diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index c8b805c..f4aba03 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -104,6 +104,8 @@ jobs:
     timeout-minutes: 30
     steps:
       - uses: actions/checkout@v4
+      - name: Headset programs match the source
+        run: sh scripts/frame-payload.sh check
       - name: Package
         run: sh scripts/build-studio.sh frame-home
       - uses: actions/upload-artifact@v4
@@ -134,6 +136,10 @@ jobs:
       - uses: actions/checkout@v4
         with:
           path: src
+      # Every download carries frame/payload: none is published beside headset programs older than the source
+      # (Studio would save environments the headset can't open).
+      - name: Headset programs match the source
+        run: sh src/scripts/frame-payload.sh check
       # What Frame Studio (studio/updater.h) and the headset's Environments panel check for updates: this commit,
       # Frame Home's identity (a hash of the headset programs, the same one the panel works out for what's installed)
       # and the files in this release.
diff --git a/docs/building.md b/docs/building.md
index 2ddfe0c..3798b0a 100644
--- a/docs/building.md
+++ b/docs/building.md
@@ -173,8 +173,17 @@ headset, copy the results into it:
 
 `frame/payload/install.sh` is the installer itself; it lives in the repository and needs no build.
 
-Commit the new payload together with the code that changed. Otherwise Studio's **Install on Steam Frame** would
-install an older Frame Home than the code says.
+Then record which source they were built from, and commit the new payload together with the code that changed:
+
+```sh
+sh scripts/frame-payload.sh stamp
+```
+
+`frame/payload/SOURCE` holds a hash of everything the headset side is built from (`src/`, `third_party/`, `layer/`,
+`CMakeLists.txt`). `sh scripts/frame-payload.sh check` tells you whether the payload is still current. The release
+build runs it too and publishes nothing while the payload is older than the source: a Studio beside an older Frame
+Home saves environments the headset can't open. Studio also asks the headset (`fenv-tool version`) before
+**Send to Frame** and says when its Frame Home needs updating.
 
 ## Repository layout
 
diff --git a/frame/payload/SOURCE b/frame/payload/SOURCE
new file mode 100644
index 0000000..a12ddf5
--- /dev/null
+++ b/frame/payload/SOURCE
@@ -0,0 +1 @@
+ed589d9db53c920be66e9334cc86e88e2893c2d410437d538477109cbf2fc02d
diff --git a/frame/payload/bin/fenv-tool b/frame/payload/bin/fenv-tool
index c40fac8..515e2a2 100755
Binary files a/frame/payload/bin/fenv-tool and b/frame/payload/bin/fenv-tool differ
diff --git a/frame/payload/bin/frame-home b/frame/payload/bin/frame-home
index fe90ebd..c2a1b99 100755
Binary files a/frame/payload/bin/frame-home and b/frame/payload/bin/frame-home differ
diff --git a/scripts/frame-payload.sh b/scripts/frame-payload.sh
new file mode 100644
index 0000000..4360a02
--- /dev/null
+++ b/scripts/frame-payload.sh
@@ -0,0 +1,34 @@
+#!/bin/sh
+# The Steam Frame programs in frame/payload are built on the headset (arm64 SteamOS, its compositor's Vulkan driver)
+# and committed; every Frame Studio download and the Frame Home installer ship them. frame/payload/SOURCE records the
+# source they were built from, so Studio is never released beside an older headset build (Studio would save
+# environments the headset can't open).
+#
+#   scripts/frame-payload.sh stamp    after copying freshly built programs into frame/payload
+#   scripts/frame-payload.sh check    fails when the headset's source changed since (CI runs it before releasing)
+set -eu
+ROOT=$(cd "$(dirname "$0")/.." && pwd)
+STAMP="$ROOT/frame/payload/SOURCE"
+
+# What the headset programs are built from (studio/ is Studio's alone), as the files are now: committed or not.
+source_hash() {
+    list=$(mktemp)
+    (cd "$ROOT" && git -c core.quotepath=off ls-files -- src third_party layer CMakeLists.txt > "$list" &&
+        git hash-object --stdin-paths < "$list" | paste -d ' ' - "$list" | sha256sum | cut -c1-64)
+    rm -f "$list"
+}
+
+case "${1:-}" in
+    stamp) source_hash > "$STAMP"
+           echo "frame/payload/SOURCE: $(cat "$STAMP")" ;;
+    check) want=$(source_hash)
+           have=$(cat "$STAMP" 2>/dev/null || true)
+           if [ "$want" != "$have" ]; then
+               echo "frame/payload is out of date: the headset's source changed since its programs were built." >&2
+               echo "Rebuild frame-home, frame-switcher and fenv-tool on the Frame, copy them into frame/payload/bin," >&2
+               echo "then run scripts/frame-payload.sh stamp (docs/building.md)." >&2
+               exit 1
+           fi
+           echo "frame/payload matches the source ($want)" ;;
+    *) sed -n '2,8p' "$0"; exit 2 ;;
+esac
diff --git a/src/fenv_tool.cpp b/src/fenv_tool.cpp
index 532e785..38d56ee 100644
--- a/src/fenv_tool.cpp
+++ b/src/fenv_tool.cpp
@@ -435,6 +435,8 @@ int tune(const std::string& home, const std::string& benchArg, int seconds, doub
 }  // namespace
 
 int main(int argc, char** argv) {
+    // The newest baked scene this build opens: Frame Studio asks before sending (an older headset can't open a newer one).
+    if (argc == 2 && !std::strcmp(argv[1], "version")) { std::printf("scene %u\n", kSceneBakeVersion); return 0; }
     if (argc >= 3 && !std::strcmp(argv[1], "info")) return info(argv[2]);
     if (argc >= 4 && !std::strcmp(argv[1], "bundle")) {
         std::string name;
@@ -529,6 +531,7 @@ int main(int argc, char** argv) {
                  "  fenv-tool upgrade file.fenv...   re-bake with this build (keeps world, edits, sound, picture)\n"
                  "  fenv-tool report [--json] <home.apk | home.fenv | footprint.apk+vista.apk>...   what it costs and what's wrong with it\n"
                  "  fenv-tool settings <home.fenv | home.apk> [JSON | --clear]   a world's own settings, shown or set\n"
-                 "  fenv-tool tune [--seconds 30] [--late 0.01] [--cool 80] [--dry-run] <home.fenv | home.apk>   its best settings on this headset, stored in it\n");
+                 "  fenv-tool tune [--seconds 30] [--late 0.01] [--cool 80] [--dry-run] <home.fenv | home.apk>   its best settings on this headset, stored in it\n"
+                 "  fenv-tool version   the newest baked scene this build opens\n");
     return 2;
 }
diff --git a/studio/studio.cpp b/studio/studio.cpp
index c8d1993..6decac5 100644
--- a/studio/studio.cpp
+++ b/studio/studio.cpp
@@ -2234,6 +2234,7 @@ struct Studio {
             setTuneStatus("Copying it to the headset\u2026");
             int rc = run(ssh + L"\"mkdir -p /tmp/frame-tune && rm -f /tmp/frame-tune/log\"", L"", out);
             if (rc != 0) { setTuneStatus("Can't reach the headset (" + host8 + "): " + lastLine(out)); tuning = false; return; }
+            if (const std::string why = headsetCantOpen(host8); !why.empty()) { fs::remove(f, ec); setTuneStatus("Not measured. " + why); tuning = false; return; }
             out.clear();
             rc = run(scp + L"\"" + f.filename().wstring() + L"\" " + widen(host8) + L":/tmp/frame-tune/tune.fenv", f.parent_path().wstring(), out);
             fs::remove(f, ec);
@@ -2382,6 +2383,20 @@ struct Studio {
         return png;
     }
 
+    // Why the headset's Frame Home can't open what this Studio saves, or "" when it can: its fenv-tool names the newest
+    // baked scene it opens ("scene N"; a build from before that question prints its usage instead).
+    std::string headsetCantOpen(const std::string& host8) {
+        std::string out;
+        const int rc = run(sshTool(L"ssh") + L"-o BatchMode=yes -o ConnectTimeout=8 " + widen(host8) + L" \"frame-home/bin/fenv-tool version\"", L"", out);
+        if (rc == 127 || out.find("not found") != std::string::npos)
+            return "Frame Home isn't installed on the headset: Headset > Install on Steam Frame first.";
+        const size_t at = out.find("scene ");
+        const long reads = at == std::string::npos ? 0 : std::strtol(out.c_str() + at + 6, nullptr, 10);
+        if (reads >= static_cast<long>(kSceneBakeVersion)) return {};
+        return "The headset's Frame Home is older than this Frame Studio and can't open what it saves: "
+               "Headset > Install on Steam Frame updates it.";
+    }
+
     // A footprint with its vista goes to the Frame as one home in one file: the pair baked into a .fenv with the
     // edits, world layer and background sound (what Save Environment writes). The pair's separate copies an earlier
     // Send left there go, so the headset lists it once.
@@ -2411,6 +2426,7 @@ struct Studio {
             setStatus("Connecting to the Frame\u2026");
             int rc = run(ssh + host + L" \"mkdir -p " + dir + L"\"", L"", out);
             if (rc != 0) { setStatus("Can't reach the Frame: " + lastLine(out)); sending = false; return; }
+            if (const std::string why = headsetCantOpen(host8); !why.empty()) { setStatus("Not sent. " + why); sending = false; return; }
             std::error_code ec2;
             char msg[200];
             std::snprintf(msg, sizeof msg, "Copying %s (%.0f MB)\u2026", name.c_str(), fs::file_size(f, ec2) / 1048576.0);