Warm the loop by the mixed bulk; record the flow check to the heater's ceiling

flow_warm_validate.py warms in rounds (the heater at 50 percent for three
minutes, off, 45 s of circulation, the two sensors' mean read) and judges
the target on that mixed bulk, not on the upstream sensor beside the
heater, which reached any target within two minutes while the bulk had
barely moved. Run with a 28 C target the loop plateaus at 27.2 C in a
20 C room; six checks at 26.2 to 27.2 C read every verdict right, the flow
band under 11.9 C and the no-flow band over 18.0 C against the 14.4 C
limit. CAMPAIGN-LOG records the run; BRINGUP item 1 keeps only the
button-latch check, the flow check's bands holding from 19 to 27 C.

No catalog consequence: a bench tool and documentation.

scripts/bench/flow_warm_validate.py

@@ -68,41 +68,53 @@ def pump(on):
     board('echo %d > /sys/glowforge/thermal/water_pump_on' % (1 if on else 0))
 
 
+WARM_ROUND_S = 180          # heater on per round, then a mix and a bulk reading
+WARM_MIX_S = 45
+WARM_PLATEAU_C = 0.15       # a round that lifts the bulk less than this is the end
+
+
 def warm_to(target, log):
-    """Warm with the loop heater, pump circulating, fans off."""
+    """Warm with the loop heater in rounds, pump circulating, fans off:
+    heater on for WARM_ROUND_S, heater off and WARM_MIX_S of circulation,
+    then the bulk read as the two sensors' mean. Judged on that mixed
+    bulk, never on the upstream sensor beside the heater, which reaches
+    any target within two minutes while the bulk has barely moved (the
+    2026-08-29 run stopped at 24.5 C that way). 50 % is the practical
+    heater ceiling: the downstream sensor sits at the element and 100 %
+    drives it past 50 C in 30 s."""
     pump(True)
     board(FANS_OFF)
-    # 50% is the practical ceiling: the downstream sensor sits AT the
-    # heater element, so 100% drives it past 50 C within 30 s while the
-    # bulk has barely moved. At 50% it plateaus near 41 C, leaving the
-    # bulk free to climb for as long as we let it.
-    heater(50)
     t0 = time.time()
-    # Plateau detection compares against the reading two minutes back:
-    # with the pump circulating, the bulk climbs only ~0.5-0.8 C/min, so
-    # a per-sample threshold mistakes normal warming for a plateau (it
-    # did exactly that on the first attempt and the whole run executed
-    # at ambient).
-    hist = []
+    last_bulk = None
     while time.time() - t0 < WARM_MAX_S:
+        heater(50)
+        r0 = time.time()
+        abort = False
+        while time.time() - r0 < WARM_ROUND_S and time.time() - t0 < WARM_MAX_S:
+            d, u = temps()
+            if d >= ABORT_C:
+                log('    warm abort: downstream %.2f C' % d)
+                abort = True
+                break
+            time.sleep(15)
+        heater(0)
+        if abort:
+            break
+        time.sleep(WARM_MIX_S)
         d, u = temps()
+        bulk = (d + u) / 2.0
         el = (time.time() - t0) / 60
-        if u >= target:
-            log('    warm target reached: up=%.2f at %.1f min' % (u, el))
+        log('      warming: %.1f min  bulk %.2f (down %.2f, up %.2f)' % (el, bulk, d, u))
+        if bulk >= target:
+            log('    warm target reached: bulk %.2f at %.1f min' % (bulk, el))
             break
-        if d >= ABORT_C:
-            log('    warm abort: downstream %.2f at %.1f min' % (d, el))
+        if last_bulk is not None and bulk - last_bulk < WARM_PLATEAU_C:
+            log('    (warming plateaued at %.2f C after %.1f min)' % (bulk, el))
             break
-        hist.append(u)
-        if len(hist) % 4 == 0:
-            log('      warming: %.1f min  down=%.2f  up=%.2f' % (el, d, u))
-        if len(hist) > 8 and u - hist[-9] < 0.3:
-            log('    (warming plateaued at %.2f C after %.1f min)' % (u, el))
-            break
-        time.sleep(15)
+        last_bulk = bulk
     heater(0)
     pump(True)
-    time.sleep(45)          # mix so the bulk is uniform before measuring
+    time.sleep(WARM_MIX_S)  # mix so the bulk is uniform before measuring
     d, u = temps()
     log('    warmed to down=%.2f up=%.2f in %.1f min' % (d, u, (time.time() - t0) / 60))
     return u