diff --git a/app/src/main/java/com/droiddeck/launcher/session/ComponentsManager.kt b/app/src/main/java/com/droiddeck/launcher/session/ComponentsManager.kt
index 118051424..7004f2d10 100644
--- a/app/src/main/java/com/droiddeck/launcher/session/ComponentsManager.kt
+++ b/app/src/main/java/com/droiddeck/launcher/session/ComponentsManager.kt
@@ -80,7 +80,11 @@ object ComponentsManager {
     data class Original(val comp: String, val protonVersion: String, val label: String, val size: Long)
     data class Package(val file: String, val comp: String, val version: String, val description: String, val size: Long)
     data class CatalogItem(val file: String, val comp: String, val release: String, val url: String, val size: Long, val digest: String)
-    data class ProtonView(val proton: Proton, val components: Map<String, Component>, val originals: List<Original>, val inUseByGame: Boolean)
+    data class ProtonView(
+        val proton: Proton, val components: Map<String, Component>, val originals: List<Original>, val inUseByGame: Boolean,
+        /** When a launch last had to put this Proton's chosen files back (epoch seconds), or 0. */
+        val reappliedAt: Long = 0,
+    )
     data class Snapshot(val protons: List<ProtonView>, val packages: List<Package>)
     data class Catalog(val items: List<CatalogItem>, val fetchedAt: Long)
 
@@ -96,6 +100,12 @@ object ComponentsManager {
     private fun originalsDir(context: Context) = File(dataDir(context), "originals").apply { mkdirs() }
     private fun stateFile(context: Context) = File(dataDir(context), "state.json")
     private fun catalogFile(context: Context) = File(dataDir(context), "catalog.json")
+    /**
+     * Inside the Linux runtime, read by the Proton launch wrappers (bannerlator-steam-compat's
+     * bl_components) before every game launch: desired.tsv + an unpacked copy of each package in use.
+     */
+    private const val LAUNCH_DIR = "root/.local/share/bannerlator-components"
+    private fun launchDir(context: Context) = File(root(context), LAUNCH_DIR)
 
     fun safeName(s: String): String = s.replace(Regex("[^A-Za-z0-9._+-]+"), "_").trim('_').ifEmpty { "unnamed" }
 
@@ -112,6 +122,8 @@ object ComponentsManager {
         val tmp = File(f.parentFile, f.name + ".tmp")
         tmp.writeText(state.toString(2))
         tmp.renameTo(f)
+        // Every change of choice reaches the launch wrappers at once.
+        runCatching { syncLaunchState(context, state) }.onFailure { Log.w(TAG, "launch state", it) }
     }
 
     private fun JSONObject.sub(key: String): JSONObject = optJSONObject(key) ?: JSONObject().also { put(key, it) }
@@ -364,6 +376,7 @@ object ComponentsManager {
         for (p in protons(context)) for (comp in COMPONENTS) {
             runCatching { ensureOriginal(context, p, comp, state) }.onFailure { Log.w(TAG, "original $comp of ${p.name}", it) }
         }
+        runCatching { syncLaunchState(context, state) }.onFailure { Log.w(TAG, "launch state", it) }
     }
 
     // ------------------------------------------------------------------ view
@@ -371,6 +384,13 @@ object ComponentsManager {
     fun snapshot(context: Context): Snapshot = synchronized(lock) {
         migratePlugin(context)
         val state = loadState(context)
+        val reapplied = HashMap<String, Long>()
+        runCatching {
+            File(launchDir(context), "reapplied.log").forEachLine { line ->
+                val parts = line.split('\t')
+                if (parts.size >= 2) parts[0].toLongOrNull()?.let { reapplied[parts[1]] = maxOf(reapplied[parts[1]] ?: 0, it) }
+            }
+        }
         val views = protons(context).map { p ->
             val comps = COMPONENTS.associateWith { comp ->
                 val detected = if (comp == "fex") fexVersion(p.dir) else readVersionFile(File(p.dir, "${COMP_DIR.getValue(comp)}/version"))
@@ -393,11 +413,73 @@ object ComponentsManager {
                     q?.optString("label"),
                 )
             }
-            ProtonView(p, comps, originals(context, p.id), inUse(p))
+            ProtonView(p, comps, originals(context, p.id), inUse(p), reapplied[p.dir.name] ?: 0)
         }
         Snapshot(views, packages(context))
     }
 
+    // ------------------------------------------------------------------ launch-time enforcement
+
+    /**
+     * Writes what each Proton should be using for the launch wrappers: desired.tsv, one line per
+     * file (tool dir, Proton build, component, file, sha256, source copy), and an unpacked copy of
+     * every package or older-build original in use to copy from. Rebuilt whole after every change, so
+     * a restored or deleted choice simply stops being enforced. The Proton's own current-build
+     * originals are not listed: the wrappers also give Steam's probe runs their own prefix, which is
+     * what overwrote files in the first place.
+     */
+    private fun syncLaunchState(context: Context, state: JSONObject) {
+        val dir = launchDir(context)
+        val store = File(dir, "store").apply { mkdirs() }
+        val all = protons(context)
+        val lines = StringBuilder()
+        val keep = HashSet<String>()
+        val active = state.sub("active")
+        for (pid in active.keys()) {
+            val p = all.firstOrNull { it.id == pid } ?: continue
+            val comps = active.optJSONObject(pid) ?: continue
+            for (comp in comps.keys()) {
+                val a = comps.optJSONObject(comp) ?: continue
+                if (a.optString("protonVersion") != p.version) continue
+                val file = a.optString("file")
+                val (key, wcp) = if (file.startsWith("original ")) {
+                    val v = file.removePrefix("original ")
+                    "original-$pid-${safeName(v)}-$comp" to File(originalsDir(context), "$pid/${safeName(v)}/$comp.wcp")
+                } else safeName(file.removeSuffix(".wcp")) to File(packagesDir(context), file)
+                if (!wcp.isFile) continue
+                val unpacked = File(store, key)
+                if (!File(unpacked, ".complete").isFile) {
+                    unpacked.deleteRecursively()
+                    readWcp(wcp) { tar ->
+                        while (true) {
+                            val e = tar.nextTarEntry ?: break
+                            val rel = normalize(e.name)
+                            if (e.isDirectory || !rel.startsWith("files/") || rel.split('/').any { it == ".." }) continue
+                            val out = File(unpacked, rel)
+                            out.parentFile?.mkdirs()
+                            FileOutputStream(out).use { tar.copyTo(it) }
+                        }
+                    }
+                    File(unpacked, ".complete").writeText("1\n")
+                }
+                keep += key
+                val files = a.optJSONObject("files") ?: continue
+                for (rel in files.keys()) {
+                    val src = File(unpacked, rel)
+                    if (!src.isFile) continue
+                    val guestSrc = "/" + src.absolutePath.removePrefix(root(context).absolutePath.trimEnd('/')).trimStart('/')
+                    lines.append(p.dir.name).append('\t').append(p.version).append('\t').append(comp).append('\t')
+                        .append(rel).append('\t').append(files.optString(rel)).append('\t').append(guestSrc).append('\n')
+                }
+            }
+        }
+        store.listFiles()?.filter { it.isDirectory && it.name !in keep }?.forEach { it.deleteRecursively() }
+        val list = File(dir, "desired.tsv")
+        val tmp = File(dir, "desired.tsv.tmp")
+        tmp.writeText(lines.toString())
+        tmp.renameTo(list)
+    }
+
     // ------------------------------------------------------------------ actions
 
     /** Applies a package now, or queues it when a game is running on that Proton. Returns what happened. */
diff --git a/app/src/main/java/com/droiddeck/launcher/ui/ComponentsPage.kt b/app/src/main/java/com/droiddeck/launcher/ui/ComponentsPage.kt
index 6640c7c96..820c9f9eb 100644
--- a/app/src/main/java/com/droiddeck/launcher/ui/ComponentsPage.kt
+++ b/app/src/main/java/com/droiddeck/launcher/ui/ComponentsPage.kt
@@ -147,8 +147,9 @@ fun ComponentsPage(
                 Row(verticalAlignment = Alignment.CenterVertically, modifier = Modifier.weight(1f)) {
                     Box(Modifier.size(8.dp).background(if (st.queued != null) Color(0xFFFFB86B) else pal.good, CircleShape))
                     Spacer(Modifier.width(6.dp))
+                    val fixedAt = if (view.reappliedAt > 0) " · re-applied at launch " + DateFormat.getTimeInstance(DateFormat.SHORT).format(Date(view.reappliedAt * 1000)) else ""
                     Text(
-                        if (st.queued != null) "Next: ${st.queued} · after the game" else "In use: ${st.inUse}",
+                        (if (st.queued != null) "Next: ${st.queued} · after the game" else "In use: ${st.inUse}") + fixedAt,
                         fontSize = 12.5.sp, color = colors.onBackground, maxLines = 1, overflow = TextOverflow.Ellipsis, modifier = Modifier.weight(1f, fill = false),
                     )
                     if (st.queued != null) { Spacer(Modifier.width(8.dp)); FocusText("Cancel", pal.signal, onClick = onCancelQueued) }
@@ -244,6 +245,7 @@ fun ComponentsPage(
             Text(
                 "FEX, DXVK and VKD3D-Proton for each Proton the Steam client runs games with.\n\n" +
                     "Tap an installed row to swap it in; it applies the next time a game starts. If a game is running on that Proton, the swap waits until it closes.\n\n" +
+                    "Your choices are also checked right before every game launch: if anything changed a Proton's files (Steam's start-up tests, for one), they are put back first, and the page says \"re-applied at launch\".\n\n" +
                     "Each Proton build's own files are kept as its ORIGINAL, so a Steam update never loses them. Packages come from the Nightlies \"-Linux\" releases (refresh) or Import .wcp.",
                 fontSize = 13.sp,
             )
diff --git a/app/src/main/java/com/droiddeck/launcher/ui/SessionOverlay.kt b/app/src/main/java/com/droiddeck/launcher/ui/SessionOverlay.kt
index 8f918fc88..7a4169e70 100644
--- a/app/src/main/java/com/droiddeck/launcher/ui/SessionOverlay.kt
+++ b/app/src/main/java/com/droiddeck/launcher/ui/SessionOverlay.kt
@@ -733,7 +733,8 @@ private fun ComponentsDrawerPage(host: MenuHost, a: DrawerActions, track: (Strin
     val p = view.proton
     SettingsGroup("Components") {
         ChoiceRow(
-            host, "cmp-proton", "Proton", p.version + if (view.inUseByGame) " · in use by the running game" else "",
+            host, "cmp-proton", "Proton", p.version + (if (view.inUseByGame) " · in use by the running game" else "") +
+                (if (view.reappliedAt > 0) " · re-applied at launch " + java.text.DateFormat.getTimeInstance(java.text.DateFormat.SHORT).format(java.util.Date(view.reappliedAt * 1000)) else ""),
             snap.protons.map { it.proton.id to it.proton.name }, p.id,
             chipModifier = track("cmp-proton"), onPick = { pick = it },
         )
diff --git a/tools/linuxfs/overlay/usr/local/bin/__pycache__/bannerlator-steam-compatcpython-313.pyc b/tools/linuxfs/overlay/usr/local/bin/__pycache__/bannerlator-steam-compatcpython-313.pyc
new file mode 100644
index 000000000..da69fcc74
Binary files /dev/null and b/tools/linuxfs/overlay/usr/local/bin/__pycache__/bannerlator-steam-compatcpython-313.pyc differ
diff --git a/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-compat b/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-compat
index 4156846a5..82644dd02 100755
--- a/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-compat
+++ b/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-compat
@@ -70,6 +70,62 @@ TOOL_MANIFEST_VDF = """"manifest"
 }
 """ % LAUNCHER
 
+
+# Steam runs its own graphics probe through EVERY registered tool at once, ~40 s after logging in,
+# all with STEAM_COMPAT_DATA_PATH=.../compatdata/0. A prefix's system32 holds links into the Proton
+# that last set it up, and the Wines of the other Protons, still running outside Proton's pfx.lock,
+# wrote their own builtin DLLs through those links - into that Proton's tree (seen on device: GE's
+# FEX DLLs replaced by Proton Experimental's at session start). So each tool's tool-0 run gets a
+# prefix of its own; games, which each have their own compatdata/<appid>, are not touched.
+BL_PROBE_PREFIX_SETUP = """
+bl_probe_prefix() {
+  case "${STEAM_COMPAT_DATA_PATH:-}" in
+    */compatdata/0|*/compatdata/0/)
+      STEAM_COMPAT_DATA_PATH="${STEAM_COMPAT_DATA_PATH%/}-$1"
+      mkdir -p "$STEAM_COMPAT_DATA_PATH"
+      export STEAM_COMPAT_DATA_PATH
+      echo "bannerlator-proton: Steam's tool-0 run gets its own prefix: $STEAM_COMPAT_DATA_PATH" >&2 ;;
+  esac
+}
+"""
+
+# The Components page's choices, enforced in the one place every game launch passes: the app keeps
+# desired.tsv (tool dir, Proton build, component, file, sha256, source copy) and an unpacked copy of
+# each package in use. A file that no longer matches - whatever changed it - is put back before
+# Proton starts. Only for the Proton build the choice was made for: after a Steam update the build
+# differs and the Proton's own new files are left alone until the user chooses again.
+BL_COMPONENTS_SETUP = """
+bl_components() {
+  base=$1
+  cm_dir="${HOME:-/root}/.local/share/bannerlator-components"
+  cm_list="$cm_dir/desired.tsv"
+  [ -f "$cm_list" ] || return 0
+  case "${STEAM_COMPAT_DATA_PATH:-}" in */compatdata/0|*/compatdata/0/|*/compatdata/0-*) return 0 ;; esac
+  cm_tool=${base##*/}
+  cm_build=$(awk 'NR == 1 { print $2 }' "$base/version" 2>/dev/null)
+  cm_fixed=0
+  cm_checked=0
+  while IFS=$'\\t' read -r t want comp rel sum src; do
+    [ "$t" = "$cm_tool" ] && [ "$want" = "$cm_build" ] || continue
+    cm_checked=$((cm_checked + 1))
+    f="$base/$rel"
+    if [ -f "$f" ] && [ "$(sha256sum "$f" | cut -d' ' -f1)" = "$sum" ]; then continue; fi
+    if [ ! -f "$src" ]; then
+      echo "bannerlator-proton: components: $comp source missing ($src), left as it is" >&2
+      continue
+    fi
+    mkdir -p "$(dirname "$f")"
+    cp -f "$src" "$f.bl-new" && mv -f "$f.bl-new" "$f" || continue
+    case "$rel" in *.so) chmod 755 "$f" ;; *) chmod 644 "$f" ;; esac
+    cm_fixed=$((cm_fixed + 1))
+  done < "$cm_list"
+  if [ "$cm_fixed" -gt 0 ]; then
+    echo "bannerlator-proton: components: re-applied $cm_fixed of $cm_checked file(s) in $cm_tool before this launch" >&2
+    printf '%s\\t%s\\t%s\\n' "$(date +%s)" "$cm_tool" "$cm_fixed" >> "$cm_dir/reapplied.log"
+  fi
+}
+"""
+
 # Resolves the depot at launch time, so the tool can be registered before the depot exists and
 # survives the client updating or replacing it. Proton takes its base directory from
 # dirname(sys.argv[0]) without resolving it, so it is run from the depot itself.
@@ -172,9 +228,11 @@ if [ -f "$fake" ]; then
     *) LD_PRELOAD="$fake${LD_PRELOAD:+:$LD_PRELOAD}"; export LD_PRELOAD ;;
   esac
 fi
+bl_probe_prefix "bannerlator-proton-arm64"
 for name in %s; do
   depot="$steam_root/steamapps/common/$name"
   if [ -d "$depot/files/bin-arm64" ] && [ -x "$depot/proton" ]; then
+    bl_components "$depot"
     bl_directaudio "$depot"
     bl_game_cpus
     bl_idtech3 "$@"
@@ -188,7 +246,8 @@ exit 1
 # and a % format would eat that into a single %, leaving a shell expansion that silently does
 # something else.
 LAUNCHER_SH = LAUNCHER_SH.replace(
-    "verb=$1; shift", "verb=$1; shift\n" + BL_DIRECTAUDIO_SETUP + BL_GAME_CPUS_SETUP + BL_IDTECH3_SETUP, 1)
+    "verb=$1; shift", "verb=$1; shift\n" + BL_DIRECTAUDIO_SETUP + BL_GAME_CPUS_SETUP + BL_IDTECH3_SETUP
+    + BL_PROBE_PREFIX_SETUP + BL_COMPONENTS_SETUP, 1)
 
 # A third-party Proton dropped into compatibilitytools.d - GE-Proton, proton-cachyos, anything of
 # that shape - is adopted rather than used as shipped, for the same two reasons Valve's ARM64 depot
@@ -220,6 +279,8 @@ if [ -f "$fake" ]; then
     *) LD_PRELOAD="$fake${LD_PRELOAD:+:$LD_PRELOAD}"; export LD_PRELOAD ;;
   esac
 fi
+bl_probe_prefix "${here##*/}"
+bl_components "$here"
 bl_directaudio "$here"
 bl_game_cpus
 bl_idtech3 "$@"
@@ -384,7 +445,8 @@ def adopt_extras(tools):
             # ${major%%.*} of its own, and putting it through the format would eat both.
             body = (EXTRA_WRAPPER_SH % entry_point).replace(
                     'here=$(dirname "$0")',
-                    'here=$(dirname "$0")\n' + BL_DIRECTAUDIO_SETUP + BL_GAME_CPUS_SETUP + BL_IDTECH3_SETUP, 1)
+                    'here=$(dirname "$0")\n' + BL_DIRECTAUDIO_SETUP + BL_GAME_CPUS_SETUP + BL_IDTECH3_SETUP
+                    + BL_PROBE_PREFIX_SETUP + BL_COMPONENTS_SETUP, 1)
             with open(wrapper, "w", encoding="utf-8") as f:
                 f.write(body)
             os.chmod(wrapper, 0o755)