feat(agent): surfacer reply dans le writer wire .response.json (D6b) — §17

Ferme le canal fichier de la messagerie inter-agents : un agent qui délègue
via le protocole .ideai/requests reçoit désormais le CONTENU de la réponse,
plus seulement l'ACK de cycle de vie.

- OrchestratorResponse gagne reply: Option<String> (skip_serializing_if
  None, camelCase). success() porte le reply ; failure() => None.
- dispatch_file passe out.reply (de l'OrchestratorOutcome D6) à success.

Champ additif : un .response.json legacy sans reply reste valide ; une
commande non-ask (agent.run, spawn_agent...) => clé reply absente du JSON.

Tests (QA) : +4 verts — ask => reply présent ET detail coexistent ;
non-ask => clé absente (garde anti-always-green sur l'absence littérale) ;
round-trip legacy ; failure => absent. cargo test --workspace : 824 passed.

Orchestration structurée bouclée : in-process (D6) + protocole fichier (D6b).

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

crates/infrastructure/src/orchestrator/mod.rs

@@ -56,15 +56,22 @@ pub struct OrchestratorResponse {
     /// Human-readable failure reason (`ok == false`).
     #[serde(skip_serializing_if = "Option::is_none")]
     pub error: Option<String>,
+    /// The queried agent's reply content, when the dispatched command produced one
+    /// (e.g. `ask` / `agent.message`). Absent for commands that return no content
+    /// (e.g. `agent.run`), so an existing `*.response.json` without this key stays
+    /// valid.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub reply: Option<String>,
 }
 
 impl OrchestratorResponse {
-    fn success(action: String, detail: String) -> Self {
+    fn success(action: String, detail: String, reply: Option<String>) -> Self {
         Self {
             ok: true,
             action: Some(action),
             detail: Some(detail),
             error: None,
+            reply,
         }
     }
     fn failure(action: Option<String>, error: String) -> Self {
@@ -73,6 +80,7 @@ impl OrchestratorResponse {
             action,
             detail: None,
             error: Some(error),
+            reply: None,
         }
     }
 }
@@ -258,6 +266,7 @@ async fn dispatch_file(
         Ok(out) => OrchestratorResponse::success(
             action.unwrap_or_else(|| "unknown".to_owned()),
             out.detail,
+            out.reply,
         ),
         Err(e) => OrchestratorResponse::failure(action, e.to_string()),
     }