fix(gmail): expose reply threading metadata

Co-authored-by: Solomon Neas <srneas@gmail.com>

internal/cmd/execute_gmail_get_test.go

@@ -100,6 +100,71 @@ func containsAll(got []string, want []string) bool {
 	return true
 }
 
+func TestExecute_GmailGet_Metadata_DefaultHeadersIncludeThreading(t *testing.T) {
+	origNew := newGmailService
+	t.Cleanup(func() { newGmailService = origNew })
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !strings.Contains(r.URL.Path, "/gmail/v1/users/me/messages/m1") {
+			http.NotFound(w, r)
+			return
+		}
+		if got := r.URL.Query().Get("format"); got != "metadata" {
+			t.Errorf("format=%q", got)
+			http.Error(w, "bad format", http.StatusBadRequest)
+			return
+		}
+		want := []string{
+			"From", "To", "Cc", "Bcc", "Subject", "Date",
+			"Message-ID", "In-Reply-To", "References", "List-Unsubscribe",
+		}
+		if gotHeaders := r.URL.Query()["metadataHeaders"]; !containsAll(gotHeaders, want) {
+			t.Errorf("metadataHeaders=%#v missing one of %v", gotHeaders, want)
+			http.Error(w, "bad metadataHeaders", http.StatusBadRequest)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"id":       "m1",
+			"threadId": "t1",
+			"payload": map[string]any{
+				"headers": []map[string]any{
+					{"name": "Message-ID", "value": "<orig@id>"},
+					{"name": "In-Reply-To", "value": "<parent@id>"},
+					{"name": "References", "value": "<parent@id> <orig@id>"},
+				},
+			},
+		})
+	}))
+	defer srv.Close()
+
+	svc, err := gmail.NewService(context.Background(),
+		option.WithoutAuthentication(),
+		option.WithHTTPClient(srv.Client()),
+		option.WithEndpoint(srv.URL+"/"),
+	)
+	if err != nil {
+		t.Fatalf("NewService: %v", err)
+	}
+	newGmailService = func(context.Context, string) (*gmail.Service, error) { return svc, nil }
+
+	out := captureStdout(t, func() {
+		_ = captureStderr(t, func() {
+			if err := Execute([]string{
+				"--json",
+				"--account", "a@b.com",
+				"gmail", "get", "m1",
+				"--format", "metadata",
+			}); err != nil {
+				t.Fatalf("Execute: %v", err)
+			}
+		})
+	})
+	if !strings.Contains(out, "<orig@id>") || !strings.Contains(out, "<parent@id>") {
+		t.Fatalf("expected threading headers in metadata JSON, got: %q", out)
+	}
+}
+
 func TestExecute_GmailGet_Raw_JSON(t *testing.T) {
 	origNew := newGmailService
 	t.Cleanup(func() { newGmailService = origNew })

internal/cmd/gmail_get.go

@@ -54,7 +54,10 @@ func (c *GmailGetCmd) Run(ctx context.Context, flags *RootFlags) error {
 	if format == gmailFormatMetadata {
 		headerList := splitCSV(c.Headers)
 		if len(headerList) == 0 {
-			headerList = []string{"From", "To", "Cc", "Bcc", "Subject", "Date"}
+			headerList = []string{
+				"From", "To", "Cc", "Bcc", "Subject", "Date",
+				"Message-ID", "In-Reply-To", "References",
+			}
 		}
 		if !hasHeaderName(headerList, "List-Unsubscribe") {
 			headerList = append(headerList, "List-Unsubscribe")
@@ -72,12 +75,15 @@ func (c *GmailGetCmd) Run(ctx context.Context, flags *RootFlags) error {
 		// Include a flattened headers map for easier querying
 		// (e.g., jq '.headers.to' instead of complex nested queries)
 		headers := map[string]string{
-			"from":    headerValue(msg.Payload, "From"),
-			"to":      headerValue(msg.Payload, "To"),
-			"cc":      headerValue(msg.Payload, "Cc"),
-			"bcc":     headerValue(msg.Payload, "Bcc"),
-			"subject": headerValue(msg.Payload, "Subject"),
-			"date":    headerValue(msg.Payload, "Date"),
+			"from":        headerValue(msg.Payload, "From"),
+			"to":          headerValue(msg.Payload, "To"),
+			"cc":          headerValue(msg.Payload, "Cc"),
+			"bcc":         headerValue(msg.Payload, "Bcc"),
+			"subject":     headerValue(msg.Payload, "Subject"),
+			"date":        headerValue(msg.Payload, "Date"),
+			"message_id":  headerValue(msg.Payload, "Message-ID"),
+			"in_reply_to": headerValue(msg.Payload, "In-Reply-To"),
+			"references":  headerValue(msg.Payload, "References"),
 		}
 		payload := map[string]any{
 			"message": msg,

internal/cmd/gmail_send.go

@@ -451,7 +451,11 @@ func fetchReplyInfo(ctx context.Context, svc *gmail.Service, replyToMessageID st
 		if err != nil {
 			return nil, err
 		}
-		return replyInfoFromMessage(msg, includeQuoteBodies), nil
+		info := replyInfoFromMessage(msg, includeQuoteBodies)
+		if info.InReplyTo == "" {
+			return nil, fmt.Errorf("reply target message %s has no Message-ID header; cannot set In-Reply-To/References", replyToMessageID)
+		}
+		return info, nil
 	}
 
 	// For thread replies, we always need just headers to select the latest message.

internal/cmd/gmail_send_reply_test.go

@@ -101,6 +101,40 @@ func TestFetchReplyInfoFromThread(t *testing.T) {
 	}
 }
 
+func TestFetchReplyInfoNoMessageIDFails(t *testing.T) {
+	origNew := newGmailService
+	t.Cleanup(func() { newGmailService = origNew })
+
+	svc, cleanup := newGmailServiceForTest(t, func(w http.ResponseWriter, r *http.Request) {
+		path := strings.TrimPrefix(r.URL.Path, "/gmail/v1")
+		if r.Method != http.MethodGet || path != "/users/me/messages/m0" {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"id":       "m0",
+			"threadId": "t0",
+			"payload": map[string]any{
+				"headers": []map[string]any{
+					{"name": "From", "value": "a@example.com"},
+					{"name": "Subject", "value": "no message id here"},
+				},
+			},
+		})
+	})
+	defer cleanup()
+	newGmailService = func(context.Context, string) (*gmail.Service, error) { return svc, nil }
+
+	_, err := fetchReplyInfo(context.Background(), svc, "m0", "", false)
+	if err == nil {
+		t.Fatal("expected error when reply target lacks Message-ID")
+	}
+	if !strings.Contains(err.Error(), "Message-ID") {
+		t.Fatalf("expected error to mention Message-ID, got: %v", err)
+	}
+}
+
 func TestWriteSendResults_JSON(t *testing.T) {
 	u, err := ui.New(ui.Options{Stdout: io.Discard, Stderr: io.Discard, Color: "never"})
 	if err != nil {