Merge branch 'signatures'

Signatures (item 152): one markdown file per signature under
~/.config/qtmaildir/signatures/, spliced into the composer buffer and
chosen from a switch on the editor bar. [compose] signature seeds a new
message, [account.<key>] signature overrides per account, and
[compose] signature_position picks end or above_quote.

Also carries three fixes found by hand-testing it: a saved draft is
indexed so it appears without a sync (item 158), the Drafts filter lists
messages rather than threads so a draft reply can be opened (item 159),
and a resumed draft no longer re-seeds its signature on a From: change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UUQS6n3cmsFrsjCNmwNtf8

1 files changed, 76 insertions, 0 deletions

diff --git a/src/signatures.h b/src/signatures.h
new file mode 100644
index 0000000..e2bfd9c
--- /dev/null
+++ b/src/signatures.h
@@ -0,0 +1,76 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#include <QString>
+#include <QStringList>
+
+/// Signatures, as markdown files spliced into the composer's buffer.
+///
+/// Free functions over values, with no widget anywhere, matching
+/// MarkdownFormat, MessageBuilder and DraftStore. The splice is the part worth
+/// testing and it is testable with no painter.
+///
+/// MARKDOWN, and that is what makes this small: MessageBuilder already builds
+/// text/plain from the buffer verbatim and text/html from MarkdownRenderer
+/// over the same string, so a signature in the buffer yields both forms with
+/// no change there and no second code path. One choice by the user serves both
+/// parts, which is what the feature was asked for.
+namespace Signatures {
+
+/// Where a newly inserted signature goes, from [compose] signature_position.
+enum class Position {
+    End,        ///< The end of the buffer. The default and the user's habit.
+    AboveQuote  ///< Before the first quoted line, or the end when there is none.
+};
+
+/// The stems of every `*.md` in \p dir, sorted, without the extension.
+///
+/// A missing or unreadable directory yields an empty list. That is not a
+/// misconfiguration: it means the user keeps no signatures, and the switch
+/// then offers only "None".
+QStringList names(const QString &dir);
+
+/// The content of `<dir>/<name>.md`, or empty when it cannot be read.
+///
+/// \p name is a stem from names(), never a path. It is rejected if it contains
+/// a path separator, so a value arriving from the config file cannot reach
+/// outside \p dir.
+QString text(const QString &dir, const QString &name);
+
+/// Returns \p buffer with \p signature spliced in.
+///
+/// Any signature already present is replaced; \p signature empty removes it
+/// and inserts nothing, which is what "None" selects.
+///
+/// \p known is the text of every signature in the directory, and it is what
+/// makes this non-destructive. A `-- ` delimiter is NOT sufficient authority
+/// to delete what follows it: the block is replaced only when its text matches
+/// one of \p known, and otherwise the new signature is INSERTED with nothing
+/// removed. `-- ` reaches a buffer without the user ever choosing a signature,
+/// most plausibly pasted in with quoted text from another client, and the
+/// unguarded rule would silently delete everything after it.
+///
+/// The failure is therefore directional, which is the whole point: a wrong
+/// guess adds a visible second signature, one undo away, rather than losing
+/// the user's own writing.
+QString replace(const QString &buffer, const QString &signature,
+                const QStringList &known, Position position);
+
+}  // namespace Signatures