Phase 5: reply drafts — template/LLM draft, edit, SMTP send (AUD-71)

Implements Phase 5 of AGENTS.md §11 (FR-8, FR-15):

- Message detail pane (GET /partials/message) with body, recommended
  action, reply identity, template picker, editable draft, and history.
- internal/reply: OmniRoute (OpenAI-compatible) chat client and a
  template-based draft generator. All non-JEV models go through
  OmniRoute (§10).
- internal/mailops: SMTP send over smtp.gmail.com:587 with STARTTLS and
  the app password, forcing IPv4 (§9); FR-15 reply identity (send as the
  arrived-at X-Pm-Original-To address, else "Sam Rolfe"); threading via
  In-Reply-To/References; -check-smtp safe verification; and a
  [Gmail]/Sent Mail thread check.
- Migration v5 stores messages.message_id_header and drafts.sent_at;
  mailfetch parses Message-ID.
- Send is user-triggered only: CSRF + UI confirm + confirm=yes guard,
  no auto-send, duplicate-send refused. A sent reply files the original
  under Replied-to/<address> and logs every step (FR-13).
- Tests for reply, mailops SMTP/identity/thread check, store drafts and
  migration v5, and the server draft/edit/send guards.
- docs/phase5-replies.md, README, .env.example, docker-compose updated.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/mailfetch/imap_write.go

@@ -10,6 +10,7 @@ package mailfetch
 
 import (
 	"errors"
+	"fmt"
 	"strconv"
 	"strings"
 )
@@ -88,17 +89,29 @@ func (c *Client) StoreFlags(uid uint32, op string, flag string) error {
 // id (X-GM-MSGID) in the currently selected mailbox. Gmail assigns a different
 // UID per label, so this is how a message is located after a move.
 func (c *Client) SearchGmailID(gmailID string) ([]uint32, error) {
-	gmailID = strings.TrimSpace(gmailID)
-	if gmailID == "" {
-		return nil, errors.New("empty x-gm-msgid")
+	return c.searchNumeric("X-GM-MSGID", gmailID)
+}
+
+// SearchGmailThreadID returns the UIDs of the messages in the given Gmail
+// thread (X-GM-THRID) in the currently selected mailbox. Phase 5 uses it to
+// confirm that a reply landed in the same thread as the original message.
+func (c *Client) SearchGmailThreadID(threadID string) ([]uint32, error) {
+	return c.searchNumeric("X-GM-THRID", threadID)
+}
+
+// searchNumeric runs a UID SEARCH for a numeric Gmail extension key.
+func (c *Client) searchNumeric(key, value string) ([]uint32, error) {
+	value = strings.TrimSpace(value)
+	if value == "" {
+		return nil, fmt.Errorf("empty %s", strings.ToLower(key))
 	}
-	for _, r := range gmailID {
+	for _, r := range value {
 		if r < '0' || r > '9' {
-			return nil, errors.New("x-gm-msgid must be numeric")
+			return nil, fmt.Errorf("%s must be numeric", strings.ToLower(key))
 		}
 	}
 	var uids []uint32
-	err := c.exec("UID SEARCH X-GM-MSGID "+gmailID, func(resp *response) error {
+	err := c.exec("UID SEARCH "+key+" "+value, func(resp *response) error {
 		if !strings.HasPrefix(strings.ToUpper(resp.line), "* SEARCH") {
 			return nil
 		}