fix: a recompute that renumbered its ring, and readouts frozen under a zoom

Three defects, all of them a window describing data that is not there.

A math edit refilled the derived ring with `clear()`, which renumbers it
from 0, leaving `produced()` short by the inputs' retained base. Since
`live_window_locked()` clamps against every channel's `produced()`, that
one lagging channel answered `n = 0` for the live view, every pause view
and every trigger capture until a whole ring of fresh data had gone by --
the reported freeze, invisible until the ring first wraps, hence its
intermittence. It now restarts with `clear_to(base)`, and
`ChannelBuffer::republish_from(base)` puts the published window back:
`acquire()` is incremental, so a rewrite in place published nothing and
the pyramid went on describing the samples the edit replaced.

The trigger's channel is an index, re-resolved by name after a renumbering
-- but only in `rebuild_enabled_locked()`, so a math add or delete went
through `set_math_channels()` with no restore, the index was clamped to
-1, and `process()` returned at once while the panel still named the
channel. The restore moves into `rebuild_channels()`, which *is* the
renumbering, so no caller can forget it.

And `update_measures()` suppressed its "the window moved" test while an
event was held -- the one mode where a gesture is the only thing that can
move it. Zooming a latched event left the pane describing the whole
captured event. A pinned window needs no exemption: it lands on the range
it already measured and fails the 2 % test by itself.

The checks that missed all three: `UDPSCOPE_PROBE_MATHWRAP_MS` edits a
graph whose ring has already wrapped, which `math_probe` structurally
cannot reach; `[measure-trace]` now prints the mode, the window on screen
and the window the numbers describe; and the dump's `marks_in_window`
counts against the window on screen instead of against the one the marks
were computed over, where it was a tautology.

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

src/model.cpp

@@ -449,6 +449,14 @@ void ScopeModel::recompute_math_locked(const std::vector<bool>& affected) {
   const std::size_t slots = static_cast<std::size_t>(store.time().size());
   if (slots == 0) return;
 
+  // The refill replays the inputs' *retained* window, which starts at this absolute index and not at
+  // zero, so an emptied derived ring has to resume its count there: `clear()` would renumber it from 0
+  // and leave its `produced()` short by `base` for a whole ring's worth of fresh data. `live_window_locked()`
+  // clamps the window against every channel's `produced()`, so that one lagging channel collapses the
+  // live view, every pause view and every trigger capture to nothing -- the "acquisition freezes after a
+  // math edit" defect, invisible until the ring has wrapped once (`base == 0` before that).
+  const std::size_t base = static_cast<std::size_t>(store.time().base());
+
   std::vector<bool> derived(channels_.size(), false);
   for (std::size_t m = 0; m < math_.size(); ++m) {
     const int channel = m < math_channel_.size() ? math_channel_[m] : -1;
@@ -456,14 +464,18 @@ void ScopeModel::recompute_math_locked(const std::vector<bool>& affected) {
     derived[static_cast<std::size_t>(channel)] = true;
     // Only the affected channels start again. The rest keep their samples *and* their runtimes: their graphs
     // are untouched, so the state they hold is the answer to the inputs they have always had.
-    if (affected[m]) store.values(static_cast<std::size_t>(channel)).clear();
+    if (!affected[m]) continue;
+    store.values(static_cast<std::size_t>(channel)).clear_to(base);
+    // And the published window with them: this is a rewrite in place, so `produced()` lands back where it
+    // started and the incremental `acquire()` would publish nothing at all -- leaving the pyramid, which is
+    // what the renderer and every measurement read, describing the samples the edit just replaced.
+    store.channel(static_cast<std::size_t>(channel)).republish_from(base);
   }
 
   // One bulk copy per channel per chunk, through the ring's own reader. A derived channel is fed a zero:
   // `math_apply_locked()` overwrites its value as it walks the list in order, and reading its half-rebuilt
   // ring here would read out of range.
   constexpr std::size_t kChunk = 1u << 14;
-  const std::size_t base = static_cast<std::size_t>(store.time().base());
   std::vector<std::vector<f32>> inputs(channels_.size());
   for (std::size_t c = 0; c < channels_.size(); ++c) {
     if (!derived[c]) inputs[c].resize(kChunk);
@@ -482,10 +494,22 @@ void ScopeModel::recompute_math_locked(const std::vector<bool>& affected) {
       math_apply_locked(slot, &affected, /*timed=*/false);
     }
   }
-  // The pyramid is the consumer's and the tick publishes it; the samples are written here.
+  // The pyramid is the consumer's and the tick publishes it (`republish_from()` above put its window
+  // back at `base` so that publish is one window's worth of work); the samples are written here.
 }
 
 void ScopeModel::rebuild_channels() {
+  // The trigger names a channel by its display name, which is stable across the renumbering this
+  // function *is*; the index is not. Captured and restored here rather than at the call sites
+  // because every caller renumbers and every caller needs it: adding a math channel appends a
+  // signal and shifts nothing, but removing one, or a CONFIG that reorders the stream's own
+  // signals, moves every index after it. `rebuild_locked()` then only clamps an out-of-range
+  // index to -1, and `TriggerEngine::process()` returns immediately on a channel of -1 -- so the
+  // panel went on naming the channel while nothing could ever fire again.
+  const std::string trigger_name =
+      (trigger_.channel >= 0 && trigger_.channel < static_cast<int>(channels_.size()))
+          ? channels_[static_cast<std::size_t>(trigger_.channel)].name
+          : std::string();
   channels_.clear();
   // Which channel each math channel ended up with, by name: a disabled one has none, and the
   // producer must not push a derived sample into another channel's ring.
@@ -524,6 +548,15 @@ void ScopeModel::rebuild_channels() {
     }
     channels_.push_back(std::move(ch));
   }
+
+  // A name that is no longer a channel -- its signal was disabled, or the stream stopped
+  // declaring it -- leaves the trigger unassigned, which is a wait rather than a silent
+  // mis-aim; re-enabling the signal brings it back here.
+  trigger_.channel = -1;
+  if (trigger_name.empty()) return;
+  for (std::size_t i = 0; i < channels_.size(); ++i) {
+    if (channels_[i].name == trigger_name) trigger_.channel = static_cast<int>(i);
+  }
 }
 
 void ScopeModel::rebuild_locked() {
@@ -639,22 +672,8 @@ bool ScopeModel::enable_locked(std::size_t signal, bool on) {
 }
 
 void ScopeModel::rebuild_enabled_locked() {
-  // The trigger names a channel by its display name, which is stable across
-  // renumbering: when its own signal is disabled the channel vanishes (the trigger
-  // then waits, and comes back when the signal is re-enabled). Read before
-  // `rebuild_channels()`, which is what renumbers.
-  const int old_trigger = trigger_.channel;
-  const std::string trigger_name =
-      (old_trigger >= 0 && old_trigger < static_cast<int>(channels_.size()))
-          ? channels_[static_cast<std::size_t>(old_trigger)].name
-          : std::string();
+  // `rebuild_channels()` carries the trigger's channel across the renumbering by name.
   rebuild_channels();
-  trigger_.channel = -1;
-  if (!trigger_name.empty()) {
-    for (std::size_t i = 0; i < channels_.size(); ++i) {
-      if (channels_[i].name == trigger_name) trigger_.channel = static_cast<int>(i);
-    }
-  }
   rebuild_locked();
   generation_.fetch_add(1, std::memory_order_release);
 }