fix(remove user): handles user removal failures more gracefully

src/dispatch/case/flows.py

@@ -184,19 +184,19 @@ def case_remove_participant_flow(
     )
 
     # we also try to remove the user from the Slack conversation
-    try:
-        slack_conversation_plugin = plugin_service.get_active_instance(
-            db_session=db_session, project_id=case.project.id, plugin_type="conversation"
-        )
+    slack_conversation_plugin = plugin_service.get_active_instance(
+        db_session=db_session, project_id=case.project.id, plugin_type="conversation"
+    )
 
-        if not slack_conversation_plugin:
-            log.warning(f"{user_email} not updated. No conversation plugin enabled.")
-            return
+    if not slack_conversation_plugin:
+        log.warning(f"{user_email} not updated. No conversation plugin enabled.")
+        return
 
-        if not case.conversation:
-            log.warning("No conversation enabled for this case.")
-            return
+    if not case.conversation:
+        log.warning("No conversation enabled for this case.")
+        return
 
+    try:
         slack_conversation_plugin.instance.remove_user(
             conversation_id=case.conversation.channel_id,
             user_email=user_email

src/dispatch/incident/flows.py

@@ -1178,19 +1178,19 @@ def incident_remove_participant_flow(
     )
 
     # we also try to remove the user from the Slack conversation
-    try:
-        slack_conversation_plugin = plugin_service.get_active_instance(
-            db_session=db_session, project_id=incident.project.id, plugin_type="conversation"
-        )
+    slack_conversation_plugin = plugin_service.get_active_instance(
+        db_session=db_session, project_id=incident.project.id, plugin_type="conversation"
+    )
 
-        if not slack_conversation_plugin:
-            log.warning(f"{user_email} not updated. No conversation plugin enabled.")
-            return
+    if not slack_conversation_plugin:
+        log.warning(f"{user_email} not updated. No conversation plugin enabled.")
+        return
 
-        if not incident.conversation:
-            log.warning("No conversation enabled for this incident.")
-            return
+    if not incident.conversation:
+        log.warning("No conversation enabled for this incident.")
+        return
 
+    try:
         slack_conversation_plugin.instance.remove_user(
             conversation_id=incident.conversation.channel_id,
             user_email=user_email

src/dispatch/plugins/dispatch_slack/case/interactive.py

@@ -469,7 +469,23 @@ def engage(
         return
 
     engagement = form_data[DefaultBlockIds.description_input]
-    user = client.users_lookupByEmail(email=user_email)
+
+    try:
+        user = client.users_lookupByEmail(email=user_email)
+    except SlackApiError as e:
+        if e.response.get("error") == SlackAPIErrorCode.USERS_NOT_FOUND:
+            log.warning(
+                f"Failed to find Slack user for email {user_email}. "
+                "User may have been deactivated or never had Slack access."
+            )
+            client.chat_postMessage(
+                text=f"Unable to engage user {user_email} - user not found in Slack workspace.",
+                channel=case.conversation.channel_id,
+                thread_ts=case.conversation.thread_id if case.has_thread else None,
+            )
+            return
+        else:
+            raise
 
     result = client.chat_postMessage(
         text="Engaging user...",
@@ -1983,9 +1999,19 @@ def edit_button_click(
     ack()
     case = case_service.get(db_session=db_session, case_id=int(context["subject"].id))
 
-    assignee_initial_user = client.users_lookupByEmail(email=case.assignee.individual.email)[
-        "user"
-    ]["id"]
+    try:
+        assignee_initial_user = client.users_lookupByEmail(email=case.assignee.individual.email)[
+            "user"
+        ]["id"]
+    except SlackApiError as e:
+        if e.response.get("error") == SlackAPIErrorCode.USERS_NOT_FOUND:
+            log.warning(
+                f"Assignee {case.assignee.individual.email} not found in Slack workspace. "
+                "Using None for initial assignee selection."
+            )
+            assignee_initial_user = None
+        else:
+            raise
 
     blocks = [
         title_input(initial_value=case.title),

src/dispatch/plugins/dispatch_slack/plugin.py

@@ -390,13 +390,48 @@ def set_description(self, conversation_id: str, description: str):
         return set_conversation_description(client, conversation_id, description)
 
     def remove_user(self, conversation_id: str, user_email: str):
-        """Removes a user from a conversation."""
+        """Removes a user from a conversation.
+
+        Args:
+            conversation_id: The Slack conversation/channel ID
+            user_email: The email address of the user to remove
+
+        Returns:
+            The API response if successful, None if user not found
+
+        Raises:
+            SlackApiError: For non-recoverable Slack API errors
+        """
         client = create_slack_client(self.configuration)
-        user_id = resolve_user(client, user_email).get("id")
-        if user_id:
-            return remove_member_from_channel(
-                client=client, conversation_id=conversation_id, user_id=user_id
-            )
+
+        try:
+            user_info = resolve_user(client, user_email)
+            user_id = user_info.get("id")
+
+            if user_id:
+                return remove_member_from_channel(
+                    client=client, conversation_id=conversation_id, user_id=user_id
+                )
+            else:
+                logger.warning(
+                    "Cannot remove user %s from conversation %s: "
+                    "User ID not found in resolve_user response",
+                    user_email, conversation_id
+                )
+                return None
+
+        except SlackApiError as e:
+            if e.response.get("error") == SlackAPIErrorCode.USERS_NOT_FOUND:
+                logger.warning(
+                    "User %s not found in Slack workspace. "
+                    "Cannot remove from conversation %s. "
+                    "User may have been deactivated or never had Slack access.",
+                    user_email, conversation_id
+                )
+                return None
+            else:
+                # Re-raise for other Slack API errors
+                raise
 
     def add_bookmark(self, conversation_id: str, weblink: str, title: str):
         """Adds a bookmark to the conversation."""