source: a synthetic probe kind, and sessions that remember their source kind

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

src/layout_store.cpp

@@ -322,6 +322,10 @@ std::vector<KnownSource> known_sources() {
       s.capture_packets = st.capture_packets;
       s.multicast = st.multicast;
       s.interface_addr = st.interface_addr;
+      if (!st.source_kind.empty()) {
+        s.kind = st.source_kind;
+        s.opts = st.source_opts;
+      }
       s.rows = static_cast<int>(st.rows.size());
       for (const LayoutState::Row& row : st.rows) {
         for (const std::string& sig : row.signals) {
@@ -558,6 +562,11 @@ bool load_layout(const std::string& path, LayoutState& out) {
         st.multicast = strip_quote(value);
       } else if (key == "interface") {
         st.interface_addr = strip_quote(value);
+      } else if (key == "source_kind") {
+        st.source_kind = strip_quote(value);
+      } else if (key.rfind("source_opt_", 0) == 0) {
+        const std::string k = key.substr(11);
+        if (SourceConfig::valid_key(k)) st.source_opts.set(k, strip_quote(value));
       } else if (key == "comment") {
         st.comment = strip_quote(value);
       } else if (key == "buffer_mb") {
@@ -699,6 +708,12 @@ bool save_layout(const std::string& path, const LayoutState& state) {
   if (!state.interface_addr.empty()) {
     o << "interface = " << toml_escape(state.interface_addr) << "\n";
   }
+  if (!state.source_kind.empty() && state.source_kind != "udps") {
+    o << "source_kind = " << toml_escape(state.source_kind) << "\n";
+    for (const auto& kv : state.source_opts.items()) {
+      o << "source_opt_" << kv.first << " = " << toml_escape(kv.second) << "\n";
+    }
+  }
   // Top level, before any table. Emitted after the `[[calibration]]` tables it belonged to the last
   // of them -- a bare key after a header is that table's key in TOML -- so the parser, correctly,
   // never saw it and a session's enable state was silently lost.