fix(release): correct metallib source — it ships in mlx-swift submodule, not built by swift build

default.metallib is a pre-built artifact inside the mlx-swift submodule
at LocalPackages/mlx-swift/Source/Cmlx/mlx/mlx/backend/metal/kernels/.
It is not produced by swift build. Update CI search path from .build/
to LocalPackages/ (with full-repo fallback), and update README to
reflect the correct clone and copy steps for building from source.

Author: solderzzc

.github/workflows/release.yml

@@ -71,12 +71,15 @@ jobs:
 
       - name: Find and copy default.metallib
         run: |
-          # The Metal shader library is compiled as part of mlx-swift during
-          # `swift build`. Find it in the build artifacts and copy it to the
-          # repo root so the package step can pick it up.
-          METALLIB=$(find .build -name "default.metallib" | head -1)
+          # default.metallib is a pre-built artifact shipped inside the
+          # mlx-swift submodule — it is NOT produced by `swift build`.
+          # Search the submodule tree for it (fallback to anywhere in repo).
+          METALLIB=$(find LocalPackages -name "default.metallib" | head -1)
           if [ -z "$METALLIB" ]; then
-            echo "ERROR: default.metallib not found in build artifacts!"
+            METALLIB=$(find . -name "default.metallib" -not -path "./.git/*" | head -1)
+          fi
+          if [ -z "$METALLIB" ]; then
+            echo "ERROR: default.metallib not found — is mlx-swift submodule checked out?"
             exit 1
           fi
           echo "Found metallib: $METALLIB"

README.md

@@ -111,12 +111,19 @@ tar -xzf SwiftLM-<version>-macos-arm64.tar.gz
 ### Build from Source
 
 ```bash
+# Must clone recursively — default.metallib ships inside the mlx-swift submodule
+git clone --recursive https://github.com/SharpAI/SwiftLM
+cd SwiftLM
 swift build -c release
 ```
 
-When building from source the Metal shader library is compiled automatically by the Swift build system and placed next to the binary in `.build/release/`. Run from that directory:
+`default.metallib` is a pre-built artifact inside the `mlx-swift` submodule at:
+`LocalPackages/mlx-swift/Source/Cmlx/mlx/mlx/backend/metal/kernels/default.metallib`
+
+Copy it next to the binary before running:
 
 ```bash
+cp LocalPackages/mlx-swift/Source/Cmlx/mlx/mlx/backend/metal/kernels/default.metallib .build/release/
 .build/release/SwiftLM \
   --model mlx-community/Qwen3.5-122B-A10B-4bit \
   --stream-experts \