Cover step timing under CPU contention; record the laser power model

Bump the grblHAL pin to the real-time producer change.

Add motion.step-timing-under-load: the catalog had nothing that
exercised step generation while userspace competed for the single core,
which is exactly the gap that let the condition go unnoticed - the ring
never runs dry, so cnc/underruns reads 0 through it. The test asserts
the producer and the shipper both hold SCHED_FIFO, then drives
2000 mm/min round trips against a deliberate nice-5 CPU hog and requires
the controller to report no clamped events.

Add the pthresh live-fire drill: a constant-power ladder from 2 % to
30 % of full on scrap. Because $35 is a percent of full duty and the
rungs are percents of $30 with $31 = 0, the lowest rung that marks reads
directly as the $35 value. It needs $35 = 0 for the run, or the floor
lifts every rung and hides the threshold.

Record both open items in BRINGUP. The laser one carries the finding
that the factory never uses duty as a power control - all five firing
jobs in the captured pulse files pin the power byte at 127 and modulate
dose by dithering the FIRE bit at 6.5-18.8 % density - so the captures
cannot supply a $35 default, and the duty to optical-power transfer
function of this supply has never been measured.

scripts/bench/README.md

@@ -32,7 +32,7 @@ page's takeover does that; from a host, stop them first.
 | `gate_a_kernel_drills.py` | Kernel laser-safety drills (run on the board with forgectrl stopped so the pulse device is free): `K1` controlled-stop deceleration floor, `K2` resume waypoint honors the locked latch, `K3` a mid-ramp latch unlock never re-arms the FIRE drive. Software witnesses (`cnc/state`, `laser_enable`, `laser_on`, `laser_on_sampled`, interlock bit 3) plus the PSU-connector LASER_ON scope point; K3 refuses to run if HV reports good. |
 | `laser_stream_test.py` | Host-side laser pulse-stream emission harness: runs the native null-sink controller with `GFSINK_DUMP`, drives small laser jobs over TCP, and checks the dumped bytes against the kernel feeder contract (leading power byte, no back-to-back power bytes, FIRE only inside cutting moves, every stream ends FIRE-clear, no FIRE on a stepless gap, no FIRE leak across cycle churn). Runs in the grblHAL repo's CI. |
 | `laser_lifecycle_test.py` | Host-side operator-armed-window lifecycle harness (null-sink controller): arm once per job with M5/M3 persistence, the M2 close, sender-change re-consent, the disarm grace counting down in Hold, and arm refusal under a blocking cooling verdict. Runs in the grblHAL repo's CI. |
-| `live_fire_drills.py` | **LIVE LASER** drills, on the board (the bench page) or from a LAN host (`GF_HOST`): `live_fire_drills.py <drill> [S] [F]` - `witness` (emission witness, lid-IR peaks vs the ambient baseline, HV current, job-based disarm on M2), `hold` (disarm grace in Hold), `faultpos` (armed job refuses a stale origin after an underrun), `ircut` (lid-IR characterization cut at S/F), `expstop` (armed kill on the expected-stop path; needs the panel token - `GF_TOKEN`, or the board's token file) and `ctrlstart` (the separate controller restart after it). Every drill waits for the operator's physical arm press; eye protection, fire watch, extinguisher, and exhaust are mandatory. |
+| `live_fire_drills.py` | **LIVE LASER** drills, on the board (the bench page) or from a LAN host (`GF_HOST`): `live_fire_drills.py <drill> [S] [F]` - `witness` (emission witness, lid-IR peaks vs the ambient baseline, HV current, job-based disarm on M2), `hold` (disarm grace in Hold), `faultpos` (armed job refuses a stale origin after an underrun), `ircut` (lid-IR characterization cut at S/F), `pthresh` (laser power-threshold ladder: 13 constant-power rungs from 2 % to 30 % of full on scrap; the lowest rung that marks is the tube's striking threshold and reads directly as the `$35` value - requires `$35` = 0 for the run), `expstop` (armed kill on the expected-stop path; needs the panel token - `GF_TOKEN`, or the board's token file) and `ctrlstart` (the separate controller restart after it). Every drill waits for the operator's physical arm press; eye protection, fire watch, extinguisher, and exhaust are mandatory. |
 | `pacing_test.py` | Protocol-loop pacing check (runs on the board, dry motion): idle and parked-in-Hold states are coarse-paced, active motion is tight-paced, and a feed-hold/resume mid-move preserves position with no feeder starve. |
 | `gfbench.py` | Not a tool: the helper the board/host tools share - `HOST`/`LOCAL` from `GF_HOST`, `board(cmd)` (local `sh -c` or ssh), the factory coolant conversion `degc()`, `data_path()` (`FORGETEST_BENCH_DATA` or next to the tool), forgectrl's HTTP API with the panel token, `setting(key)` (from forgectrl, or from `/data/forgefirm.conf` on the board while forgectrl is stopped). |
 | `fan_test.py` | Fan/coolant bench (board or host; controller running): snapshots fan PWMs/tachs/temps, drives M8 → cut fans, M9 → cooldown → idle, verifying via tach readbacks. |