laser.pause-resume-lid-cancel: cut in M3 so the restart mark is visible

M4 scales power with speed, which is exactly what hides a restart in the cut -
the thing the test asks the operator to look at. At constant power the resumed
cut accelerates from zero under full power and leaves the deeper spot where it
picked up, which is the artifact worth seeing (and the one the plan wanted
characterized for M3 and M4).

forgetest/forgetest/suite/laser.py

@@ -79,6 +79,11 @@ MARK_JOB = ["G91", "G21", "M4", "S400",
             "G1 X40 F200", "G1 Y40 F200", "G1 X-40 F200", "G1 Y-40 F200",
             "M5", "G90", "M2"]
 
+# The same square at constant power. M4 scales power with speed, which hides
+# what a restart does to the cut; M3 puts it on the scrap where the operator
+# can see it - the deeper spot where a resumed cut accelerates from zero.
+MARK_JOB_M3 = ["M3" if ln == "M4" else ln for ln in MARK_JOB]
+
 
 def arm_and_fire(ctx, g, room="40 mm +X and +Y", job=None, timeout=240):
     """The arm cue, the job, and the wait for the emission witness - the
@@ -521,7 +526,8 @@ def arm_wait_lid(ctx):
                   "them. Press: the job feed-holds, emission stops, and the latch stays UNLOCKED "
                   "with the armed window open - a pause is not a cancel. Press again: the cut "
                   "resumes from where it stopped (GRBL has no backtrack; the kernel refuses one on "
-                  "a live-streamed ring). Lid: emission stops in hardware, the job is cancelled "
+                  "a live-streamed ring), and the cut is M3 so the restart leaves a mark to "
+                  "look at rather than one M4 hides. Lid: emission stops in hardware, the job is cancelled "
                   "with the reason reported, the controller resets with the position kept and no "
                   "alarm, the armed window closes and the kernel latch relocks, the hardware button "
                   "latch reads SET, and the head returns to the job start with the lid still open.")
@@ -533,7 +539,7 @@ def pause_resume_lid_cancel(ctx):
         k0 = kernel_xy_mm(ctx)
         ev["start"] = start
         ev["kernel_start"] = k0
-        smp = arm_and_fire(ctx, g)
+        smp = arm_and_fire(ctx, g, job=MARK_JOB_M3)
         ev["emission_running"] = smp["emission"]
         ctx.log("emission live (%s) - asking the operator to pause", smp["emission"])