feat: livrable ticket #91 — notification fin BackgroundTask enrichie

- Backend: enrichissement HeadlessRendezvous avec requester/target/conversationId
- Frontend: toast 'Requester -> Target completed/...' explicite
- Clic ouvrant viewer de conversation pour visualiser l'échange

crates/application/src/orchestrator/service.rs

@@ -127,6 +127,22 @@ fn resolve_background_cwd(
     ProjectPath::new(path).map_err(|_| AppError::Invalid("invalid background task cwd".to_owned()))
 }
 
+fn rendezvous_context_for_task(task: &BackgroundTask) -> Option<domain::RendezvousContext> {
+    match &task.kind {
+        BackgroundTaskKind::HeadlessRendezvous {
+            requester_agent_id,
+            target_agent_id,
+            conversation_id,
+            ..
+        } => Some(domain::RendezvousContext {
+            requester_agent_id: *requester_agent_id,
+            target_agent_id: *target_agent_id,
+            conversation_id: *conversation_id,
+        }),
+        _ => None,
+    }
+}
+
 fn normalize_path_no_parent(path: &Path) -> Result<PathBuf, AppError> {
     let mut out = PathBuf::new();
     for component in path.components() {
@@ -847,22 +863,26 @@ impl OrchestratorService {
         if task.is_terminal() {
             return Ok(());
         }
+        let rendezvous = rendezvous_context_for_task(&task);
         let event = match &result {
             BackgroundTaskResult::Success { .. } => DomainEvent::BackgroundTaskCompleted {
                 project_id: project.id,
                 task_id,
                 owner_agent_id,
+                rendezvous,
             },
             BackgroundTaskResult::Failure { .. } => DomainEvent::BackgroundTaskFailed {
                 project_id: project.id,
                 task_id,
                 owner_agent_id,
+                rendezvous,
             },
             BackgroundTaskResult::Cancelled { .. } | BackgroundTaskResult::Expired { .. } => {
                 DomainEvent::BackgroundTaskCancelled {
                     project_id: project.id,
                     task_id,
                     owner_agent_id,
+                    rendezvous,
                 }
             }
         };
@@ -2967,6 +2987,52 @@ mod tests {
         assert_eq!(submit.delay_ms, Some(CODEX_SUBMIT_DELAY_MS));
     }
 
+    #[test]
+    fn rendezvous_context_is_extracted_from_headless_background_task_kind() {
+        let requester = aid(1);
+        let target = aid(2);
+        let conversation_id = domain::ConversationId::from_uuid(uuid::Uuid::from_u128(3));
+        let task = BackgroundTask::new(
+            TaskId::from_uuid(uuid::Uuid::from_u128(4)),
+            domain::ProjectId::from_uuid(uuid::Uuid::from_u128(5)),
+            target,
+            BackgroundTaskKind::HeadlessRendezvous {
+                requester_agent_id: Some(requester),
+                target_agent_id: target,
+                ticket_id: TicketId::from_uuid(uuid::Uuid::from_u128(6)),
+                conversation_id,
+            },
+            BackgroundTaskWakePolicy::RecordOnly,
+            100,
+            None,
+        )
+        .unwrap();
+
+        let context = rendezvous_context_for_task(&task).expect("rendezvous context");
+
+        assert_eq!(context.requester_agent_id, Some(requester));
+        assert_eq!(context.target_agent_id, target);
+        assert_eq!(context.conversation_id, conversation_id);
+    }
+
+    #[test]
+    fn rendezvous_context_is_absent_for_command_background_task() {
+        let task = BackgroundTask::new(
+            TaskId::from_uuid(uuid::Uuid::from_u128(7)),
+            domain::ProjectId::from_uuid(uuid::Uuid::from_u128(8)),
+            aid(9),
+            BackgroundTaskKind::Command {
+                label: "cargo test".to_owned(),
+            },
+            BackgroundTaskWakePolicy::RecordOnly,
+            100,
+            None,
+        )
+        .unwrap();
+
+        assert_eq!(rendezvous_context_for_task(&task), None);
+    }
+
     #[test]
     fn explicit_profile_submit_delay_is_preserved() {
         let p = profile(3, "OpenAI Codex CLI", "codex")