fix(runtime): stop/restart d'agent visible robuste — kill réel, état stopped, relance froide (#196, QA verte)

Solidifie le cycle stop/restart d'un agent visible en cellule:

- terminal/registry: kill effectif de la TUI native et de la CLI custom, arrêt idempotent du live runtime (PTY + structuré), distinction nette « agent stoppé » vs « pas de session ».

- workstate + lifecycle: projection d'un état runtime explicite « stopped » (AgentRuntimeState: running/stopping/stopped/failedStart), réconcilié avec le live state; traitement des courses « agent not found ».

- relance froide via freshStart: repart de zéro sans réattacher une session morte et recharge la configuration courante de l'agent (y compris changement de modèle).

- contrat projeté côté adapters frontend (ports/domain/normalization/mock) pour la consommation UI future (#197/#198), sans surface UI ici.

Tests QA verts: workstate_actions, orchestrator_service stop_agent, agent_lifecycle (reopen/fresh_start), workstate stopped runtime state, vitest adapter stop_live_agent.

crates/application/tests/agent_lifecycle.rs

@@ -1193,6 +1193,7 @@ fn launch_input(agent_id: AgentId) -> LaunchAgentInput {
         mcp_runtime: None,
         allow_structured_alongside_pty: false,
         require_structured: false,
+        fresh_start: false,
     }
 }
 
@@ -2946,6 +2947,33 @@ async fn launch_reopen_with_existing_conversation_id_resumes_without_new_id() {
     );
 }
 
+#[tokio::test]
+async fn launch_fresh_start_ignores_existing_conversation_id_and_mints_new_one() {
+    let (launch, agent, _fs, _pty, _bus, _sessions, _tr, session) = launch_fixture_with_profile(
+        profile_with_session(pid(9), Some("--session-id"), "--resume"),
+        Some(ContextInjectionPlan::Stdin),
+    );
+
+    let mut input = launch_input(agent.id);
+    input.conversation_id = Some("conv-dead-session".to_owned());
+    input.fresh_start = true;
+    let out = launch.execute(input).await.expect("fresh restart launch");
+
+    let expected = Uuid::from_u128(1).to_string();
+    assert_eq!(
+        out.assigned_conversation_id.as_deref(),
+        Some(expected.as_str()),
+        "fresh restart must mint a new conversation id"
+    );
+    assert_eq!(
+        *session.lock().unwrap(),
+        Some(SessionPlan::Assign {
+            conversation_id: expected
+        }),
+        "fresh restart must not reuse the dead conversation id"
+    );
+}
+
 #[tokio::test]
 async fn launch_profile_without_session_block_passes_none() {
     // Non-regression: a profile with no session block behaves exactly as before.