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.

frontend/src/adapters/mock/index.ts

@@ -401,6 +401,8 @@ export class MockAgentGateway implements AgentGateway {
   private liveSessionByAgent = new Map<string, string>();
   /** Runtime kind per live agent (`agentId → kind`). */
   private liveKindByAgent = new Map<string, "pty" | "structured">();
+  /** Last stopped runtime per agent for idempotent stop. */
+  private stoppedByAgent = new Map<string, StoppedLiveAgent>();
   /** Retained structured reply chunks per live chat session. */
   private chatScrollback = new Map<string, ReplyChunk[]>();
   /** Persisted custom chat drafts keyed by project/layout/node. */
@@ -460,6 +462,7 @@ export class MockAgentGateway implements AgentGateway {
         nodeId,
         sessionId: this.liveSessionByAgent.get(agentId)!,
         kind: this.liveKindByAgent.get(agentId) ?? "pty",
+        runtimeState: "running",
       }));
   }
 
@@ -509,6 +512,7 @@ export class MockAgentGateway implements AgentGateway {
       nodeId,
       sessionId,
       kind: this.liveKindByAgent.get(agentId) ?? "pty",
+      runtimeState: "running",
     };
   }
 
@@ -523,6 +527,8 @@ export class MockAgentGateway implements AgentGateway {
     }
     const sessionId = this.liveSessionByAgent.get(agentId);
     if (!sessionId) {
+      const stopped = this.stoppedByAgent.get(agentId);
+      if (stopped) return stopped;
       const err: GatewayError = {
         code: "NOT_FOUND",
         message: `agent ${agentId} has no live session`,
@@ -537,7 +543,14 @@ export class MockAgentGateway implements AgentGateway {
     this.liveByAgent.delete(agentId);
     const kind = this.liveKindByAgent.get(agentId) ?? "pty";
     this.liveKindByAgent.delete(agentId);
-    return { agentId, sessionId, kind };
+    const stopped: StoppedLiveAgent = {
+      agentId,
+      sessionId,
+      kind,
+      runtimeState: "stopped",
+    };
+    this.stoppedByAgent.set(agentId, stopped);
+    return stopped;
   }
 
   async createAgent(projectId: string, input: CreateAgentInput): Promise<Agent> {
@@ -781,6 +794,7 @@ export class MockAgentGateway implements AgentGateway {
       this.liveByAgent.set(agentId, options.nodeId);
       this.liveSessionByAgent.set(agentId, sessionId);
       this.liveKindByAgent.set(agentId, "pty");
+      this.stoppedByAgent.delete(agentId);
     }
     const clearLive = () => {
       if (this.liveByAgent.get(agentId) === options.nodeId) {
@@ -807,7 +821,7 @@ export class MockAgentGateway implements AgentGateway {
     // Simulate session assignment (T4b): a fresh cell (no conversation id) gets a
     // newly-minted id surfaced on the handle so the caller persists it; a cell
     // that already carries an id resumes it and nothing new is assigned.
-    if (!options.conversationId) {
+    if (options.freshStart || !options.conversationId) {
       return {
         ...handle,
         assignedConversationId: `mock-conversation-${sessionId}`,
@@ -848,11 +862,12 @@ export class MockAgentGateway implements AgentGateway {
       this.liveByAgent.set(agentId, options.nodeId);
       this.liveSessionByAgent.set(agentId, sessionId);
       this.liveKindByAgent.set(agentId, "structured");
+      this.stoppedByAgent.delete(agentId);
     }
     return {
       sessionId,
       cellKind: "chat",
-      ...(!options.conversationId
+      ...(options.freshStart || !options.conversationId
         ? { assignedConversationId: `mock-conversation-${sessionId}` }
         : {}),
     };