fix: avoid persisting signed draft attachment urls

Co-authored-by: multica-agent <github@multica.ai>

packages/views/modals/create-issue.test.tsx

@@ -490,10 +490,17 @@ describe("CreateIssueModal", () => {
           expect.objectContaining({
             id: "11111111-2222-3333-4444-555555555555",
             filename: "shot.png",
+            download_url: "",
           }),
         ],
       });
     });
+    const draftAttachmentsCall = mockSetDraft.mock.calls.find(
+      ([patch]) => Array.isArray(patch.attachments),
+    )?.[0] as { attachments?: Array<{ download_url: string }> } | undefined;
+    expect(draftAttachmentsCall?.attachments?.[0]?.download_url).not.toContain(
+      "Signature=",
+    );
   });
 
   it("reuses draft attachments after reopening manual create so pasted images can render and bind", async () => {
@@ -509,7 +516,7 @@ describe("CreateIssueModal", () => {
       uploader_id: "user-1",
       filename: "shot.png",
       url: "https://cdn.example.test/shot.png",
-      download_url: "https://cdn.example.test/shot.png?Signature=fresh",
+      download_url: "",
       markdown_url: "https://multica-api.copilothub.ai/api/attachments/11111111-2222-3333-4444-555555555555/download",
       content_type: "image/png",
       size_bytes: 123,

packages/views/modals/create-issue.tsx

@@ -18,7 +18,7 @@ import {
 } from "lucide-react";
 import { cn } from "@multica/ui/lib/utils";
 import { toast } from "sonner";
-import type { Issue, IssueStatus, IssuePriority, IssueAssigneeType } from "@multica/core/types";
+import type { Issue, IssueStatus, IssuePriority, IssueAssigneeType, Attachment } from "@multica/core/types";
 import { contentReferencesAttachment } from "@multica/core/types";
 import {
   DialogContent,
@@ -58,6 +58,17 @@ import { PillButton } from "../common/pill-button";
 import { IssuePickerModal } from "./issue-picker-modal";
 import { useT } from "../i18n";
 
+function toDraftAttachment(attachment: Attachment): Attachment {
+  return {
+    ...attachment,
+    // `download_url` is minted for the current API response and may be a
+    // short-lived signed URL. Drafts survive across dialog closes and app
+    // restarts, so persist only durable fields and let render/download paths
+    // re-resolve through id/markdown_url when needed.
+    download_url: "",
+  };
+}
+
 // ---------------------------------------------------------------------------
 // ManualCreatePanel — manual-mode body of the create-issue dialog. Renders
 // DialogContent + everything inside; the surrounding `<Dialog>` is owned by
@@ -156,7 +167,7 @@ export function ManualCreatePanel({
         useIssueDraftStore.getState().draft.attachments ?? [];
       const attachments = currentAttachments.some((a) => a.id === result.id)
         ? currentAttachments
-        : [...currentAttachments, result];
+        : [...currentAttachments, toDraftAttachment(result)];
       setDraft({ attachments });
     }
     return result;