In essence, they are `[]byte` -> `[]byte, error` functions.

It is not possible to return *both* an error and a response.

Handlers are registered on the manager using `(*Manager).RegisterSingleHandler(id HandlerID, h SingleHandlerFn, subroute ...string)`.

The server handler function has this signature: `type SingleHandlerFn func(payload []byte) ([]byte, *RemoteErr)`.

Sample handler:

API, and should be named after the issue number of the API proposal.
For example, if the directory `6-stdlib/99-minor` is present,
then an `api/next` file with the line

    pkg net/http, function F #12345

should have a corresponding file named `doc/next/6-stdlib/99-minor/net/http/12345.md`.
At a minimum, that file should contain either a full sentence or a TODO,

   between services in the cluster and from a service to external
   services. The proxies form a _secure microservice mesh_ providing a rich
   set of functions like discovery, rich layer-7 routing, circuit breakers,
   policy enforcement and telemetry recording/reporting
   functions.

  > Note: The service mesh is not an overlay network. It
  > simplifies and enhances how microservices in an application talk to each

   actually using the new version with Tensorflow.

2) In the `WORKSPACE` file, add the new version to the `python_versions`
   parameter of the `python_register_multi_toolchains` function.

3) In the `BUILD.bazel` file, add a load statement for the new version, e.g.

   ```
      load("@python//3.11:defs.bzl",
           compile_pip_requirements_3_11 = "compile_pip_requirements")
   ```

        `TFCI_` variables shared to it.
3.  Top-level scripts (`wheel.sh`, etc.) reference `env` variables and call
    `utilities/` scripts.
    -   The `tfrun` function makes a command run correctly in Docker if Docker