Merge pull request 'fix: -DHAVE_CURL for el_runtime OTLP — resolves emit_metric linker error' (#8) from fix/have-curl-define into stage

Dockerfile.stage

@@ -28,7 +28,10 @@ COPY runtime/el_runtime.c runtime/el_runtime.h ./
 # Pre-compile el_runtime as a separate cached layer.
 # el_runtime.c changes rarely; main.c changes every run.
 # Splitting this out means el_runtime.o is cached across builds when only main.c changes.
-RUN cc -O2 -c el_runtime.c -I. -o el_runtime.o
+# -DHAVE_CURL: the staged el_runtime.c (from el.git) guards the OTLP observability
+# section (emit_metric, emit_log, trace_span_*) behind #ifdef HAVE_CURL.
+# libcurl IS installed above, so define HAVE_CURL to enable those functions.
+RUN cc -O2 -DHAVE_CURL -c el_runtime.c -I. -o el_runtime.o
 
 # ── Build neuron-web ──────────────────────────────────────────────────────────
 #
@@ -44,15 +47,12 @@ RUN cc -O2 -rdynamic \
        -lcurl -lpthread -ldl -lm -lssl -lcrypto
 
 # ── Build soul-demo ───────────────────────────────────────────────────────────
-# Compile soul-demo.c with el_runtime.c directly (not el_runtime.o) so that
-# all runtime symbols — including emit_metric, emit_log, trace_span_* — are
-# always resolved from the staged source rather than a cached object file.
 COPY dist/soul-demo.c ./
 COPY dist/vessel_stubs.c ./
 
 RUN cc -O2 -rdynamic \
        -o soul-demo \
-       soul-demo.c vessel_stubs.c el_runtime.c \
+       soul-demo.c vessel_stubs.c el_runtime.o \
        -lcurl -lpthread -ldl -lm -lssl -lcrypto
 
 # ── Stage 2: runtime image ────────────────────────────────────────────────────