Add cooling.flow-under-load: the flow check with the tube lit through its window

A live catalog case: two 30 x 4 mm fills at full power on the press, the
window held open until the engine's flow verdict lands in the forgectrl
log, then M2 and the head brought back. PASS needs a verified line with
the laser's share on it (at least 0.3 C: the window and the fire
overlapped) and the judged rise at least 1 C under cool_flow_rise; an arm
refused by a gate names the gate. Passed on image 20260829190323
(heater rise 11.9 C judged, laser 0.6 off 12.5).

CAMPAIGN-LOG records the run and the day's two air-assist gate holds (a
bench connection, reseated); BRINGUP item 21 names the case.

Catalog: the case covers forgectrl src/cool.* and its neighbors; a new
test, so the manifest's coverage widens rather than moves.

docs/BRINGUP.md

@@ -1463,11 +1463,11 @@ Open items only. Anything closed is in `CAMPAIGN-LOG.md`.
     and toggles between two levels in between. Together they put an
     ordinary job's check within a few tenths of the limit. The engine now
     reads means and takes the tube's share off (`cool_laser_heat_cw`,
-    `cool_laser_heat_density`). Owed: a `cooling.*` catalog case with an
-    armed CW load; a re-measure of the two coefficients once a second
-    machine is on the bench (one tube, one supply so far); and if a lit
-    check still trips, the void-on-emission design with the tube as its
-    own flow tracer.
+    `cool_laser_heat_density`), and `cooling.flow-under-load` is the
+    catalog's case. Owed: a re-measure of the two coefficients once a
+    second machine is on the bench (one tube, one supply so far); and if a
+    lit check still trips, the void-on-emission design with the tube as
+    its own flow tracer.
     Open question, the offset's source: the timing points at the airflow
     drive (the step lands one sample after the fans go to run duty, before
     any HV, and lifts when they go idle, long after the tube is dark), but

docs/CAMPAIGN-LOG.md

@@ -4388,6 +4388,38 @@ and the reset came twice, 0.1 s apart: the tail of the blast arrived after
 the first reset had flushed the ring and overran it again. Harmless, the
 job was already stopped.
 
+## 2026-08-29: the air-assist fan and the airflow gate, twice
+
+Twice in the day the airflow gate held a job at the end of its 15 s grace
+with the air-assist tach still at its idle reading (1895 at 17:09 in a
+`flowload t2 40` run, 2207 at 20:19 in the first bench run of
+`cooling.flow-under-load`; the floor is 6000 and every other session of the
+day read about 10,700 within 5 s of the run profile). The head probed clean
+and the kernel log carried no I2C error; the fan read normal at idle both
+times. The gate did what it is for: the hold came before the arm, the
+operator's press was refused, the session closed with the fans, and no job
+ran without air. The operator's reading is a bench hardware glitch, the
+head's pogo-pin connection to the air assist; the machine was powered down
+and the head reseated, and the case was run again. Not a project item.
+
+## 2026-08-29: `cooling.flow-under-load`, the catalog's case for the lit check
+
+The catalog case for BRINGUP item 21 (`forgetest/suite/cooling.py`, kind
+live, mode grbl, one press): two 30 x 4 mm fills at full power on the press,
+the window held open until the engine's verdict lands in the forgectrl log,
+then M2. PASS needs `coolant flow verified` with the laser's share on the
+line (at least 0.3 C, the proof the window and the fire overlapped) and the
+judged rise at least 1 C under `cool_flow_rise`; an arm refused by a gate
+names the gate. First run on image 20260829190323 (the module staged over
+the installed suite, forgetest restarted; the prerequisites overridden, no
+campaign results on this image yet): the airflow gate held before the arm
+(the entry above). Second run after the head reseat: **PASS**, the engine
+line `coolant flow verified (heater rise 11.9 C, dT 9.5 C; laser 0.6 off
+12.5)`, 66 s from job to verdict, the window closed 0.0 s after M2, the
+head jogged back by the baseline; the case now brings the head back
+itself. The case rides the next image; its campaign standing comes with
+that image's campaign.
+
 ## Superseded status notes
 
 ### Shared machine services — remaining polish, as listed 2026-08-13