fix: batch_ is now learned in both stream and relative-time modes so hole reservation fires in stream mode.

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

src/acquisition.cpp

@@ -143,18 +143,19 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
   stamps_.assign(n, 0.0);
   abs_stamps_.assign(n, 0.0);
 
-  // Relative mode: the stamp is a pure function of position and the *declared* rate. Nothing
-  // below this block runs -- not the arrival-cadence override, not the degeneracy guard, not
-  // the glitch bridge, not the monotonic clamp's reason for existing -- because a position
-  // cannot jitter, cannot fail to advance and cannot jump.
-  if (cfg_.relative_time) {
+  // Samples per packet, needed in both modes: relative stamping must advance `slot_base_`
+  // past the reserved hole before placing this frame's own stamps, and `on_data` must size
+  // the hole before calling this function -- both operations require knowing how many samples
+  // a missing packet represents, which is only knowable from the first frame that arrives.
   if (batch_ == 0) {
     batch_ = n;
+    if (cfg_.relative_time) {
       std::fprintf(stderr,
                    "[udpscope] relative time: batch=%u samples/packet, rate=%.6g S/s declared\n",
                    batch_, model_.partition().base_dt > 0.0 ? 1.0 / model_.partition().base_dt
                                                             : 0.0);
       std::fflush(stderr);
+    }
   } else if (n != batch_) {
     // A frame whose length disagrees with the first one is an inconsistency in the
     // producer, not a loss: the counter still names one packet. Warn once and keep the
@@ -169,6 +170,12 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
       std::fflush(stderr);
     }
   }
+
+  // Relative mode: the stamp is a pure function of position and the *declared* rate. Nothing
+  // below this block runs -- not the arrival-cadence override, not the degeneracy guard, not
+  // the glitch bridge, not the monotonic clamp's reason for existing -- because a position
+  // cannot jitter, cannot fail to advance and cannot jump.
+  if (cfg_.relative_time) {
     double dt = model_.partition().base_dt;
     if (!(dt > 0.0)) dt = 1.0e-3;
     // The reserved hole for the missing packets advances `slot_base_` so this frame's