fix(background-task): découpler la détection de fin de tâche du drain output PTY (#2)

Le runner de tâches de fond détectait la fin d'un process via l'EOF du drain de
sortie PTY, couplant le cycle de vie du process au flux d'output. Un output
encore ouvert (ou drainé ailleurs) pouvait masquer ou retarder la détection de
fin.

Ajoute wait/try_wait au port figé PtyPort :
- wait : bloquant, rend un ExitStatus idempotent ;
- try_wait : non bloquant, rend Option<ExitStatus> ;
- exit status mémorisé pour garder wait/try_wait/kill cohérents.
Implémentation dans PortablePtyAdapter (état d'exit mémorisé). Le
CommandBackgroundRunner détecte désormais la fin via pty.wait (select sur
cancel/deadline) au lieu de l'EOF du drain. Tous les fakes PtyPort du workspace
sont complétés en conséquence.

Le tee live UI reste hors périmètre (traité en #58). Aucun breaking IPC/front.

Tests : infrastructure/tests/background_task_runner.rs (nouveau) + pty_adapter.rs
verts, non-régression application/app-tauri OK (hors échecs réseau du sandbox).

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

crates/application/tests/agent_lifecycle.rs

@@ -554,6 +554,12 @@ impl PtyPort for FakePty {
     fn scrollback(&self, _handle: &PtyHandle) -> Result<Vec<u8>, PtyError> {
         Ok(Vec::new())
     }
+    async fn wait(&self, _handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
+        Ok(ExitStatus { code: Some(0) })
+    }
+    fn try_wait(&self, _handle: &PtyHandle) -> Result<Option<ExitStatus>, PtyError> {
+        Ok(Some(ExitStatus { code: Some(0) }))
+    }
     async fn kill(&self, _handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
         Ok(ExitStatus { code: Some(0) })
     }

crates/application/tests/change_agent_profile.rs

@@ -427,6 +427,12 @@ impl PtyPort for FakePty {
     fn scrollback(&self, _handle: &PtyHandle) -> Result<Vec<u8>, PtyError> {
         Ok(Vec::new())
     }
+    async fn wait(&self, _handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
+        Ok(ExitStatus { code: Some(0) })
+    }
+    fn try_wait(&self, _handle: &PtyHandle) -> Result<Option<ExitStatus>, PtyError> {
+        Ok(Some(ExitStatus { code: Some(0) }))
+    }
     async fn kill(&self, handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
         self.kills.lock().unwrap().push(handle.session_id);
         Ok(ExitStatus { code: Some(0) })

crates/application/tests/orchestrator_service.rs

@@ -370,6 +370,12 @@ impl PtyPort for FakePty {
     fn scrollback(&self, _handle: &PtyHandle) -> Result<Vec<u8>, PtyError> {
         Ok(Vec::new())
     }
+    async fn wait(&self, _handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
+        Ok(ExitStatus { code: Some(0) })
+    }
+    fn try_wait(&self, _handle: &PtyHandle) -> Result<Option<ExitStatus>, PtyError> {
+        Ok(Some(ExitStatus { code: Some(0) }))
+    }
     async fn kill(&self, handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
         self.kills.lock().unwrap().push(handle.session_id);
         Ok(ExitStatus { code: Some(0) })

crates/application/tests/structured_launch_d3.rs

@@ -357,6 +357,12 @@ impl PtyPort for FakePty {
     fn scrollback(&self, _handle: &PtyHandle) -> Result<Vec<u8>, PtyError> {
         Ok(Vec::new())
     }
+    async fn wait(&self, _handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
+        Ok(ExitStatus { code: Some(0) })
+    }
+    fn try_wait(&self, _handle: &PtyHandle) -> Result<Option<ExitStatus>, PtyError> {
+        Ok(Some(ExitStatus { code: Some(0) }))
+    }
     async fn kill(&self, handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
         self.kills.lock().unwrap().push(handle.session_id);
         Ok(ExitStatus { code: Some(0) })

crates/application/tests/terminal_usecases.rs

@@ -106,6 +106,14 @@ impl PtyPort for FakePty {
         Ok(Vec::new())
     }
 
+    async fn wait(&self, _handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
+        Ok(ExitStatus { code: Some(0) })
+    }
+
+    fn try_wait(&self, _handle: &PtyHandle) -> Result<Option<ExitStatus>, PtyError> {
+        Ok(Some(ExitStatus { code: Some(0) }))
+    }
+
     async fn kill(&self, handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
         let mut inner = self.0.lock().unwrap();
         inner.calls.push(Call::Kill {

crates/application/tests/workstate_actions.rs

@@ -85,6 +85,12 @@ impl PtyPort for FakePty {
     fn scrollback(&self, _handle: &PtyHandle) -> Result<Vec<u8>, PtyError> {
         Ok(Vec::new())
     }
+    async fn wait(&self, _handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
+        Ok(ExitStatus { code: Some(0) })
+    }
+    fn try_wait(&self, _handle: &PtyHandle) -> Result<Option<ExitStatus>, PtyError> {
+        Ok(Some(ExitStatus { code: Some(0) }))
+    }
     async fn kill(&self, handle: &PtyHandle) -> Result<ExitStatus, PtyError> {
         self.kills.lock().unwrap().push(handle.session_id);
         Ok(ExitStatus { code: Some(0) })