[FIX] mail, im_livechat: make livechat work properly

- fix traceback on receiving first livechat message due to bad computation of
  correspondent
- fix missing [0] in return of country name_get in channel_info
- fix visitor/correspondent computation to work when chatting with oneself
- reintroduce livechat ordered by last message in discuss sidebar
- improve mock server to make these fixes possible to test
- introduce corresponding tests

PR: #56243
task-2323670

closes odoo/odoo#56414

X-original-commit: f623bfd2c8819604c709bc723153c071dca6e3cc
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/addons/mail/static/src/models/message/message.js b/addons/mail/static/src/models/message/message.js
index 582745e28f2..e982df36667 100644
--- a/addons/mail/static/src/models/message/message.js
+++ b/addons/mail/static/src/models/message/message.js
@@ -607,12 +607,13 @@ function factory(dependencies) {
         tracking_value_ids: attr({
             default: [],
         }),
-
         /**
-         * All channels that this message is linked to (from server message
-         * format).
+         * All channels containing this message on the server.
+         * Equivalent of python field `channel_ids`.
          */
-        serverChannels: many2many('mail.thread'),
+        serverChannels: many2many('mail.thread', {
+            inverse: 'messagesAsServerChannel',
+        }),
     };
 
     Message.modelName = 'mail.message';