feat: add MainWindow wiring query, list, message, and sync

Wires the worker thread, thread list, message pane, sync process and undo
stack together, and replaces the placeholder main() with real startup:
custom URL schemes registered before QApplication, a libnotmuch ABI check,
and config loading.

Four fixes against the drafted version:

- onWorkerError() only set a status label. Its own comment elsewhere
  claimed it reverted the optimistic update, and the spec requires that;
  it did not, so a rejected write left the list showing a tag the database
  never received. The pending change is now recorded and rolled back, and
  a confirmed tagsApplied clears it so a later unrelated error cannot undo
  a write that succeeded.
- runCurrentQuery() cleared the model but left the undo stack pointing at
  rows that no longer exist. Undoing after a new query would have written
  to the database while the visible list stayed put. The stack is cleared
  with the model.
- m_currentMessages was assigned on every thread load and never read.
  Removed.
- buildUi() connected sync output to m_syncLog and errors to m_statusLabel
  before either existed. Both are constructed before the wiring now.

cidPrefix generation lives here, this being its only producer in the
application, and is pinned by tests: it must never contain '!' and must be
distinct per message, which are the invariants the cid: namespacing rests
on. A second test holds registeredActionNames() against
KeyMap::knownActions(), since those two hand-maintained lists drifting
either way silently breaks a user's key binding. Mutation-verified that
dropping an action fails the test by name.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 36 insertions, 3 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 9c7b977..2c5dc13 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,10 +1,43 @@
 #include <QApplication>
-#include <QLabel>
+#include <QMessageBox>
+#include <QWebEngineUrlScheme>
+
+#include <notmuch.h>
+
+#include "config.h"
+#include "mainwindow.h"
 
 int main(int argc, char *argv[])
 {
+    // Custom schemes must be registered before QApplication is constructed.
+    {
+        QWebEngineUrlScheme scheme(QByteArrayLiteral("cid"));
+        scheme.setFlags(QWebEngineUrlScheme::SecureScheme
+                        | QWebEngineUrlScheme::ContentSecurityPolicyIgnored);
+        QWebEngineUrlScheme::registerScheme(scheme);
+    }
+    {
+        QWebEngineUrlScheme scheme(QByteArrayLiteral("qtmaildir"));
+        scheme.setFlags(QWebEngineUrlScheme::SecureScheme);
+        QWebEngineUrlScheme::registerScheme(scheme);
+    }
+
     QApplication app(argc, argv);
-    QLabel label(QStringLiteral("qtmaildir"));
-    label.show();
+    app.setApplicationName(QStringLiteral("qtmaildir"));
+    app.setOrganizationName(QStringLiteral("qtmaildir"));
+
+    // Fail loudly on an ABI mismatch rather than crashing later.
+    if (LIBNOTMUCH_MAJOR_VERSION < 5) {
+        QMessageBox::critical(nullptr, QObject::tr("qtmaildir"),
+            QObject::tr("libnotmuch 5 or newer is required."));
+        return 1;
+    }
+
+    Config config;
+    config.load(Config::defaultPath());
+
+    MainWindow window(config);
+    window.show();
+
     return app.exec();
 }