setup.focus: the test reads the LASER_ON count and the tube current from sysfs itself at every poll of the burn

The focus burn's emission was judged from the burn's result alone: the
daemon's own 25 Hz reads of cnc/laser_on_sampled and pic/hv_current,
reported as laser_on_samples and hv_max. The one live catalog test of
the wizard's burn took the daemon under test at its word for the
emission it reported, where the laser.* tests judge from the test's own
/status samples.

run_check takes on_poll(doc), called once per poll of /wiz/dark with
the status document, a caller's own witness read beside the check's;
the default keeps every positional caller as it is. Witnesses, in
setup_burns, reads the two attributes from sysfs at every poll and
keeps each at its peak and the count of polls that read both. burn()
passes it to run_check, and emission_ok(ctx, last, seen) keeps the
result's three checks and adds the test's own: at least one poll read
both witnesses, the LASER_ON count read nonzero from here, and the tube
current read over HV_ON (30, the daemon's own rule for a lit burn,
jobstream.h JOBSTREAM_HV_ON) from here. Once the result's three checks
pass, the evidence carries the two peaks and the read count as
emission_seen; the two readings are not compared with each other. The beam sensor's handling is unchanged, and
the description names both readings.

Proof: tests/test_setup_burns.py, the Unit tests step of
forgetest-ci.yml (python -B -m unittest discover -s tests), 20 tests
OK on Windows and on Linux, with tests/test_setup_dark.py (20 OK) for
the positional callers of run_check. BurnRunTests plants
cnc/laser_on_sampled and pic/hv_current under GF_SYSFS_ROOT (the shape
of a bench record), the lit burn's evidence carries the two peaks with
reads over zero, and a burn whose result reports a lit burn while the
two attributes read 0 from here fails on the LASER_ON count, with the
setting put back and the controller restarted on it. pyflakes reports
no undefined name. Negative control on a scratch copy: with
setup_burns.py and setup_dark.py as they were before this change, that
same case passes (Failed not raised) and the evidence has no
emission_seen; the two new assertions catch both.

Acceptance: setup.focus's fingerprint moves (its own text, and the
shared text of setup_burns.py and setup_dark.py), and every test of
setup_dark.py moves through run_check: setup.check-switches,
setup.check-airflow, setup.check-motion, setup.check-lens and
setup.cloud-header-capture. motion.release does not move (its run_check
import is inside the function body). The next campaign runs setup.focus
with both readings on the bench.

forgetest/tests/test_setup_burns.py

@@ -9,11 +9,14 @@ sender, the page, and the driver's laser module; and the burn against a
 scripted daemon: the preview and the program read, the start, the
 prompts answered in order (the gantry stops, the head at home, the scrap,
 its thickness in the machine's units, the arm, the machine's own press
-prompt, the pick), the witnesses judged, the record read at version 1,
-the setting the burn wrote put back as found, and the controller started
+prompt, the pick), the witnesses judged (the burn's own, and the two the
+test reads from sysfs at every poll), the record read at version 1, the
+setting the burn wrote put back as found, and the controller started
 again on the edge and the window put back."""
 import os
+import shutil
 import sys
+import tempfile
 import unittest
 
 sys.path.insert(0, os.path.dirname(__file__))
@@ -279,6 +282,13 @@ class ScriptedDaemon:
 
 class BurnRunTests(unittest.TestCase):
     def setUp(self):
+        # the two witnesses as sysfs serves them through a lit burn (the
+        # shape of a bench record: the LASER_ON count and the tube current)
+        self.sysfs = tempfile.mkdtemp(prefix="forgetest-burn-")
+        self.plant("cnc/laser_on_sampled", "118")
+        self.plant("pic/hv_current", "431")
+        self.saved_root = os.environ.get("GF_SYSFS_ROOT")
+        os.environ["GF_SYSFS_ROOT"] = self.sysfs + "/"
         self.fake = helpers.FakeForgectrl().start()
         self.daemon = ScriptedDaemon(self.fake)
         self.poll = setup_dark.POLL_S
@@ -287,6 +297,17 @@ class BurnRunTests(unittest.TestCase):
     def tearDown(self):
         setup_dark.POLL_S = self.poll
         self.fake.stop()
+        if self.saved_root is None:
+            os.environ.pop("GF_SYSFS_ROOT", None)
+        else:
+            os.environ["GF_SYSFS_ROOT"] = self.saved_root
+        shutil.rmtree(self.sysfs, ignore_errors=True)
+
+    def plant(self, attr, value):
+        path = os.path.join(self.sysfs, *attr.split("/"))
+        os.makedirs(os.path.dirname(path), exist_ok=True)
+        with open(path, "w") as f:
+            f.write(value + "\n")
 
     def run_test(self, tid):
         t = catalog.load_suite()[tid]
@@ -312,6 +333,10 @@ class BurnRunTests(unittest.TestCase):
         self.assertNotIn("lens_hall_edge_z_mm", start)
         self.assertEqual((start["lens_stop_below_steps"], start["lens_stop_above_steps"]), ("14", "20"))
         self.assertEqual(run.evidence["result"]["emission"]["hv_max"], 610)
+        # the witnesses read from here at every poll: each at its peak
+        seen = run.evidence["emission_seen"]
+        self.assertEqual((seen["laser_on_max"], seen["hv_max"]), (118, 431))
+        self.assertGreater(seen["reads"], 0)
         fw = run.evidence["focus_window"]
         self.assertEqual(fw["window"]["below"], 14)
         self.assertEqual(fw["window"]["above"], 20)
@@ -404,6 +429,18 @@ class BurnRunTests(unittest.TestCase):
         self.assertIn("the tube current never rose", str(cm.exception))
         self.assert_found()
 
+    def test_a_burn_the_test_itself_never_saw_fails_and_still_restores(self):
+        # The burn's result reports a lit burn, and the test's own reads
+        # of the two witnesses never leave zero: the burn is judged on
+        # what was read from here, not on the daemon's word alone.
+        self.plant("cnc/laser_on_sampled", "0")
+        self.plant("pic/hv_current", "0")
+        with self.assertRaises(Failed) as cm:
+            self.run_test("setup.focus")
+        self.assertIn("LASER_ON count never read nonzero", str(cm.exception))
+        self.assert_found()
+        self.assert_restarted_on_found()
+
     def test_a_burn_with_a_silent_beam_sensor_passes(self):
         # A head whose beam sensor gives no output: the tube current and
         # LASER_ON saw the beam, so the burn counts.