Foundry376/Mailspring · error

Message '${messageId}' has no attachment with id '${fileId}'

Error message

Message '${messageId}' has no attachment with id '${fileId}'

What it means

Resource handler guard in registerResources: the message was found and allowed, but no file in message.files has an id matching the fileId segment of the resource URI. The attachment reference is stale or mistyped; the attachment may have been removed from the message.

Source

Thrown at app/internal_packages/mcp-server/lib/mcp-tools.ts:359

          toolName: 'resources/read',
          params: uri.href.slice(0, 200),
          resultSummary,
          durationMs: Date.now() - start,
        });

      try {
        // Variables come from the SDK's template match on the raw URI, so
        // they preserve the ids' case (unlike uri.host, which URL lowercases).
        const messageId = decodeURIComponent(String(variables.messageId));
        const fileId = decodeURIComponent(String(variables.fileId));

        const message = await DatabaseStore.find<Message>(Message, messageId);
        if (!message || !isMessageAllowed(message)) {
          throw new Error(`Message '${messageId}' not found`);
        }
        const file = (message.files || []).find((f) => f.id === fileId);
        if (!file) {
          throw new Error(`Message '${messageId}' has no attachment with id '${fileId}'`);
        }
        const filePath = await attachmentPathOnDisk(file);
        if (!filePath) {
          throw new Error(
            `Attachment '${file.displayName()}' has not been downloaded — call the get_attachment tool first.`
          );
        }

        const buffer = await fs.promises.readFile(filePath);
        audit('ok');
        return {
          contents: [
            { uri: uri.href, mimeType: mimeTypeForFile(file), blob: buffer.toString('base64') },
          ],
        };
      } catch (err) {
        audit(`error: ${(err as Error).message}`.slice(0, 100));
        throw err;

View on GitHub (pinned to 648c685d60)

Solutions

1. Re-read the message's files list (e.g. via a messages tool) and use the current attachment id
2. Ensure percent-encoding of the file id matches what the resource list emitted

When it happens

Trigger: Thrown at app/internal_packages/mcp-server/lib/mcp-tools.ts:359 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Foundry376/Mailspring@648c685d60 (2026-09-03). Data as JSON: /api/errors/0243276df05b5331. Report an issue: GitHub.