fix(chat): restaure le collage des images dans le composer custom CLI (#184)

Le collage d'une image (ex. capture d'écran) échouait en environnement desktop : le presse-papier image n'est souvent pas exposé comme un File synchrone dans clipboardData.files, mais uniquement via l'Async Clipboard API. On ajoute donc un repli sur navigator.clipboard.read() (MIME image/*) quand l'événement de collage ne fournit aucun fichier. Le preventDefault() n'est émis que lorsqu'on a effectivement lu des fichiers issus de l'événement, afin de ne pas bloquer le collage texte quand le repli async ne remonte rien.

- refactor clipboardFiles(event) -> dataTransferFiles(DataTransfer) réutilisable
- dedupeKey robuste pour les images sans nom (mime + taille + contenu base64)
- ReplyChunk::UserPrompt porte désormais les labels d'attachments (DTO + accounting reply_chunk_bytes, skip_serializing_if Vec::is_empty)
- tests ciblés frontend (+219) et backend (chat_bridge/dto/attachments) verts

QA : tests ciblés verts. Réserve : environnement headless, pas de validation manuelle desktop — validation AppImage à confirmer en suivi.

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

frontend/src/features/agents/CustomAgentChatView.tsx

@@ -134,10 +134,33 @@ function appendAgentDelta(turns: ChatTurn[], text: string): ChatTurn[] {
   return next;
 }
 
-function appendUserPrompt(turns: ChatTurn[], text: string): ChatTurn[] {
+function attachmentLabels(value: unknown): string[] {
+  return Array.isArray(value)
+    ? value.filter((item): item is string => typeof item === "string" && item.trim() !== "")
+    : [];
+}
+
+function appendUserPrompt(
+  turns: ChatTurn[],
+  text: string,
+  attachments: string[] = [],
+): ChatTurn[] {
   const last = turns[turns.length - 1];
-  if (last?.role === "user" && last.text === text) return turns;
-  return [...turns, { role: "user", text }];
+  if (
+    last?.role === "user" &&
+    last.text === text &&
+    JSON.stringify(last.attachments ?? []) === JSON.stringify(attachments)
+  ) {
+    return turns;
+  }
+  return [
+    ...turns,
+    {
+      role: "user",
+      text,
+      ...(attachments.length > 0 ? { attachments } : {}),
+    },
+  ];
 }
 
 function isReplyProgressSource(value: unknown): value is ReplyProgressSource {
@@ -341,19 +364,21 @@ function bytesToBase64(bytes: Uint8Array): string {
 
 async function clipboardFileToAttachment(file: File): Promise<AttachmentDraft> {
   const mime = file.type || "application/octet-stream";
+  const contentBase64 = bytesToBase64(new Uint8Array(await file.arrayBuffer()));
   const filename =
     file.name ||
     (mime.startsWith("image/")
       ? `clipboard-image-${Date.now()}.${fileExtension(mime)}`
       : `clipboard-file-${Date.now()}`);
-  const contentBase64 = bytesToBase64(new Uint8Array(await file.arrayBuffer()));
   return {
     id: `clipboard-${Date.now()}-${Math.random().toString(36).slice(2)}`,
     label: filename,
     previewUrl: mime.startsWith("image/")
       ? `data:${mime};base64,${contentBase64}`
       : undefined,
-    dedupeKey: fileMetadataKey(file),
+    dedupeKey: file.name
+      ? fileMetadataKey(file)
+      : `${mime}\u0000${file.size}\u0000${contentBase64}`,
     input: {
       filename,
       contentBase64,
@@ -367,12 +392,12 @@ function fileMetadataKey(file: File): string {
   return `${file.name}\u0000${file.type}\u0000${file.size}\u0000${file.lastModified}`;
 }
 
-function clipboardFiles(event: ClipboardEvent<HTMLTextAreaElement>): File[] {
-  const clipboardItems = event.clipboardData.items
-    ? Array.from(event.clipboardData.items)
+function dataTransferFiles(clipboardData: DataTransfer): File[] {
+  const clipboardItems = clipboardData.items
+    ? Array.from(clipboardData.items)
     : [];
-  const clipboardFiles = event.clipboardData.files
-    ? Array.from(event.clipboardData.files)
+  const clipboardFiles = clipboardData.files
+    ? Array.from(clipboardData.files)
     : [];
   const fromItems = clipboardItems
     .filter((item) => item.kind === "file")
@@ -387,6 +412,25 @@ function clipboardFiles(event: ClipboardEvent<HTMLTextAreaElement>): File[] {
   });
 }
 
+async function asyncClipboardImageFiles(): Promise<File[]> {
+  if (
+    typeof navigator === "undefined" ||
+    typeof navigator.clipboard?.read !== "function"
+  ) {
+    return [];
+  }
+  const items = await navigator.clipboard.read();
+  const files: File[] = [];
+  for (const item of items) {
+    for (const type of item.types) {
+      if (!type.startsWith("image/")) continue;
+      const blob = await item.getType(type);
+      files.push(new File([blob], "", { type, lastModified: 0 }));
+    }
+  }
+  return files;
+}
+
 function slashCommandPrefix(draft: string): string | null {
   if (!draft.startsWith("/")) return null;
   if (/\s/.test(draft)) return null;
@@ -453,7 +497,11 @@ function foldChunk(turns: ChatTurn[], raw: unknown): ChatTurn[] {
     }
     case "userPrompt":
     case "UserPrompt":
-      return appendUserPrompt(turns, String(raw.text ?? raw.prompt ?? ""));
+      return appendUserPrompt(
+        turns,
+        String(raw.text ?? raw.prompt ?? ""),
+        attachmentLabels(raw.attachments),
+      );
     default:
       return [...turns, { role: "unknown", text: unknownChunkLabel(raw) }];
   }
@@ -1059,14 +1107,17 @@ export function CustomAgentChatView({
   async function pasteClipboardFiles(
     event: ClipboardEvent<HTMLTextAreaElement>,
   ) {
-    const files = clipboardFiles(event);
-    if (files.length === 0) return;
-
-    event.preventDefault();
+    const target = event.currentTarget;
     const pastedText = event.clipboardData.getData("text/plain");
-    const selectionStart = event.currentTarget.selectionStart;
-    const selectionEnd = event.currentTarget.selectionEnd;
+    const selectionStart = target.selectionStart;
+    const selectionEnd = target.selectionEnd;
+    const filesFromEvent = dataTransferFiles(event.clipboardData);
     try {
+      const files =
+        filesFromEvent.length > 0 ? filesFromEvent : await asyncClipboardImageFiles();
+      if (files.length === 0) return;
+
+      if (filesFromEvent.length > 0) event.preventDefault();
       const nextAttachments = await Promise.all(
         files.map(clipboardFileToAttachment),
       );
@@ -1084,7 +1135,7 @@ export function CustomAgentChatView({
         });
         return unique.length > 0 ? [...prev, ...unique] : prev;
       });
-      if (pastedText) {
+      if (filesFromEvent.length > 0 && pastedText) {
         if (!draftHydratedRef.current) draftEditedBeforeHydrationRef.current = true;
         setDraft((prev) =>
           prev.slice(0, selectionStart) +