schenksj opened a new issue, #4522:
URL: https://github.com/apache/datafusion-comet/issues/4522

   ### Background
   
   The V1 path in `CometScanRule` rejects any scan referencing metadata columns 
with "Metadata column is not supported", and that check runs *before* 
`transformV1Scan`. With that ordering, a V1 scan handler can never see — let 
alone claim — a scan that carries synthetic metadata columns, even if it does 
support them.
   
   ### Proposal
   
   Move the metadata-column bailout to *inside* `transformV1Scan`, after V1 
scan handling gets first crack. For non-contrib V1 scans this is equivalent to 
the prior check (it still declines); it only changes ordering so a V1 handler 
can claim metadata-column scans it supports.
   
   This is a generic match-ordering change worth reviewing on its own merits 
(it affects all V1 scans), but it is **enablement for a V1 scan contrib** 
rather than a standalone correctness bug.
   
   ### Relationship to the Delta integration
   
   **Required by the in-progress `contrib/delta` integration**: Delta scans 
carry `_metadata.*` columns that the generic check rejects before the contrib 
can claim them. Extracting it here so the ordering change can be evaluated 
independently of Delta. Please prioritize accordingly.
   
   ### Tests
   
   - Existing V1 scans referencing metadata columns still decline (behavior 
unchanged for non-contrib paths).


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