feat(telemetry): record backing-binary versions on spans, captured at build time

build/capture-version.sh

@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+# Captures the version of a backing binary into a per-module file that the
+# running Gotenberg process reads via gotenberg.BuildVersion, so it never spawns
+# the binary just to report a version. This keeps cold start and the first
+# request cheap, which matters on serverless platforms.
+#
+# Failure-tolerant by design: a probe that errors writes an empty file, and the
+# runtime falls back to detecting the version live. A failing probe must never
+# fail the image build.
+#
+# Usage: capture-version.sh <output-dir> <module-id> <bin> [args...]
+set -u
+
+dir="$1"
+id="$2"
+shift 2
+
+mkdir -p "$dir"
+
+# Run the probe once. On failure, keep going with empty output.
+raw="$("$@" 2>/dev/null)" || raw=""
+
+case "$id" in
+pdfcpu)
+    # pdfcpu prints "pdfcpu: <version>"; keep only the part the runtime parser
+    # keeps so the recorded value matches the live-detection fallback.
+    version="$(printf '%s\n' "$raw" | grep -m1 '^pdfcpu:' | sed 's/^pdfcpu:[[:space:]]*//')"
+    ;;
+*)
+    version="$(printf '%s\n' "$raw" | head -n1)"
+    ;;
+esac
+
+printf '%s' "$version" | tr -d '\r' >"$dir/$id"