fix(delegation): résout idea_ask_agent quand la cible revient au prompt sans idea_reply

Introduit le seam TurnResolution : sur prompt-ready, après un délai de grâce,
la délégation en attente est résolue de façon typée plutôt que de rester bloquée
indéfiniment (jusquà 24h). Couvre domain (mailbox), infrastructure (mailbox/input)
et application (orchestrator/error), avec tests étendus.

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

crates/application/src/error.rs

@@ -57,6 +57,18 @@ pub enum AppError {
         node_id: NodeId,
     },
 
+    /// The delegation target finished its turn and **returned to its prompt without
+    /// calling `idea_reply`**, so the rendezvous could produce no answer. Surfaced
+    /// promptly (after a short grace window) instead of blocking the caller until the
+    /// long safety timeout. **Retryable**: the caller may re-ask, ideally reminding the
+    /// target to render its result via `idea_reply` (never plain text). Carries the
+    /// target's display name.
+    #[error(
+        "agent {0} returned to its prompt without calling idea_reply (no answer was \
+         rendered); retry the request and ensure the agent replies via idea_reply"
+    )]
+    TargetReturnedNoReply(String),
+
     /// An unexpected internal error.
     #[error("internal error: {0}")]
     Internal(String),
@@ -76,6 +88,7 @@ impl AppError {
             Self::Git(_) => "GIT",
             Self::Remote(_) => "REMOTE",
             Self::AgentAlreadyRunning { .. } => "AGENT_ALREADY_RUNNING",
+            Self::TargetReturnedNoReply(_) => "TARGET_RETURNED_NO_REPLY",
             Self::Internal(_) => "INTERNAL",
         }
     }