak and snap entries in ~/.config/autostart.

Two things found on the way: a client update left the undo copy holding the
script from before the update, so undoing would have put an old version back;
and a shortcut edited in place and later deleted would have been recreated by
`disable`.

src/lib/patch.sh

@@ -349,51 +349,117 @@ mca_desktop_apply() {
 }
 
 # ---------------------------------------------------------------------------
-# Autostart entries
+# Entries outside the search path
 # ---------------------------------------------------------------------------
-# Applications that start themselves at login write their own entry into
-# ~/.config/autostart, pointing straight at their binary. Those bypass the
-# desktop entry in the menu completely, which is why Discord launched at login
-# used to behave differently from Discord launched from the menu.
+# Two directories hold desktop entries that no part of the XDG search path
+# looks at, so nothing the scan does can reach them:
 #
-# Steam is here too, even though it is not a Chromium process itself: its entry
-# needs -noverifyfiles exactly like the menu one, and it is the entry most
-# likely to exist, because Steam writes it as soon as "run at startup" is
-# ticked. Without it, a Steam started at login restores the patched web helper
-# script and the watcher patches it back, over and over.
+#   ~/.config/autostart, where applications that start themselves at login
+#   write their own entry, pointing straight at their binary. Those bypass the
+#   entry in the menu completely, which is why Discord launched at login used
+#   to behave differently from Discord launched from the menu.
+#
+#   The desktop folder, where a shortcut somebody dragged out of the menu -
+#   or asked Steam for - lives and nowhere else.
+#
+# Steam is in both, even though it is not a Chromium process itself: its
+# entries need -noverifyfiles exactly like the menu one. The autostart entry is
+# the one most likely to exist, because Steam writes it as soon as "run at
+# startup" is ticked; without it a Steam started at login restores the patched
+# web helper script and the watcher patches it back, over and over. The desktop
+# ones are the gap behind "autoscroll works, except sometimes": starting a game
+# from the desktop is a Steam start like any other, and a Steam start without
+# the switch costs the interface its autoscroll for the rest of the session.
+#
+# Neither can be shadowed from anywhere, so both are edited where they stand,
+# with the original kept.
+
+# _mca_entry_patch_inplace <file> <gate: autostart|apps>
+# One desktop entry that lives outside the XDG search path, edited where it is
+# because there is nowhere to shadow it from.
+#
+# Anything that starts Steam gets Steam's own switch; a Chromium application
+# gets the flag. What decides whether a Chromium application here is in scope
+# differs by where the entry came from, which is what the gate says: an
+# autostart entry follows the autostart setting, a shortcut follows the same
+# rules as the application it is a shortcut to.
+_mca_entry_patch_inplace() {
+	local file="$1" gate="$2"
+	local id prog packaging=native content backup kind
+
+	grep -q "^$MCA_MARK_INPLACE=" "$file" 2>/dev/null && return 0
+
+	_mca_desktop_read "$file"
+	[[ -n $DE_EXEC ]] || return 0
+	[[ $DE_HIDDEN == true ]] && return 0
+
+	mca_exec_program "$DE_EXEC" || return 0
+	prog="$MCA_PROG"
+
+	# A Flatpak or a snap entry names the wrapper rather than the application.
+	# The scan resolves those into an id; outside the scan the same has to
+	# happen here, or every Flatpak looks like the flatpak program itself.
+	if [[ ${prog##*/} == flatpak ]]; then
+		mca_exec_flatpak_id "$DE_EXEC" || return 0
+		prog="flatpak:$MCA_PROG"
+		packaging=flatpak
+	elif mca_snap_name "$prog"; then
+		prog="snap:$MCA_PROG"
+		packaging=snap
+	fi
+
+	if mca_prog_is_steam "$prog"; then
+		[[ $CFG_STEAM == yes ]] || return 0
+		content="$(_mca_desktop_transform "$file" "$MCA_MARK_INPLACE" \
+			"$MCA_STEAM_LAUNCH_FLAG" "$(mca_steam_flag_position "$packaging")")"
+	else
+		case "$packaging" in
+			flatpak) mca_flatpak_is_chromium "${prog#flatpak:}" || return 0 ;;
+			snap)    mca_snap_is_chromium "${prog#snap:}" || return 0 ;;
+			*)       mca_is_chromium "$prog" || return 0 ;;
+		esac
+
+		if [[ $gate == autostart ]]; then
+			[[ $CFG_AUTOSTART == yes ]] || return 0
+		else
+			id="${file##*/}"; id="${id%.desktop}"
+			mca_desktop_is_browser && kind=browser || kind=app
+			mca_kind_wanted "$kind" "$id" "$packaging" || return 0
+		fi
+
+		content="$(_mca_desktop_transform "$file" "$MCA_MARK_INPLACE")"
+	fi
+
+	[[ -n $content ]] || return 0
+	[[ "$content" == "$(< "$file")" ]] && return 0
+
+	backup="$(mca_backup "$file")" || return 0
+	if mca_write_if_changed "$file" "$content"$'\n'; then
+		MCA_CHANGES=$(( MCA_CHANGES + 1 ))
+	fi
+	mca_ledger_add inplace "$file" "$backup"
+}
 
 mca_autostart_apply() {
-	local dir="$MCA_XDG_CONFIG/autostart" file exec_line prog content backup
+	local dir="$MCA_XDG_CONFIG/autostart" file
 
 	[[ -d $dir ]] || return 0
 
 	for file in "$dir"/*.desktop; do
 		[[ -f $file ]] || continue
-		grep -q "^$MCA_MARK_INPLACE=" "$file" 2>/dev/null && continue
+		_mca_entry_patch_inplace "$file" autostart
+	done
+}
 
-		exec_line="$(mca_desktop_get "$file" Exec)"
-		[[ -n $exec_line ]] || continue
+mca_shortcuts_apply() {
+	local dir file
+	dir="$(mca_desktop_folder)"
 
-		mca_exec_program "$exec_line" || continue
-		prog="$MCA_PROG"
+	[[ -d $dir ]] || return 0
 
-		if [[ ${prog##*/} == steam || ${prog##*/} == steam-runtime ]]; then
-			[[ $CFG_STEAM == yes ]] || continue
-			content="$(_mca_desktop_transform "$file" "$MCA_MARK_INPLACE" \
-				"$MCA_STEAM_LAUNCH_FLAG" after-program)"
-		else
-			[[ $CFG_AUTOSTART == yes ]] || continue
-			mca_is_chromium "$prog" || continue
-			content="$(_mca_desktop_transform "$file" "$MCA_MARK_INPLACE")"
-		fi
-		[[ -n $content ]] || continue
-		[[ "$content" == "$(< "$file")" ]] && continue
-
-		backup="$(mca_backup "$file")" || continue
-		if mca_write_if_changed "$file" "$content"$'\n'; then
-			MCA_CHANGES=$(( MCA_CHANGES + 1 ))
-		fi
-		mca_ledger_add inplace "$file" "$backup"
+	for file in "$dir"/*.desktop; do
+		[[ -f $file ]] || continue
+		_mca_entry_patch_inplace "$file" apps
 	done
 }
 
@@ -446,13 +512,15 @@ mca_spotify_apply() {
 # ---------------------------------------------------------------------------
 
 # mca_prune_orphans
-# Removes generated entries whose application is gone.
+# Forgets changes there is no longer anything to undo.
 #
 # Uninstalling something deletes its entry from /usr/share/applications, but the
 # copy shadowing it is in the user's home and pacman knows nothing about it. It
 # would sit in the menu forever, offering to start a program that is no longer
 # installed - and the watcher would not notice, because a plain apply only ever
-# looks at what is there now.
+# looks at what is there now. A file that was edited where it stood and has
+# since been deleted is the same problem from the other side: its record would
+# have `disable` put the file back.
 mca_prune_orphans() {
 	local kind path source line
 	local -a lines=()
@@ -462,6 +530,17 @@ mca_prune_orphans() {
 
 	for line in "${lines[@]}"; do
 		IFS=$'\t' read -r kind path source <<< "$line"
+
+		# An entry that was edited where it stood and has since been deleted -
+		# a game shortcut dragged to the wastebasket, an autostart entry the
+		# application removed. There is nothing left to put back, and keeping
+		# the record would have `disable` recreate a file the user threw away.
+		if [[ $kind == inplace && ! -e $path ]]; then
+			[[ -n $source ]] && rm -f -- "$MCA_BACKUPDIR/$source"
+			mca_ledger_forget "$path"
+			continue
+		fi
+
 		[[ $kind == shadow && -n $source ]] || continue
 		[[ -e $source ]] && continue