fix(view-windows): réconcilier l'état des fenêtres détachées au boot (#50)

Branche le consommateur frontend sur la commande backend
`list_open_view_windows` : le port window expose la liste des fenêtres
de panneaux détachées réellement ouvertes côté OS, l'adaptateur Tauri
(et son double mock) l'implémente, et `ProjectsView` réconcilie le
placement des vues au démarrage à partir de ce snapshot au lieu de
supposer un état. Couvre `viewPlacement` et la réconciliation par des
tests dédiés.

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

frontend/src/features/projects/viewPlacement.test.ts

@@ -0,0 +1,89 @@
+/**
+ * #50 — startup reconciliation of `placements` with the detached view windows
+ * already open at the OS level. Unit-tests the pure `isDetachablePanel` guard
+ * and `reconcileDetachedWindows`, covering every Architect invariant:
+ * only-visible, known-detachable-only (projects/unknown excluded), and the
+ * no-clobber rule (never overwrite a non-closed placement).
+ */
+import { describe, it, expect } from "vitest";
+
+import type { ViewWindowSnapshot } from "@/ports";
+import {
+  isDetachablePanel,
+  reconcileDetachedWindows,
+  type ViewPlacements,
+} from "./viewPlacement";
+
+const snap = (
+  panel: string,
+  visible = true,
+): ViewWindowSnapshot => ({ panel, label: panel, visible });
+
+describe("isDetachablePanel (#50)", () => {
+  it("accepts every known panel except projects", () => {
+    expect(isDetachablePanel("git")).toBe(true);
+    expect(isDetachablePanel("tickets")).toBe(true);
+    expect(isDetachablePanel("memory")).toBe(true);
+  });
+
+  it("excludes projects (main-window-only chrome) and unknown panels", () => {
+    expect(isDetachablePanel("projects")).toBe(false);
+    expect(isDetachablePanel("bogus")).toBe(false);
+    expect(isDetachablePanel("")).toBe(false);
+  });
+});
+
+describe("reconcileDetachedWindows (#50)", () => {
+  it("marks a visible detachable snapshot as detached from an empty state", () => {
+    const next = reconcileDetachedWindows({}, [snap("git")]);
+    expect(next).toEqual({ git: "detached" });
+  });
+
+  it("reconciles several panels at once", () => {
+    const next = reconcileDetachedWindows({}, [snap("git"), snap("tickets")]);
+    expect(next).toEqual({ git: "detached", tickets: "detached" });
+  });
+
+  it("ignores non-visible snapshots", () => {
+    const prev: ViewPlacements = {};
+    const next = reconcileDetachedWindows(prev, [snap("git", false)]);
+    expect(next).toBe(prev); // referentially unchanged
+  });
+
+  it("excludes the projects panel", () => {
+    const prev: ViewPlacements = {};
+    const next = reconcileDetachedWindows(prev, [snap("projects")]);
+    expect(next).toBe(prev);
+  });
+
+  it("ignores unknown panel ids", () => {
+    const prev: ViewPlacements = {};
+    const next = reconcileDetachedWindows(prev, [snap("bogus")]);
+    expect(next).toBe(prev);
+  });
+
+  it("never clobbers a non-closed placement (floating/dock/detached preserved)", () => {
+    const prev: ViewPlacements = {
+      git: "floating",
+      tickets: { dock: "left" },
+      memory: "detached",
+    };
+    const next = reconcileDetachedWindows(prev, [
+      snap("git"),
+      snap("tickets"),
+      snap("memory"),
+    ]);
+    expect(next).toBe(prev); // nothing changed → same reference
+  });
+
+  it("reconciles only the closed panels, leaving others intact", () => {
+    const prev: ViewPlacements = { git: "floating" };
+    const next = reconcileDetachedWindows(prev, [snap("git"), snap("agents")]);
+    expect(next).toEqual({ git: "floating", agents: "detached" });
+  });
+
+  it("returns the same reference when there is nothing to reconcile", () => {
+    const prev: ViewPlacements = {};
+    expect(reconcileDetachedWindows(prev, [])).toBe(prev);
+  });
+});