Laser: the rapids after an M5 ship dark and the next job fires; the performance-curve drill

Stream harness rules 16 and 17 with their sessions: an M5 executed with
the planner drained and the kernel run over must darken the rapids that
follow it (m5-idle), and a job whose M3 runs at the level the previous
job ended at must still fire its first cut (next-job). The second rule
is the core's contract: set_state records the rpm and the per-segment
update is skipped while it is unchanged, so the driver's set_state is
the only thing that can light that move. Both sessions run under both
dose models; the bench build that went dark on its second job fails
next-job with one fire span.

Bench drills: pcurve (a per-level ladder of 100 mm lines read from the
HV current and the head thermopile at 25 Hz, with the instrument checks
and the JSON record) and m5dark (one line, M5, two rapids, judged on the
current trace and laser_on_sampled until the armed window closes).

Catalog: laser.m5-rapid-dark, a live test of the M5 case (46 tests; the
counts in BRINGUP follow). CAMPAIGN-LOG carries the day's record: the
two curve ladders, the defect pair, the root cause, the host and bench
proof.

forgetest/forgetest/suite/laser.py

@@ -396,6 +396,83 @@ def emission_witness(ctx):
             "dark, mark confirmed", peak, ev["hv_min"], ev["hv_max"], beam["delta"], dt)
 
 
+HV_DARK_MAX = 20            # hv_current_raw reads 0 with the tube off; hundreds under fire
+
+
+@test("laser.m5-rapid-dark", title="The rapids after an M5 ship dark",
+      subsystem="laser", kind="live", mode="grbl", est_min=3,
+      covers=_LASER_COVERS,
+      requires=["laser.emission-witness"], actions=["button"],
+      steps=["Scrap under the head with 20 mm of free +X travel; lid closed; exhaust on.",
+             "Press the physical button when it lights white (the arm)."],
+      description="A 20 mm line at constant power (M3 S400/F600), then M5, a dwell, a rapid back "
+                  "over the line, a dwell, a rapid forward, a dwell, and the program end. M5 "
+                  "executes with the planner drained and the kernel run over, and the core "
+                  "issues no per-segment laser update for moves made with the spindle off, so "
+                  "only the stream's own wanted state decides whether those rapids fire; a stale "
+                  "true there lights them at the last level, full duty under the density model. "
+                  "The kernel's LASER_ON sample count must go to 0 after the M5 and stay 0 "
+                  "through both rapids, and the HV current must stay at its idle reading.")
+def m5_rapid_dark(ctx):
+    ev = ctx.evidence
+    with ctx.grbl() as g, LiveJob(ctx, g):
+        prepare(ctx, g)
+        base = sample(ctx)
+        ctx.check(base, "forgectrl /status or /cool/status unavailable")
+        ctx.check(not base["emission"], "emission_samples nonzero before the job (%s)", base["emission"])
+        ctx.ready(ARM_CUE % "20 mm +X")
+        job = ["G91", "G21", "M3", "S400",
+               "G1 X20 F600",
+               "M5", "G4 P2.5",
+               "G0 X-20", "G4 P2.5",
+               "G0 X20", "G4 P2.5",
+               "G90", "M2"]
+        ctx.arm_press()
+        try:
+            samples = run_and_sample(ctx, g, job)
+            # The controller reports Idle inside a G4 dwell, so the sampler
+            # above can return before the rapids; the window closing at M2
+            # is the end of the job. Keep sampling until then.
+            t0 = time.time()
+            while time.time() - t0 < 30:
+                ctx.checkpoint()
+                smp = sample(ctx)
+                if smp:
+                    samples.append(smp)
+                    if not smp["armed"]:
+                        break
+                time.sleep(0.125)
+        finally:
+            ctx.clear_notice()
+    emis = [(s["t"], s["emission"], s["hv"]) for s in samples if s["emission"] is not None]
+    peak = max((e for _t, e, _hv in emis), default=0)
+    ctx.check(peak > 0, "no emission witnessed on the G1 (emission_samples stayed 0)")
+    # The first zero after the peak is the dark window the M5 and its dwell
+    # produce; everything after it is the two rapids and their dwells.
+    i_peak = max(range(len(emis)), key=lambda i: emis[i][1])
+    after = [x for x in emis[i_peak:] if x[1] == 0]
+    ctx.check(after, "emission_samples never returned to 0 after the M5")
+    t_dark = after[0][0]
+    tail = [x for x in emis if x[0] >= t_dark]
+    relit = [x for x in tail if x[1]]
+    hv_tail = max((hv for _t, _e, hv in tail if hv is not None), default=0)
+    ev.update({"samples": len(samples), "emission_peak": peak, "tail_samples": len(tail),
+               "relit_samples": len(relit), "hv_tail_max": hv_tail,
+               "relit_first": relit[0] if relit else None})
+    ctx.log("emission peak %s; dark from +%.1f s; %d samples after it spanning %.1f s, %d with "
+            "emission, HV max after dark %s", peak, t_dark - emis[0][0], len(tail),
+            tail[-1][0] - t_dark, len(relit), hv_tail)
+    ctx.check(tail[-1][0] - t_dark >= 5.0, "sampling ended %.1f s after the dark point, before "
+              "both rapids and their dwells (~5.2 s) had run", tail[-1][0] - t_dark)
+    ctx.check(not relit, "the laser emitted after the M5: %d samples, first at +%.1f s "
+              "(emission_samples %s) - a rapid after M5 fired at the last level",
+              len(relit), (relit[0][0] - t_dark) if relit else 0, relit[0][1] if relit else None)
+    ctx.check(hv_tail <= HV_DARK_MAX, "HV current %s after the M5 (idle reads ~0): the discharge "
+              "ran through a rapid", hv_tail)
+    ctx.log("PASS: emission peak %s on the G1, 0 through both rapids, HV %s after the M5",
+            peak, hv_tail)
+
+
 @test("laser.disarm-in-hold", title="Disarm grace counts down in Hold", subsystem="laser",
       kind="live", mode="grbl", est_min=4,
       covers=_LASER_COVERS,