fix(switch): prefer Yellow/Blue asset bytes when mount overlay lies

Probe generated canaries after mountVersion and always readActive for
prefixed caches so sprites are not blanked by empty PhysFS stubs.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/import/CacheFs.lua

@@ -409,6 +409,32 @@ local function mountGeneratedTrees(prefix)
   return mounted
 end
 
+-- True when unprefixed generated cache is actually readable (not merely a
+-- directory stub PhysFS can see). Used after Blue/Yellow mounts so NX cannot
+-- silently boot with a broken overlay.
+local function generatedCacheVisible()
+  if not (love and love.filesystem) then return false end
+  local canaries = {
+    "assets/generated/fonts/font.png",
+    "data/generated/constants.lua",
+  }
+  for _, path in ipairs(canaries) do
+    local bytes = love.filesystem.read(path)
+    if type(bytes) == "string" and #bytes > 0 then return true end
+  end
+  return false
+end
+
+local function noteMountProbe(version, prefix, ok)
+  local okReq, Diag = pcall(require, "src.debug.SwitchDiagnostics")
+  if okReq and Diag and Diag.onEvent then
+    Diag.onEvent(ok and "mount_probe_ok" or "mount_probe_failed", {
+      version = tostring(version or ""),
+      prefix = tostring(prefix or ""),
+    })
+  end
+end
+
 function CacheFs.mountVersion(version)
   local prefix = require("src.core.GameVersion").cachePrefix(version)
   local sub = prefix:gsub("/+$", "")
@@ -432,6 +458,27 @@ function CacheFs.mountVersion(version)
 
   -- Version-scoped generated trees → un-prefixed paths (Red prefix is "").
   mountGeneratedTrees(prefix)
+
+  -- Blue/Yellow: verify the overlay actually exposes generated files. A failed
+  -- mount still returns true so Play can fall back through CacheFs.readActive,
+  -- but we retry once and leave a SwitchDiagnostics breadcrumb when enabled.
+  if sub ~= "" then
+    if not generatedCacheVisible() then
+      mountGeneratedTrees(prefix)
+    end
+    local ok = generatedCacheVisible()
+    noteMountProbe(version, prefix, ok)
+    if not ok then
+      -- Last resort: root mount alone sometimes leaves assets/ hidden behind
+      -- fused archive assets/; re-issue both mounts once more.
+      if love.filesystem.mount and love.filesystem.getInfo(sub, "directory") then
+        love.filesystem.mount(sub, "", false)
+      end
+      mountGeneratedTrees(prefix)
+      noteMountProbe(version, prefix, generatedCacheVisible())
+    end
+  end
+
   return true
 end
 

src/render/Assets.lua

@@ -43,15 +43,26 @@ function Assets.resolve(path)
   return loader:derivedPath(rel) or path
 end
 
--- When PhysFS hides Blue/Yellow prefixed trees (fused NX), load generated
--- asset bytes the same way Data:load does via CacheFs.readActive.
+-- When PhysFS hides or mis-exposes Blue/Yellow prefixed trees (fused NX),
+-- load generated asset bytes the same way Data:load does via CacheFs.readActive.
+-- Blue/Yellow prefer versioned bytes whenever present: getInfo can succeed on a
+-- broken overlay while sprites decode as blank (OBP keys white → transparent).
 local function generatedFileData(resolved)
   if type(resolved) ~= "string" or resolved:sub(1, #GENERATED) ~= GENERATED then
     return nil
   end
+  local CacheFs = require("src.import.CacheFs")
+  local prefix = require("src.core.GameVersion").cachePrefix()
+  if prefix ~= "" then
+    local bytes = CacheFs.readActive(resolved)
+    if type(bytes) == "string" and #bytes > 0 then
+      return love.filesystem.newFileData(bytes, resolved)
+    end
+    return nil
+  end
   if exists(resolved) then return nil end
-  local bytes = require("src.import.CacheFs").readActive(resolved)
-  if type(bytes) ~= "string" then return nil end
+  local bytes = CacheFs.readActive(resolved)
+  if type(bytes) ~= "string" or #bytes == 0 then return nil end
   return love.filesystem.newFileData(bytes, resolved)
 end
 

tests/engine/assets_version_fallback_test.lua

@@ -57,6 +57,15 @@ check(redImg ~= nil, "Assets.image loads Red tileset from unprefixed path")
 eq(love.filesystem.read(PNG), "red-png-bytes",
   "Red still stores generated assets at the save-dir root")
 
+-- --- Stale unprefixed path must not win over Yellow bytes (NX mount lie)
+GameVersion.set("yellow")
+Assets.flush()
+love.filesystem.write(PNG, "")  -- visible but empty → would bake blank sprites
+love.filesystem.write("yellow/" .. PNG, "yellow-real-png")
+local staleImg = Assets.image(PNG)
+check(staleImg ~= nil, "Assets.image prefers Yellow bytes over empty unprefixed stub")
+eq(staleImg.path, PNG, "stale-path fallback still names the logical generated path")
+
 -- --- Missing generated file: no invented bytes
 GameVersion.set("yellow")
 Assets.flush()

tests/engine/cache_fs_blue_mount_test.lua

@@ -4,13 +4,16 @@ if not _G.love then _G.love = require("tests.love_stub") end
 
 local T = require("tests.harness")
 local check = T.check
+local eq = T.eq
 
 local CacheFs = require("src.import.CacheFs")
+local GameVersion = require("src.core.GameVersion")
 
 love.filesystem._mounts = {}
 -- Imply blue/data/generated and blue/assets/generated directories via file keys.
 love.filesystem.write("blue/data/generated/maps.lua", "return {}")
-love.filesystem.write("blue/assets/generated/fonts/font.png", "x")
+love.filesystem.write("blue/data/generated/constants.lua", "return {}")
+love.filesystem.write("blue/assets/generated/fonts/font.png", "font-bytes")
 
 check(CacheFs.mountVersion("blue") == true, "mountVersion(blue) returns true")
 
@@ -32,4 +35,19 @@ check(sawBlueRoot, "prepend-mounts save-dir relative blue/")
 check(sawDataGen, "prepend-mounts blue/data/generated -> data/generated")
 check(sawAssetsGen, "prepend-mounts blue/assets/generated -> assets/generated")
 
+eq(love.filesystem.read("assets/generated/fonts/font.png"), "font-bytes",
+  "post-mount probe can read unprefixed assets/generated canary")
+eq(love.filesystem.read("data/generated/constants.lua"), "return {}",
+  "post-mount probe can read unprefixed data/generated canary")
+
+-- Yellow-only: same overlay contract
+love.filesystem._mounts = {}
+GameVersion.set("yellow")
+love.filesystem.write("yellow/data/generated/constants.lua", "return {y=1}")
+love.filesystem.write("yellow/assets/generated/fonts/font.png", "yellow-font")
+check(CacheFs.mountVersion("yellow") == true, "mountVersion(yellow) returns true")
+eq(love.filesystem.read("assets/generated/fonts/font.png"), "yellow-font",
+  "Yellow mount exposes fonts/font.png at the unprefixed path")
+
+GameVersion.set("red")
 T.finish()

tests/love_stub.lua

@@ -125,14 +125,70 @@ stub.math = {
 
 stub.filesystem = {
   write = function(name, content) files[name] = content return true end,
-  read = function(name) return files[name] end,
   remove = function(name) files[name] = nil return true end,
   newFileData = function(contents, name)
     return { _fileData = true, contents = contents, name = name or "" }
   end,
   createDirectory = function() return true end,
-  -- directories are implied by key prefixes ("mods/x/manifest.json")
-  getInfo = function(name, filter)
+  -- Record mounts for CacheFs.mountVersion tests (NX Blue/Yellow overlay).
+  _mounts = {},
+  mount = function(archive, mountpoint, appendToPath)
+    stub.filesystem._mounts[#stub.filesystem._mounts + 1] = {
+      archive = archive, mountpoint = mountpoint or "",
+      append = appendToPath and true or false,
+    }
+    return true
+  end,
+  unmount = function(archive)
+    local mounts = stub.filesystem._mounts
+    for i = #mounts, 1, -1 do
+      if mounts[i].archive == archive then
+        table.remove(mounts, i)
+        return true
+      end
+    end
+    return false
+  end,
+  getSaveDirectory = function() return "/tmp/pokeport-stub-save" end,
+  isFused = function() return false end,
+}
+
+-- Resolve a PhysFS path through recorded mounts (prepend first, newest wins).
+local function resolveViaMounts(name)
+  local mounts = stub.filesystem._mounts
+  for i = #mounts, 1, -1 do
+    local m = mounts[i]
+    if not m.append then
+      local mp = m.mountpoint or ""
+      local key
+      if mp == "" then
+        key = m.archive .. "/" .. name
+      elseif name == mp then
+        key = m.archive
+      elseif name:sub(1, #mp + 1) == mp .. "/" then
+        local rel = name:sub(#mp + 2)
+        key = m.archive .. "/" .. rel
+      end
+      if key then
+        if files[key] then return key, "file" end
+        local prefix = key .. "/"
+        for k in pairs(files) do
+          if k:sub(1, #prefix) == prefix then return key, "directory" end
+        end
+      end
+    end
+  end
+  return nil
+end
+
+function stub.filesystem.read(name)
+  if files[name] then return files[name] end
+  local key = resolveViaMounts(name)
+  if key and files[key] then return files[key] end
+  return nil
+end
+
+function stub.filesystem.getInfo(name, filter)
   if files[name] then
     if filter and filter ~= "file" then return nil end
     return { type = "file" }
@@ -144,52 +200,55 @@ stub.filesystem = {
       return { type = "directory" }
     end
   end
+  local key, kind = resolveViaMounts(name)
+  if key and kind then
+    if filter and filter ~= kind then return nil end
+    return { type = kind }
+  end
   return nil
-  end,
-  load = function(name)
-    if not files[name] then return nil, "no file" end
-    return load(files[name], name)
-  end,
-  getDirectoryItems = function(name)
+end
+
+stub.filesystem.load = function(name)
+  local data = stub.filesystem.read(name)
+  if not data then return nil, "no file" end
+  return load(data, name)
+end
+
+stub.filesystem.getDirectoryItems = function(name)
   local seen, items = {}, {}
   name = name or ""
-    -- "" / "/" = save-dir root (RomImporter Android ROM scan)
-    if name == "" or name == "/" then
-      for key in pairs(files) do
-        local child = key:match("^[^/]+")
+  local function addChild(child)
     if child and not seen[child] then
       seen[child] = true
       items[#items + 1] = child
     end
   end
+  -- "" / "/" = save-dir root (RomImporter Android ROM scan)
+  if name == "" or name == "/" then
+    for key in pairs(files) do
+      addChild(key:match("^[^/]+"))
+    end
   else
     local prefix = name .. "/"
     for key in pairs(files) do
       if key:sub(1, #prefix) == prefix then
-          local child = key:sub(#prefix + 1):match("^[^/]+")
-          if child and not seen[child] then
-            seen[child] = true
-            items[#items + 1] = child
+        addChild(key:sub(#prefix + 1):match("^[^/]+"))
+      end
+    end
+    -- Also surface children exposed via mounts.
+    local key = resolveViaMounts(name)
+    if key then
+      local mprefix = key .. "/"
+      for k in pairs(files) do
+        if k:sub(1, #mprefix) == mprefix then
+          addChild(k:sub(#mprefix + 1):match("^[^/]+"))
         end
       end
     end
   end
   table.sort(items)
   return items
-  end,
-  -- Record mounts for CacheFs.mountVersion tests (NX Blue/Yellow overlay).
-  _mounts = {},
-  mount = function(archive, mountpoint, appendToPath)
-    stub.filesystem._mounts[#stub.filesystem._mounts + 1] = {
-      archive = archive, mountpoint = mountpoint or "",
-      append = appendToPath and true or false,
-    }
-    return true
-  end,
-  unmount = function() return true end,
-  getSaveDirectory = function() return "/tmp/pokeport-stub-save" end,
-  isFused = function() return false end,
-}
+end
 
 -- table-backed SoundData so ChipAudio's offline render seam
 -- (_renderMusicForTest) runs headless; modkit bounce writes WAVs from it