fix(import): mount Blue/Yellow save-dir cache without FFI

NX Play for Blue failed because mountVersion relied on absolute
PHYSFS_mount first. Prefer love.filesystem.mount of blue|yellow, overlay
generated trees by version prefix, and align CacheFs.prefix in bootGame.

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

docs/switch-hardware-evidence.md

@@ -79,28 +79,26 @@ T19 hardware gate: **closed**. No stuck input, duplicate audio, or crash reporte
 
 ---
 
-## T24 — fused NRO alone + NRO-only update — PARTIAL / FAIL (Play)
+## T24 — fused NRO — Red PASS; Blue Play FAIL (open)
 
 | Field | Value |
 | ----- | ----- |
-| Commit tested | `6fb5602` |
-| Artifact | `dist/switch/gen1recomp-6fb5602-switch.nro` |
+| Commit (first fused attempt) | `6fb5602` |
+| Artifact | `gen1recomp-6fb5602-switch.nro` |
 | SHA-256 | `b019e2e82c7fe6ec3cf4339e1bc71e8752c8140b6242028bb0b662fcf20daac2` |
-| Deploy | isolated folder, **no** adjacent `game.love` |
-| MTP round-trip | skipped |
+| Deploy | isolated folder, no adjacent `game.love` |
 | Boot fused | **pass** |
-| ROM import (inbox) | **pass** |
-| Play after import | **fail** — app closed immediately |
+| ROM import | **pass** |
+| Play **Red** (operator follow-up) | **pass** — same import flow as loose; fused not the differentiator |
+| Play **Blue** (operator follow-up) | **fail** — app closed on Play (was mis-attributed to fused-only) |
 | NRO-only replace / save survive | **not tested** |
 
-### lua-error.log (operator)
+### Revised root cause
 
-Two events ~1 min apart; body was fully `<redacted>` because `redactString` treated newlines in stack traces as binary. Fix: allow TAB/LF/CR in diagnostics (`SwitchDiagnostics`).
+Blue/Yellow caches live under `blue/` / `yellow/`. `CacheFs.mountVersion` preferred absolute `PHYSFS_mount(save/blue)` (FFI), which fails on NX; the save-dir-relative `love.filesystem.mount("blue", …)` was only a fallback after that path assumed a usable `base`. Red (`cachePrefix == ""`) never needed that mount → Play OK.
 
-### Suspected root cause (fix in flight)
+### Fix follow-up
 
-Fused `game.love` contains a `data/` tree (scripts). PhysFS does not merge that with save-dir `data/generated/` after import → `Data:load` / `require("data.generated.*")` fails on Play while launcher `isReady` still sees CacheFs files. Loose mode search order differed enough that Play worked earlier.
+Mount save-dir-relative version folder first; always `mountGeneratedTrees(prefix)` for `blue/data/generated` → `data/generated`; set `CacheFs.prefix` in `bootGame`; Data:load reads version-prefixed cache on require miss.
 
-Mitigations: `CacheFs.mountVersion` prepend-mounts `data/generated` + `assets/generated`; `Data.loadModule` falls back to `CacheFs.read`+`loadstring`; Boot.run skips on NX (`networkValidated == false`).
-
-**T24 remains OPEN** until fused Play re-verify + NRO-only save test.
+**T24**: fused Red OK is evidence for fused boot/import/play(Red). Full T24 (NRO-only update) + Blue Play still need re-verify.

main.lua

@@ -177,7 +177,11 @@ local function bootGame(version)
   -- data, so data/generated + assets/generated resolve to that version's files.
   local GameVersion = require("src.core.GameVersion")
   GameVersion.set(version or os.getenv("POKEPORT_VERSION") or "red")
-  require("src.import.CacheFs").mountVersion(GameVersion.get())
+  local CacheFs = require("src.import.CacheFs")
+  -- Keep CacheFs.prefix aligned for any CacheFs.read fallback during Data:load
+  -- (Blue/Yellow caches live under blue/ / yellow/).
+  CacheFs.prefix = GameVersion.cachePrefix()
+  CacheFs.mountVersion(GameVersion.get())
   if love.window and love.window.setTitle then
     local Version = require("src.core.Version")
     love.window.setTitle(Version.title(

src/core/Data.lua

@@ -198,11 +198,20 @@ local function loadModule(dir, name)
   end
   local ok, mod = pcall(require, "data.generated." .. name)
   if ok then return true, mod end
-  -- Fused PhysFS may hide save-dir data/generated behind the archive's
-  -- data/ tree even after mountVersion; load bytes explicitly as fallback.
+  -- Fused PhysFS / Blue|Yellow prefix: load bytes from the active version's
+  -- cache explicitly when require cannot see the mounted tree.
   local CacheFs = require("src.import.CacheFs")
-  local path = "data/generated/" .. name .. ".lua"
+  local GameVersion = require("src.core.GameVersion")
+  local prefix = GameVersion.cachePrefix()
+  local path = prefix .. "data/generated/" .. name .. ".lua"
+  local saved = CacheFs.prefix
+  CacheFs.prefix = ""
   local bytes = CacheFs.read(path)
+  CacheFs.prefix = saved
+  if type(bytes) ~= "string" then
+    -- Also try with CacheFs.prefix if the caller set it for this version.
+    bytes = CacheFs.read("data/generated/" .. name .. ".lua")
+  end
   if type(bytes) == "string" then
     local chunk, err = loadstring(bytes, "@" .. path)
     if not chunk then return false, err or mod end

src/import/CacheFs.lua

@@ -361,18 +361,15 @@ end
 
 -- Overlay the active version's extracted cache onto the un-prefixed read
 -- paths, so require("data.generated.*") and love.graphics.newImage(
--- "assets/generated/*") resolve to that version's files.  Red lives at the
--- cache root and needs nothing; non-Red versions (blue/, yellow/, …) are
--- *prepended* so they win over any Red copy at the root and over the game
--- source.  Called once at boot, before Game:load (main.lua).  Returns true
--- when nothing was needed or the mount succeeded.
+-- "assets/generated/*") resolve to that version's files.
 --
--- Fused builds also ship a `data/` tree (scripts, palettes) inside game.love.
--- PhysFS does not merge directories across archives: that `data/` can hide
--- `data/generated/` written to the save directory after ROM import.  Loose
--- play often still works (search order / mount layout differs); fused NX
--- Play-after-import then fails Data:load with a missing-module error.
--- Explicitly prepend-mount the generated subtrees so they win.
+-- Non-Red versions live under blue/ / yellow/ in the save directory.  On
+-- desktop fused+portable we PHYSFS_mount that folder by absolute path.  On
+-- NX (and any host without a working FFI mount) love.filesystem.mount of
+-- the save-dir-relative name must succeed, or Play boots with Red's paths
+-- and Data:load dies.  Always also prepend-mount the version's
+-- data/generated + assets/generated onto the un-prefixed paths so PhysFS
+-- directory non-merge (archive data/ vs save generated) cannot hide them.
 local function mountGeneratedTrees(prefix)
   prefix = prefix or ""
   if not (love and love.filesystem and love.filesystem.mount) then
@@ -396,30 +393,28 @@ end
 
 function CacheFs.mountVersion(version)
   local prefix = require("src.core.GameVersion").cachePrefix(version)
-  if prefix == "" then
-    mountGeneratedTrees("")
-    return true
+  local sub = prefix:gsub("/+$", "")
+
+  -- Save-dir relative mount first (NX / no-FFI). Prepend so blue|yellow win.
+  if sub ~= "" and love.filesystem.mount
+      and love.filesystem.getInfo(sub, "directory") then
+    love.filesystem.mount(sub, "", false)
   end
-  local sub = prefix:gsub("/+$", "")              -- "blue/" / "yellow/" -> bare dir
-  -- The cache root is the portable game folder when active, else LÖVE's OS
-  -- save directory (where love.filesystem wrote blue/... or yellow/...).
-  local base = CacheFs.root()
-  if not base and love.filesystem.getSaveDirectory then
-    base = love.filesystem.getSaveDirectory()
+
+  -- Portable / desktop fused: absolute PHYSFS_mount of the version folder.
+  if sub ~= "" then
+    local base = CacheFs.root()
+    if not base and love.filesystem.getSaveDirectory then
+      base = love.filesystem.getSaveDirectory()
+    end
+    if base then
+      mountReadable(base .. SEP .. sub, false)
+    end
   end
-  if not base then return false end
-  if mountReadable(base .. SEP .. sub, false) then
-    mountGeneratedTrees("")
-    return true
-  end
-  -- Fallback when FFI/PHYSFS_mount is unavailable: LÖVE can mount a folder
-  -- that lives in the save directory by name (prepended: appendToPath=false).
-  if love.filesystem.mount then
-    local ok = love.filesystem.mount(sub, "", false)
-    mountGeneratedTrees("")
-    return ok
-  end
-  return false
+
+  -- Version-scoped generated trees → un-prefixed paths (Red prefix is "").
+  mountGeneratedTrees(prefix)
+  return true
 end
 
 -- Undo mountVersion.  A process normally mounts exactly one version and then

tests/engine/cache_fs_blue_mount_test.lua

@@ -0,0 +1,35 @@
+-- Blue/Yellow mountVersion must overlay save-dir caches without FFI (NX).
+package.path = "./?.lua;./?/init.lua;" .. package.path
+if not _G.love then _G.love = require("tests.love_stub") end
+
+local T = require("tests.harness")
+local check = T.check
+
+local CacheFs = require("src.import.CacheFs")
+
+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")
+
+check(CacheFs.mountVersion("blue") == true, "mountVersion(blue) returns true")
+
+local sawBlueRoot, sawDataGen, sawAssetsGen = false, false, false
+for _, m in ipairs(love.filesystem._mounts) do
+  if m.archive == "blue" and m.mountpoint == "" and m.append == false then
+    sawBlueRoot = true
+  end
+  if m.archive == "blue/data/generated" and m.mountpoint == "data/generated"
+      and m.append == false then
+    sawDataGen = true
+  end
+  if m.archive == "blue/assets/generated" and m.mountpoint == "assets/generated"
+      and m.append == false then
+    sawAssetsGen = true
+  end
+end
+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")
+
+T.finish()

tests/love_stub.lua

@@ -160,6 +160,18 @@ stub.filesystem = {
     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,
 }
 
 -- table-backed SoundData so ChipAudio's offline render seam