diff --git a/scripts/test.sh b/scripts/test.sh
index b759d434..9a2b4dd7 100755
--- a/scripts/test.sh
+++ b/scripts/test.sh
@@ -67,6 +67,11 @@ run_tier() {
 
 run_tier "T0 switch CI workflow content gate" "$LUA" tests/switch_ci_workflows_test.lua
 run_tier "T0 switch transfer docs gate" "$LUA" tests/switch_transfer_docs_test.lua
+# NX Blue/Yellow asset overlay: ROM-free, must run on every checkout so a
+# Sound.lua / overlay regression is not gated only on switch-changes paths.
+run_tier "T0 NX asset overlay fallback" "$LUA" tests/engine/assets_version_fallback_test.lua
+run_tier "T0 NX generated-path static guard" "$LUA" tests/engine/nx_generated_guard_test.lua
+run_tier "T0 NX Yellow/Blue boot (dynamic paths)" "$LUA" tests/engine/nx_yellow_boot_test.lua
 run_tier "T1/T2 engine invariants + parity gates" "$LUA" tests/run_engine.lua
 run_tier "T4 mod-SDK" "$LUA" tests/run_modkit.lua
 
diff --git a/tests/engine/assets_version_fallback_test.lua b/tests/engine/assets_version_fallback_test.lua
index 333d5af9..464f17e9 100644
--- a/tests/engine/assets_version_fallback_test.lua
+++ b/tests/engine/assets_version_fallback_test.lua
@@ -44,7 +44,7 @@ eq(Assets.resolve(PNG), PNG,
 local rawWrite = love.filesystem.write
 local rawRemove = love.filesystem.remove
 local rawGetInfo = love.filesystem.getInfo
-seed_chunk = "assets/generated/boot_chunk.lua"
+local seed_chunk = "assets/generated/boot_chunk.lua"
 love.filesystem.write("yellow/" .. seed_chunk, "return 42")
 
 Overlay.install()
diff --git a/tests/engine/nx_yellow_boot_test.lua b/tests/engine/nx_yellow_boot_test.lua
index c7fe36bb..96270190 100644
--- a/tests/engine/nx_yellow_boot_test.lua
+++ b/tests/engine/nx_yellow_boot_test.lua
@@ -76,12 +76,26 @@ love.filesystem.read = function(path, ...)
   return rawRead(path, ...)
 end
 
+-- widenMono re-reads the caller's bare path via newSoundData; without this
+-- recorder the boot suite only saw newSource and could not catch a missing
+-- sound.newSoundData wrap (the silent hole that motivated the full-surface
+-- overlay).  Installed before Overlay.install so the overlay wraps us.
+local rawNewSoundData = love.sound.newSoundData
+love.sound.newSoundData = function(samples, ...)
+  record("sounddata", samples)
+  return rawNewSoundData(samples, ...)
+end
+
 local Source = {}
 Source.__index = Source
 function Source:play() self.playing = true end
 function Source:stop() self.playing = false end
 function Source:setVolume() end
 function Source:isPlaying() return self.playing end
+-- Mono so Sound.widenMono actually reaches newSoundData (the stub's path
+-- form then fails inside the pcall and widenMono keeps this Source --
+-- enough to prove the overlay rewrote the re-read path).
+function Source:getChannelCount() return 1 end
 
 love.audio = {
   newSource = function(path, mode)
@@ -212,11 +226,23 @@ eq(pre and pre.nidoFrames and pre.nidoFrames[3]
   "data-driven nidorino frame resolves to the yellow/ copy")
 
 -- Yellow's voiced Pikachu clip: a FORMATTED path (cry_%02d.wav), invisible
--- to the static guard
+-- to the static guard.  playPikaCry also runs widenMono, which re-reads the
+-- same bare path via newSoundData -- that second hop is what the full-surface
+-- overlay exists to cover.
 local cry = Sound.playPikaCry({ audio = { pikaCries = 1 } }, 1)
 check(cry ~= nil, "playPikaCry returns a source on NX Yellow")
 eq(cry and cry.path, "yellow/assets/generated/audio/pika_cries/cry_01.wav",
   "the formatted pika-cry path resolves to the yellow/ copy")
+local sawCrySoundData = false
+for _, r in ipairs(recorded) do
+  if r.kind == "sounddata"
+      and r.path == "yellow/assets/generated/audio/pika_cries/cry_01.wav" then
+    sawCrySoundData = true
+    break
+  end
+end
+check(sawCrySoundData,
+  "widenMono re-read the cry via newSoundData with the yellow/ path")
 
 check(countRecorded("yellow/assets/generated/") >= 20,
   "the boot pulled its generated art through the yellow/ prefix")
@@ -312,6 +338,7 @@ Overlay.uninstall()
 check(not Overlay.isInstalled(), "overlay uninstalls")
 love.graphics.newImage = rawNewImage
 love.filesystem.read = rawRead
+love.sound.newSoundData = rawNewSoundData
 love.audio = nil
 for _, path in ipairs(seeded) do
   love.filesystem.remove(path)
diff --git a/tests/switch_ci_workflows_test.lua b/tests/switch_ci_workflows_test.lua
index a7690432..8225cc46 100644
--- a/tests/switch_ci_workflows_test.lua
+++ b/tests/switch_ci_workflows_test.lua
@@ -180,6 +180,10 @@ mustContain(test_sh, "tests/switch_ci_workflows_test.lua", "scripts/test.sh")
 mustContain(test_sh, "T0 switch CI workflow content gate", "scripts/test.sh")
 mustContain(test_sh, "tests/switch_transfer_docs_test.lua", "scripts/test.sh")
 mustContain(test_sh, "T0 switch transfer docs gate", "scripts/test.sh")
+-- NX suites also run in the unified entry point (not only switch-selftest)
+mustContain(test_sh, "tests/engine/assets_version_fallback_test.lua", "scripts/test.sh")
+mustContain(test_sh, "tests/engine/nx_generated_guard_test.lua", "scripts/test.sh")
+mustContain(test_sh, "tests/engine/nx_yellow_boot_test.lua", "scripts/test.sh")
 mustContain(build_doc, "tests/switch_ci_workflows_test.lua", "switch-build.md path list")
 mustContain(build_doc, "tests/switch_transfer_docs_test.lua", "switch-build.md path list")