feat(frontend): viewer humain fil-par-paire en lecture seule (LS7)

Frontend pur, lecture seule, consomme read_conversation_page (LS6) ; aucun changement backend.
- adapters : conversation.ts (gateway) + conversationNormalization.ts.
- features/conversations : useConversationThread, ConversationViewer, index.
- domain (types LS7), ports (port + Gateways.conversation), adapters/index, mock (+ clé inventaire).
- features/workstate : ProjectWorkStatePanel prop onOpenConversation.
- features/projects : ProjectsView swap viewer.
- tests (QA, verts) : conversationNormalization, mock/conversationGateway,
  useConversationThread, ConversationViewer, ProjectsView.ls7. tsc 0, vitest 443/443 (+36).

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

frontend/src/adapters/mock/conversationGateway.test.ts

@@ -0,0 +1,144 @@
+/**
+ * LS7 — `MockConversationGateway` real pagination, mirroring the LS6 backend
+ * slicing (strict anchor, clamp `[1,200]`/default 50, `hasMore`, `nextAnchor` =
+ * last/most-recent turn of the page, full text preserved).
+ */
+import { describe, it, expect, beforeEach } from "vitest";
+
+import type { TurnView } from "@/domain";
+import { MockConversationGateway } from "./index";
+
+const P = "proj";
+const C = "conv";
+
+function turn(n: number, text = `texte ${n}`): TurnView {
+  return {
+    id: `t${n}`,
+    atMs: 1_700_000_000_000 + n,
+    role: n % 2 === 0 ? "response" : "prompt",
+    source: { kind: "human" },
+    text,
+    textLen: text.length,
+  };
+}
+
+function seed(gw: MockConversationGateway, count: number): void {
+  gw._setTurns(
+    P,
+    C,
+    Array.from({ length: count }, (_, i) => turn(i + 1)),
+  );
+}
+
+let gw: MockConversationGateway;
+beforeEach(() => {
+  gw = new MockConversationGateway();
+});
+
+describe("MockConversationGateway.readPage", () => {
+  it("backward with no anchor returns the LAST page (most recent), oldest→newest", async () => {
+    seed(gw, 10);
+    const page = await gw.readPage(P, C, { direction: "backward", limit: 4 });
+    expect(page.turns.map((t) => t.id)).toEqual(["t7", "t8", "t9", "t10"]);
+    expect(page.hasMore).toBe(true); // older turns exist
+    expect(page.nextAnchor).toBe("t10"); // last/most-recent of the page
+  });
+
+  it("backward anchored returns the strictly-older turns, ascending", async () => {
+    seed(gw, 10);
+    const page = await gw.readPage(P, C, {
+      direction: "backward",
+      anchor: "t7",
+      limit: 3,
+    });
+    // Strictly before t7, closest three: t4,t5,t6 — ascending.
+    expect(page.turns.map((t) => t.id)).toEqual(["t4", "t5", "t6"]);
+    expect(page.hasMore).toBe(true); // t1..t3 remain
+    expect(page.nextAnchor).toBe("t6");
+  });
+
+  it("forward anchored returns the strictly-newer turns, ascending", async () => {
+    seed(gw, 10);
+    const page = await gw.readPage(P, C, {
+      direction: "forward",
+      anchor: "t4",
+      limit: 3,
+    });
+    expect(page.turns.map((t) => t.id)).toEqual(["t5", "t6", "t7"]);
+    expect(page.hasMore).toBe(true);
+    expect(page.nextAnchor).toBe("t7");
+  });
+
+  it("forward with no anchor returns the FIRST page (oldest)", async () => {
+    seed(gw, 10);
+    const page = await gw.readPage(P, C, { direction: "forward", limit: 4 });
+    expect(page.turns.map((t) => t.id)).toEqual(["t1", "t2", "t3", "t4"]);
+    expect(page.hasMore).toBe(true);
+  });
+
+  it("clamps the limit to [1, 200] and defaults to 50", async () => {
+    seed(gw, 60);
+    // Default (no limit) ⇒ 50.
+    const def = await gw.readPage(P, C, { direction: "backward" });
+    expect(def.turns).toHaveLength(50);
+    // 0 ⇒ default 50.
+    const zero = await gw.readPage(P, C, { direction: "backward", limit: 0 });
+    expect(zero.turns).toHaveLength(50);
+    // Over 200 ⇒ clamped (only 60 exist, so all 60 here, proving > limit never throws).
+    const big = await gw.readPage(P, C, { direction: "backward", limit: 999 });
+    expect(big.turns).toHaveLength(60);
+    // A non-positive (negative) limit is treated as "unset" ⇒ default 50.
+    const neg = await gw.readPage(P, C, { direction: "backward", limit: -5 });
+    expect(neg.turns).toHaveLength(50);
+    // An explicit positive 1 is honoured (lower bound of the clamp).
+    const one = await gw.readPage(P, C, { direction: "forward", limit: 1 });
+    expect(one.turns).toHaveLength(1);
+  });
+
+  it("clamps a limit above 200 down to 200", async () => {
+    seed(gw, 250);
+    const page = await gw.readPage(P, C, { direction: "forward", limit: 500 });
+    expect(page.turns).toHaveLength(200);
+    expect(page.hasMore).toBe(true);
+  });
+
+  it("returns an empty page for an empty conversation", async () => {
+    const page = await gw.readPage(P, C, { direction: "backward" });
+    expect(page.turns).toEqual([]);
+    expect(page.hasMore).toBe(false);
+    expect(page.nextAnchor).toBeUndefined();
+  });
+
+  it("returns an empty page for an unknown anchor", async () => {
+    seed(gw, 5);
+    const page = await gw.readPage(P, C, {
+      direction: "forward",
+      anchor: "does-not-exist",
+    });
+    expect(page.turns).toEqual([]);
+    expect(page.hasMore).toBe(false);
+  });
+
+  it("hasMore is false when the page reaches the thread end", async () => {
+    seed(gw, 3);
+    const page = await gw.readPage(P, C, { direction: "backward", limit: 50 });
+    expect(page.turns.map((t) => t.id)).toEqual(["t1", "t2", "t3"]);
+    expect(page.hasMore).toBe(false);
+  });
+
+  it("preserves the full (unbounded) turn text", async () => {
+    const big = "Z".repeat(30_000);
+    gw._setTurns(P, C, [turn(1, big)]);
+    const page = await gw.readPage(P, C, { direction: "backward" });
+    expect(page.turns[0].text).toHaveLength(30_000);
+  });
+
+  it("isolates threads per (project, conversation)", async () => {
+    gw._setTurns(P, C, [turn(1)]);
+    gw._setTurns(P, "other", [turn(2), turn(3)]);
+    const a = await gw.readPage(P, C, { direction: "backward" });
+    const b = await gw.readPage(P, "other", { direction: "backward" });
+    expect(a.turns.map((t) => t.id)).toEqual(["t1"]);
+    expect(b.turns.map((t) => t.id)).toEqual(["t2", "t3"]);
+  });
+});