fix(ui): reliable attachment download and preview error IPC

Export bytes to download-cache, use saved-path for large files, and always
send download/preview error events when fetch fails.

Co-authored-by: Cursor <[email protected]>

index.js

@@ -1384,47 +1384,81 @@ async function dispatchUiMessage (platform, msg, hooks = {}) {
     return true
   }
   if (t === 'request-attachment-preview') {
-    const preview = await platform.readAttachmentPreview(msg.attachmentId)
-    send({
-      type: 'attachment-preview',
-      preview,
-      fetchSource: preview?.fetchSource || null
-    })
+    const attachmentId = msg.attachmentId
+    try {
+      const preview = await platform.readAttachmentPreview(attachmentId)
+      send({
+        type: 'attachment-preview',
+        preview,
+        fetchSource: preview?.fetchSource || null
+      })
+    } catch (err) {
+      try {
+        send({
+          type: 'attachment-preview-error',
+          attachmentId,
+          message: err?.message || String(err)
+        })
+      } catch {
+        /* pipe closed */
+      }
+    }
     return true
   }
   if (t === 'request-attachment-download') {
     const attachmentId = msg.attachmentId
     const downloadTimeoutMs = Number(process.env.PEARCORD_ATTACHMENT_DOWNLOAD_MS || 30000)
-    const maxInlineBytes = Number(process.env.PEARCORD_ATTACHMENT_DOWNLOAD_MAX || 6 * 1024 * 1024)
+    const maxInlineBytes = Number(process.env.PEARCORD_ATTACHMENT_DOWNLOAD_MAX || 512 * 1024)
+    const sendDownloadError = (message) => {
+      try {
+        send({
+          type: 'attachment-download-error',
+          attachmentId,
+          message: message || 'download failed'
+        })
+      } catch {
+        /* pipe closed */
+      }
+    }
     try {
-      const row = await platform.attachments?.get(attachmentId)
-      if (!row) throw new Error('attachment not found')
-      const { buf, source } = await Promise.race([
-        platform.readAttachmentBytesWithSource(attachmentId),
+      const exported = await Promise.race([
+        platform.exportAttachmentForDownload(attachmentId),
         new Promise((_, reject) => {
           setTimeout(() => reject(new Error('download timed out')), downloadTimeoutMs)
         })
       ])
-      if (!buf?.length) throw new Error('attachment file empty')
-      if (buf.length > maxInlineBytes) {
-        throw new Error(
-          `file too large to download inline (${Math.round(buf.length / 1024 / 1024)} MB)`
-        )
+      if (!exported?.filePath) throw new Error('attachment file empty')
+      if (exported.size > maxInlineBytes) {
+        try {
+          send({
+            type: 'attachment-download-saved',
+            attachmentId,
+            filename: exported.filename || 'download',
+            filePath: exported.filePath,
+            mimeType: exported.mimeType || 'application/octet-stream',
+            size: exported.size
+          })
+        } catch (err) {
+          sendDownloadError(err?.message || String(err))
+        }
+        return true
+      }
+      const fs = require('bare-fs')
+      const buf = fs.readFileSync(exported.filePath)
+      try {
+        send({
+          type: 'attachment-download',
+          attachmentId,
+          filename: exported.filename || 'download',
+          mimeType: exported.mimeType || 'application/octet-stream',
+          dataBase64: b4a.toString(buf, 'base64'),
+          fetchSource: 'export-cache'
+        })
+      } catch (err) {
+        sendDownloadError(err?.message || String(err))
       }
-      send({
-        type: 'attachment-download',
-        attachmentId: row.id,
-        filename: row.filename || 'download',
-        mimeType: row.mimeType || 'application/octet-stream',
-        dataBase64: b4a.toString(buf, 'base64'),
-        fetchSource: source
-      })
     } catch (err) {
-      send({
-        type: 'attachment-download-error',
-        attachmentId,
-        message: err?.message || String(err)
-      })
+      sendDownloadError(err?.message || String(err))
     }
     return true
   }