feat(tickets): ajoute les pièces jointes sur tickets (#108)

Stockage flat côté ticket + métadonnées d'attachments, lecture exposée côté
backend/MCP, et UI minimale de liste/ajout dans TicketDetail. Traverse le
domaine (Issue, ports), l'application (usecases + assistant de ticket), les
adaptateurs infra/MCP (issues store, orchestrateur), les DTO backend/web-
server/app-tauri, et le frontend (domain/ports/adapters/hooks/UI).

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

frontend/src/adapters/mock/index.ts

@@ -66,6 +66,7 @@ import type {
   SystemPermissionSet,
   TerminalSession,
   Ticket,
+  TicketAttachmentContent,
   TicketBulkResult,
   TicketCarnet,
   TicketChat,
@@ -179,6 +180,22 @@ function sameTicketCreator(
   return true;
 }
 
+function filenameFromPath(path: string): string {
+  return path.split(/[\\/]/).filter(Boolean).at(-1) ?? "attachment";
+}
+
+function inferAttachmentMime(filename: string, supplied?: string | null): string {
+  if (supplied?.trim()) return supplied.trim();
+  const lower = filename.toLowerCase();
+  if (lower.endsWith(".md")) return "text/markdown";
+  if (lower.endsWith(".txt")) return "text/plain";
+  if (lower.endsWith(".json")) return "application/json";
+  if (lower.endsWith(".png")) return "image/png";
+  if (lower.endsWith(".jpg") || lower.endsWith(".jpeg")) return "image/jpeg";
+  if (lower.endsWith(".pdf")) return "application/pdf";
+  return "application/octet-stream";
+}
+
 export class MockSystemGateway implements SystemGateway {
   private listeners = new Set<(e: DomainEvent) => void>();
 
@@ -219,6 +236,11 @@ export class MockSystemGateway implements SystemGateway {
     return "/home/user/mock-plugin.ideaplug";
   }
 
+  /** Returns a deterministic fake path — never opens a native dialog. */
+  async pickFile(): Promise<string | null> {
+    return "/home/user/mock-attachment.txt";
+  }
+
   private exitGuardListeners = new Set<(state: AppExitWorkGuardState) => void>();
   /** Count of `confirmAppExit()` calls, for test assertions. */
   confirmAppExitCallCount = 0;
@@ -2710,6 +2732,7 @@ export class MockTicketGateway implements TicketGateway {
   /** Open assistant chats, keyed by `issueRef` → sessionId (ticket #8). */
   private chatSessions = new Map<string, string>();
   private chatCounter = 0;
+  private attachmentCounter = 0;
 
   constructor(private readonly system?: MockSystemGateway) {}
 
@@ -2717,6 +2740,7 @@ export class MockTicketGateway implements TicketGateway {
   _seedTicket(projectId: string, ticket: Ticket): Ticket {
     const stored = structuredClone(ticket);
     if (stored.sprintId === undefined) stored.sprintId = null;
+    stored.attachments ??= [];
     this.projectTickets(projectId).set(stored.ref, stored);
     this.counters.set(
       projectId,
@@ -2810,6 +2834,7 @@ export class MockTicketGateway implements TicketGateway {
       sprintId: null,
       links: [],
       assignedAgentIds: [...(input.assignedAgentIds ?? [])],
+      attachments: [],
       createdBy: { kind: "user" },
       updatedBy: { kind: "user" },
       createdAt: now,
@@ -3021,6 +3046,83 @@ export class MockTicketGateway implements TicketGateway {
     return structuredClone(ticket);
   }
 
+  async addAttachment(
+    projectId: string,
+    ref: string,
+    path: string,
+    expectedVersion: number,
+    mime?: string | null,
+  ): Promise<Ticket> {
+    const ticket = this.require(projectId, ref);
+    this.guard(ticket, expectedVersion);
+    const filename = filenameFromPath(path);
+    this.attachmentCounter += 1;
+    ticket.attachments.push({
+      id: `att-${this.attachmentCounter}`,
+      filename,
+      mime: inferAttachmentMime(filename, mime),
+      sizeBytes: Math.max(1, filename.length * 128),
+      addedBy: { kind: "user" },
+      addedAt: Date.now(),
+      summarizedInCarnet: false,
+      summarizedBy: null,
+      summarizedAt: null,
+    });
+    this.bump(ticket);
+    this.system?.emit({
+      type: "issueUpdated",
+      issueRef: ref,
+      version: ticket.version,
+    });
+    return structuredClone(ticket);
+  }
+
+  async readAttachment(
+    projectId: string,
+    ref: string,
+    attachmentId: string,
+  ): Promise<TicketAttachmentContent> {
+    const ticket = this.require(projectId, ref);
+    const attachment = ticket.attachments.find((item) => item.id === attachmentId);
+    if (!attachment) {
+      throw {
+        code: "NOT_FOUND",
+        message: `attachment ${attachmentId} not found`,
+      } as GatewayError;
+    }
+    return {
+      attachment: structuredClone(attachment),
+      contentBase64: btoa(`mock content for ${attachment.filename}`),
+    };
+  }
+
+  async markAttachmentSummarized(
+    projectId: string,
+    ref: string,
+    attachmentId: string,
+    expectedVersion: number,
+  ): Promise<Ticket> {
+    const ticket = this.require(projectId, ref);
+    this.guard(ticket, expectedVersion);
+    const attachment = ticket.attachments.find((item) => item.id === attachmentId);
+    if (!attachment) {
+      throw {
+        code: "NOT_FOUND",
+        message: `attachment ${attachmentId} not found`,
+      } as GatewayError;
+    }
+    attachment.summarizedInCarnet = true;
+    attachment.summarizedBy = { kind: "user" };
+    attachment.summarizedAt = Date.now();
+    this.bump(ticket);
+    this.system?.emit({
+      type: "issueUpdated",
+      issueRef: ref,
+      version: ticket.version,
+    });
+    return structuredClone(ticket);
+  }
+
   async link(
     projectId: string,
     ref: string,