ui: a signal's details sit directly under its name; its unit is user-changeable and saved with the session

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

src/model.hpp

@@ -465,6 +465,17 @@ class ScopeModel {
   /// no channel to read it from, and the record is what a dialog must show.
   std::pair<double, double> calibration(std::size_t signal);
 
+  /// Renames the unit a streamed signal is shown, read and exported in. Stored by the signal's *name*
+  /// like the calibration, and re-applied to every later CONFIG, so a rename survives a reconnect.
+  /// An empty `unit` removes the override and restores the unit the stream declared. A math channel's
+  /// unit belongs to its graph and is ignored here. Bumps `generation()` when it changed something,
+  /// which is what makes the panels re-read the signal list.
+  void set_signal_unit(std::size_t signal, const std::string& unit);
+  /// The unit the stream declared for that signal, whatever the user renamed it to.
+  std::string declared_unit(std::size_t signal);
+  /// The renames in force, `{name, unit}`, for the session file.
+  std::vector<std::pair<std::string, std::string>> unit_overrides();
+
   std::size_t channel_count() const noexcept { return channels_.size(); }
   const Partition& partition() const noexcept { return part_; }
 
@@ -868,6 +879,9 @@ class ScopeModel {
   std::atomic<bool> paused_{false};
   /// Per-signal-name calibration (see `set_calibration`).
   std::unordered_map<std::string, std::pair<double, double>> calibration_;
+  /// Per-signal-name unit renames (see `set_signal_unit`) and the units the stream declared.
+  std::unordered_map<std::string, std::string> unit_override_;
+  std::unordered_map<std::string, std::string> declared_unit_;
   std::atomic<std::uint64_t> event_seq_{0};
   std::atomic<double> display_epoch_{0.0};
   std::atomic<bool> trigger_armed_{false};