Fix image uploads using the wrong format (#2380)

* fix(app): preserve image attachment MIME types

Image intake discarded clipboard and desktop path metadata, then guessed JPEG when a later file object had no type. Resolve MIME once at the platform boundary and require it downstream.

* fix(app): honor native picker MIME metadata

packages/app/src/utils/image-attachments-from-files.test.ts

@@ -92,7 +92,7 @@ describe("collectImageFilesFromClipboardData", () => {
       ],
     });
 
-    expect(files).toEqual([imagePng]);
+    expect(files).toEqual([{ file: imagePng, mimeType: "image/png" }]);
   });
 
   it("ignores SVG clipboard files", () => {
@@ -127,7 +127,10 @@ describe("filesToImageAttachments", () => {
       type: "",
     });
 
-    const attachments = await filesToImageAttachments([pngFile, typeLessFile]);
+    const attachments = await filesToImageAttachments([
+      { file: pngFile, mimeType: "image/png" },
+      { file: typeLessFile, mimeType: "image/png" },
+    ]);
 
     expect(attachments).toEqual([
       {
@@ -141,7 +144,7 @@ describe("filesToImageAttachments", () => {
       },
       {
         id: "att-2",
-        mimeType: "image/jpeg",
+        mimeType: "image/png",
         storageType: "web-indexeddb",
         storageKey: "att-2",
         fileName: "second",
@@ -156,7 +159,7 @@ describe("filesToImageAttachments", () => {
       type: "image/png",
     });
 
-    const [attachment] = await filesToImageAttachments([large]);
+    const [attachment] = await filesToImageAttachments([{ file: large, mimeType: "image/png" }]);
 
     expect(attachment?.storageType).toBe("web-indexeddb");
     expect(attachment?.byteSize).toBe(4 * 1024 * 1024);

packages/app/src/utils/image-attachments-from-files.ts

@@ -1,6 +1,6 @@
 import type { AttachmentMetadata } from "@/attachments/types";
 import { persistAttachmentFromBlob } from "@/attachments/service";
-import { isRasterImageMimeType } from "@/attachments/file-types";
+import { resolveRasterImageMimeType } from "@/attachments/file-types";
 
 export interface ClipboardItemLike {
   kind?: string;
@@ -14,40 +14,46 @@ export interface ClipboardDataLike {
 
 export type ImageAttachmentFromFile = AttachmentMetadata;
 
+export interface ClipboardImageFile {
+  file: File;
+  mimeType: string;
+}
+
 export function collectImageFilesFromClipboardData(
   clipboardData?: ClipboardDataLike | null,
-): File[] {
+): ClipboardImageFile[] {
   if (!clipboardData?.items) {
     return [];
   }
 
-  const files: File[] = [];
+  const files: ClipboardImageFile[] = [];
   for (const item of Array.from(clipboardData.items)) {
     if (item?.kind !== "file") {
       continue;
     }
-    if (!isRasterImageMimeType(item.type)) {
+    const mimeType = resolveRasterImageMimeType({ mimeType: item.type });
+    if (!mimeType) {
       continue;
     }
     const file = item.getAsFile?.();
     if (!file) {
       continue;
     }
-    files.push(file);
+    files.push({ file, mimeType });
   }
 
   return files;
 }
 
 export async function filesToImageAttachments(
-  files: readonly File[],
+  files: readonly ClipboardImageFile[],
 ): Promise<ImageAttachmentFromFile[]> {
   const attachments = await Promise.all(
-    files.map(async (file) => {
+    files.map(async ({ file, mimeType }) => {
       try {
         return await persistAttachmentFromBlob({
           blob: file,
-          mimeType: file.type || "image/jpeg",
+          mimeType,
           fileName: file.name,
         });
       } catch (error) {