Prove the dose curve and the recorder; document S-means-light

The stream harness gains rule 19: with the bench-default curve in force
a ladder of S rungs renders the curve's densities exactly (half light
lands near 80 percent density), monotonic, floored and ceiled by
$35/$36; every other session pins laser_dose_curve = off so its
S-to-level arithmetic stays exact, and the arm-report checks carry the
curve name. The lifecycle harness asserts the published state file
names the curve in force. The catalog's forgectrl.panel-serves asserts
the curve field in the grbl report, /curve/status and the ladder
G-code, and its covers name the recorder.

BRINGUP describes S-commands-light through the measured curve and the
owner recorder; the MOTION table gains laser_dose_curve; LIGHTBURN
tells the operator power now means light and how to record their own
tube's curve from the panel.

docs/BRINGUP.md

@@ -238,16 +238,26 @@ spot. The arm report names it (`laser armed (density, floor 10 %)`), and
 a floor of 0 is honored with a note (the ladders run that way). The
 cooling report carries the model with the job state.
 
-**Measured dose response (this bench, 2026-08-30, by the head thermopile,
-the tube current and the operator's eye on Thick Draftboard and acrylic).**
-Density delivers about half of the CW light at 80 % density, a third at
-60 %, a fifth at 45 % and a fourteenth at 30 %: the curve is the tube's
-(pulsed against CW), not the sensor's, and it is the same physics behind
-the factory's 18.9 to 79.5 % mapping with Full Power kept apart. An S
-correction from that curve (E4 in the working file) is the open item that
-follows. Rasters hold their tonality down to ~14 pulse slots per pixel
-(508 DPI at 6000 mm/min): the dither accumulator's cross-pixel averaging
-recovers the levels, with no visible dither pattern.
+**S commands light, through the measured curve.** The tube's output is
+convex in pulse density (this bench, 2026-08-30, by the head thermopile,
+the tube current and the operator's eye: 80 % density delivers about
+half the CW light, 60 % a third, 45 % a fifth, 30 % a fourteenth - the
+same physics behind the factory's 18.9 to 79.5 % mapping with Full
+Power kept apart). So the driver maps the commanded fraction through
+the measured curve's inverse onto the density that delivers it:
+`laser_dose_curve` in the machine config holds density:light percent
+pairs, ships with the bench-measured default compiled in, accepts
+`off` for the identity, falls back loudly on a bad value, and is
+reloaded at every precompute with the arm naming it (`laser armed
+(density, floor 10 %, curve bench-default)`). `$35`/`$36` still floor
+and ceil the result. An owner measures their own curve from the panel:
+the dose-curve recorder hands them a ladder G-code to run from their
+sender - every arm gate stands, forgectrl records the tube current and
+the head thermopile passively, fits the rungs, and Apply writes the
+result (`forgectrl/docs/SERVICES.md`). Rasters hold their tonality down
+to ~14 pulse slots per pixel (508 DPI at 6000 mm/min): the dither
+accumulator's cross-pixel averaging recovers the levels, with no
+visible dither pattern.
 
 An S word takes effect whether or not motion is in progress. Per-segment
 updates carry the level inside a laser block, but an S executed between

docs/LIGHTBURN.md

@@ -152,12 +152,16 @@ restart the controller with the head re-parked.)
 The controller drives the tube the way the factory does: every pulse
 fires at full power, and the power setting decides how many ticks of
 each 710 us period fire. Every power level marks, low levels included,
-because no pulse is ever too weak to strike. The response is not linear:
-on this machine 80 % gives about half the light of 100 %, 60 % about a
-third, 30 % about a fourteenth - so pick engrave power by test card, and
-prefer setting darkness with speed. Grayscale images fade cleanly into
-the shadows (a low level becomes sparse full-power pulses), and 254 to
-508 DPI rasters hold their tonal steps.
+because no pulse is ever too weak to strike. The raw response is not
+linear - 80 % of the pulses deliver about half the light - so the
+controller maps your power setting through a measured dose curve: 50 %
+commands half the light, not half the pulses. The machine ships with
+the bench-measured curve; record your own tube's from the control
+panel (GRBL tab, "Dose-curve recorder": download the ladder file, press
+Record, run the file from LightBurn on scrap, press the button, Apply
+the fit). Grayscale images fade cleanly into the shadows (a low level
+becomes sparse full-power pulses), and 254 to 508 DPI rasters hold
+their tonal steps.
 
 `$35`, the power floor, is set by the controller from the machine config
 (the control panel's GRBL tab, "Laser dose"): do not type it, it is

docs/MOTION.md

@@ -427,6 +427,7 @@ only be changed while the machine is idle.
 | `laser_button_timeout_s` | 300 | How long the machine waits at the button prompt. |
 | `laser_disarm_s` | 60 | Spindle-off grace before the armed window closes. |
 | `laser_floor_density` | 10 | The S-range floor, percent of full: the lowest pulse density that still marks. Loaded into `$35` at every spindle precompute; `$35` is derived, never typed. |
+| `laser_dose_curve` | (bench default) | The measured dose curve as density:light percent pairs; S commands a light fraction and the driver maps it onto the density that delivers it. `off` = identity; a bad value falls back to the default. The panel's recorder measures and applies a machine's own. |
 | `laser_pulse_ticks` | 20 | Density base period in machine ticks (35.5 us each). |
 | `laser_pulse_min_ticks` | 3 | Shortest density pulse in ticks; below it a period is skipped and its debt carried. |
 | `rail_settle_s` | 2.5 | Motor-rail off period when a controller takes the device standalone. |