feat(terminals): reprise de conversation par cellule + fix ordre d'écriture

Permet de recharger la conversation CLI précédente de chaque cellule à la
réouverture du projet, de façon universelle (indépendant du modèle/CLI).

- profil AgentRuntime: bloc déclaratif optionnel `session { assignFlag, resumeFlag }`
- LeafCell: `conversationId` (persistant, distinct du SessionId PTY) + `agentWasRunning`
- runtime: SessionPlan (None/Assign/Resume) + composition pure des args
- LaunchAgent: décide Assign vs Resume, génère l'UUID, remonte l'id assigné
  (persistance par l'appelant via setCellConversation — découplage SRP)
- close: SnapshotRunningAgents fige `agentWasRunning` avant le kill-all
  (statut clot/en cours universel, sans parsing CLI)
- SessionInspector: port optionnel best-effort + adapter ClaudeTranscriptInspector
- popup de reprise par cellule (statut + sujet/tokens si dispo), intercalée
  avant le Resume auto, jamais sur le chemin reattach

fix(terminals): sérialise les écritures PTY (file FIFO par handle) — corrige
les caractères mélangés/accents dus au réordonnancement des invoke Tauri concurrents

fix(layout): l'opération `move` préservait mal les champs du leaf (perdait `agent`)

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

frontend/src/features/layout/setCellAgent.test.tsx

@@ -2,7 +2,7 @@
  * #3 — Agent dropdown per cell: setCellAgent persists in the layout, and the
  * terminal re-mounts with the agent opener; "Plain" reverts to a plain terminal.
  */
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import { render, screen, waitFor, fireEvent } from "@testing-library/react";
 
 import type { Gateways } from "@/ports";
@@ -19,10 +19,11 @@ function renderGrid(
   layout: MockLayoutGateway,
   agent: MockAgentGateway,
   projectId = "p1",
+  terminal: MockTerminalGateway = new MockTerminalGateway(),
 ) {
   const gateways = {
     layout,
-    terminal: new MockTerminalGateway(),
+    terminal,
     agent,
   } as unknown as Gateways;
   return render(
@@ -134,6 +135,114 @@ describe("setCellAgent (agent dropdown per cell)", () => {
     });
   });
 
+  it("changing the agent resets the cell session to null (Bug #3)", async () => {
+    const layout = new MockLayoutGateway();
+    const agent = new MockAgentGateway();
+    const a = await agent.createAgent("p1", { name: "MyAgent", profileId: "p" });
+
+    // Pre-set a running session on the leaf (as if a plain terminal had opened).
+    const tree = await layout.loadLayout("p1");
+    const leafId = leaves(tree)[0].id;
+    await layout.mutateLayout("p1", {
+      type: "setSession",
+      target: leafId,
+      session: "old-session",
+    });
+
+    renderGrid(layout, agent);
+    await waitFor(() => expect(screen.getByRole("combobox")).toBeTruthy());
+
+    fireEvent.change(screen.getByRole("combobox"), { target: { value: a.id } });
+
+    await waitFor(async () => {
+      const fresh = await layout.loadLayout("p1");
+      const l = leaves(fresh)[0];
+      expect(l.agent).toBe(a.id);
+      // The stale session must be cleared so the new agent opens fresh.
+      expect(l.session === null || l.session === undefined).toBe(true);
+    });
+  });
+
+  it("changing the agent kills the previous PTY (Bug #3)", async () => {
+    const layout = new MockLayoutGateway();
+    const agent = new MockAgentGateway();
+    const terminal = new MockTerminalGateway();
+    const closeSpy = vi.spyOn(terminal, "closeTerminal");
+    const a = await agent.createAgent("p1", { name: "MyAgent", profileId: "p" });
+
+    const tree = await layout.loadLayout("p1");
+    const leafId = leaves(tree)[0].id;
+    await layout.mutateLayout("p1", {
+      type: "setSession",
+      target: leafId,
+      session: "old-session",
+    });
+
+    renderGrid(layout, agent, "p1", terminal);
+    await waitFor(() => expect(screen.getByRole("combobox")).toBeTruthy());
+
+    fireEvent.change(screen.getByRole("combobox"), { target: { value: a.id } });
+
+    await waitFor(() => {
+      expect(closeSpy).toHaveBeenCalledWith("old-session");
+    });
+  });
+
+  it("does not kill any PTY when the cell had no session (Bug #3)", async () => {
+    const layout = new MockLayoutGateway();
+    const agent = new MockAgentGateway();
+    const terminal = new MockTerminalGateway();
+    const closeSpy = vi.spyOn(terminal, "closeTerminal");
+    const a = await agent.createAgent("p1", { name: "MyAgent", profileId: "p" });
+
+    renderGrid(layout, agent, "p1", terminal);
+    await waitFor(() => expect(screen.getByRole("combobox")).toBeTruthy());
+
+    fireEvent.change(screen.getByRole("combobox"), { target: { value: a.id } });
+
+    await waitFor(async () => {
+      const fresh = await layout.loadLayout("p1");
+      expect(leaves(fresh)[0].agent).toBe(a.id);
+    });
+    expect(closeSpy).not.toHaveBeenCalled();
+  });
+
+  it("closing a cell kills the dropped cell's PTY (no orphan)", async () => {
+    const layout = new MockLayoutGateway();
+    const agent = new MockAgentGateway();
+    const terminal = new MockTerminalGateway();
+    const closeSpy = vi.spyOn(terminal, "closeTerminal");
+
+    // Split the root into two cells, then give the second a running session.
+    const tree = await layout.loadLayout("p1");
+    const rootId = leaves(tree)[0].id;
+    const afterSplit = await layout.mutateLayout("p1", {
+      type: "split",
+      target: rootId,
+      direction: "row",
+      newLeaf: "leaf-b",
+      container: "split-c",
+    });
+    const droppedId = leaves(afterSplit)[1].id;
+    await layout.mutateLayout("p1", {
+      type: "setSession",
+      target: droppedId,
+      session: "dropped-session",
+    });
+
+    renderGrid(layout, agent, "p1", terminal);
+
+    // Close the SECOND cell: keep the first, drop the second → its PTY dies.
+    await waitFor(() => {
+      expect(screen.getByLabelText(`close ${droppedId}`)).toBeTruthy();
+    });
+    fireEvent.click(screen.getByLabelText(`close ${droppedId}`));
+
+    await waitFor(() => {
+      expect(closeSpy).toHaveBeenCalledWith("dropped-session");
+    });
+  });
+
   it("agent selector shows project agents as options", async () => {
     const layout = new MockLayoutGateway();
     const agent = new MockAgentGateway();