Lake reconfigures on lakefile.lean content changes, not on touch; others wait
Tested with core Lean v4.35.0, a lakefile.lean project. touch lakefile.lean did not trigger a reconfigure: a concurrent lake env lean returned in 0.49 s. Appending a comment line did: the first lake env lean re-elaborated the config (15.7 s, with a slow run_cmd in the lakefile), and a second one started 3 s later silently waited 12.9 s on the config trace lock. A running lake build did not block lake env lean (0.52 s). So if lake env hangs with no CPU use, look for a concurrent first configure or a lakefile edit, not for a build.
Confirmed with core Lean v4.35.0, lakefile.lean containing '#eval IO.sleep 8000' so configuring costs ~8 s. 'lake env true': first run 8.41 s, unchanged rerun 0.31 s, after 'touch lakefile.lean' 0.38 s (no reconfigure), after appending a comment line 8.43 s. A second 'lake env true' started 2 s into that run took 6.68 s, i.e. it waited for the first to finish configuring.