fix(worker): reopen the notmuch handle so queries see new mail

A read-only notmuch handle is a Xapian snapshot taken when it is opened,
so it never observes a write made by another process afterwards. The
worker opened one handle and kept it for the process lifetime, which made
the sync script's `notmuch new` invisible: every query after startup was
answered from the index as it stood when the application launched.

The symptom was mail arriving while the window was open and not appearing
until a restart. It was not confined to the post-sync refresh, which is
what made it hard to place: a query typed by hand also found nothing,
since it hits the same handle. Tag writes were unaffected throughout,
because applyTags opens its own read-write handle per call.

Reopen in openReadOnly() rather than at each call site: every read path
begins by asking for the handle. A reopen failure is deliberately not
fatal, since the existing handle is still usable and answering from a
slightly stale index beats refusing to answer.

The suite could not reproduce this before: the test helper builds a fresh
worker per query, so it opens a fresh handle every time. The new test
holds one worker across two queries and indexes between them from a
second process.

Item 104.

1 files changed, 21 insertions, 1 deletions

diff --git a/src/notmuchworker.cpp b/src/notmuchworker.cpp
index f510fd5..f3a76ea 100644
--- a/src/notmuchworker.cpp
+++ b/src/notmuchworker.cpp
@@ -288,8 +288,28 @@ QByteArray NotmuchWorker::configPathArg() const
 
 bool NotmuchWorker::openReadOnly()
 {
-    if (m_db)
+    if (m_db) {
+        // A read-only handle is a Xapian SNAPSHOT taken when it was opened, so
+        // it never observes a write made by another process afterwards. The
+        // sync script's `notmuch new` is exactly that, which made mail arriving
+        // while the window was open invisible until the application restarted:
+        // not only to the post-sync refresh, but to any query the user typed by
+        // hand, since all of them are answered from the same handle. Item 104.
+        //
+        // Reopening here rather than at each call site covers every read path,
+        // which all begin by asking for the handle. It is cheap and it is what
+        // notmuch provides the call for; a failure is deliberately NOT fatal,
+        // since the existing handle is still usable and serving slightly stale
+        // results beats refusing to answer at all.
+        const notmuch_status_t status =
+            notmuch_database_reopen(m_db, NOTMUCH_DATABASE_MODE_READ_ONLY);
+        if (status != NOTMUCH_STATUS_SUCCESS) {
+            emit errorOccurred(
+                QStringLiteral("Cannot refresh notmuch database: %1")
+                    .arg(QString::fromUtf8(notmuch_status_to_string(status))));
+        }
         return true;
+    }
 
     const QByteArray configPath = configPathArg();
     char *error = nullptr;