Merge branch 'compose-and-send': composing and sending mail

Item 123, built over 2026-08-20 to 2026-08-23 in thirteen tasks against
docs/superpowers/specs/2026-08-20-compose-and-send-design.md.

The application writes mail now. A composer window per message, markdown as
the body, drafts autosaving into the account's Maildir, and sending through a
per-account command on stdin rather than any network protocol of this
program's own. A countdown with an Undo stands between pressing Send and the
command running.

Two things came in alongside it. The notmuch auto-tagging hooks moved here
from the retiring `mailctl` project and learned that mail this application
files itself never arrived, so sent mail and drafts stop appearing in the
inbox. And the v1/v2 language is retired: semver on the user-visible surface
is the rule, and those labels described a split that composing made obsolete.

Hand tested against a fake send command rather than a real one, deliberately:
New, Reply and Forward all produce correct messages, a forwarded attachment
survives intact, and the sent copy is filed. That testing found the two
defects fixed on this branch, and both were invisible to the suite: a composer
orphaned by quitting the main window, and every sent message tagged `inbox`.

Twenty-two defects were found in the plan document's own draft code while
building it, which is why CLAUDE.md says to treat every code block in a plan
as a draft.

1 files changed, 29 insertions, 0 deletions

diff --git a/src/messageview.cpp b/src/messageview.cpp
index 469d148..5682858 100644
--- a/src/messageview.cpp
+++ b/src/messageview.cpp
@@ -416,6 +416,17 @@ MessageView::MessageView(QWidget *parent)
     staleRow->addStretch();
     m_staleBar->hide();
 
+    // Receive-only ribbon (item 123). Hidden until a message from an account
+    // with no send_command is displayed.
+    m_receiveOnlyRibbon = new QLabel(this);
+    m_receiveOnlyRibbon->setObjectName(QStringLiteral("receiveOnlyRibbon"));
+    // Qt::PlainText explicitly. The account key comes from configuration
+    // rather than from a stranger, but a QLabel guesses under Qt::AutoText and
+    // this is the same protection MessageDetailsDialog states on every value.
+    m_receiveOnlyRibbon->setTextFormat(Qt::PlainText);
+    m_receiveOnlyRibbon->setWordWrap(true);
+    m_receiveOnlyRibbon->hide();
+
     m_attachmentBar = new QWidget(this);
     m_attachmentBar->setObjectName(QStringLiteral("attachmentBar"));
     new QHBoxLayout(m_attachmentBar);
@@ -442,6 +453,7 @@ MessageView::MessageView(QWidget *parent)
     auto *layout = new QVBoxLayout(this);
     layout->addLayout(headerRow);
     layout->addLayout(blockedRow);
+    layout->addWidget(m_receiveOnlyRibbon);
     layout->addWidget(m_staleBar);
     layout->addWidget(m_view, 1);
     layout->addWidget(m_attachmentBar);
@@ -1234,6 +1246,23 @@ void MessageView::saveAttachment(const Attachment &attachment)
     emit statusMessage(tr("Saved %1").arg(written));
 }
 
+void MessageView::setReceiveOnlyAccount(const QString &accountKey)
+{
+    if (accountKey.isEmpty()) {
+        m_receiveOnlyRibbon->hide();
+        return;
+    }
+
+    // Names the account AND the key to add. A ribbon saying only "you cannot
+    // reply" leaves the user with nothing to do about it, and the shape is
+    // expressed by omission, so there is no setting to go and look for.
+    m_receiveOnlyRibbon->setText(
+        tr("This account is receive-only. Add send_command to [account.%1] "
+           "to send from it.")
+            .arg(accountKey));
+    m_receiveOnlyRibbon->show();
+}
+
 void MessageView::setStaleThread(const QString &threadId,
                                  const QString &messageId)
 {