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/app-tauri/src/chat.rs

@@ -196,6 +196,7 @@ fn reply_chunk_bytes(chunk: &ReplyChunk) -> usize {
         ReplyChunk::TextDelta { text } => text.len(),
         ReplyChunk::ToolActivity { label } => label.len(),
         ReplyChunk::Final { content } => content.len(),
+        ReplyChunk::Error { message } => message.len(),
     }
 }
 
@@ -214,7 +215,16 @@ pub fn chunk_from_event(event: ReplyEvent) -> Option<ReplyChunk> {
     match event {
         ReplyEvent::TextDelta { text } => Some(ReplyChunk::TextDelta { text }),
         ReplyEvent::ToolActivity { label } => Some(ReplyChunk::ToolActivity { label }),
-        ReplyEvent::Final { content } => Some(ReplyChunk::Final { content }),
+        ReplyEvent::Error { message } => Some(ReplyChunk::Error { message }),
+        ReplyEvent::Final { content } => {
+            if content.trim().is_empty() {
+                Some(ReplyChunk::Error {
+                    message: "Réponse vide du modèle.".to_owned(),
+                })
+            } else {
+                Some(ReplyChunk::Final { content })
+            }
+        }
         ReplyEvent::Announcement { .. } => None,
         ReplyEvent::Heartbeat => None,
         ReplyEvent::RateLimited { .. } => None,

crates/app-tauri/src/commands.rs

@@ -1659,6 +1659,7 @@ pub async fn agent_send(
     let service = std::sync::Arc::clone(&state.session_limit_service);
     let meta = state.structured_sessions.meta_for_session(&sid);
     std::thread::spawn(move || {
+        let mut terminal_visible = false;
         for event in stream {
             // Non-terminal, sans contenu chat : un signal de limite alimente le service
             // (le badge UI vient du bus `AgentRateLimited`, pas du flux chat) puis on
@@ -1682,12 +1683,23 @@ pub async fn agent_send(
             let Some(chunk) = crate::chat::chunk_from_event(event) else {
                 continue;
             };
+            if matches!(chunk, ReplyChunk::Final { .. } | ReplyChunk::Error { .. }) {
+                terminal_visible = true;
+            }
             // `send_output` always records into the conversation scrollback; the
             // boolean only reflects live delivery. If the view navigated away
             // (no channel at this generation) we keep draining so the turn still
             // completes and the scrollback stays whole for the next re-attach.
             let _ = bridge.send_output(&sid, chunk);
         }
+        if !terminal_visible {
+            let _ = bridge.send_output(
+                &sid,
+                ReplyChunk::Error {
+                    message: "Le modèle n'a renvoyé aucune réponse.".to_owned(),
+                },
+            );
+        }
         bridge.detach_if(&sid, gen);
     });
 

crates/app-tauri/src/dto.rs

@@ -1745,10 +1745,11 @@ impl From<TerminalSession> for TerminalSessionDto {
 /// twin of a [`domain::ports::ReplyEvent`]: the `agent_send` pump maps each turn
 /// event to one of these and pushes it to the frontend `AgentChatView`.
 ///
-/// Tagged on `kind` (camelCase: `"textDelta"` | `"toolActivity"` | `"final"`), so
-/// the front branches without positional parsing. `Final` is the **deterministic
-/// terminal** chunk of a turn — after it the turn is frozen and the stream ends.
-/// `Deserialize` is derived too so tests (and a mock gateway) can round-trip it.
+/// Tagged on `kind` (camelCase: `"textDelta"` | `"toolActivity"` | `"final"` |
+/// `"error"`), so the front branches without positional parsing. `Final` is the
+/// normal deterministic terminal chunk of a turn; `Error` is a visible terminal
+/// fallback for an otherwise silent/empty turn. `Deserialize` is derived too so
+/// tests (and a mock gateway) can round-trip it.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(tag = "kind", rename_all = "camelCase")]
 pub enum ReplyChunk {
@@ -1770,6 +1771,12 @@ pub enum ReplyChunk {
         /// The aggregated final content of the turn.
         content: String,
     },
+    /// A visible terminal fallback when the model stream produced no usable answer.
+    #[serde(rename_all = "camelCase")]
+    Error {
+        /// Human-readable explanation to render in the chat cell.
+        message: String,
+    },
 }
 
 /// Response DTO for `reattach_agent_chat`: the retained **conversation