Execute a Dataverse Web API $batch request to bundle multiple operations in a single HTTP round trip

Steps

1. Compose a multipart/mixed request body with a unique batch boundary string; each individual operation is a MIME part separated by --batch_<boundary>.
2. For non-atomic read or write operations, add each individual request as a separate MIME part with its own Content-Type: application/http and Content-Transfer-Encoding: binary headers followed by the raw HTTP request line and body.
3. To make multiple writes atomic (all succeed or all fail), group them inside a changeset part: use --changeset_<boundary> sub-parts within a Content-Type: multipart/mixed; boundary=changeset_<boundary> parent part.
4. POST the assembled batch to https://<org>.crm.dynamics.com/api/data/v9.2/$batch with Content-Type: multipart/mixed; boundary=batch_<boundary>.
5. Parse the multipart response body; each sub-response contains its own HTTP status code — a changeset either fully succeeds (all 204s) or fully fails (the changeset part returns a single error response).
6. Reference the result of an earlier operation within the same batch using the Content-ID header: set Content-ID: 1 on a create operation, then reference it as $1 in a subsequent operation's URL within the same changeset.