Redirect a backend selection: swap the backend and restamp mode / tier / tier name from the registry, recording the reason shown on the fit.

A redirect off an EXPLICIT request (anything but mode = "auto") is an override, not a resolution: the fit does what the model structure requires instead of what the caller asked for. That is recorded on the selection – sel$overridden for callers, and a clause appended to the reason the fit reports – so an overridden fit is distinguishable from one that was never asked for a mode at all. Only the FIRST override is recorded: with several redirects in a chain, the request the user actually made is the one worth naming, not the intermediate backend a previous redirect chose.

Usage

.sel_redirect(sel, backend, reason, notify = TRUE)

Details

notify says whether tulpa() should additionally WARN. It is for the case where the requested backend could have fitted the model and the redirect takes a capability away – a smoother sending an eb / agq request to the nested kernels loses the random-effect SD those two would have estimated. It is off where the requested mode is not expressible for the structure at all and the redirect is the documented resolution rather than a loss: a random slope has no scalar sigma_re for mode = "laplace" to condition on, and an SPDE field redirected from nested_laplace to spde is the same mode and tier reaching its own integrator. Those are recorded, not warned about, so a documented route does not warn on every fit.