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/detect.sh

@@ -99,17 +99,6 @@ mca_desktop_dirs() {
 	)
 }
 
-# mca_desktop_get <file> <key>
-# A single value from the [Desktop Entry] group. Desktop Action groups repeat
-# the same keys, and reading past the first group would pick up the wrong one.
-mca_desktop_get() {
-	local file="$1" key="$2"
-	awk -v key="$key" '
-		/^[[:space:]]*\[/ { inentry = ($0 ~ /^[[:space:]]*\[Desktop Entry\][[:space:]]*$/); next }
-		inentry && index($0, key "=") == 1 { print substr($0, length(key) + 2); exit }
-	' "$file" 2>/dev/null
-}
-
 # _mca_desktop_read <file>
 # Every key the scan needs, in one pass and without a single fork. There are a
 # couple of hundred desktop entries on an ordinary system, and doing this with
@@ -231,8 +220,22 @@ mca_exec_is_steam_link() {
 	local line="$1" prog="$2"
 
 	[[ $line == *steam://* ]] || return 1
+	mca_prog_is_steam "$prog"
+}
+
+# mca_prog_is_steam <program>
+# Whether running this program starts the Steam client. Every packaging is in
+# here and every name Valve and the distributions give the launcher, because
+# the answer decides whether an entry gets Steam's own switch - and an entry
+# that starts Steam without it undoes the web helper patch on the way up.
+#
+# The program is what a scan leaves behind: an absolute path for a native
+# install, flatpak:<id> or snap:<name> for the other two.
+mca_prog_is_steam() {
+	local prog="$1"
+
 	case "${prog##*/}" in
-		steam|steam-runtime) return 0 ;;
+		steam|steam-runtime|steam-native|steam-jupiter) return 0 ;;
 	esac
 	[[ $prog == flatpak:com.valvesoftware.Steam || $prog == snap:steam ]]
 }
@@ -580,6 +583,8 @@ MCA_PACKAGING=()  # native | flatpak | snap
 # kept at all: the Steam module gives them Steam's own switch.
 MCA_STEAM_LINKS=()       # desktop file id
 MCA_STEAM_LINK_FILES=()  # the entry that is in effect for it
+MCA_STEAM_LINK_PACK=()   # native | flatpak | snap, which decides where the
+                         # switch goes on the command line
 
 # A scan reads every desktop entry on the system, so the menu does it once and
 # then redraws from what it found. Applying rescans on its own, so nothing else
@@ -598,7 +603,7 @@ mca_scan() {
 
 	MCA_IDS=(); MCA_FILES=(); MCA_NAMES=(); MCA_PROGS=(); MCA_KINDS=()
 	MCA_PACKAGING=()
-	MCA_STEAM_LINKS=(); MCA_STEAM_LINK_FILES=()
+	MCA_STEAM_LINKS=(); MCA_STEAM_LINK_FILES=(); MCA_STEAM_LINK_PACK=()
 
 	# Pass one: read the entries and work out what each of them starts. No
 	# detection yet - that needs a stat per program, and those are collected so
@@ -641,6 +646,13 @@ mca_scan() {
 			if mca_exec_is_steam_link "$exec_line" "$prog"; then
 				MCA_STEAM_LINKS+=("$id")
 				MCA_STEAM_LINK_FILES+=("$file")
+				if [[ $prog == flatpak:* ]]; then
+					MCA_STEAM_LINK_PACK+=(flatpak)
+				elif [[ $prog == snap:* ]]; then
+					MCA_STEAM_LINK_PACK+=(snap)
+				else
+					MCA_STEAM_LINK_PACK+=(native)
+				fi
 				continue
 			fi
 
@@ -664,10 +676,13 @@ mca_scan() {
 		packaging=native
 
 		if [[ $prog == flatpak:* ]]; then
-			prog="${prog#flatpak:}"
 			packaging=flatpak
-			mca_flatpak_is_chromium "$prog" \
-				&& { (( c_browser[i] )) && kind=browser || kind=app; }
+			if mca_prog_is_steam "$prog"; then
+				kind=steam
+			elif mca_flatpak_is_chromium "${prog#flatpak:}"; then
+				(( c_browser[i] )) && kind=browser || kind=app
+			fi
+			prog="${prog#flatpak:}"
 		elif [[ $prog == snap:* ]]; then
 			prog="${prog#snap:}"
 			packaging=snap
@@ -676,7 +691,7 @@ mca_scan() {
 			elif mca_snap_is_chromium "$prog"; then
 				(( c_browser[i] )) && kind=browser || kind=app
 			fi
-		elif [[ ${prog##*/} == steam || ${prog##*/} == steam-runtime ]]; then
+		elif mca_prog_is_steam "$prog"; then
 			# Steam is Chromium inside, but nothing about it can be changed
 			# from a command line argument; it has its own module.
 			kind=steam