bench: every board-runnable tool ported to the bench page

The remaining bench diagnostics run from forgetest's #bench tab. The
tools that also run from a LAN host share scripts/bench/gfbench.py:
GF_HOST names a remote machine (host mode, sysfs through ssh, Grbl and
forgectrl over the LAN); unset, the tool runs on the board itself
(local mode, sysfs directly, everything on 127.0.0.1), which is how the
page runs them - with GF_HOST=127.0.0.1, the panel token in GF_TOKEN
and their data files under <data>/bench/ (FORGETEST_BENCH_DATA). The
helper also reads a machine setting from forgectrl, or from the settings
file on the board while forgectrl is stopped.

Ported: pwm_sweep / pwm_hold (scope = a takeover; the latch relocked,
the write refused if FIRE or LASER_ON reads active), pwm_stream_test
(PASS/FAIL exit), flow_characterize, flow_recheck_char,
flow_warm_validate and flow_matrix (takeovers: forgectrl owns the
thermal hardware, so the page's takeover replaces the tools' own
controller stop/restart, whose command line predated the supervisor;
results and logs in the bench data directory), flow_sustained,
fan_test, temp_calibrate (dry; watch bounded in seconds; the threshold
and the coolant conversion from the shared code), flow_escalate_drill
(cool_confirm_max_s shortened through forgectrl's settings for the
drill and restored; the setting's minimum is the default budget), and
live_fire_drills (<drill> [S] [F], all six drills, host from GF_HOST,
token from the board). flow_matrix joins the registry. What stays
unported cannot run against the machine at all: the two null-sink CI
harnesses and the .puls decoder.

Runner: a scope tool runs inside the takeover wrapper; the bench
environment above is passed to every tool. Tests: test_bench_registry
(registry <-> scripts/bench consistency, every ported tool builds its
command line, every script compiles, gfbench host/local modes) and the
server test (scope tool takeover, the environment reaching the tool).
Local mode smoke-run on the bench (temp_calibrate watch, setting, token)
from /tmp, removed after.

No catalog consequence: bench tools are not image components (dev-only
forgetest); the acceptance catalog is unchanged.

scripts/bench/pwm_hold.py

@@ -1,6 +1,12 @@
 #!/usr/bin/env python3
 """Hold LASER_PWM at one duty value for a measurement window, then restore.
-Usage: pwm_hold.py [sar] [seconds]  (defaults: 8, 30)"""
+Usage: pwm_hold.py [sar] [seconds]  (defaults: 8, 30)
+
+The duty register (PWMSAR) is the laser power SETPOINT only. Locked
+state only: run with the controller and forgectrl stopped (the bench
+page's takeover), the pulse device closed. The latch is relocked here
+as well, and the hold refuses to write if the FIRE line reads driven or
+LASER_ON reads active."""
 import mmap, struct, sys, time
 
 PWM2_BASE = 0x02084000
@@ -9,6 +15,26 @@ SAR_OFF = 0x0C
 sar = int(sys.argv[1]) if len(sys.argv) > 1 else 8
 secs = int(sys.argv[2]) if len(sys.argv) > 2 else 30
 
+
+def rd(name):
+    with open('/sys/glowforge/' + name) as f:
+        return f.read().strip()
+
+
+def wr(name, val):
+    with open('/sys/glowforge/' + name, 'w') as f:
+        f.write(str(val))
+
+
+try:
+    wr('cnc/laser_latch', 1)
+except OSError as e:
+    raise SystemExit('could not lock the laser latch: %s' % e)
+time.sleep(0.2)
+en, on = rd('cnc/laser_enable'), rd('cnc/laser_on')
+if en != '0' or on != '0':
+    raise SystemExit('not the locked state: laser_enable=%s laser_on=%s' % (en, on))
+
 with open('/dev/mem', 'r+b') as f:
     m = mmap.mmap(f.fileno(), 4096, mmap.MAP_SHARED,
                   mmap.PROT_READ | mmap.PROT_WRITE, offset=PWM2_BASE)
@@ -16,9 +42,11 @@ with open('/dev/mem', 'r+b') as f:
     m[SAR_OFF:SAR_OFF + 4] = struct.pack('<I', sar)
     print('PWMSAR=%d held for %d s (was %d)...' % (sar, secs, sar0))
     sys.stdout.flush()
-    time.sleep(secs)
-    m[SAR_OFF:SAR_OFF + 4] = struct.pack('<I', sar0)
-    print('restored PWMSAR=%d' % sar0)
-    with open('/sys/glowforge/cnc/laser_on_sampled') as s:
-        print('laser_on_sampled =', s.read().strip())
-    m.close()
+    try:
+        time.sleep(secs)
+    finally:
+        m[SAR_OFF:SAR_OFF + 4] = struct.pack('<I', sar0)
+        print('restored PWMSAR=%d' % sar0)
+        print('laser_enable=%s laser_on=%s laser_on_sampled=%s'
+              % (rd('cnc/laser_enable'), rd('cnc/laser_on'), rd('cnc/laser_on_sampled')))
+        m.close()