The Safe decorator wraps runner.Function with defer/recover, converting
panics into internalerr.Error. The service wraps the parsed step with
WithPanicRecovery before passing it to job.Run().

Job.Status() now maps j.err to a StatusError with the appropriate
ErrorKind: internalerr.Error → internal, context cancellation →
cancelled, other → step_failure.

Add ErrorKind type to client.Status and read it from proto StatusError.
Create panic-recovery spec and update grpc-api spec to document the
structured error model.

The fix from a87db07b was lost during the function.Safe refactor.
Read j.err under j.mux.RLock() before logging, preventing a race
with Close()'s timer branch which writes j.err under j.mux.Lock().

This also avoids a nil-panic risk where the read checked j.err
but the log statement called err.Error() — onRunCompletion can set
j.err non-nil while the local err is nil.

Move the domain infrastructure-error type from pkg/internal/internalerr
into pkg/runner as `StepRunnerError`. Resolves package/type stutter
(`internalerr.Error`) and places the type in the domain layer where
the concept belongs (analogous to gl-runner's `BuildError`).

- Add `runner.StepRunnerError` and `runner.NewStepRunnerError`.
- Update callers in pkg/runner/function/safe.go and
  pkg/api/internal/jobs/jobs.go.
- Delete pkg/internal/internalerr.

Collapse the inline StatusError construction in Job.Status() into a
single call site. The helper now takes the error and returns the full
proto.StatusError, classifying the kind as part of the construction.

No change to the wire format: StatusError.kind is populated identically,
so Runner-side alerting on kind is preserved.

Mark `Status.message` with `[deprecated = true]` in proto/step.proto
to match the intent already expressed in docs/spec/grpc-api.md. The
server still populates the field for backwards compatibility, with a
targeted //nolint to acknowledge the deprecated write.

- Migrate basic/client.go to populate client.Status.Message from
  `st.Error.Message` when present.
- Migrate tests to assert against `Error.Message` / `Error == nil`,
  removing reads of the deprecated field.

Add an explicit comment noting that client.ErrorKind values must match
proto.StatusError_ErrorKind, so future maintainers do not have to trace
through the cast in basic/client.go to find the contract.

Add panic recovery and structured error reporting to job status

See merge request !469