bench+docs: IG threshold LSB is FS/256; factory HA* seed values recovered

The captured pulse headers carry the factory's IG programming: hunts
off, travels abort-only (HAar=133 at +/-4 g), the cut alert-only
(HAxr=132, HAyr=112), Z and idle never armed. The factory abort value
itself rules out an FS/128 LSB (4.16 g would sit over the measurable
range), and two Z-only bench windows bracket gravity between
thresholds 100 and 150, which only FS/256 explains. The drill script's
printed g conversion is corrected, and the stale motion-profile
reading of HAxr/HAyr/HAar as accel limits is corrected in the facts
bank.

No catalog consequence: a bench script's printed conversion and the
docs record; no shipped behavior changes.

docs/BRINGUP.md

@@ -890,8 +890,10 @@ is committed.
   all-positive from that corner.
 - **Factory motion profile** (measured from captured factory pulse streams
   with `puls_profile.py`): accel ≈ 700 mm/s² X / 590 mm/s² Y on v2.6.0 firmware
-  (2018 firmware used ≈1000); header HAxr=132/HAyr=112/HAar=133 ⇒ ≈5.3 mm/s²
+  (2018 firmware used ≈1000). The HAxr/HAyr/HAar header tags are NOT motion
-  per HA unit. Travel moves peak 202 mm/s vector (≈ 8 in/s) at STfr=28160 Hz;
+  accel limits; they are LIS2HH12 IG threshold register values (the crash
+  detector, "The head accelerometer" below).
+  Travel moves peak 202 mm/s vector (≈ 8 in/s) at STfr=28160 Hz;
   prints and hunts run STfr=10000. Cut feed in the sample print: 145 mm/s. Z
   cadence ≈ 61–115 ms per half-step (≈ 5.7 mm/s max).
 - **Factory analog config** (constant across all captured jobs, 2018→2026):
@@ -1048,11 +1050,17 @@ is committed.
   running ODR, so an armed detector must set the ODR itself and re-assert it
   after any liveness read (each one-shot powers the part down again). The IG
   registers coexist with the bound driver over i2c-dev (I2C_SLAVE_FORCE):
-  IG_SRC1 polls at ~166 Hz from Python with `st_accel` raw reads intact. At
+  IG_SRC1 polls at ~166 Hz from Python with `st_accel` raw reads intact. The
-  the factory +/-2 g full scale the threshold LSB is ~15.6 mg, so 1 g ~= 64;
+  IG_THS LSB is **full scale / 256** (bench-confirmed against gravity: at
-  gravity rides Z on the head (raw ~-16916), so Z trips any sub-1 g
+  +/-2 g, threshold 100 = 0.78 g trips on the 1.03 g gravity reading and
-  threshold at rest while X and Y stay silent at rest and through a jog at
+  threshold 150 = 1.17 g does not; FS/128 would make the trip at 100
-  threshold 40 (~0.62 g).
+  impossible). Gravity rides Z on the head (raw ~-16916), so Z trips any
+  sub-1 g threshold at rest while X and Y stay silent at rest and through a
+  jog at threshold 40 (0.31 g). The factory arms the IG per job from the
+  HA* header tags: hunts all-zero (off), travel files abort-only
+  (`HAar=133` at `HAsr=4`, +/-4 g, ~2.08 g), the cut job alert-only
+  (`HAxr=132` ~2.06 g, `HAyr=112` ~1.75 g, +/-4 g), Z and the idle
+  thresholds zero in every captured header.
 - **Beam detect in the head MCU.** PTE16 into ADC0 gives reg 0x16, the raw
   analog level (`beam_detect_analog`, a head sysfs attr): near 1834 dark, 2600
   to 2890 during S300/S400 fire (the acceptance suite's mark witness),

docs/CAMPAIGN-LOG.md

@@ -6828,6 +6828,36 @@ one gentle jog (`$J=G91 X5 F1000`, +X first). No emission, no unbind.
   the strike magnitude, 3x and more over a threshold that gravity
   already trips; a physical tap would add nothing the design needs.
 
+## 2026-08-31: IG threshold LSB confirmed FS/256; the factory HA* seed values recovered
+
+Two facts that size the crash detector's thresholds, found while seeding
+them from the captured headers. They correct the previous entry's g
+conversion, which assumed FS/128 (values half of what it stated: the
+drill's threshold 40 is 0.31 g, not 0.62 g).
+
+- **The captured headers carry the factory's IG programming.** All 23
+  captured `.puls` headers parse (gfutilities `PulseSource`): hunts ship
+  every HA threshold zero (detector off, `HAsi/HAsr=2`); travel files
+  ship abort-only (`HAar=133`, `HAsr=4`); the cut job ships alert-only
+  (`HAxr=132`, `HAyr=112`, `HAsr=4`, `HAar=0`). `HAz*` and every idle
+  (`*i`) threshold are zero in every header. So the factory never arms
+  Z (the gravity axis), never arms the idle state, pauses cuts on a
+  ~2 g event and fails travels on one.
+- **IG_THS LSB = full scale / 256, twice proven.** By the factory's own
+  values: at FS/128 the travel abort 133 would be 4.16 g at +/-4 g,
+  over the measurable range, an abort that could never trip. On the
+  bench (two Z-only coexist windows, dev 20260831204710): threshold
+  100 trips on the 1.03 g gravity reading and threshold 150 does not;
+  under FS/256 those are 0.78 g and 1.17 g, bracketing gravity, while
+  under FS/128 the trip at 100 (1.56 g) would be impossible. The
+  datasheet states no IG_THS LSB (only ACT_THS = FS/128), so the bench
+  check was the proof. The drill script's printed conversion is fixed
+  to FS/256 in the same change.
+- **The factory seed values in g**: X alert 132 = 2.06 g, Y alert
+  112 = 1.75 g, abort 133 = 2.08 g, all at the +/-4 g run full scale.
+  Normal commanded motion reads under 0.2 g and a rail strike 1.8 g
+  and up, so the factory band sits where the bench says it should.
+
 ## Reference notes
 
 ### Head-IRQ source validation — the beam-emission hypothesis

scripts/bench/accel_crash_probe.py

@@ -41,8 +41,9 @@ Usage:
             but liveness is down meanwhile, so stop the controller and
             forgectrl first)
   --ths N   per-axis threshold register value 0..255 (default 40); the
-            LSB is full-scale dependent, so the printed CTRL4 FS fixes
+            LSB is full scale / 256 (bench-confirmed against gravity:
-            the g conversion (+/-2 g default: ~15.6 mg/LSB, 1 g ~= 64)
+            +/-2 g gives ~7.8 mg/LSB, 1 g ~= 128), so the printed CTRL4
+            FS fixes the g conversion
   --dur N   IG_DUR1 duration counter, samples at the running ODR
             (default 0 = fire on the first over-threshold sample)
   --axes    which axes arm high events (default xyz)
@@ -172,7 +173,7 @@ def main():
     if (ctrl1 & 0x70) == 0:      # ODR bits 6:4 zero = power-down; IG needs
         wr(fd, CTRL1, 0x6F)      # a running ODR: 800 Hz, BDU, XYZ on
         ctrl1 = rd(fd, CTRL1)
-    lsb_mg = (fs * 1000.0 / 128.0) if isinstance(fs, int) else 0
+    lsb_mg = (fs * 1000.0 / 256.0) if isinstance(fs, int) else 0
     print('WHO_AM_I=0x%02x CTRL1=0x%02x CTRL4=0x%02x  FS=+/-%sg  '
           'ths=%d (~%.0f mg, ~%.2f g)  dur=%d  axes=%s  mode=%s'
           % (who, ctrl1, ctrl4, fs, ths, ths * lsb_mg, ths * lsb_mg / 1000.0,