fix(ota_plugin): forward use_sim_time to OTA-spawned processes

ProcessRunner::spawn was running the new binary with execl(path, path,
nullptr) - no --ros-args, no parameters. After an OTA execute the
post-update node (fixed_lidar after the update flow,
obstacle_classifier_v2 after install) was therefore born with
use_sim_time=false while the rest of the demo runs on /clock from
gz-sim.

Result: every /scan / /diagnostics message stamped by the new node
landed outside the gateway's TF cache, nav2's costmaps logged
"Message Filter dropping message ... earlier than all the data in
the transform cache" on every tick, the obstacle layer stayed empty,
and NavigateToPose came back ABORTED with no progress - "robot
stops responding" from the operator's seat.

Pass --ros-args -p use_sim_time:=true to execl so the spawned node
joins the same clock domain as the rest of the stack. Robot resumes
following goals after the OTA swap.

This is the minimum viable param plumbing for the demo. A full
production plugin should plumb arbitrary parameters from the catalog
entry through to execve - but for now use_sim_time is the only param
the OTA-managed nodes care about.

Author: bburda

demos/ota_nav2_sensor_fix/ota_update_plugin/src/process_runner.cpp

@@ -138,7 +138,23 @@ tl::expected<int, std::string> ProcessRunner::spawn(const std::string & executab
     }
     if (grandchild == 0) {
       setsid();
-      execl(executable_path.c_str(), executable_path.c_str(), nullptr);
+      // Forward use_sim_time so the spawned node aligns with the
+      // gateway's clock domain. Without this, nodes started by OTA
+      // (post-update fixed_lidar, post-install obstacle_classifier)
+      // run on wall time while the rest of the stack runs on
+      // /clock from gz-sim - their /scan / /diagnostics timestamps
+      // fall outside nav2's TF buffer and the costmap drops every
+      // message: "the timestamp on the message is earlier than all
+      // the data in the transform cache". Robot stops responding.
+      //
+      // Note: this is the minimum viable param plumbing. A full
+      // production plugin should plumb arbitrary parameters from
+      // the catalog entry through to execve.
+      execl(executable_path.c_str(),
+            executable_path.c_str(),
+            "--ros-args",
+            "-p", "use_sim_time:=true",
+            static_cast<char *>(nullptr));
       std::fprintf(stderr, "execl %s failed: %s\n", executable_path.c_str(),
                    std::strerror(errno));
       _exit(127);