feat(cli): références d'attachments [file n]/[image n] dans le transcript + zone chat redimensionnable — #188 (QA verte)

- Attachments: projection canonique ChatPromptAttachmentDto (référence [file n]/[image n] par compteur de type, ordre d'import) insérée dans le prompt modèle et transportée par ReplyChunk::UserPrompt (attachmentRefs) ; rendu compact côté CustomAgentChatView.
- Resize: la zone chat (LeafView/LayoutGrid) est redimensionnable, taille actuelle conservée par défaut, préférence locale persistée.
- Tests: commands (projection des refs), dto_chat, chat_bridge, CustomAgentChatView, LayoutGrid.chat.

frontend/src/features/agents/CustomAgentChatView.test.tsx

@@ -78,7 +78,7 @@ describe("CustomAgentChatView", () => {
     __resetProjectCliInteractionActivityForTests();
   });
 
-  it("repaints attachment labels from user prompt scrollback", async () => {
+  it("repaints compact attachment refs from legacy user prompt scrollback", async () => {
     const agent = {
       launchAgentChat: vi.fn(),
       reattachAgentChat: vi.fn(async (sessionId: string) => ({
@@ -119,7 +119,68 @@ describe("CustomAgentChatView", () => {
     );
 
     expect(await screen.findByText("describe this")).toBeTruthy();
-    expect(screen.getByText("Fichier: clipboard.png")).toBeTruthy();
+    expect(screen.getByText("[image 1] clipboard.png")).toBeTruthy();
+  });
+
+  it("prefers canonical attachment refs from user prompt scrollback", async () => {
+    const agent = {
+      launchAgentChat: vi.fn(),
+      reattachAgentChat: vi.fn(async (sessionId: string) => ({
+        sessionId,
+        scrollback: [
+          {
+            kind: "userPrompt" as const,
+            text: "compare these",
+            attachments: ["screenshot.png", "error.log"],
+            attachmentRefs: [
+              {
+                reference: "[image 1]",
+                filename: "screenshot.png",
+                mime: "image/png",
+                sizeBytes: 12,
+                readablePath: "/repo/.ideai/attachments/screenshot.png",
+              },
+              {
+                reference: "[file 1]",
+                filename: "error.log",
+                mime: "text/plain",
+                sizeBytes: 34,
+                readablePath: "/repo/.ideai/attachments/error.log",
+              },
+            ],
+          },
+        ],
+      })),
+      sendAgentChat: vi.fn(async () => {}),
+      cancelAgentChat: vi.fn(async () => {}),
+      closeAgentChat: vi.fn(async () => {}),
+    };
+
+    render(
+      <DIProvider
+        gateways={{
+          agent,
+          system: { pickFile: vi.fn(async () => null) },
+        } as unknown as Gateways}
+      >
+        <CustomAgentChatView
+          projectId="project-1"
+          agentId="agent-1"
+          agentName="Worker"
+          profile={profile}
+          cwd="/repo"
+          nodeId="node-1"
+          sessionId="chat-session-1"
+          conversationId="conversation-1"
+          onSessionId={vi.fn()}
+          onConversationId={vi.fn()}
+        />
+      </DIProvider>,
+    );
+
+    expect(await screen.findByText("compare these")).toBeTruthy();
+    expect(screen.getByText("[image 1] screenshot.png")).toBeTruthy();
+    expect(screen.getByText("[file 1] error.log")).toBeTruthy();
   });
 
   it("detaches on unmount then reattaches with missed scrollback chunks", async () => {
@@ -2342,7 +2403,7 @@ describe("CustomAgentChatView", () => {
       },
     );
     expect(screen.getByText("Pièce jointe")).toBeTruthy();
-    expect(screen.getByText("Fichier: paste-image.png")).toBeTruthy();
+    expect(screen.getByText("[image 1] paste-image.png")).toBeTruthy();
   });
 
   it("accepts pasted generic files exposed only through clipboardData.files", async () => {
@@ -2503,7 +2564,7 @@ describe("CustomAgentChatView", () => {
       },
     );
     expect(screen.getByText("prefix inserted")).toBeTruthy();
-    expect(screen.getByText("Fichier: mixed.txt")).toBeTruthy();
+    expect(screen.getByText("[file 1] mixed.txt")).toBeTruthy();
   });
 
   it("deduplicates clipboard files by metadata across clipboard sources and repeated paste", async () => {