feat: compile ladybug CGO with Zig, not gcc (#24)

API image is Go-only (compose target api). Python rebuild is profile
index. bin/cgo/zig pins Zig 0.14.1, liblbug, and tokenizers.

Dockerfile

@@ -1,5 +1,13 @@
 # syntax=docker/dockerfile:1
-FROM python:3.12-slim AS base
+#
+#   docker build --target api -t 2dph:api .
+#   docker build --target index -t 2dph:index .
+#
+# API: Go + ladybug via Zig CGO (no CPython).
+# Index: Python write path (profile `index` until brain/add is v2).
+
+# --- Python sidecar (Ladybug write / rebuild) ---
+FROM python:3.12-slim AS index
 
 ENV PYTHONUNBUFFERED=1 \
     PYTHONDONTWRITEBYTECODE=1 \
@@ -9,25 +17,11 @@ ENV PYTHONUNBUFFERED=1 \
 WORKDIR /app
 RUN id -u 2dph 2>/dev/null || useradd --create-home --uid 1001 2dph
 
-# deps layer-first: rebuild only on dependency change
 COPY requirements.lock.txt /tmp/requirements.lock.txt
 RUN python -m pip install --no-cache-dir -r /tmp/requirements.lock.txt \
     && rm /tmp/requirements.lock.txt
 
-# Go services: static binaries, no interpreter at runtime
-FROM golang:1.25 AS go-build
-WORKDIR /src
-COPY go.mod ./
-COPY bin/server ./bin/server
-COPY bin/watch ./bin/watch
-RUN CGO_ENABLED=0 go build -o /serve ./bin/server \
-    && CGO_ENABLED=0 go build -o /watch ./bin/watch
-
-# runtime: python toolchain + Go services
-FROM base
 COPY . .
-COPY --from=go-build /serve /app/bin/serve
-COPY --from=go-build /watch /app/bin/watch
 RUN chmod +x /app/bin/docker-entrypoint \
     && chown -R 2dph:2dph /app
 USER 2dph
@@ -37,5 +31,51 @@ ENV PATH="/app/bin:${PATH}" \
     KB_ROOT=/app
 HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
     CMD python -c "import model2vec, ladybug, mistune; print('ok')" || exit 1
+ENTRYPOINT ["/app/bin/docker-entrypoint"]
 
-ENTRYPOINT ["/app/bin/docker-entrypoint"]
+# --- Go API: CGO with Zig, not gcc ---
+FROM golang:1.26-bookworm AS api-build
+WORKDIR /src
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends curl xz-utils ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY bin/cgo ./bin/cgo
+RUN chmod +x bin/cgo/zig bin/cgo/zcc bin/cgo/zc++ \
+    && ./bin/cgo/zig env >/dev/null
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+ENV CGO_RPATH=/usr/local/lib
+RUN eval "$(./bin/cgo/zig env)" \
+    && go build -tags brain_serve,system_ladybug -o /out/brain-serve ./bin/brain/serve.go \
+    && go build -tags system_ladybug -o /out/brain-search ./bin/brain/search.go \
+    && CGO_ENABLED=0 go build -tags brain_watch -o /out/brain-watch ./bin/brain/watch.go
+
+FROM debian:bookworm-slim AS api
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends libssl3 ca-certificates wget \
+    && rm -rf /var/lib/apt/lists/* \
+    && useradd --create-home --uid 1001 2dph
+COPY --from=api-build /out/brain-serve /usr/local/bin/brain-serve
+COPY --from=api-build /out/brain-search /usr/local/bin/brain-search
+COPY --from=api-build /out/brain-watch /usr/local/bin/brain-watch
+COPY --from=api-build /src/lib-ladybug/liblbug.so.0.19.1 /usr/local/lib/liblbug.so.0.19.1
+COPY bin/docker-entrypoint /usr/local/bin/docker-entrypoint
+RUN chmod +x /usr/local/bin/docker-entrypoint \
+    && ln -s liblbug.so.0.19.1 /usr/local/lib/liblbug.so.0 \
+    && ln -s liblbug.so.0 /usr/local/lib/liblbug.so \
+    && ldconfig
+USER 2dph
+ENV KB_ROOT=/data \
+    KB_PORT=8630 \
+    LD_LIBRARY_PATH=/usr/local/lib \
+    HF_HOME=/data/hf
+WORKDIR /data
+EXPOSE 8630
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+    CMD wget -qO- http://127.0.0.1:8630/health || exit 1
+ENTRYPOINT ["/usr/local/bin/docker-entrypoint"]
+CMD ["serve"]