Fan/thermal control done and bench-verified; docs updated

BRINGUP records the gate as complete with tach-verified results;
LIGHTBURN.md documents the per-layer Air Assist toggle driving the
cut-profile ventilation; fan_test.py joins the bench kit.

docs/BRINGUP.md

@@ -220,18 +220,20 @@ hardware I/O — host testing).
      mapping) plus a chain-armed first-light procedure; the hardware
      verification prerequisites are complete. Interlock-trip recovery
      behavior remains to be exercised (non-scope check).
-   - **Additional laser-on prerequisite (operator-mandated
-     2026-08-02): fan/thermal control must be implemented first** —
-     air assist + purge (head), exhaust + intake (thermal), and the
-     coolant loop (water pump, TEC, water-temp monitoring). Factory
-     run/idle/cooldown values are in the captured pulse headers
-     (AAid/AArd/AAwd, EFid/EFrd/EFwd, IFid/IFrd/IFwd + CM/CT water
-     thresholds — see `_RESOURCES/*.info` and the gfutilities
-     settings map); kernel interfaces exist under
-     /sys/glowforge/head and /sys/glowforge/thermal. Map into the
-     driver as job-state-driven config (run at cycle start, cooldown
-     after, idle thereafter) like the factory's
-     `_config_from_pulse` scheme.
+   - **Fan/thermal control (operator-mandated laser-on prerequisite):
+     DONE 2026-08-02, bench-verified** (`glowforge_cooling.c` in the
+     driver; test `scripts/bench/fan_test.py`). Factory pulse-header
+     values throughout: init = pump on / TEC off / purge on / idle
+     fans (air assist 204); **M8** (coolant flood — LightBurn's
+     per-layer Air Assist) = cut profile (air 1023, exhaust 65535,
+     intake 43278); **M9** = 15 s cooldown (`GFCOOL_COOLDOWN_S`) then
+     idle. Water temp polled at 1 Hz vs the ~31 °C factory run
+     ceiling → one-shot controller warning (laser milestone upgrades
+     it to a hard fire gate). Verified via tach readbacks: air tach
+     period 4439→699 under M8, exhaust stopped→full, intakes ~3×,
+     cooldown hold, clean return to idle; coolant temp visibly
+     dropped during the blast. TEC/heater control remain for the
+     thermal part of the laser milestone.
    - **Interlock readback semantics cross-check: OPEN** (see
      factory-laser-safety-readbacks notes).
 3. **Homing (design decided 2026-08-02)**: the factory machine has NO

docs/LIGHTBURN.md

@@ -65,6 +65,15 @@ re-parked.)
 - **Console tab**: raw grbl — `?` status, `$$` settings, `$X` unlock,
   `$J=G91X10F1200` jog.
 
+## Air assist / fans
+
+Each cut/engrave layer has an **Air Assist** toggle (in the layer's cut
+settings). Turning it on makes LightBurn emit M8/M9 around that layer,
+which drives the machine's full cut-profile ventilation: air assist to
+full, exhaust and intake fans to factory run speeds, then a ~15 s
+cooldown after the layer before returning to idle. Leave it ON for
+anything that will eventually involve the beam; expect real fan noise.
+
 ## A good first job
 
 1. Draw a rectangle (~100 × 60 mm) with a circle inside.