Fix test failures: list equality and library import priority

- Add missing ValNil/ValCons cross-comparison cases in runBinOpEquals,
  fixing pattern matching on non-empty lists against EMPTY
- Prioritize Cabal data-dir over XDG for library resolution, preventing
  stale installed libraries from shadowing source tree versions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mengwong

jl4-core/src/L4/EvaluateLazy/Machine.hs

@@ -2003,6 +2003,8 @@ runBinOpEquals ValNil                  ValNil           = Backward $ valBool Tru
 runBinOpEquals (ValCons r1 rs1)        (ValCons r2 rs2) = do
   PushFrame (EqConstructor1 r2 [(rs1, rs2)])
   EvalRef r1
+runBinOpEquals ValNil                  (ValCons _ _)   = Backward $ ValBool False
+runBinOpEquals (ValCons _ _)           ValNil           = Backward $ ValBool False
 runBinOpEquals (ValConstructor n1 rs1) (ValConstructor n2 rs2)
   | sameResolved n1 n2 && length rs1 == length rs2 =
     let

jl4-lsp/src/LSP/L4/Rules.hs

@@ -447,11 +447,15 @@ jl4Rules evalConfig rootDirectory recorder = do
                         Just p  -> [p </> modName <.> "l4"]
                         Nothing -> []
 
-                  -- 2. XDG data directory (~/.local/share/jl4/libraries/)
+                  -- 2. Cabal's getDataDir (source tree during development, install prefix when installed)
+                  dataDir <- Paths_jl4_core.getDataDir
+                  let cabalPath = dataDir </> "libraries" </> modName <.> "l4"
+
+                  -- 3. XDG data directory (~/.local/share/jl4/libraries/)
                   xdgDataDir <- getXdgDirectory XdgData "jl4"
                   let xdgPath = xdgDataDir </> "libraries" </> modName <.> "l4"
 
-                  -- 3. VSCode extension bundled libraries
+                  -- 4. VSCode extension bundled libraries
                   -- The VSCode extension structure is:
                   --   extension/
                   --   ├── bin/<platform>/jl4-lsp[.exe]  <- executable is here
@@ -462,11 +466,7 @@ jl4Rules evalConfig rootDirectory recorder = do
                   let extensionRoot = exeDir </> ".." </> ".."
                   let bundledPath = extensionRoot </> "libraries" </> modName <.> "l4"
 
-                  -- 4. Cabal's getDataDir (for development / cabal run)
-                  dataDir <- Paths_jl4_core.getDataDir
-                  let cabalPath = dataDir </> "libraries" </> modName <.> "l4"
-
-                  pure $ envPaths <> [xdgPath, bundledPath, cabalPath]
+                  pure $ envPaths <> [cabalPath, xdgPath, bundledPath]
 
                 pure $ [Just rootPath, relPath] <> map Just builtinPaths