feat: HTTP registry, app/bench harnesses, and DWARF #line maps

Ship QUALITY_PLAN sessions 31–33: fetchable package index URLs, showcase
app and micro/nexus benchmarks, and debugger-friendly C codegen.

- Registry: BUX_REGISTRY accepts http(s) URLs (curl/wget → ~/.bux/cache)
- E.2: make test-apps smoke for nexus/boko/simpledb/jwt-pitbul
- E.5: benches/micro + C/Nim/Zig twins; make bench-nexus (wrk)
- E.4: HIR locs → #line .bux; default -O0 -g; --release -O2; make test-dwarf

tools/bench_nexus.sh

@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+# Nexus HTTP throughput bench (E.5) — wrk against /api/health
+set -euo pipefail
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+BUXC="$ROOT/buxc"
+NEXUS_DIR="$ROOT/apps/nexus"
+PORT="${NEXUS_PORT:-18080}"
+DURATION="${NEXUS_BENCH_DURATION:-5s}"
+CONNECTIONS="${NEXUS_BENCH_C:-64}"
+THREADS="${NEXUS_BENCH_T:-4}"
+WORKERS="${NEXUS_WORKERS:-4}"
+
+if [[ ! -x "$BUXC" ]]; then
+  (cd "$ROOT" && make build >/dev/null)
+fi
+
+if ! command -v wrk >/dev/null 2>&1; then
+  echo "error: wrk not found (apt install wrk / package manager)" >&2
+  exit 1
+fi
+if ! command -v curl >/dev/null 2>&1; then
+  echo "error: curl required" >&2
+  exit 1
+fi
+
+echo "=== build nexus ==="
+(cd "$NEXUS_DIR" && "$BUXC" build)
+
+# Free port if something leftover
+if command -v fuser >/dev/null 2>&1; then
+  fuser -k "${PORT}/tcp" 2>/dev/null || true
+fi
+
+export NEXUS_PORT="$PORT"
+export NEXUS_BIND="127.0.0.1"
+export NEXUS_WORKERS="$WORKERS"
+export NEXUS_PUBLIC="$NEXUS_DIR/public"
+
+PID=""
+cleanup() {
+  if [[ -n "$PID" ]]; then
+    kill "$PID" 2>/dev/null || true
+    wait "$PID" 2>/dev/null || true
+  fi
+}
+trap cleanup EXIT
+
+echo "=== start nexus :${PORT} (workers=${WORKERS}) ==="
+(
+  cd "$NEXUS_DIR"
+  ./build/nexus
+) >"$ROOT/benches/nexus_run.log" 2>&1 &
+PID=$!
+
+URL="http://127.0.0.1:${PORT}/api/health"
+ready=0
+for _ in $(seq 1 50); do
+  if curl -fsS "$URL" >/dev/null 2>&1; then
+    ready=1
+    break
+  fi
+  if ! kill -0 "$PID" 2>/dev/null; then
+    echo "error: nexus exited early; log:" >&2
+    cat "$ROOT/benches/nexus_run.log" >&2 || true
+    exit 1
+  fi
+  sleep 0.1
+done
+if [[ "$ready" -ne 1 ]]; then
+  echo "error: nexus did not become ready on $URL" >&2
+  cat "$ROOT/benches/nexus_run.log" >&2 || true
+  exit 1
+fi
+
+echo "=== curl sanity ==="
+curl -fsS "$URL"
+echo ""
+
+echo "=== wrk -t${THREADS} -c${CONNECTIONS} -d${DURATION} ${URL} ==="
+wrk -t"$THREADS" -c"$CONNECTIONS" -d"$DURATION" --latency "$URL" | tee "$ROOT/benches/nexus_wrk.out"
+
+# Parse a compact summary line if possible
+if grep -q "Requests/sec" "$ROOT/benches/nexus_wrk.out"; then
+  rps=$(grep "Requests/sec" "$ROOT/benches/nexus_wrk.out" | awk '{print $2}')
+  echo "BENCH nexus_health rps=${rps} port=${PORT} workers=${WORKERS} c=${CONNECTIONS} t=${THREADS} d=${DURATION}"
+fi
+
+echo "PASS: nexus throughput bench"