Fix In-Reply-To multi-ID parsing, duplicate labels, and resume message

deriveThreadKey: parse In-Reply-To as a msg-id list per RFC 2822
instead of trimming the whole header string. Multi-ID headers like
"<a@x> <b@x>" now correctly extract the first ID instead of
producing malformed keys like "a@x> <b@x".

Label merge: exclude the current mailbox when appending from
msgIDToLabels to avoid duplicate label IDs that violate the
message_labels primary key constraint. Trash/Spam-only messages
on Gmail would fail ingest because the mailbox appeared twice.

Resume message: tell IMAP users that the next run restarts from
the beginning (skipping already-imported messages) instead of the
misleading "Run again to resume."

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: wesm

cmd/msgvault/cmd/syncfull.go

@@ -278,7 +278,11 @@ func runFullSync(ctx context.Context, s *store.Store, oauthMgr *oauth.Manager, s
 	summary, err := syncer.Full(ctx, src.Identifier)
 	if err != nil {
 		if ctx.Err() != nil {
-			fmt.Println("\nSync interrupted. Run again to resume.")
+			if opts.NoResume {
+				fmt.Println("\nSync interrupted. Run again to restart (already-imported messages will be skipped).")
+			} else {
+				fmt.Println("\nSync interrupted. Run again to resume.")
+			}
 			return nil
 		}
 		return fmt.Errorf("sync failed: %w", err)

internal/imap/client.go

@@ -777,12 +777,18 @@ func (c *Client) GetMessagesRawBatch(ctx context.Context, messageIDs []string) (
 				// Merge labels from other mailboxes via the
 				// label map built during listing. The map keys
 				// on RFC822 Message-ID and maps to the other
-				// mailbox names the message appears in.
+				// mailbox names the message appears in. Skip the
+				// current mailbox to avoid duplicates that would
+				// violate the message_labels primary key.
 				if c.msgIDToLabels != nil &&
 					msgBuf.Envelope != nil &&
 					msgBuf.Envelope.MessageID != "" {
 					if extra, ok := c.msgIDToLabels[msgBuf.Envelope.MessageID]; ok {
-						labels = append(labels, extra...)
+						for _, lbl := range extra {
+							if lbl != mailbox {
+								labels = append(labels, lbl)
+							}
+						}
 					}
 				}
 

internal/sync/sync.go

@@ -716,27 +716,40 @@ func joinEmails(addrs []mime.Address) string {
 // replies, then to the message's own Message-ID. Returns "" when
 // no threading info is available.
 //
-// Angle brackets are stripped for consistency: parseReferences
-// already strips them, but InReplyTo/MessageID retain them from
-// the raw header. Without normalization the root message (using
-// MessageID "<X>") and its replies (using References "X") would
-// get different thread keys.
+// InReplyTo is parsed as a msg-id list per RFC 2822 (it may
+// contain multiple IDs and comments); only the first valid ID
+// is used. Angle brackets are stripped for consistency with
+// parseReferences.
 func deriveThreadKey(parsed *mime.Message) string {
 	if len(parsed.References) > 0 {
 		return parsed.References[0]
 	}
 	if parsed.InReplyTo != "" {
-		return stripAngleBrackets(parsed.InReplyTo)
+		if ids := parseMsgIDList(parsed.InReplyTo); len(ids) > 0 {
+			return ids[0]
+		}
 	}
 	if parsed.MessageID != "" {
-		return stripAngleBrackets(parsed.MessageID)
+		if ids := parseMsgIDList(parsed.MessageID); len(ids) > 0 {
+			return ids[0]
+		}
 	}
 	return ""
 }
 
-// stripAngleBrackets removes surrounding < > from a message ID.
-func stripAngleBrackets(s string) string {
-	return strings.Trim(s, "<>")
+// parseMsgIDList splits a header value containing one or more
+// angle-bracketed message-IDs (as in References or In-Reply-To)
+// and returns them with brackets stripped. Tokens without angle
+// brackets are ignored per RFC 2822 msg-id syntax.
+func parseMsgIDList(s string) []string {
+	var result []string
+	for _, tok := range strings.Fields(s) {
+		tok = strings.Trim(tok, "<>")
+		if tok != "" {
+			result = append(result, tok)
+		}
+	}
+	return result
 }
 
 // extractSubjectFromSnippet attempts to extract a subject from the message snippet.

internal/sync/sync_test.go

@@ -1576,6 +1576,11 @@ func TestDeriveThreadKey(t *testing.T) {
 			msg:     &mime.Message{MessageID: "<self@ex>"},
 			wantKey: "self@ex",
 		},
+		{
+			name:    "Multi-ID InReplyTo uses first entry",
+			msg:     &mime.Message{InReplyTo: "<a@ex> <b@ex>", MessageID: "<self@ex>"},
+			wantKey: "a@ex",
+		},
 		{
 			name:      "Empty when no threading info",
 			msg:       &mime.Message{},