fix(ticket-assistant): rendre visible l'échec « aucune réponse » de l'assistant de ticket (#60)

Introduit un variant terminal `ReplyEvent::Error { message }` (domain/ports)
propagé jusqu'au chat : l'adapter OpenAI-compat récupère `reasoning_content`
quand `content` est vide, et un `Final` vide est converti en `Error` visible
plutôt qu'un tour silencieux qui pend. Le front (`ReplyChunk` + useTicketAssistant)
rend ce message d'erreur dans la cellule.

- domain: variant `ReplyEvent::Error`, bras non terminal (readiness, structured drain)
- infra/session: parse `reasoning_content` (delta/completion), fallback visible
- app-tauri: mapping ReplyEvent::Error -> ReplyChunk::Error, Final vide -> Error
- frontend: ReplyChunk `error`, rendu dans useTicketAssistant (+ test .test.tsx)

NB: commit sur la feature branch, PAS un merge. #60 reste inProgress.
Les 10 tests `cargo test -p infrastructure --lib session` échouent SOUS SANDBOX
uniquement (bind loopback 127.0.0.1:0 interdit -> Os PermissionDenied), pas une
régression : revérification hors-sandbox requise avant tout merge vers develop.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/infrastructure/src/session/mod.rs

@@ -887,6 +887,46 @@ mod tests {
         );
     }
 
+    /// `item.type == error` ⇒ Error terminal visible, avec message réel.
+    #[test]
+    fn codex_error_item_is_error_event_with_real_message() {
+        let r = codex::parse_event(
+            r#"{"type":"item.completed","item":{"id":"i0","type":"error","text":"auth failed"}}"#,
+        )
+        .unwrap();
+        assert_eq!(
+            r.events,
+            vec![ReplyEvent::Error {
+                message: "auth failed".into()
+            }]
+        );
+
+        let nested = codex::parse_event(
+            r#"{"type":"item.completed","item":{"id":"i0","type":"error","error":{"message":"quota exceeded"}}}"#,
+        )
+        .unwrap();
+        assert_eq!(
+            nested.events,
+            vec![ReplyEvent::Error {
+                message: "quota exceeded".into()
+            }]
+        );
+    }
+
+    /// `item.type == error` sans champ exploitable ⇒ fallback stable.
+    #[test]
+    fn codex_error_item_without_message_uses_fallback() {
+        let r =
+            codex::parse_event(r#"{"type":"item.completed","item":{"id":"i0","type":"error"}}"#)
+                .unwrap();
+        assert_eq!(
+            r.events,
+            vec![ReplyEvent::Error {
+                message: "Codex a renvoyé une erreur.".into()
+            }]
+        );
+    }
+
     /// `agent_message` ⇒ Final (porte le texte de réponse).
     #[test]
     fn codex_agent_message_is_final() {
@@ -982,6 +1022,37 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn codex_error_item_surfaces_error_without_final() {
+        let fake = FakeCli::printing(&[
+            r#"{"type":"thread.started","thread_id":"c"}"#,
+            r#"{"type":"turn.started"}"#,
+            r#"{"type":"item.completed","item":{"id":"i0","type":"error","text":"auth failed"}}"#,
+            r#"{"type":"turn.completed","usage":{}}"#,
+        ]);
+        let s = CodexExecSession::new(
+            SessionId::new_random(),
+            fake.command(),
+            "/",
+            None,
+            Vec::new(),
+            Vec::new(),
+            None,
+            None,
+        );
+        let events: Vec<_> = s.send("x").await.expect("send").collect();
+        assert!(events.iter().any(|event| matches!(
+            event,
+            ReplyEvent::Error { message } if message.contains("auth failed")
+        )));
+        assert!(
+            events
+                .iter()
+                .all(|event| !matches!(event, ReplyEvent::Final { .. })),
+            "Codex error must not be fabricated as a successful Final"
+        );
+    }
+
     #[tokio::test]
     async fn codex_two_agent_messages_preserve_first_as_announcement_and_last_as_final() {
         let fake = FakeCli::printing(&[