A test that does not hand the machine back fails

The baseline has always examined the machine after every run and recorded
what the run left behind. It did nothing else with it: the leftovers went
to the log and the evidence, and the test still reported PASS. So a check
could measure correctly, walk away with the machine in a state nobody
chose, and be recorded green.

That is how the purge fan came to be left off by the airflow check. The
leftover was not even watched, but had it been, it would have been noted
and the test would have passed anyway, and an operator would still have
met the airflow hold at their first fire.

A post-run leftover now fails the run. One the baseline put back fails it
too: the restore is the bench cleaning up after a defect, not the defect's
absence. The message names what was left.

The baseline watches the head as well as the motion side now: purge air
on, which is how the machine idles, and the lens motor at its hold current
in half step, which the lens checks and the sheet cards take and must hand
back. The airflow check proves the machine is whole rather than merely
measured: afterward the purge fan must read commanded-on and must draw
above the floor the check itself just wrote.

The pin takes forgectrl 0.1.13 (a2d73ef), which restores the idle posture
after a diagnostic, fixes the lens session's takeover flag, and gives the
setup a Download logs button, since the panel's Logs tab is unreachable
until the setup is complete.

Expect this to find things. A test that has been handing the machine back
imperfectly has been passing until now, and the first campaign under the
rule is where that shows.

forgetest/forgetest/suite/commission_dark.py

@@ -167,7 +167,8 @@ def check_sensors(ctx):
                   "for 35 s, the purge is measured on and off, and five settings are written: the "
                   "four floors at 55 percent of steady and the grace from the slowest spin-up. Each "
                   "fan must read at least 1000 rpm. The five settings are put back as found at the "
-                  "end and the controller must be running again.")
+                  "end, the purge fan is on again and drawing over the floor the check just wrote, "
+                  "and the controller must be running again.")
 def check_airflow(ctx):
     keys = ["cool_tach_exhaust_min_rpm", "cool_tach_intake_min_rpm", "cool_tach_air_assist_min_rpm",
             "cool_purge_min_current", "cool_fan_grace_s"]
@@ -186,6 +187,20 @@ def check_airflow(ctx):
         for k in keys:
             ctx.check(s.get(k) == floors.get(k), "%s reads %r, the check wrote %r", k, s.get(k), floors.get(k))
         ctx.log("floors: %s", json.dumps(floors))
+        # The check switches purge air off to read its off current. Leaving
+        # it off costs the next job an airflow hold mid-cut, judged against
+        # the very floor written above, and nothing puts it back until the
+        # daemon restarts: the engine's idle phase never re-applies its own
+        # duties. Prove the machine is whole, not just measured.
+        purge_on = ctx.sysfs("head/purge_air")
+        ctx.check(purge_on == "1", "purge air reads %r after the check, expected 1 (on)", purge_on)
+        gate = ((ctx.forgectrl.get("/cool/status")[1] or {}).get("fan_gates") or {}).get("purge") or {}
+        ctx.evidence["purge_after"] = {"purge_air": purge_on, "gate": gate}
+        ctx.log("purge after the check: commanded %s, drawing %s against the %s floor",
+                purge_on, gate.get("reading"), gate.get("floor"))
+        ctx.check((gate.get("reading") or 0) >= (gate.get("floor") or 0),
+                  "purge draws %s, under the %s floor the check just wrote: the next job would be held",
+                  gate.get("reading"), gate.get("floor"))
     ok = ctx.wait_for(lambda: (ctx.forgectrl.get("/mode")[1] or {}).get("controller") == "running", 60)
     ctx.check(ok is not None, "the controller did not come back after the check")