feat(inter-agent): backend des annonces live d'agent (B0-B3)

Redémarre le ticket #4 sur la base develop. Émission d'annonces live d'un
agent vers l'UI, distinctes du Final de délégation :

- domain: ReplyEvent::Announcement/Final et DomainEvent::AgentAnnouncement
  (events.rs), port d'émission (ports.rs), gating de readiness (readiness.rs).
- application: mapping des événements structurés en annonces
  (agent/structured.rs, agent/mod.rs, lib.rs) et relais côté orchestrateur
  (orchestrator/service.rs).
- infrastructure/session: parse des annonces + fix du Final pour Claude et
  Codex, propagé aux adaptateurs et à la conformance
  (claude.rs, codex.rs, conformance.rs, mod.rs, process.rs, sandbox_e2e.rs).
- app-tauri: relais Tauri des annonces vers le front (events.rs, chat.rs).

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

crates/domain/src/events.rs

@@ -1,6 +1,7 @@
 //! Domain events published on the [`crate::ports::EventBus`] and relayed to the
 //! presentation layer (ARCHITECTURE §3.2).
 
+use crate::conversation::ConversationParty;
 use crate::ids::{AgentId, IssueId, ProfileId, ProjectId, SessionId, SkillId, TaskId, TemplateId};
 use crate::issue::{IssueLinkKind, IssuePriority, IssueRef, IssueStatus, IssueVersion};
 use crate::mailbox::TicketId;
@@ -156,6 +157,22 @@ pub enum DomainEvent {
         /// Number of bytes in the reply content (preview metric, not the payload).
         reply_len: usize,
     },
+    /// Intermediate assistant announcement emitted live during an inter-agent
+    /// structured turn. Ephemeral observability event: never persisted, never terminal.
+    AgentAnnouncement {
+        /// Owning project.
+        project_id: ProjectId,
+        /// Human or source agent that requested the turn.
+        requester: ConversationParty,
+        /// Target agent producing the announcement.
+        target: AgentId,
+        /// FIFO ticket correlating this turn.
+        ticket: TicketId,
+        /// Announcement text.
+        text: String,
+        /// Wall-clock timestamp in epoch milliseconds.
+        at_ms: u64,
+    },
     /// An agent's process exited.
     AgentExited {
         /// The agent.