test: the mock can inject an alternating-sign impulse train on sine

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tools/mock_udpstreamer.py

@@ -82,6 +82,9 @@ def build_data(
     glitch_at=-1.0,
     glitch_width=0.0,
     quiet_at=-1.0,
+    spike_every=0.0,
+    spike_amp=0.0,
+    spike_width=0,
 ):
     stamps = [t0 + i * dt for i in range(batch)]
     # `time_spike` models a device whose clock glitches for one packet: the stamps jump
@@ -103,6 +106,16 @@ def build_data(
         ]
     else:
         sine = [math.sin(2.0 * math.pi * freq * t) for t in stamps]
+    if spike_every > 0.0 and spike_amp != 0.0 and spike_width > 0:
+        # An impulse of `spike_width` samples at the start of every `spike_every`
+        # window, the sign alternating window to window so the train carries no
+        # DC a median could track. `stamps` are absolute stream seconds.
+        stamps_arr = np.array(stamps)
+        period = np.floor(stamps_arr / spike_every)
+        into = stamps_arr - period * spike_every
+        hit = into < (spike_width * dt)
+        sign = np.where((period.astype(np.int64) & 1) == 0, 1.0, -1.0)
+        sine = np.array(sine) + np.where(hit, sign * spike_amp, 0.0)
     square = [
         1.0 if math.sin(2.0 * math.pi * freq * 0.5 * t) >= 0.0 else -1.0 for t in stamps
     ]
@@ -240,6 +253,12 @@ def main():
         "opposite side of zero, so --quiet-at is its last zero crossing: the shape a "
         "dropout trigger is read against. -1 = never",
     )
+    ap.add_argument("--spike-every", type=float, default=0.0,
+                    help="seconds between impulses on sine (0 disables)")
+    ap.add_argument("--spike-amp", type=float, default=0.0,
+                    help="impulse amplitude, alternating sign window to window")
+    ap.add_argument("--spike-width", type=int, default=0,
+                    help="impulse length in samples")
     ap.add_argument(
         "--blackout-at",
         type=float,
@@ -435,6 +454,9 @@ def main():
             args.glitch_at,
             args.glitch_width,
             args.quiet_at,
+            args.spike_every,
+            args.spike_amp,
+            args.spike_width,
         )
         burst = max(1, args.drop_burst)
         if args.drop_every > 0 and drop_left == 0 and counter % args.drop_every == 0: