Fix callTool() crash on JSON-RPC error responses

[Copilot]

callTool() unconditionally accessed response["result"]["content"], throwing if the server returned a JSON-RPC error object (response["error"]) instead of a result — masking the real error and breaking test determinism.

Changes

• e2e-apps.test.ts — callTool() error handling: Added early-return branch for response["error"], returning a structured { isError: true, text, parsed, raw } instead of throwing:

if (response["error"]) {
  const err = response["error"] as Record<string, unknown>;
  const code = err["code"] != null ? ` (code: ${err["code"]})` : "";
  const text = String(err["message"] ?? JSON.stringify(err)) + code;
  return { raw: response, text, parsed: err, isError: true };
}

Both JSON-RPC-level errors and application-level isError results now surface consistently through the same isError signal.

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[Copilot]

Pull request overview

This PR fixes a crash in the callTool() test helper function when the MCP server returns a JSON-RPC error response. Previously, the function unconditionally accessed response["result"]["content"], which would throw if the server returned a JSON-RPC error object (response["error"]) instead. This masked the real error and broke test determinism.

Changes:

• Added early-return error handling in callTool() to check for response["error"] before accessing response["result"]
• Error responses are now returned with a structured { isError: true, text, parsed, raw } format, consistent with application-level errors
• Both JSON-RPC protocol errors and application-level isError results surface consistently through the same isError signal

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