echo is not currently a supported entity for files with the T1w suffix. There is an open issue about possibly supporting it though: Add support for multi-echo T1w scans · Issue #654 · bids-standard/bids-specification · GitHub
In terms of inferring this from the specification, there are two places within the specification to check for these things: the MRI entity table and the anatomical MRI section’s filename templates.
In the MRI entity table, the first row includes the T1w suffix, and the corresponding cell under the echo column does not contain “OPTIONAL” or “REQUIRED”: Redirecting...
The filename templates in the anatomical MRI section of the specification are less clear (Redirecting...). There are so many anatomical MRI suffixes with equivalent rules that the templates combine them under “<suffix>”. It wouldn’t be clear which suffixes fall under each group. However, for the two patterns that use this suffix consolidation, neither supports echo.
I don’t believe fMRIPrep supports multi-echo T1w scans. However, I do remember seeing a similar question about MEMPRAGEs at MEMPRAGE RMS (not echoes) for recon-all with fMRIprep. The recommendation was to (1) calculate the RMS image (which I think is what Freesurfer wants) and (2) name that file as if it was a normal T1w so that fMRIPrep would use it.
I hope that helps.