feat: locked panes for a returning user, and the trigger is persisted

Two panes, two modes. **Locked** is what a returning user gets: the trigger pane shows one line saying
what it is set to, the signal list shows only the signals that are on, and neither offers a control that
changes the configuration — each heading has an `[edit]` button (the Adwaita `emblem-system-symbolic`,
swapping to `emblem-ok-symbolic` in configuration mode) that flips its pane. A **first run** — no session
file for that source — never reaches `apply_layout()` and comes up in configuration mode, because
configuring the host is what a first run is for. The mode is a mode and not a setting, so it is
deliberately not persisted.

The locked signal list drops the rows of every signal that is off, which is the whole of "show active
signals": the list already filters on nothing, so the lock is one `continue`. With the rows go the acquire
tick, the overflow menu (Information, Calibrate…, Delete, rename) and the `MATH` divider's `+` — and the
colour chip stops being clickable, because choosing a colour is configuration too. Dragging a signal onto
a plot stays: that is which view shows what, not what the scope is set up to do.

**The trigger is persisted, settings and state both** — the settings *even while it is off*, which is the
point: a trigger configured once and switched off is still the trigger you come back to. `LayoutState`
gains fifteen flat `trigger_*` keys; the channel is stored by *name* (every rebuild renumbers the
channels, the model's own rule) and the two enumerations as **the words the panel's dropdowns show**,
because an index ties the file to a declaration order — the lesson `math_op_at()` already carries. The
words are shared with the panel now (`trigger_type_text()` and friends build the dropdown arrays), so the
two cannot drift.

Two ordering traps, both found by running it:

- **The channel name resolves twice over.** `rebuild_trigger_signals()` picks up
  `App::pending_trigger_channel` when the stream arrives *after* the load, and `apply_trigger_layout()`
  resolves it itself when the channels are already there — without the second path the name stayed
  pending past the one rebuild that would have used it, and the trigger silently sat on channel 0
  (`summary='pulse width · sine …'` where the session said `square`).
- **The trigger's state is applied by pressing the control, not by setting a flag**: the toggle is set
  *outside* the `updating_panels` window `apply_layout()` uses, because a toggle set inside it emits
  `toggled` into a handler that returns at once and nothing would happen — no arming, no events button,
  no sensitivity.

Verified, in both modes and both directions:

    panes: trigger=locked signals=locked body_visible=0 summary='window · square · 0.3…0.6 · 20 % pre'
    panes: trigger=config signals=config body_visible=1 summary=''
    signals panel: labels=2 list=1 rows=7 signals=2 math=4 divider=1

The locked trigger pane is 42 px tall against 580 unlocked. A hand-written session round-trips: every
value it named came back in the panel's own controls, `trigger=1/1` (the state arrived and the pane's
switch followed it), and the file the app wrote back carried all fifteen keys with the untouched ones at
their defaults. `[side-tab-probe] … advanced=4` on its documented recipe; `make test-ui` 14 files; zero
`Gtk-CRITICAL` and no missing icon.

Docs: the `panes:` reading with what each field means, the corrected `labels=` note (the panel's frame is
counted above the list now, because the heading sits in a heading row), the invariants for both the
persistence and the lock, the README's deviation note, and the removal of its claim that the trigger has
never been persisted — it is now, and the locked view is built from exactly that.

README.md

@@ -1111,8 +1111,11 @@ assertion, being a stream stamp rebased by whichever rebuild last dropped histor
 `probe-readings.md`.
 
 A shape's own rows are the only ones shown; the rest are hidden, so the panel never offers a
-width to a window trigger. The condition is **not** persisted in the session file — the session
-has never persisted the trigger — so a restart comes up on an edge trigger.
+width to a window trigger. The condition **is** persisted in the session file, together with trigger
+mode itself: the settings are written even while the trigger is off, because a trigger set up once and
+switched off is still the trigger you come back to. The signal it names is stored by *name* — every
+rebuild renumbers the channels — and the shapes by the words the panel's dropdowns show, so a
+reordered enumeration cannot reinterpret a file.
 
 ### Searching the buffer
 
@@ -2397,7 +2400,11 @@ now — they are listed so they are not mistaken for anything else:
   cursors and the ruler for Measure, a sine crossing its trigger level and the channel list
   for Signals (the same picture the toolbar's trigger button carries), drawn as a
   32x16 pair so both motifs are legible at a glance — with the words kept as each pill's tooltip and
-  accessible name. Each pane's heading also carries its **own switch**, the same control as the
+  accessible name. Both panes also have a **locked** mode, which is what a returning user gets: the
+  trigger pane shows one line saying what it is set to, the signal list shows only the signals that are
+  on, and neither offers a control that changes the configuration — each heading has an `[edit]` button
+  to switch to the full pane, and back. A **first run** (no session file for that source) comes up
+  unlocked, because configuring the host is what a first run is for. Each pane's heading also carries its **own switch**, the same control as the
   header bar's button — clicking either moves both — because a pane that is *disabled* while its
   feature is off is a pane whose controls you would otherwise have to leave to turn it back on. The
   design spec had the switcher showing *titles* and neither page an

docs/claude/invariants-session-and-export.md

@@ -4,6 +4,21 @@ What a session persists and in what order, when a save is refused, and when an e
 
 Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to learn; read the ones touching the area you are editing before you edit it.
 
+- **The trigger is persisted, settings and state both.** Its condition, its channel (by *name*), its
+  pre-trigger share, hold-off and mode, and whether trigger mode was on — written even while it is off,
+  because a trigger configured once and switched off is still the trigger you come back to. The two
+  enumerations are stored as the *words the panel's dropdowns show*, not as their indexes: an index ties
+  the file to a declaration order, which is the lesson `math_op_at()` carries, and the words are shared
+  with the panel so the two cannot drift. The channel resolves when the acquired channels exist
+  (`rebuild_trigger_signals()` picks up `App::pending_trigger_channel`, or `apply_trigger_layout()`
+  resolves it itself when they are already there) — a name that resolved to nothing would silently move
+  the trigger to channel 0.
+- **A session that loaded is what locks the two panes.** Locked is the returning user's mode: the
+  trigger pane shows one compact line, the signal list only the signals that are on, and neither offers
+  a control that changes the configuration. A *first run* — no session file for that source — never
+  reaches `apply_layout()` and stays in configuration mode, which is what a first run is for. The mode
+  is a mode and not a setting: it is deliberately not persisted, so a scope reopened tomorrow starts
+  where a returning user expects to start.
 - **The session is the layout.** `LayoutState` persists what makes a reopened scope look like the
   one that was closed: the window, the rows and their slot signals, the calibration, **the enabled
   signals**, **the chosen trace colours** (`[[color]]`, `name` + `rgb = "#RRGGBB"` — only the

docs/claude/probe-readings.md

@@ -1139,6 +1139,29 @@ library measures and draws the rect in tests of its own.
   defect this reading exists for, and it was invisible from the frame alone: the file view pinning its
   axis from the ring each frame is what swallowed the gesture.
 
+## `panes:` — the locked and configuration modes
+
+```
+[udpscope]   panes: trigger=locked signals=locked body_visible=0 summary='window · square · 0.25…0.5 · 20 % pre'
+[udpscope]   panes: trigger=config signals=config body_visible=1 summary=''
+```
+
+Both panes have two modes. **Locked** is what a returning user gets — the trigger pane shows the one line
+in `summary`, the signal list shows only the signals that are on, and neither offers a control that
+changes the configuration — and **config** is the full pane, which is what a *first run* gets, because a
+session file that loaded is what "we have been here before" means. Each heading's `[edit]` button flips
+its pane.
+
+- **`summary`** is the locked trigger pane's whole content, so it is read rather than assumed: empty here
+  is a locked pane showing nothing at all. It quotes the shape, the channel, the figures that shape
+  actually reads (a level, two levels, a width plus its comparison, or a timeout) and the pre-trigger
+  share — never a figure the shape ignores.
+- **`body_visible=0`** is the settings being off screen, which is what makes the pane 42 px tall instead
+  of 580 in `panels:`.
+- **The locked signal list drops the rows of the signals that are off**, so `rows` counts what is on:
+  `signals panel: … rows=3 signals=2 divider=1` is two on signals and the `MATH` divider, not four
+  signals. Its `+` goes with them — a `+` on a locked list opens the editor the lock exists to keep shut.
+
 ## `panel switches:` and the trigger panel's default sensitivity
 
 ```
@@ -1330,7 +1353,8 @@ The signals panel's frame read from the window, and in the same line the *shape*
 the heading and the hint the `.ui` gives it, the list the rows go in, how many rows that list holds
 (`rows`), how many of them are streamed signals (`signals`), how many math channels the app has (`math`),
 and `divider`, which is 1 when `rows == signals + 1 + math` and 0 otherwise. `labels=1` is a `.ui` that lost
-one of the two labels, `list=0` one that lost the list -- both of which otherwise show as a panel quietly
+one of the two labels — counted over the panel's subtree *above* the list, because the rows' own name
+and unit labels are the code's and the heading sits in a heading row beside the pane's `[edit]` button — `list=0` one that lost the list -- both of which otherwise show as a panel quietly
 missing a piece -- and **`divider=0` is the merged list that lost its `+`**, the one control that can create
 a math channel. The first line above is a run with no math channels at all: the divider is there anyway,
 because a `+` that only appeared once a channel existed could never create the first one. `panels: …

src/layout_store.cpp

@@ -476,6 +476,48 @@ bool load_layout(const std::string& path, LayoutState& out) {
       return v;
     };
 
+    /// One `trigger_*` key, by its name after the prefix. Text for the two enumerations and for the
+    /// signal, numbers for the rest; `value` arrives unquoted.
+    const auto trigger_key = [](LayoutState::Trigger& t, const std::string& k, const std::string& v) {
+      const auto num = [&](double& out) {
+        try {
+          out = std::stod(v);
+        } catch (...) {
+        }
+      };
+      if (k == "enabled") {
+        t.enabled = v == "true";
+      } else if (k == "signal") {
+        t.channel = v;
+      } else if (k == "type") {
+        t.type = v;
+      } else if (k == "edge") {
+        t.edge = v;
+      } else if (k == "cmp") {
+        t.cmp = v;
+      } else if (k == "mode") {
+        t.mode = v;
+      } else if (k == "level") {
+        num(t.level);
+        t.level_given = true;
+      } else if (k == "level2") {
+        num(t.level2);
+      } else if (k == "width") {
+        num(t.width_s);
+      } else if (k == "width2") {
+        num(t.width2_s);
+      } else if (k == "timeout") {
+        num(t.timeout_s);
+      } else if (k == "pre") {
+        num(t.pretrigger_pct);
+      } else if (k == "holdoff") {
+        num(t.holdoff_s);
+      } else if (k == "band") {
+        num(t.noise_band);
+      } else if (k == "hf") {
+        num(t.hf_fc);
+      }
+    };
     if (section == Section::Top) {
       if (key == "window_s") {
         try {
@@ -498,6 +540,8 @@ bool load_layout(const std::string& path, LayoutState& out) {
         st.measure_stats = value == "true";
       } else if (key == "side_tab") {
         st.side_tab = strip_quote(value);
+      } else if (key.rfind("trigger_", 0) == 0) {
+        trigger_key(st.trigger, key.substr(8), strip_quote(value));
       } else if (key == "multicast") {
         st.multicast = strip_quote(value);
       } else if (key == "interface") {
@@ -648,6 +692,24 @@ bool save_layout(const std::string& path, const LayoutState& state) {
   }
   o << "measure_stats = " << (state.measure_stats ? "true" : "false") << "\n";
   o << "side_tab = \"" << state.side_tab << "\"\n";
+  // The trigger, settings and state both. Written even when it is off: that is the point of it.
+  o << "trigger_enabled = " << (state.trigger.enabled ? "true" : "false") << "\n";
+  if (!state.trigger.channel.empty()) {
+    o << "trigger_signal = " << toml_escape(state.trigger.channel) << "\n";
+  }
+  o << "trigger_type = " << toml_escape(state.trigger.type) << "\n";
+  o << "trigger_edge = " << toml_escape(state.trigger.edge) << "\n";
+  o << "trigger_cmp = " << toml_escape(state.trigger.cmp) << "\n";
+  o << "trigger_mode = " << toml_escape(state.trigger.mode) << "\n";
+  o << "trigger_level = " << state.trigger.level << "\n";
+  o << "trigger_level2 = " << state.trigger.level2 << "\n";
+  o << "trigger_width = " << state.trigger.width_s << "\n";
+  o << "trigger_width2 = " << state.trigger.width2_s << "\n";
+  o << "trigger_timeout = " << state.trigger.timeout_s << "\n";
+  o << "trigger_pre = " << state.trigger.pretrigger_pct << "\n";
+  o << "trigger_holdoff = " << state.trigger.holdoff_s << "\n";
+  o << "trigger_band = " << state.trigger.noise_band << "\n";
+  o << "trigger_hf = " << state.trigger.hf_fc << "\n";
   if (!state.comment.empty()) o << "comment = " << toml_escape(state.comment) << "\n";
   if (state.buffer_mb > 0.0) o << "buffer_mb = " << state.buffer_mb << "\n";
   o << "relative_time = " << (state.relative_time ? "true" : "false") << "\n";

src/layout_store.hpp

@@ -73,6 +73,36 @@ struct LayoutState {
   /// The measurements pane, by signal *name* and with the type and options a row was built with.
   std::vector<Measure> measures;
 
+  /// The trigger: its settings *and* whether trigger mode was on. Both, and the settings even while
+  /// it is off, because a trigger set up once and switched off is still the trigger you come back to
+  /// -- and the pane's locked view is built from exactly this.
+  ///
+  /// The signal and the two enumerations are stored as *text*: the signal by name, because every
+  /// rebuild renumbers the channels (the model's own rule), and the shapes by the words the panel's
+  /// dropdowns show, because an index would tie this file to a declaration order -- which the math
+  /// channel's op index already taught this store once.
+  struct Trigger {
+    bool enabled = false;
+    std::string channel;                ///< the acquired channel's name; empty is "none chosen"
+    std::string type = "edge";          ///< edge | pulse width | window | dropout
+    std::string edge = "rising";        ///< rising | falling | both
+    std::string cmp = "greater";        ///< pulse width: `<` | `>` | within | outside
+    std::string mode = "normal";        ///< normal | single
+    double level = 0.0;
+    double level2 = 0.0;                ///< window: the band's other edge
+    double width_s = 1.0e-3;
+    double width2_s = 2.0e-3;
+    double timeout_s = 1.0e-3;
+    double pretrigger_pct = 50.0;
+    double holdoff_s = 0.010;
+    double noise_band = 0.0;
+    double hf_fc = 0.0;
+    /// Whether the file said anything about the level. A session that did keeps it; one that did not
+    /// leaves the panel's own "follow the channel's range" default alone.
+    bool level_given = false;
+  };
+  Trigger trigger;
+
   /// Free text the user attached to this configuration: what it is for, what to look at first.
   /// A configuration is a *named* session, and the name alone rarely says what makes it different
   /// from its neighbour.

src/ui.cpp

@@ -982,6 +982,18 @@ void rebuild_trigger_signals(App& app) {
   g_object_unref(list);
 
   TriggerConfig& tc = app.model->trigger();
+  // A session stores the trigger's channel by *name*: resolved here, where the acquired channels
+  // exist. The pending name is cleared either way, so a name this stream does not have falls through
+  // to the default below rather than being retried on every rebuild.
+  if (!app.pending_trigger_channel.empty()) {
+    for (std::size_t c = 0; c < channels.size(); ++c) {
+      if (channels[c].name == app.pending_trigger_channel) {
+        tc.channel = static_cast<int>(c);
+        break;
+      }
+    }
+    app.pending_trigger_channel.clear();
+  }
   if (tc.channel < 0 && !channels.empty()) tc.channel = 0;
   const int sel = tc.channel;
   gtk_drop_down_set_selected(GTK_DROP_DOWN(app.trigger_signal_drop),
@@ -4388,6 +4400,39 @@ void on_panel_switch_toggled(GObject* obj, GParamSpec*, gpointer user) {
   sync_panel_switches(*app);
 }
 
+/// Both panes' modes, applied together: the trigger's body against its summary line, the two [edit]
+/// buttons against what they would do, and the signal list rebuilt because the lock decides what a row
+/// carries. Idempotent, so a caller only flips a flag and calls this.
+void apply_pane_lock(App& app) {
+  if (app.trigger_body != nullptr) gtk_widget_set_visible(app.trigger_body, !app.trigger_locked);
+  if (app.trigger_summary != nullptr) {
+    gtk_widget_set_visible(app.trigger_summary, app.trigger_locked);
+  }
+  const auto edit_button = [](GtkWidget* button, bool locked, const char* what) {
+    if (button == nullptr) return;
+    gtk_button_set_icon_name(GTK_BUTTON(button),
+                             locked ? "emblem-system-symbolic" : "emblem-ok-symbolic");
+    const std::string tip = std::string(locked ? "configure " : "keep this configuration of ") + what;
+    gtk_widget_set_tooltip_text(button, tip.c_str());
+  };
+  edit_button(app.trigger_edit, app.trigger_locked, "the trigger");
+  edit_button(app.signals_edit, app.signals_locked, "the signals");
+  sync_trigger_summary(app);
+  // The list, because the lock is what decides whether a row carries a tick, a menu and the `+`.
+  if (app.signal_list != nullptr) rebuild_signal_panels(app);
+}
+
+/// Either pane's [edit] button: one handler, because the two differ only in which flag they flip.
+void on_pane_edit_clicked(GtkButton* button, gpointer user) {
+  App* app = static_cast<App*>(user);
+  if (GTK_WIDGET(button) == app->trigger_edit) {
+    app->trigger_locked = !app->trigger_locked;
+  } else if (GTK_WIDGET(button) == app->signals_edit) {
+    app->signals_locked = !app->signals_locked;
+  }
+  apply_pane_lock(*app);
+}
+
 void run_app_action(App& app, AppAction action) {
   const auto toggle = [](GtkWidget* button) {
     if (button == nullptr) return;
@@ -5677,13 +5722,23 @@ int run_ui(int argc, char** argv, const Config& cfg, ScopeModel& model, Acquisit
       // list the file gives it. A `.ui` that lost one of them reads here -- `labels=1` or `list=0` -- rather
       // than showing as a panel quietly missing its hint.
       GtkWidget* panel = app.signal_list != nullptr ? gtk_widget_get_parent(app.signal_list) : nullptr;
+      // Counted over the panel's *subtree*, not its direct children: the heading lives in a heading row
+      // beside the pane's [edit] button, and a count of children would read 1 whatever the file lost.
       int labels = 0;
       int lists = 0;
-      for (GtkWidget* c = panel != nullptr ? gtk_widget_get_first_child(panel) : nullptr; c != nullptr;
-           c = gtk_widget_get_next_sibling(c)) {
-        if (GTK_IS_LABEL(c)) ++labels;
-        if (GTK_IS_LIST_BOX(c)) ++lists;
-      }
+      const std::function<void(GtkWidget*)> count = [&](GtkWidget* w) {
+        // The list stops the walk: its rows are the code's, and this reading is about the file's frame.
+        if (GTK_IS_LIST_BOX(w)) {
+          ++lists;
+          return;
+        }
+        if (GTK_IS_LABEL(w)) ++labels;
+        for (GtkWidget* c = gtk_widget_get_first_child(w); c != nullptr;
+             c = gtk_widget_get_next_sibling(c)) {
+          count(c);
+        }
+      };
+      if (panel != nullptr) count(panel);
       // The list's shape, beside the frame: `rows` is what the list holds, `signals` the streamed
       // ones, and the `MATH` divider plus the math channels account for the rest -- so
       // `rows == signals + 1 + math` is the invariant, and `divider=0` is a list that lost its `+`.
@@ -5720,6 +5775,10 @@ int run_ui(int argc, char** argv, const Config& cfg, ScopeModel& model, Acquisit
                 app.dbg_trigger_sensitive, app.dbg_switcher_visible,
                 rows.cursors_visible() ? 1 : 0, rows.time_window(),
                 app.window_limit_s);
+    std::printf("[udpscope]   panes: trigger=%s signals=%s body_visible=%d summary='%s'\n",
+                app.dbg_trigger_locked ? "locked" : "config",
+                app.dbg_signals_locked ? "locked" : "config", app.dbg_trigger_body_visible,
+                app.dbg_trigger_summary.c_str());
     std::printf("[udpscope]   panel switches: trigger=%d/%d cursors=%d/%d drove_toolbar=%d "
                 "(pane switch / header bar button; `drove_toolbar` is the pane's own switch having "
                 "moved the button)\n",

src/ui/signals-panel.ui

@@ -21,9 +21,27 @@
     <property name="margin-start">8</property>
     <property name="margin-end">8</property>
     <child>
-      <object class="GtkLabel" id="signals_heading">
-        <property name="label" translatable="yes">Signals</property>
-        <property name="halign">start</property>
+      <!-- The heading row, with the button that switches this pane between its two modes: locked, where
+           the list shows the signals that are on and nothing else, and configuration, which is the list
+           with every control on it. It is the code that swaps the icon and the tooltip, because the mode
+           is the code's. -->
+      <object class="GtkBox" id="signals_head">
+        <property name="orientation">horizontal</property>
+        <property name="spacing">8</property>
+        <child>
+          <object class="GtkLabel" id="signals_heading">
+            <property name="label" translatable="yes">Signals</property>
+            <property name="halign">start</property>
+            <property name="hexpand">1</property>
+          </object>
+        </child>
+        <child>
+          <object class="GtkButton" id="signals_edit">
+            <property name="icon-name">emblem-system-symbolic</property>
+            <property name="valign">center</property>
+            <property name="css-classes">flat</property>
+          </object>
+        </child>
       </object>
     </child>
     <child>

src/ui_app.hpp

@@ -258,6 +258,26 @@ struct App {
   /// True while `sync_panel_switches()` is writing the switches: setting a `GtkSwitch` emits its own
   /// `notify::active`, and without this the program's own write would come back as a click.
   bool panel_switch_sync = false;
+  /// The channel a session's trigger names, until `rebuild_trigger_signals()` can resolve it: the
+  /// file stores a *name* and the trigger needs an index into the acquired channels, which do not
+  /// exist until the stream has been described. Empty means "nothing pending".
+  std::string pending_trigger_channel;
+  /// The two panes' modes. *Locked* is the one a returning user gets: the trigger pane shows a line
+  /// that says what it is set to, the signal list shows only the signals that are on, and neither
+  /// offers a control that changes the configuration. A first run -- no session file for this source
+  /// -- starts in configuration mode, because that is what a first run is for. The flags last for the
+  /// session: a lock is a mode, not a setting, so it is not persisted.
+  bool trigger_locked = false;
+  bool signals_locked = false;
+  GtkWidget* trigger_summary = nullptr;
+  GtkWidget* trigger_edit = nullptr;
+  GtkWidget* signals_edit = nullptr;
+  int dbg_trigger_locked = -1;
+  int dbg_signals_locked = -1;
+  int dbg_trigger_body_visible = -1;
+  /// The compact line the locked trigger pane shows. It is the pane's whole content in that mode, so it
+  /// is read rather than assumed: empty here is a locked pane showing nothing at all.
+  std::string dbg_trigger_summary;
   /// The cursors pane: listing what the instruments read -- T0/T1/dT always, per row an Y1/Y2/dY
   /// where rulers are up, and in `mix` mode the value each cursor crosses each trace at.
   GtkWidget* cursors_mode_drop = nullptr;
@@ -1279,7 +1299,7 @@ void on_signal_color_chosen(GObject* source, GAsyncResult* res, gpointer user);
 void open_signal_color(App& app, std::size_t signal);
 void rebuild_signal_list(App& app, const std::vector<SignalInfo>& signals);
 /// The `MATH` divider row in the one channel list, and the `+` it carries.
-GtkWidget* make_math_divider(App& app);
+GtkWidget* make_math_divider(App& app, bool with_add);
 void on_math_add_clicked(GtkButton* button, gpointer user);
 /// The index in `App::math` of the channel a synthetic signal is named after, or `-1`.
 int math_index_for_signal(App& app, const std::string& name);
@@ -1413,6 +1433,25 @@ void select_side_tab(App& app, const char* name);
 /// Reads each pane's own switch back off the header bar's button, and the other way round: the two are
 /// one control in two places, and `panel_switch_sync` keeps the write from looking like a click.
 void sync_panel_switches(App& app);
+/// The trigger's four enumerations as words: the panel's dropdown labels and the session file's
+/// vocabulary, in one place so the two cannot drift.
+const char* trigger_type_text(TriggerType t);
+TriggerType trigger_type_from_text(const std::string& s);
+const char* trigger_edge_text(TriggerEdge e);
+TriggerEdge trigger_edge_from_text(const std::string& s);
+const char* width_cmp_text(WidthCmp c);
+WidthCmp width_cmp_from_text(const std::string& s);
+const char* trigger_mode_text(TriggerMode m);
+TriggerMode trigger_mode_from_text(const std::string& s);
+/// The panel's controls from the model, and the session's trigger into both.
+void write_trigger_widgets(App& app);
+/// The compact line the trigger pane shows while it is locked, and the lock itself: the panes'
+/// bodies, their [edit] buttons and the signal list's rows all follow from `trigger_locked` and
+/// `signals_locked`.
+void sync_trigger_summary(App& app);
+void apply_pane_lock(App& app);
+void on_pane_edit_clicked(GtkButton* button, gpointer user);
+void apply_trigger_layout(App& app, const LayoutState::Trigger& t);
 void on_panel_switch_toggled(GObject* obj, GParamSpec*, gpointer user);
 void update_side_visibility(App& app);
 void on_sidebar_toggled(GtkToggleButton* button, gpointer user);

src/ui_layout.cpp

@@ -59,6 +59,30 @@ LayoutState collect_layout(App& app) {
   st.measures = app.measures;
   st.measure_stats = app.measure_stats_on;
   st.side_tab = app.side_tab;
+  // The trigger, its settings *and* whether it was on. The channel goes by name, like every identity
+  // in this file: every rebuild renumbers the channels.
+  {
+    const TriggerConfig& tc = app.model->trigger();
+    const std::vector<ChannelInfo>& channels = app.model->channels();
+    st.trigger.enabled = tc.enabled;
+    if (tc.channel >= 0 && tc.channel < static_cast<int>(channels.size())) {
+      st.trigger.channel = channels[static_cast<std::size_t>(tc.channel)].name;
+    }
+    st.trigger.type = trigger_type_text(tc.condition.type);
+    st.trigger.edge = trigger_edge_text(tc.condition.edge);
+    st.trigger.cmp = width_cmp_text(tc.condition.cmp);
+    st.trigger.mode = trigger_mode_text(tc.mode);
+    st.trigger.level = tc.condition.level;
+    st.trigger.level2 = tc.condition.level2;
+    st.trigger.width_s = tc.condition.width_s;
+    st.trigger.width2_s = tc.condition.width2_s;
+    st.trigger.timeout_s = tc.condition.timeout_s;
+    st.trigger.pretrigger_pct = tc.pretrigger_pct;
+    st.trigger.holdoff_s = tc.holdoff_s;
+    st.trigger.noise_band = tc.condition.noise_band;
+    st.trigger.hf_fc = tc.condition.hf_fc;
+    st.trigger.level_given = true;  // written means given, so a load keeps it
+  }
   // The connection is the session's too: the file's name carries only host and port.
   st.multicast = app.source_multicast;
   st.interface_addr = app.source_interface;
@@ -289,6 +313,56 @@ void schedule_layout_save(App& app) {
 /// Applies a loaded layout: rows, slot assignments, calibration, window. Names
 /// that no longer exist in the stream are skipped rather than freeing their slot
 /// (a stream that renamed a signal must not blank the user's layout).
+/// The session's trigger into the model and the panel, called from `apply_layout()`. The *channel* it
+/// names is resolved where the channels exist -- `rebuild_trigger_signals()` picks up
+/// `App::pending_trigger_channel` -- because at this point the stream may not have described its
+/// signals yet, and a name that resolves to nothing would silently move the trigger to channel 0.
+void apply_trigger_layout(App& app, const LayoutState::Trigger& t) {
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    TriggerConfig& tc = app.model->trigger();
+    tc.condition.type = trigger_type_from_text(t.type);
+    tc.condition.edge = trigger_edge_from_text(t.edge);
+    tc.condition.cmp = width_cmp_from_text(t.cmp);
+    tc.mode = trigger_mode_from_text(t.mode);
+    tc.condition.level = t.level;
+    tc.condition.level2 = t.level2;
+    tc.condition.width_s = t.width_s;
+    tc.condition.width2_s = t.width2_s;
+    tc.condition.timeout_s = t.timeout_s;
+    tc.condition.noise_band = t.noise_band;
+    tc.condition.hf_fc = t.hf_fc;
+    tc.pretrigger_pct = t.pretrigger_pct;
+    tc.holdoff_s = t.holdoff_s;
+  }
+  // A file that carried a level keeps it: the panel's own default follows the channel's range, and
+  // `trigger_level_touched` is what says the user has a level of their own.
+  if (t.level_given) app.trigger_level_touched = true;
+  app.pending_trigger_channel = t.channel;
+  {
+    // If the stream has already described its channels, resolve the name *now*: the signals rebuild that
+    // would otherwise do it has already been and gone, so a pending name would leave the trigger on
+    // channel 0 -- which is a trigger on whichever signal happens to be first.
+    const std::vector<ChannelInfo>& channels = app.model->channels();
+    for (std::size_t c = 0; c < channels.size(); ++c) {
+      if (channels[c].name != app.pending_trigger_channel) continue;
+      std::lock_guard<std::mutex> lock(app.model->mutex());
+      app.model->trigger().channel = static_cast<int>(c);
+      app.pending_trigger_channel.clear();
+      break;
+    }
+  }
+  write_trigger_widgets(app);
+  // The state is applied by *pressing the same control a user would*: the handler is what arms, tells
+  // the events button, greys the body and syncs the pane's own switch. Deliberately outside the
+  // `updating_panels` window `apply_layout()` uses for the panels, because a toggle set inside it
+  // would emit `toggled` into a handler that returns at once and nothing would happen.
+  if (app.trigger_toggle != nullptr) {
+    gtk_toggle_button_set_active(GTK_TOGGLE_BUTTON(app.trigger_toggle), t.enabled);
+  }
+  sync_panel_switches(app);
+}
+
 void apply_layout(App& app, const LayoutState& st) {
   ScopeModel& model = *app.model;
   const auto& signals = model.signals();
@@ -410,6 +484,17 @@ void apply_layout(App& app, const LayoutState& st) {
   if (app.area != nullptr) app.area->set_figure(&app.rows->figure());
   app.relayout_pending = true;
   rebuild_signal_panels(app);
+  // The trigger last: its channel names an *acquired* channel, so it is resolved once the enables
+  // above have built the channel list.
+  apply_trigger_layout(app, st.trigger);
+
+  // A session that loaded is a user who has been here before, and that is what the lock means: the two
+  // panes come up showing what they are set to rather than showing every control. A first run -- no
+  // file for this source -- never reaches this function and stays in configuration mode, which is what
+  // a first run is for.
+  app.trigger_locked = true;
+  app.signals_locked = true;
+  apply_pane_lock(app);
 }
 
 void on_layout_row_remove(GtkButton* button, gpointer user) {

src/ui_probe.cpp

@@ -2322,6 +2322,13 @@ gboolean exit_probe_step1(gpointer user) {
   App* a = static_cast<App*>(user);
   // Record the panel states before the toggles are exercised.
   a->dbg_trigger_sensitive_default = gtk_widget_get_sensitive(a->trigger_body) ? 1 : 0;
+  a->dbg_trigger_locked = a->trigger_locked ? 1 : 0;
+  a->dbg_signals_locked = a->signals_locked ? 1 : 0;
+  a->dbg_trigger_body_visible =
+      a->trigger_body != nullptr && gtk_widget_get_visible(a->trigger_body) ? 1 : 0;
+  if (a->trigger_summary != nullptr) {
+    a->dbg_trigger_summary = gtk_label_get_text(GTK_LABEL(a->trigger_summary));
+  }
   a->dbg_panel_switch_live =
       a->trigger_switch != nullptr && gtk_widget_get_sensitive(a->trigger_switch) &&
               a->cursors_switch != nullptr && gtk_widget_get_sensitive(a->cursors_switch)

src/ui_signals.cpp

@@ -166,7 +166,7 @@ int math_index_for_signal(App& app, const std::string& name) {
 /// The `MATH` boundary in the one channel list, carrying the `+` that creates a channel. Not
 /// selectable and not activatable: it is a heading, and a heading that highlights under the
 /// pointer reads as a row you can plot.
-GtkWidget* make_math_divider(App& app) {
+GtkWidget* make_math_divider(App& app, bool with_add) {
   GtkWidget* row = gtk_list_box_row_new();
   gtk_list_box_row_set_selectable(GTK_LIST_BOX_ROW(row), FALSE);
   gtk_list_box_row_set_activatable(GTK_LIST_BOX_ROW(row), FALSE);
@@ -180,11 +180,16 @@ GtkWidget* make_math_divider(App& app) {
   gtk_widget_set_halign(label, GTK_ALIGN_START);
   gtk_widget_set_hexpand(label, TRUE);
   gtk_box_append(GTK_BOX(box), label);
-  GtkWidget* add = gtk_button_new_from_icon_name("list-add-symbolic");
-  gtk_widget_add_css_class(add, "flat");
-  gtk_widget_set_tooltip_text(add, "add a math channel");
-  g_signal_connect(add, "clicked", G_CALLBACK(on_math_add_clicked), &app);
-  gtk_box_append(GTK_BOX(box), add);
+  // Locked: the heading stays, because the list it divides is the one being read, but the `+` that
+  // creates a channel does not. A `+` on a locked list is a button that opens the editor the lock
+  // exists to keep shut.
+  if (with_add) {
+    GtkWidget* add = gtk_button_new_from_icon_name("list-add-symbolic");
+    gtk_widget_add_css_class(add, "flat");
+    gtk_widget_set_tooltip_text(add, "add a math channel");
+    g_signal_connect(add, "clicked", G_CALLBACK(on_math_add_clicked), &app);
+    gtk_box_append(GTK_BOX(box), add);
+  }
   gtk_list_box_row_set_child(GTK_LIST_BOX_ROW(row), box);
   return row;
 }
@@ -278,6 +283,9 @@ void rebuild_signal_list(App& app, const std::vector<SignalInfo>& signals) {
   std::size_t plain = 0;
   for (std::size_t i = 0; i < signals.size(); ++i) {
     if (ScopeModel::is_time_signal(signals, i)) continue;  // the time base is not plottable
+    // Locked: a row per signal that is *on*, which is the list a user reads rather than the list they
+    // configure. Turning one on is what the pane's [edit] button is for.
+    if (app.signals_locked && !app.model->signal_enabled(i)) continue;
     const std::string base = layer_base_name(signals[i].name);
     bool seen = false;
     for (std::size_t j = 0; j < i && !seen; ++j) {
@@ -293,7 +301,7 @@ void rebuild_signal_list(App& app, const std::vector<SignalInfo>& signals) {
     // `+` that creates the first one.
     if (sig.math && !math_divider_done) {
       math_divider_done = true;
-      gtk_list_box_append(GTK_LIST_BOX(list), make_math_divider(app));
+      gtk_list_box_append(GTK_LIST_BOX(list), make_math_divider(app, !app.signals_locked));
     }
     if (!sig.math) ++plain;
     GtkWidget* row = gtk_list_box_row_new();
@@ -309,7 +317,7 @@ void rebuild_signal_list(App& app, const std::vector<SignalInfo>& signals) {
         chip, !app.model->signal_enabled(i) ? "not acquired"
               : plotted ? "the colour this signal is plotted in -- click to change it"
                         : "on no plot, so there is no trace to colour");
-    if (plotted) {
+    if (plotted && !app.signals_locked) {
       // A gesture on the label rather than a `GtkButton` around it: a button brings its own
       // padding, and padding on this row is what made the list twice as tall once already (see
       // this function's note). The chip also has to stay exactly one disc wide, or the names
@@ -343,7 +351,9 @@ void rebuild_signal_list(App& app, const std::vector<SignalInfo>& signals) {
     gtk_widget_set_visible(enable, sig.math || app.waveform_name.empty());
     g_object_set_data(G_OBJECT(enable), "udpscope-signal", GSIZE_TO_POINTER(i));
     g_signal_connect(enable, "notify::active", G_CALLBACK(on_signal_switch), &app);
-    gtk_box_append(GTK_BOX(box), enable);
+    // Locked: the switch decides what is acquired, so it is a configuration control and it goes with
+    // the rest of them.
+    if (!app.signals_locked) gtk_box_append(GTK_BOX(box), enable);
 
     GtkWidget* name = gtk_label_new(sig.name.c_str());
     gtk_widget_set_hexpand(name, true);
@@ -435,7 +445,9 @@ void rebuild_signal_list(App& app, const std::vector<SignalInfo>& signals) {
     gtk_menu_button_set_popover(GTK_MENU_BUTTON(more), popover);
     gtk_widget_add_css_class(more, "flat");
     gtk_widget_set_tooltip_text(more, "information and calibration");
-    gtk_box_append(GTK_BOX(box), more);
+    // Locked: the menu holds calibration, deletion and a rename, which are exactly what this mode is
+    // not for. The popover is left unattached, so nothing can reach it.
+    if (!app.signals_locked) gtk_box_append(GTK_BOX(box), more);
 
     gtk_list_box_row_set_child(GTK_LIST_BOX_ROW(row), box);
 
@@ -451,7 +463,9 @@ void rebuild_signal_list(App& app, const std::vector<SignalInfo>& signals) {
   }
   // Appended when there are no math channels at all: the `+` is the only way to create the first
   // one, so it cannot be conditional on one already existing.
-  if (!math_divider_done) gtk_list_box_append(GTK_LIST_BOX(list), make_math_divider(app));
+  if (!math_divider_done) {
+    gtk_list_box_append(GTK_LIST_BOX(list), make_math_divider(app, !app.signals_locked));
+  }
   app.dbg_signal_plain = plain;
   app.dbg_signal_rows = 0;
   for (GtkWidget* c = gtk_widget_get_first_child(list); c != nullptr;
@@ -567,6 +581,10 @@ GtkWidget* build_signal_panel(App& app) {
   GtkBuilder* ui = ui_load(app, "/org/udpscope/ui/signals-panel.ui");
   GtkWidget* box = GTK_WIDGET(gtk_builder_get_object(ui, "signal_panel"));
   app.signal_list = GTK_WIDGET(gtk_builder_get_object(ui, "signal_list"));
+  app.signals_edit = GTK_WIDGET(gtk_builder_get_object(ui, "signals_edit"));
+  if (app.signals_edit != nullptr) {
+    g_signal_connect(app.signals_edit, "clicked", G_CALLBACK(on_pane_edit_clicked), &app);
+  }
   if (box == nullptr || app.signal_list == nullptr) {
     // A missing id is a mistake in the `.ui`: the panel comes up empty rather than taking the window with
     // it, and `[udpscope] signals panel:` reads the difference.

src/ui_trigger.cpp

@@ -5,6 +5,8 @@
 
 #include "ui_app.hpp"
 
+#include <cstring>
+
 #include <gtk/gtk.h>
 
 #include <string>
@@ -40,6 +42,164 @@ void on_arm_clicked(GtkButton* button, gpointer user) {
 
 /// The trigger type dropdown's order, as a table rather than a cast: the dropdown lists
 /// only the conditions that are implemented, so its index is not `TriggerType`'s value.
+/// The trigger's four enumerations as words, and back. These are the panel's dropdown labels *and*
+/// what the session file stores: an index would tie the file to a declaration order, which is the
+/// lesson `math_op_at()` already carries, and two vocabularies (one for the UI, one for the file)
+/// drift apart the moment one of them gains a member.
+const char* trigger_type_text(TriggerType t) {
+  switch (t) {
+    case TriggerType::Edge: return "edge";
+    case TriggerType::PulseWidth: return "pulse width";
+    case TriggerType::Window: return "window";
+    case TriggerType::Dropout: return "dropout";
+  }
+  return "edge";
+}
+TriggerType trigger_type_from_text(const std::string& s) {
+  if (s == "pulse width") return TriggerType::PulseWidth;
+  if (s == "window") return TriggerType::Window;
+  if (s == "dropout") return TriggerType::Dropout;
+  return TriggerType::Edge;
+}
+const char* trigger_edge_text(TriggerEdge e) {
+  switch (e) {
+    case TriggerEdge::Rising: return "rising";
+    case TriggerEdge::Falling: return "falling";
+    case TriggerEdge::Both: return "both";
+  }
+  return "rising";
+}
+TriggerEdge trigger_edge_from_text(const std::string& s) {
+  if (s == "falling") return TriggerEdge::Falling;
+  if (s == "both") return TriggerEdge::Both;
+  return TriggerEdge::Rising;
+}
+const char* width_cmp_text(WidthCmp c) {
+  switch (c) {
+    case WidthCmp::Less: return "<";
+    case WidthCmp::Greater: return ">";
+    case WidthCmp::Within: return "within";
+    case WidthCmp::Outside: return "outside";
+  }
+  return ">";
+}
+WidthCmp width_cmp_from_text(const std::string& s) {
+  if (s == "<") return WidthCmp::Less;
+  if (s == "within") return WidthCmp::Within;
+  if (s == "outside") return WidthCmp::Outside;
+  return WidthCmp::Greater;
+}
+const char* trigger_mode_text(TriggerMode m) {
+  return m == TriggerMode::Single ? "single" : "normal";
+}
+TriggerMode trigger_mode_from_text(const std::string& s) {
+  return s == "single" ? TriggerMode::Single : TriggerMode::Normal;
+}
+
+/// The dropdown's row for a piece of text, or 0. Asked of the widget's own model, so the mapping from
+/// a stored word to a selection is the list the user sees and not a second table to keep in step.
+static guint dropdown_index_of(GtkWidget* drop, const char* text) {
+  GListModel* model = drop != nullptr ? gtk_drop_down_get_model(GTK_DROP_DOWN(drop)) : nullptr;
+  const guint n = model != nullptr ? g_list_model_get_n_items(model) : 0;
+  for (guint i = 0; i < n; ++i) {
+    GtkStringObject* item = GTK_STRING_OBJECT(g_list_model_get_item(model, i));
+    const bool hit = item != nullptr && std::strcmp(gtk_string_object_get_string(item), text) == 0;
+    if (item != nullptr) g_object_unref(item);
+    if (hit) return i;
+  }
+  return 0;
+}
+
+/// The panel's controls from the model: what a session load has just put in the model, so the pane
+/// shows the trigger it is about to run. Guarded, because a control's own handler publishes what it
+/// holds and this is the other direction.
+void write_trigger_widgets(App& app) {
+  if (app.trigger_level_spin == nullptr) return;
+  TriggerConfig tc;
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    tc = app.model->trigger();
+  }
+  const bool was = app.updating_panels;
+  app.updating_panels = true;
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_level_spin), tc.condition.level);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_pre_spin), tc.pretrigger_pct);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_holdoff_spin), tc.holdoff_s);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_width_spin), tc.condition.width_s);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_width2_spin), tc.condition.width2_s);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_level2_spin), tc.condition.level2);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_timeout_spin), tc.condition.timeout_s);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_band_spin), tc.condition.noise_band);
+  gtk_spin_button_set_value(GTK_SPIN_BUTTON(app.trigger_hf_spin), tc.condition.hf_fc);
+  gtk_drop_down_set_selected(GTK_DROP_DOWN(app.trigger_type_drop),
+                             dropdown_index_of(app.trigger_type_drop,
+                                               trigger_type_text(tc.condition.type)));
+  gtk_drop_down_set_selected(GTK_DROP_DOWN(app.trigger_edge_drop),
+                             dropdown_index_of(app.trigger_edge_drop,
+                                               trigger_edge_text(tc.condition.edge)));
+  gtk_drop_down_set_selected(GTK_DROP_DOWN(app.trigger_cmp_drop),
+                             dropdown_index_of(app.trigger_cmp_drop,
+                                               width_cmp_text(tc.condition.cmp)));
+  gtk_drop_down_set_selected(GTK_DROP_DOWN(app.trigger_mode_drop),
+                             dropdown_index_of(app.trigger_mode_drop,
+                                               trigger_mode_text(tc.mode)));
+  app.updating_panels = was;
+  sync_trigger_rows(app);
+}
+
+/// The compact line: what the pane is set to, in the words the panel's own controls use. Read from the
+/// model rather than from the widgets, because the widgets are not on screen in this mode and are not
+/// rebuilt when a session loads.
+void sync_trigger_summary(App& app) {
+  if (app.trigger_summary == nullptr) return;
+  TriggerConfig tc;
+  std::string channel;
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    tc = app.model->trigger();
+    const std::vector<ChannelInfo>& channels = app.model->channels();
+    if (tc.channel >= 0 && tc.channel < static_cast<int>(channels.size())) {
+      channel = channels[static_cast<std::size_t>(tc.channel)].name;
+    }
+  }
+  char buf[192];
+  std::string text = trigger_type_text(tc.condition.type);
+  text += " · ";
+  text += channel.empty() ? "no channel" : channel;
+  switch (tc.condition.type) {
+    case TriggerType::PulseWidth:
+      std::snprintf(buf, sizeof(buf), " · %s %.6g ms", width_cmp_text(tc.condition.cmp),
+                    tc.condition.width_s * 1000.0);
+      text += buf;
+      break;
+    case TriggerType::Window:
+      std::snprintf(buf, sizeof(buf), " · %.6g…%.6g", tc.condition.level, tc.condition.level2);
+      text += buf;
+      break;
+    case TriggerType::Dropout:
+      std::snprintf(buf, sizeof(buf), " · %.6g ms", tc.condition.timeout_s * 1000.0);
+      text += buf;
+      break;
+    case TriggerType::Edge:
+      std::snprintf(buf, sizeof(buf), " · level %.6g", tc.condition.level);
+      text += buf;
+      break;
+  }
+  if (!(tc.condition.noise_band > 0.0) || tc.condition.type == TriggerType::Dropout) {
+    // A band is not offered for a dropout, so it is not quoted for one either.
+  } else {
+    std::snprintf(buf, sizeof(buf), " · band %.6g", tc.condition.noise_band);
+    text += buf;
+  }
+  if (tc.condition.hf_fc > 0.0) {
+    std::snprintf(buf, sizeof(buf), " · HF %.6g Hz", tc.condition.hf_fc);
+    text += buf;
+  }
+  std::snprintf(buf, sizeof(buf), " · %.6g %% pre", tc.pretrigger_pct);
+  text += buf;
+  gtk_label_set_text(GTK_LABEL(app.trigger_summary), text.c_str());
+}
+
 TriggerType trigger_type_at(guint i) {
   switch (i) {
     case 1:
@@ -248,17 +408,24 @@ GtkWidget* build_trigger_panel(App& app) {
                    G_CALLBACK(on_trigger_signal_changed), &app);
   row_for(ui, "signal_row", app.trigger_signal_drop);
 
-  const char* types[] = {"edge", "pulse width", "window", "dropout", nullptr};
+  const char* types[] = {trigger_type_text(TriggerType::Edge),
+                         trigger_type_text(TriggerType::PulseWidth),
+                         trigger_type_text(TriggerType::Window),
+                         trigger_type_text(TriggerType::Dropout), nullptr};
   app.trigger_type_drop = gtk_drop_down_new_from_strings(types);
   gtk_widget_set_tooltip_text(app.trigger_type_drop,
                               "what counts as an event; the fields below change to suit it");
   row_for(ui, "condition_row", app.trigger_type_drop);
 
-  const char* edges[] = {"rising", "falling", "both", nullptr};
+  const char* edges[] = {trigger_edge_text(TriggerEdge::Rising),
+                         trigger_edge_text(TriggerEdge::Falling),
+                         trigger_edge_text(TriggerEdge::Both), nullptr};
   app.trigger_edge_drop = gtk_drop_down_new_from_strings(edges);
   row_for(ui, "edge_row", app.trigger_edge_drop);
 
-  const char* cmps[] = {"<", ">", "within", "outside", nullptr};
+  const char* cmps[] = {width_cmp_text(WidthCmp::Less), width_cmp_text(WidthCmp::Greater),
+                        width_cmp_text(WidthCmp::Within), width_cmp_text(WidthCmp::Outside),
+                        nullptr};
   app.trigger_cmp_drop = gtk_drop_down_new_from_strings(cmps);
   gtk_widget_set_tooltip_text(app.trigger_cmp_drop,
                               "how the measured pulse width is compared: '<' is the glitch "
@@ -307,7 +474,8 @@ GtkWidget* build_trigger_panel(App& app) {
   app.trigger_hf_spin = spin(0.0, 1.0e7, 1.0, 3, 0.0);
   row_for(ui, "hf_row", app.trigger_hf_spin);
 
-  const char* modes[] = {"normal", "single", nullptr};
+  const char* modes[] = {trigger_mode_text(TriggerMode::Normal),
+                         trigger_mode_text(TriggerMode::Single), nullptr};
   app.trigger_mode_drop = gtk_drop_down_new_from_strings(modes);
   row_for(ui, "mode_row", app.trigger_mode_drop);
 
@@ -440,6 +608,20 @@ GtkWidget* build_trigger_panel(App& app) {
   gtk_widget_set_halign(title, GTK_ALIGN_START);
   gtk_widget_set_hexpand(title, TRUE);
   gtk_box_append(GTK_BOX(head), title);
+  // What the pane is set to, for the mode where its settings are not on screen.
+  app.trigger_summary = gtk_label_new("");
+  gtk_widget_add_css_class(app.trigger_summary, "dim-label");
+  gtk_label_set_ellipsize(GTK_LABEL(app.trigger_summary), PANGO_ELLIPSIZE_END);
+  gtk_widget_set_halign(app.trigger_summary, GTK_ALIGN_START);
+  gtk_widget_set_hexpand(app.trigger_summary, TRUE);
+  gtk_widget_set_visible(app.trigger_summary, FALSE);
+  gtk_box_append(GTK_BOX(head), app.trigger_summary);
+  app.trigger_edit = gtk_button_new_from_icon_name("emblem-system-symbolic");
+  gtk_widget_add_css_class(app.trigger_edit, "flat");
+  gtk_widget_set_valign(app.trigger_edit, GTK_ALIGN_CENTER);
+  gtk_widget_set_tooltip_text(app.trigger_edit, "configure the trigger");
+  g_signal_connect(app.trigger_edit, "clicked", G_CALLBACK(on_pane_edit_clicked), &app);
+  gtk_box_append(GTK_BOX(head), app.trigger_edit);
   app.trigger_switch = gtk_switch_new();
   gtk_widget_set_valign(app.trigger_switch, GTK_ALIGN_CENTER);
   gtk_widget_set_tooltip_text(app.trigger_switch,