diff --git a/docs/STEAM-3-MACHINE-TEST.md b/docs/STEAM-3-MACHINE-TEST.md
index a6d3e47..c09a8a6 100644
--- a/docs/STEAM-3-MACHINE-TEST.md
+++ b/docs/STEAM-3-MACHINE-TEST.md
@@ -9,13 +9,13 @@ the first live test.
 1. Steam client installed, logged in (different account per machine),
    and RUNNING.
 2. Copy the `dist\` folder onto the machine.
-3. In the dist folder, create `steam_appid.txt` containing exactly:
-   `480`
-   (Spacewar, Valve's public dev AppID — replaced by the real AppID
-   once the store page exists.)
-4. Add to `environ.ini`:
-   `RP412STEAM=1`
-5. Start with `start-windowed.bat` as usual.
+3. Start with `start-windowed.bat` as usual.
+
+The packed dist already contains `steam_appid.txt` (480 — Spacewar,
+Valve's public dev AppID, replaced by the real one once the store page
+exists) and ships `RP412STEAM=1` in `environ.ini`. If a machine has an
+older dist, check both before blaming the network: a missing appid
+file makes SteamAPI_Init fail and the game quietly falls back to TCP.
 
 Sanity check per machine: `rpl4.log` should show
 `SteamNetTransport: up as 169.254.x.y (fake ports N console, M game)`.
diff --git a/pack-dist.ps1 b/pack-dist.ps1
index a755af9..da17500 100644
--- a/pack-dist.ps1
+++ b/pack-dist.ps1
@@ -47,6 +47,13 @@ if (Test-Path $pdb) { Copy-Item $pdb $dist }
 # only activates with RP412STEAM=1; plain desktop runs never touch it.
 Copy-Item (Join-Path $root 'extern\steamworks_sdk_164\sdk\redistributable_bin\steam_api.dll') $dist
 
+# steam_appid.txt: until RP412 has its own AppID, Steam testing runs
+# under Spacewar (480). Without this file SteamAPI_Init fails and the
+# game falls back to plain TCP - which is exactly the confusing symptom
+# testers hit when the file goes missing. Delete it once we ship under
+# our own AppID (the Steam client provides it then).
+Set-Content -Path "$dist\steam_appid.txt" -Encoding ascii -Value '480'
+
 # --- game data -------------------------------------------------------------
 foreach ($dir in 'AUDIO', 'GAUGE', 'VIDEO') {
     Write-Host "  copying $dir..."