chore(wip): checkpoint P8/C avant chantier Codex inter-agents

Sauvegarde de l'arbre de travail en cours (persistance P8, conversations
C-series, write-portal frontend, médiation d'entrée) avant d'attaquer le
support de la délégation inter-agents pour les profils Codex.

Le round-trip inter-agent question/réponse est couvert sans tokens par
les tests loopback existants (state::mcp_e2e_loopback_tests).

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

crates/domain/tests/layout.rs

@@ -837,12 +837,7 @@ fn move_session_preserves_resume_fields_on_both_leaves() {
 // ---------------------------------------------------------------------------
 
 /// Builds an agent-bearing leaf with explicit resume signals.
-fn agent_leaf_full(
-    id: u128,
-    agent: u128,
-    conv: Option<&str>,
-    running: bool,
-) -> LeafCell {
+fn agent_leaf_full(id: u128, agent: u128, conv: Option<&str>, running: bool) -> LeafCell {
     LeafCell {
         id: node(id),
         session: None,