feat(terminals): durcit le portail d'écriture de délégation

Fiabilise la livraison des délégations inter-agents dans le terminal :
écriture par chunks UTF-8 bornés (512 o, délai 8 ms) pour éviter les
comportements de paste/drop des TUI sur agents froids, et réconciliation
de l'attachement front (frontAttachedAgentRef / reconcileFrontAttachment)
pour ne reporter « front attaché » qu'une fois les DelegationReady
réellement consommés. Tests vitest associés.

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

frontend/src/features/terminals/useWritePortal.test.tsx

@@ -120,6 +120,25 @@ describe("useWritePortal (§20)", () => {
     ]);
   });
 
+  it("chunks long delegated text before submit and acks after the submit", async () => {
+    const { system, input, view } = setup();
+    const { handle, writes } = makeHandle();
+    act(() => view.result.current.portal.bindHandle(handle));
+    const text = `début ${"x".repeat(1200)} fin`;
+
+    await act(async () => {
+      system.emit(PROFILELESS("t1", text));
+      await vi.runAllTimersAsync();
+    });
+
+    expect(writes.length).toBeGreaterThan(2);
+    expect(writes[writes.length - 1]).toBe("\r");
+    expect(writes.slice(0, -1).join("")).toBe(text);
+    expect(input.delivered).toEqual([
+      { projectId: "p1", agentId: "ag1", ticket: "t1" },
+    ]);
+  });
+
   it("K=2 race → exactly two \\x7f backspaces before the text (never Ctrl-U)", async () => {
     const { system, view } = setup();
     const { handle, writes } = makeHandle();
@@ -255,6 +274,26 @@ describe("useWritePortal (§20)", () => {
     expect(input.delivered.length).toBe(1);
   });
 
+  it("reports front attachment only after the delegation subscription is ready", async () => {
+    const { input, view } = setup();
+    const { handle } = makeHandle();
+
+    act(() => view.result.current.portal.bindHandle(handle));
+    expect(input.frontAttached).toEqual([]);
+
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    expect(input.frontAttached).toEqual([{ agentId: "ag1", attached: true }]);
+
+    act(() => view.result.current.portal.unbindHandle());
+    expect(input.frontAttached).toEqual([
+      { agentId: "ag1", attached: true },
+      { agentId: "ag1", attached: false },
+    ]);
+  });
+
   it("is inert for a plain (agent-less) cell", async () => {
     const { system, view } = setup(null);
     const { handle, writes } = makeHandle();