reuse verified native platform version without duplicate query

tools/ci/macos-native-readiness.sh

@@ -99,6 +99,26 @@ read_scalar() {
   SCALAR="$value"
 }
 
+# BEGIN successful sw_vers version parser
+read_product_version() {
+  local value status line version="" fields=0
+  # Read the entire successful native output. EOF is mandatory; a NUL delimiter
+  # or reaching the 1025-byte sentinel must never hide a suffix.
+  LC_ALL=C IFS= read -r -n 1025 -d '' value < "$LAST_OUTPUT"; status=$?
+  (( status == 1 && ${#value} <= 1024 )) || return 1
+  while IFS= read -r line || [ -n "$line" ]; do
+    if [[ "$line" =~ ^[[:blank:]]*ProductVersion: ]]; then
+      fields=$((fields + 1))
+      (( fields == 1 )) || return 1
+      [[ "$line" =~ ^[[:blank:]]*ProductVersion:[[:blank:]]*([0-9]+\.[0-9]+(\.[0-9]+)?)[[:blank:]]*$ ]] || return 1
+      version="${BASH_REMATCH[1]}"
+    fi
+  done <<< "$value"
+  (( fields == 1 )) || return 1
+  SCALAR="$version"
+}
+
+# END successful sw_vers version parser
 # BEGIN disk IPC diagnostic
 # Optional observations have their own child/timer ownership. No service is
 # loaded, restarted or changed, and samples target only this probe's diskutil.
@@ -280,9 +300,9 @@ if (( platform_exit != 0 )); then
   platform_exit="$LAST_EXIT"
 fi
 (( platform_exit == 0 )) || fail_probe sw_vers_failed
-run_command version /usr/bin/sw_vers -productVersion
-(( LAST_EXIT == 0 )) || fail_probe product_version_failed
-read_scalar || fail_probe product_version_invalid
+# BEGIN successful sw_vers version extraction
+read_product_version || fail_probe product_version_invalid
+# END successful sw_vers version extraction
 os_version="$SCALAR"
 [[ "$os_version" =~ ^[0-9]+\.[0-9]+(\.[0-9]+)?$ ]] || fail_probe product_version_invalid
 (( ${os_version%%.*} >= 13 )) || fail_probe unsupported_macos_version