Function track_spawned 

pub fn track_spawned(block_id: &str, pid: u32)

Assign a freshly-spawned child PID to block_id’s tracker, creating the tracker if needed. The single call site every Controller impl should use immediately after its own spawn — no-ops silently if the registry global isn’t initialized (tests), and with a warn log if the platform tracker rejects the PID, since this is opportunistic enrichment, not a liveness signal on its own (see broker::process::ProcessStatus’s own doc comment).