feat: update status on agent bot assignment (#14870)

Assigning a conversation to an Agent Bot now moves it to pending.
Assigning a bot-owned pending conversation to a human opens it again,
while other assignment changes preserve the existing status. This makes
existing Agent Bot ownership behave like an AI handoff without depending
on the assignment dropdown UI work.

Closes:
https://linear.app/chatwoot/issue/CW-7448/apply-agent-bot-assignment-behavior

## Why
Agent Bot ownership should remove conversations from the main open queue
while the bot is handling them. Explicit human takeover should bring a
bot-owned pending conversation back to the open queue and clear the bot
owner.

## What changed
- Agent Bot assignment clears the human assignee and marks the
conversation pending.
- Human assignment clears the Agent Bot owner and opens the conversation
only when it was bot-owned and pending.
- Ordinary human assignment, non-pending bot takeover, and unassignment
preserve the existing conversation status.
- Manual human takeover uses the existing assignment and status events.
Bot-initiated handoffs continue to use the existing bot-handoff event
path.

## Validation
- Assign an open conversation to an Agent Bot through the assignment API
and verify it becomes pending.
- Assign that bot-owned pending conversation to a human and verify it
becomes open.
- Verify ordinary human assignment, non-pending bot takeover, and
unassignment do not force a status change.

spec/services/conversations/assignment_service_spec.rb

@@ -19,20 +19,55 @@ describe Conversations::AssignmentService do
         expect(conversation.assignee_id).to be_nil
         expect(conversation.assignee_agent_bot_id).to be_nil
       end
+
+      it 'preserves conversation status' do
+        conversation.update!(status: :snoozed, snoozed_until: 1.day.from_now)
+
+        described_class.new(conversation: conversation, assignee_id: nil).perform
+
+        expect(conversation.reload.status).to eq('snoozed')
+      end
     end
 
     context 'when assigning a user' do
       before do
-        conversation.update!(assignee_agent_bot: agent_bot, assignee: nil)
+        conversation.update!(assignee_agent_bot: agent_bot, assignee: nil, status: :pending)
       end
 
-      it 'sets the agent and clears agent bot' do
+      it 'sets the agent, clears agent bot and opens the conversation' do
         result = described_class.new(conversation: conversation, assignee_id: agent.id).perform
 
         conversation.reload
         expect(result).to eq(agent)
         expect(conversation.assignee_id).to eq(agent.id)
         expect(conversation.assignee_agent_bot_id).to be_nil
+        expect(conversation.status).to eq('open')
+      end
+
+      it 'starts the waiting clock when opening a bot-owned pending conversation' do
+        conversation.update!(waiting_since: nil)
+
+        freeze_time do
+          described_class.new(conversation: conversation, assignee_id: agent.id).perform
+
+          expect(conversation.reload.waiting_since).to eq(Time.current)
+        end
+      end
+
+      it 'preserves status for ordinary human assignment changes' do
+        conversation.update!(assignee_agent_bot: nil, status: :resolved)
+
+        described_class.new(conversation: conversation, assignee_id: agent.id).perform
+
+        expect(conversation.reload.status).to eq('resolved')
+      end
+
+      it 'preserves status when taking over a bot-owned non-pending conversation' do
+        conversation.update!(assignee_agent_bot: agent_bot, status: :resolved)
+
+        described_class.new(conversation: conversation, assignee_id: agent.id).perform
+
+        expect(conversation.reload.status).to eq('resolved')
       end
     end
 
@@ -45,8 +80,8 @@ describe Conversations::AssignmentService do
         )
       end
 
-      it 'sets the agent bot and clears human assignee' do
-        conversation.update!(assignee: agent, assignee_agent_bot: nil)
+      it 'sets the agent bot, clears human assignee and marks the conversation pending' do
+        conversation.update!(assignee: agent, assignee_agent_bot: nil, status: :open)
 
         result = service.perform
 
@@ -54,6 +89,25 @@ describe Conversations::AssignmentService do
         expect(result).to eq(agent_bot)
         expect(conversation.assignee_agent_bot_id).to eq(agent_bot.id)
         expect(conversation.assignee_id).to be_nil
+        expect(conversation.status).to eq('pending')
+      end
+
+      it 'marks a resolved conversation pending' do
+        conversation.update!(status: :resolved)
+
+        service.perform
+
+        expect(conversation.reload.status).to eq('pending')
+      end
+
+      it 'marks a snoozed conversation pending and clears the snooze timestamp' do
+        conversation.update!(status: :snoozed, snoozed_until: 1.day.from_now)
+
+        service.perform
+
+        conversation.reload
+        expect(conversation.status).to eq('pending')
+        expect(conversation.snoozed_until).to be_nil
       end
     end
   end