feat(agent): backend hot-swap profil (A0+A1) + inventaire reprise session (B1) — L15

Cadrage Architecture §15 (figé) : « agent = entité à session persistante ».

- A0 (domaine) : Agent::with_profile, LayoutTree::leaf, event AgentProfileChanged
  (+ DTO miroir DomainEventDto camelCase).
- A1 (application) : use case ChangeAgentProfile — no-op si profil identique,
  mutation manifeste, nettoyage conversation_id/agent_was_running sur layouts
  persistés, swap à chaud (kill PTY + relance même cellule via composition de
  LaunchAgent), event AgentProfileChanged. Décision : repartir à neuf (on garde
  .md + mémoire, on jette l'historique de conversation).
- B1 (application) : use case ListResumableAgents (lecture seule) — inventaire des
  cellules was_running||conversation_id, resume_supported selon profil, best-effort.

Aucun nouveau port/adapter (composition de l'existant). Hexagonal strict.
Tests : domaine 11 + app-tauri dto + ChangeAgentProfile 9 + ListResumableAgents 8,
suite application complète verte (0 régression).

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

crates/domain/src/agent.rs

@@ -107,6 +107,16 @@ impl Agent {
         })
     }
 
+    /// Change le profil runtime de l'agent. Le contexte `.md`, l'origine template
+    /// et la synchronisation sont **inchangés** (décision verrouillée : on garde le
+    /// `.md`/mémoire, on ne touche qu'au moteur). Pur, infaillible (un `ProfileId`
+    /// est déjà un VO validé).
+    #[must_use]
+    pub fn with_profile(mut self, profile_id: ProfileId) -> Self {
+        self.profile_id = profile_id;
+        self
+    }
+
     /// Returns a copy of this agent carrying the given assigned skills,
     /// deduplicated by `skill_id` (keeping first occurrence).
     #[must_use]

crates/domain/src/events.rs

@@ -1,7 +1,7 @@
 //! Domain events published on the [`crate::ports::EventBus`] and relayed to the
 //! presentation layer (ARCHITECTURE §3.2).
 
-use crate::ids::{AgentId, ProjectId, SessionId, SkillId, TemplateId};
+use crate::ids::{AgentId, ProfileId, ProjectId, SessionId, SkillId, TemplateId};
 use crate::memory::MemorySlug;
 use crate::template::TemplateVersion;
 
@@ -32,6 +32,13 @@ pub enum DomainEvent {
         /// Exit code.
         code: i32,
     },
+    /// An agent's runtime profile was changed (hot-swap of the AI engine).
+    AgentProfileChanged {
+        /// The agent.
+        agent_id: AgentId,
+        /// The new runtime profile it now uses.
+        profile_id: ProfileId,
+    },
     /// A template was updated (content changed, version bumped).
     TemplateUpdated {
         /// The template.

crates/domain/src/layout.rs

@@ -620,6 +620,24 @@ impl LayoutTree {
         out
     }
 
+    /// Retrouve la [`LeafCell`] portant l'identifiant `node`.
+    ///
+    /// Renvoie `None` si aucun node ne porte cet id, **ou** si le node existe mais
+    /// est un split/grid (pas une feuille). Traversée pure en lecture seule, dans
+    /// le même esprit que [`Self::agent_leaves`] / [`Self::session_in_leaf`].
+    #[must_use]
+    pub fn leaf(&self, node: NodeId) -> Option<&LeafCell> {
+        fn find(n: &LayoutNode, id: NodeId) -> Option<&LeafCell> {
+            match n {
+                LayoutNode::Leaf(leaf) if leaf.id == id => Some(leaf),
+                LayoutNode::Leaf(_) => None,
+                LayoutNode::Split(split) => split.children.iter().find_map(|c| find(&c.node, id)),
+                LayoutNode::Grid(grid) => grid.cells.iter().find_map(|c| find(&c.node, id)),
+            }
+        }
+        find(&self.root, node)
+    }
+
     /// Returns `Ok(Some(session))` / `Ok(None)` for the session held by the leaf
     /// `id`, or [`LayoutError::NodeNotFound`] if no such leaf exists.
     fn session_in_leaf(&self, id: NodeId) -> Result<Option<SessionId>, LayoutError> {