feat(workstate): snapshot des délégations en file par agent (Lot B backend)

Ajoute un port de lecture ségrégué `AgentQueueSnapshot` (ISP) distinct du
`AgentMailbox` mutant : il expose `queue_for(agent)` qui renvoie des
`QueuedTicketSnapshot` clonés, ordonnés FIFO, avec position recalculée
(0 = tête). Observer la file ne la mute jamais ; le one-shot reply sender
reste dans l'adaptateur.

- domain : value object `QueuedTicketSnapshot` + trait `AgentQueueSnapshot`
  (object-safe, partagé en `Arc<dyn …>`).
- infrastructure : `InMemoryMailbox` implémente la vue lecture en plus de la
  vue mutation ; positions recalculées à chaque appel.
- application : le read-model work-state liste les délégations en attente via
  ce port, troncature de l'aperçu de tâche en conservant la longueur d'origine.
- app-tauri : DTO `camelCase` des tickets en file câblé dans l'état.

Tests verts : domain mailbox (6), infrastructure mailbox (13),
application workstate (12), app-tauri dto_agents (20).

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

crates/domain/src/lib.rs

@@ -82,7 +82,10 @@ pub use profile::{
     McpServerWiring, RateLimitPattern, SessionStrategy,
 };
 
-pub use mailbox::{AgentMailbox, MailboxError, PendingReply, Ticket, TicketId};
+pub use mailbox::{
+    AgentMailbox, AgentQueueSnapshot, MailboxError, PendingReply, QueuedTicketSnapshot, Ticket,
+    TicketId,
+};
 
 pub use conversation::{
     Conversation, ConversationError, ConversationId, ConversationParty, ConversationRegistry,

crates/domain/src/mailbox.rs

@@ -33,6 +33,47 @@ use crate::conversation::ConversationId;
 use crate::ids::AgentId;
 use crate::input::InputSource;
 
+/// A read-only, cloned view of one queued [`Ticket`] in a target agent's FIFO.
+///
+/// Carries **only the data** of a ticket (never the one-shot reply sender, which
+/// stays inside the adapter), plus its `position` in the FIFO at snapshot time
+/// (`0` = head). Pure value object used by the [`AgentQueueSnapshot`] read port so
+/// the work-state read model can list pending delegations without touching the
+/// mutating [`AgentMailbox`] surface (ISP).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct QueuedTicketSnapshot {
+    /// Stable id of the queued ticket.
+    pub id: TicketId,
+    /// The origin of the input (Human or a delegating Agent).
+    pub source: InputSource,
+    /// The conversation thread this task enters.
+    pub conversation: ConversationId,
+    /// Display name (or id) of the requester.
+    pub requester: String,
+    /// The full task/message text (preview/truncation is the caller's concern).
+    pub task: String,
+    /// Position in the FIFO at snapshot time (`0` = head, recomputed each call).
+    pub position: u32,
+}
+
+/// Read-only inspection port over the per-agent delegation FIFO.
+///
+/// Segregated from the mutating [`AgentMailbox`] (Interface Segregation): the
+/// work-state read model depends on this port to *observe* the queue, never on
+/// `enqueue`/`resolve`/`cancel`. Implementations return **cloned** snapshots in
+/// FIFO order with recomputed positions; observing the queue must never mutate it.
+///
+/// Object-safe (`&self`) so the application layer holds it as
+/// `Arc<dyn AgentQueueSnapshot>`; one concrete `InMemoryMailbox` can be shared as
+/// both an [`AgentMailbox`] (mutation) and an [`AgentQueueSnapshot`] (read) view.
+pub trait AgentQueueSnapshot: Send + Sync {
+    /// Returns a cloned, FIFO-ordered snapshot of `agent`'s queued tickets.
+    ///
+    /// An agent with no queue yields an empty `Vec`. Positions are recomputed from
+    /// the current order (`0` = head). Pure read: the queue is left untouched.
+    fn queue_for(&self, agent: AgentId) -> Vec<QueuedTicketSnapshot>;
+}
+
 /// Identifies one queued [`Ticket`] within a target agent's mailbox.
 ///
 /// Newtype around [`uuid::Uuid`]; minted by the adapter on `enqueue`. It is **never
@@ -310,4 +351,22 @@ mod tests {
         let a = AgentId::from_uuid(uuid::Uuid::from_u128(1));
         assert_ne!(MailboxError::NoPendingRequest(a), MailboxError::Cancelled);
     }
+
+    #[test]
+    fn queued_ticket_snapshot_carries_ticket_data_and_position() {
+        let conv = ConversationId::from_uuid(uuid::Uuid::from_u128(3));
+        let from = AgentId::from_uuid(uuid::Uuid::from_u128(4));
+        let snap = QueuedTicketSnapshot {
+            id: TicketId::from_uuid(uuid::Uuid::from_u128(8)),
+            source: InputSource::agent(from),
+            conversation: conv,
+            requester: "Main".to_owned(),
+            task: "delegate".to_owned(),
+            position: 2,
+        };
+        assert_eq!(snap.source.as_agent(), Some(from));
+        assert_eq!(snap.conversation, conv);
+        assert_eq!(snap.position, 2);
+        assert_eq!(snap.task, "delegate");
+    }
 }