feat(backends): darwin/Metal build for the privacy-filter backend (timeboxed try)

The privacy-filter.cpp engine is already Metal-capable on Apple Silicon: it pulls
ggml and never forces GGML_METAL=OFF, and ggml defaults Metal ON on Apple, so a
plain Darwin build is Metal-enabled. grpc++/protobuf resolve from Homebrew via
find_package(... CONFIG). It just had no darwin build path - the existing
package.sh and run.sh are Linux-only and there was no make target / workflow step.

Adds the bespoke darwin path, modeled on the ds4 one:
- scripts/build/privacy-filter-darwin.sh: native make grpc-server, otool -L dylib
  bundling, create-oci-image (no Linux package.sh).
- Makefile: backends/privacy-filter-darwin target (+ .NOTPARALLEL).
- .github/workflows/backend_build_darwin.yml: gated build step for privacy-filter.
- scripts/changed-backends.js: inferBackendPathDarwin special-case -> backend/cpp.
- .github/backend-matrix.yml: includeDarwin entry (lang go, like ds4/llama-cpp).
- backend/index.yaml: metal: capability + metal-privacy-filter(-development) entries.
- backend/cpp/privacy-filter/run.sh: DYLD_LIBRARY_PATH branch on Darwin.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Assisted-by: Claude:opus-4.8 [Claude Code]

.github/backend-matrix.yml

@@ -4941,6 +4941,12 @@ includeDarwin:
     tag-suffix: "-metal-darwin-arm64-sam3-cpp"
     build-type: "metal"
     lang: "go"
+  # privacy-filter (PII/NER) is a C++/ggml backend built by a bespoke darwin
+  # script (make backends/privacy-filter-darwin); ggml defaults Metal ON on Apple
+  # so the build is Metal-enabled. lang=go drives runner/toolchain selection only.
+  - backend: "privacy-filter"
+    tag-suffix: "-metal-darwin-arm64-privacy-filter"
+    lang: "go"
   - backend: "voxtral"
     tag-suffix: "-metal-darwin-arm64-voxtral"
     build-type: "metal"

.github/workflows/backend_build_darwin.yml

@@ -228,8 +228,17 @@ jobs:
         run: |
           make backends/ds4-darwin
 
+      # privacy-filter is a C++/ggml backend like ds4 - a single grpc-server with
+      # otool dylib bundling - so it gets its own bespoke darwin script rather than
+      # the generic build-darwin-go-backend path.
+      - name: Build privacy-filter backend (Darwin Metal)
+        if: inputs.backend == 'privacy-filter'
+        run: |
+          make protogen-go
+          make backends/privacy-filter-darwin
+
       - name: Build ${{ inputs.backend }}-darwin
-        if: inputs.backend != 'llama-cpp' && inputs.backend != 'ds4'
+        if: inputs.backend != 'llama-cpp' && inputs.backend != 'ds4' && inputs.backend != 'privacy-filter'
         run: |
           make protogen-go
           BACKEND=${{ inputs.backend }} BUILD_TYPE=${{ inputs.build-type }} USE_PIP=${{ inputs.use-pip }} make build-darwin-${{ inputs.lang }}-backend

Makefile

@@ -1,5 +1,5 @@
 # Disable parallel execution for backend builds
-.NOTPARALLEL: backends/diffusers backends/llama-cpp backends/turboquant backends/outetts backends/piper backends/stablediffusion-ggml backends/whisper backends/crispasr backends/parakeet-cpp backends/faster-whisper backends/silero-vad backends/local-store backends/huggingface backends/rfdetr backends/rfdetr-cpp backends/insightface backends/speaker-recognition backends/kitten-tts backends/kokoro backends/chatterbox backends/llama-cpp-darwin backends/neutts build-darwin-python-backend build-darwin-go-backend backends/mlx backends/diffuser-darwin backends/mlx-vlm backends/mlx-audio backends/mlx-distributed backends/stablediffusion-ggml-darwin backends/vllm backends/vllm-omni backends/sglang backends/moonshine backends/pocket-tts backends/qwen-tts backends/faster-qwen3-tts backends/qwen-asr backends/nemo backends/voxcpm backends/whisperx backends/ace-step backends/acestep-cpp backends/fish-speech backends/voxtral backends/opus backends/trl backends/llama-cpp-quantization backends/kokoros backends/sam3-cpp backends/qwen3-tts-cpp backends/omnivoice-cpp backends/vibevoice-cpp backends/localvqe backends/tinygrad backends/sherpa-onnx backends/ds4 backends/ds4-darwin backends/liquid-audio backends/supertonic backends/depth-anything-cpp backends/privacy-filter
+.NOTPARALLEL: backends/diffusers backends/llama-cpp backends/turboquant backends/outetts backends/piper backends/stablediffusion-ggml backends/whisper backends/crispasr backends/parakeet-cpp backends/faster-whisper backends/silero-vad backends/local-store backends/huggingface backends/rfdetr backends/rfdetr-cpp backends/insightface backends/speaker-recognition backends/kitten-tts backends/kokoro backends/chatterbox backends/llama-cpp-darwin backends/neutts build-darwin-python-backend build-darwin-go-backend backends/mlx backends/diffuser-darwin backends/mlx-vlm backends/mlx-audio backends/mlx-distributed backends/stablediffusion-ggml-darwin backends/vllm backends/vllm-omni backends/sglang backends/moonshine backends/pocket-tts backends/qwen-tts backends/faster-qwen3-tts backends/qwen-asr backends/nemo backends/voxcpm backends/whisperx backends/ace-step backends/acestep-cpp backends/fish-speech backends/voxtral backends/opus backends/trl backends/llama-cpp-quantization backends/kokoros backends/sam3-cpp backends/qwen3-tts-cpp backends/omnivoice-cpp backends/vibevoice-cpp backends/localvqe backends/tinygrad backends/sherpa-onnx backends/ds4 backends/ds4-darwin backends/liquid-audio backends/supertonic backends/depth-anything-cpp backends/privacy-filter backends/privacy-filter-darwin
 
 GOCMD=go
 GOTEST=$(GOCMD) test
@@ -1129,6 +1129,10 @@ backends/ds4-darwin: build
 	bash ./scripts/build/ds4-darwin.sh
 	./local-ai backends install "ocifile://$(abspath ./backend-images/ds4.tar)"
 
+backends/privacy-filter-darwin: build
+	bash ./scripts/build/privacy-filter-darwin.sh
+	./local-ai backends install "ocifile://$(abspath ./backend-images/privacy-filter.tar)"
+
 build-darwin-python-backend: build
 	bash ./scripts/build/python-darwin.sh
 

backend/cpp/privacy-filter/run.sh

@@ -2,7 +2,13 @@
 # Entry point for the privacy-filter backend image / BACKEND_BINARY mode.
 set -e
 CURDIR=$(dirname "$(realpath "$0")")
-export LD_LIBRARY_PATH="$CURDIR/lib:$LD_LIBRARY_PATH"
+# macOS has no bundled ld.so; the darwin package ships only dylibs under lib/,
+# resolved via DYLD_LIBRARY_PATH (the ld.so branch below is skipped there).
+if [ "$(uname)" = "Darwin" ]; then
+    export DYLD_LIBRARY_PATH="$CURDIR/lib:$DYLD_LIBRARY_PATH"
+else
+    export LD_LIBRARY_PATH="$CURDIR/lib:$LD_LIBRARY_PATH"
+fi
 if [ -f "$CURDIR/lib/ld.so" ]; then
     exec "$CURDIR/lib/ld.so" "$CURDIR/grpc-server" "$@"
 fi

backend/index.yaml

@@ -1093,6 +1093,7 @@
     amd: "vulkan-privacy-filter"
     intel: "vulkan-privacy-filter"
     vulkan: "vulkan-privacy-filter"
+    metal: "metal-privacy-filter"
 - &faster-whisper
   icon: https://avatars.githubusercontent.com/u/1520500?s=200&v=4
   description: |
@@ -2935,6 +2936,16 @@
   uri: "quay.io/go-skynet/local-ai-backends:master-gpu-vulkan-privacy-filter"
   mirrors:
     - localai/localai-backends:master-gpu-vulkan-privacy-filter
+- !!merge <<: *privacyfilter
+  name: "metal-privacy-filter"
+  uri: "quay.io/go-skynet/local-ai-backends:latest-metal-darwin-arm64-privacy-filter"
+  mirrors:
+    - localai/localai-backends:latest-metal-darwin-arm64-privacy-filter
+- !!merge <<: *privacyfilter
+  name: "metal-privacy-filter-development"
+  uri: "quay.io/go-skynet/local-ai-backends:master-metal-darwin-arm64-privacy-filter"
+  mirrors:
+    - localai/localai-backends:master-metal-darwin-arm64-privacy-filter
 - !!merge <<: *privacyfilter
   name: "cuda13-privacy-filter"
   uri: "quay.io/go-skynet/local-ai-backends:latest-gpu-nvidia-cuda-13-privacy-filter"

scripts/build/privacy-filter-darwin.sh

@@ -0,0 +1,58 @@
+#!/bin/bash
+# Darwin/Metal build for the privacy-filter backend. Mirrors ds4-darwin.sh:
+# native make of the single grpc-server, otool -L dylib bundling, then assemble
+# an OCI tar that `local-ai backends install` can consume.
+#
+# privacy-filter.cpp pulls ggml, which defaults GGML_METAL=ON on Apple - the
+# engine's CMake never forces it off, so a plain Darwin build is Metal-enabled.
+# grpc++/protobuf are resolved from Homebrew via find_package(... CONFIG).
+set -ex
+
+IMAGE_NAME="${IMAGE_NAME:-localai/privacy-filter-darwin}"
+
+pushd backend/cpp/privacy-filter
+make grpc-server
+popd
+
+mkdir -p build/darwin
+mkdir -p build/darwin/lib
+mkdir -p backend-images
+
+cp -rf backend/cpp/privacy-filter/grpc-server build/darwin/
+cp -rf backend/cpp/privacy-filter/run.sh      build/darwin/
+
+# Apple Silicon: pick up Homebrew-installed protobuf utf8_validity if present
+# (same as ds4-darwin.sh - it is a transitive dep otool may not surface).
+if [[ "$(uname -s)" == "Darwin" && "$(uname -m)" == "arm64" ]]; then
+    ADDITIONAL_LIBS=${ADDITIONAL_LIBS:-$(ls /opt/homebrew/Cellar/protobuf/**/lib/libutf8_validity*.dylib 2>/dev/null)}
+else
+    ADDITIONAL_LIBS=${ADDITIONAL_LIBS:-""}
+fi
+for file in $ADDITIONAL_LIBS; do
+    cp -rfv "$file" build/darwin/lib
+done
+
+# Walk dylibs via otool -L and bundle anything that isn't a system framework.
+for file in build/darwin/grpc-server; do
+    LIBS="$(otool -L "$file" | awk 'NR > 1 { system("echo " $1) } ' | xargs echo)"
+    for lib in $LIBS; do
+        if [[ "$lib" == *.dylib ]] && [[ -e "$lib" ]]; then
+            cp -rvf "$lib" build/darwin/lib
+        fi
+    done
+done
+
+echo "Bundled libraries:"
+ls -la build/darwin/lib
+
+# Build an OCI image tar (with manifest.json) that `local-ai backends install`
+# can consume - mirrors ds4-darwin.sh.
+PLATFORMARCH="${PLATFORMARCH:-darwin/arm64}"
+
+./local-ai util create-oci-image \
+        build/darwin/. \
+        --output ./backend-images/privacy-filter.tar \
+        --image-name "$IMAGE_NAME" \
+        --platform "$PLATFORMARCH"
+
+rm -rf build/darwin

scripts/changed-backends.js

@@ -71,6 +71,11 @@ function inferBackendPathDarwin(item) {
   if (item.backend === "ds4") {
     return `backend/cpp/ds4/`;
   }
+  // privacy-filter is C++ too (built via `make backends/privacy-filter-darwin`);
+  // same lang=go-for-runner convention, source under backend/cpp.
+  if (item.backend === "privacy-filter") {
+    return `backend/cpp/privacy-filter/`;
+  }
   if (!item.lang) {
     return `backend/python/${item.backend}/`;
   }