Export command (CSV + ODS), file dialog, error modal, path persistence.

New user-facing features:
- `export connections <file>` writes a tabular dump of every wire pair:
  connection, transform, left/right module/part/pin/signal/type/suspect,
  mixed-types flag. Dispatch on extension: `.csv` (flat file) or `.ods`
  (one sheet per connection). Any other extension shows an error and
  writes nothing.
- Bare `export` (or dashboard `[x]`, or palette `export`) opens an
  interactive file-picker dialog with a CSV/ODS toggle at the top.
  Picking a filter rewrites the filename's extension. Last-used
  directory and filename are remembered per-call-site.
- Two new CLI flags on the binary: `--source FILE` to run a script at
  boot, `--restore FILE` to restore a snapshot at boot. Combinable.

Reusable infrastructure:
- `OdsWriter` (`src/imports/ods_writer.{hpp,cpp}`): minimal .ods writer
  using libzip + pugixml (already in the build for the importer).
  Multi-sheet workbook of string cells. ~180 lines, no new dep.
- Generic file-picker dialog (`screen_filedialog.cpp`): one Modal
  reused for any "pick a path" interaction via
  `OpenFileDialog(title, persist_key, default_filename, filters, cb)`.
  Validates the picked extension against the filter whitelist;
  unknown ones stay in the dialog with a status message. Persists
  (dir, filename) per `persist_key`.
- Generic error modal (`screen_error.cpp`, `ShowError(msg)`): centred
  red-titled popup, dismissable with Esc/Enter. Used by the export
  failures (open-for-write, ODS save, unknown extension/kind);
  ready for adoption elsewhere.
- Per-key path persistence (`SaveLastUsed`/`LoadLastUsed` in
  `shell.cpp`): two-line file per key under the user-data dir.
- `UserDataDir()` extracted from the history path helper so the new
  per-key persistence shares the same XDG/AppData logic.
- New help-screen topic "Export"; user-facing `doc/user/analysis.md`
  gains an "Exporting" section; `DESIGN.md` gains a generics
  section covering the dialog / error modal / persistence / ODS
  writer; `DumpCommandsMd` now respects the `hidden` flag (the
  `connect` alias no longer appears in the auto-gen reference).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/tui/shell.cpp

@@ -16,6 +16,21 @@
 #include <system_error>
 #include <thread>
 
+void Tui::BootDispatch(const std::string &raw) {
+    // Called before Run() — no FTXUI screen yet, so any `Source()` invoked
+    // from here takes the headless synchronous branch (drains the script
+    // without the event-paced loop). Output goes to `output` and is
+    // visible as soon as the screen starts.
+    //
+    // We pin `screen_idx = 0` (console) for the duration of the dispatch
+    // so the source loop's "is interactive (would open a screen)" guard
+    // doesn't trip on the constructor's boot value of 4 (dashboard).
+    // After execution, restore to 4 so the user lands on the dashboard.
+    screen_idx = 0;
+    Dispatch(raw);
+    screen_idx = 4;
+}
+
 void Tui::OpenSignalTypeDialog(const std::string &mod_name,
                                const std::string &sig_name) {
     if (!sys) return;
@@ -228,26 +243,73 @@ std::string Tui::ExpandVars(const std::string &s) const {
 
 namespace {
 
-std::filesystem::path HistoryPath() {
+// User-data dir, platform-aware. Returns the base directory under which
+// every persistent file lives (history, export-last, …). Empty if none
+// of the expected env vars are set.
+std::filesystem::path UserDataDir() {
     namespace fs = std::filesystem;
 #ifdef _WIN32
     if (const char *p = std::getenv("LOCALAPPDATA"); p && *p)
-        return fs::path(p) / "essim" / "history";
+        return fs::path(p) / "essim";
     if (const char *p = std::getenv("APPDATA"); p && *p)
-        return fs::path(p) / "essim" / "history";
+        return fs::path(p) / "essim";
     if (const char *p = std::getenv("USERPROFILE"); p && *p)
-        return fs::path(p) / "AppData" / "Local" / "essim" / "history";
+        return fs::path(p) / "AppData" / "Local" / "essim";
 #else
     if (const char *p = std::getenv("XDG_DATA_HOME"); p && *p)
-        return fs::path(p) / "essim" / "history";
+        return fs::path(p) / "essim";
     if (const char *p = std::getenv("HOME"); p && *p)
-        return fs::path(p) / ".local" / "share" / "essim" / "history";
+        return fs::path(p) / ".local" / "share" / "essim";
 #endif
     return {};
 }
 
+std::filesystem::path HistoryPath() {
+    auto d = UserDataDir();
+    return d.empty() ? std::filesystem::path{} : (d / "history");
+}
+
 }  // namespace
 
+// Free helpers for "last used (dir, filename) per purpose". Stored as a
+// tiny two-line file per key under the user-data dir. Used by the file
+// dialog so each call site (export, save, restore, …) gets its own
+// memory without further plumbing.
+namespace {
+
+std::filesystem::path LastUsedPath(const std::string &key) {
+    auto d = UserDataDir();
+    return d.empty() ? std::filesystem::path{} : (d / (key + ".last"));
+}
+
+}  // namespace
+
+void SaveLastUsed(const std::string &key,
+                   const std::string &dir,
+                   const std::string &filename) {
+    auto p = LastUsedPath(key);
+    if (p.empty()) return;
+    std::error_code ec;
+    std::filesystem::create_directories(p.parent_path(), ec);
+    std::ofstream f(p);
+    if (!f) return;
+    f << dir << '\n' << filename << '\n';
+}
+
+bool LoadLastUsed(const std::string &key,
+                   std::string &dir, std::string &filename) {
+    auto p = LastUsedPath(key);
+    if (p.empty()) return false;
+    std::ifstream f(p);
+    if (!f) return false;
+    std::string d, n;
+    if (std::getline(f, d) && std::getline(f, n) && !d.empty() && !n.empty()) {
+        dir = d; filename = n;
+        return true;
+    }
+    return false;
+}
+
 void Tui::LoadHistory() {
     auto p = HistoryPath();
     if (p.empty()) return;
@@ -365,6 +427,7 @@ void Tui::DumpCommandsMd(std::ostream &out) const {
         bool printed_title = false;
         for (const auto &kv : commands) {
             const CommandSpec &spec = kv.second;
+            if (spec.hidden) continue;          // aliases & internal entries
             if (spec.interactive != want_interactive) continue;
             if (!printed_title) {
                 out << "\n## " << title << "\n\n";