Constant PLACEMENT_LOG_PATH 

pub const PLACEMENT_LOG_PATH: &str = "/tmp/ktstr-placement.log";

Path of the scenario placement-history log. Captures placement events from both apply_setup (worker / payload spawn) and apply_ops (Op::MoveAllTasks pre/post cgroup.procs snapshots). Tests that assert on per-cgroup worker placement can read this file on failure to see exactly which PIDs landed in which cgroup at spawn time AND how Op::MoveAllTasks migrated them. The file lives in tmpfs and survives the scenario teardown (only the cgroup directories are rmdir’d; this file stays put). The log is append-only and is never cleared between runs (the only writer, append_placement_log, opens with .append(true) and never truncates), so lines from prior runs accumulate — a reader that needs only the current run’s placement must filter accordingly.