* s3api/iceberg: report the reason a table schema was rejected
newTableMetadata swallowed the iceberg-go error and returned nil, so every
schema the metadata builder refused came back as a bare 500 "Failed to build
table metadata". A v3-only column type is the common case: creating a table
with a variant field but no format-version 3 property leaves the client with
nothing, while "variant is not supported until v3" sits in the server log.
Return the error instead and classify it. Schema, spec and argument failures
are the caller's input, so they answer 400 with the underlying reason; the
rest stay 500. Paths that build placeholder metadata with no schema keep
their existing 500 via newEmptyTableMetadata.
* s3api/iceberg: fail LoadTable when placeholder metadata cannot be built
buildLoadTableResult dropped a nil from the placeholder path straight into
the response. That serializes as "metadata":null under HTTP 200, which no
Iceberg client can parse -- a worse outcome than the 500 the nil was meant
to signal.
Return an error instead and let the five callers answer 500. The nil-return
convention goes away with it, so the commit and transaction paths check an
error rather than a sentinel.
* s3api/iceberg: route rejected schemas through writeManagerError
The two helpers added here duplicated work the package already does.
writeManagerError is the canonical error-to-response mapper -- it already
downgrades client-input failures to 400 and defaults the rest to 500 -- so
teach it the iceberg-go schema and spec sentinels instead of standing up a
parallel classifier. The placeholder wrapper was a pure alias for
newTableMetadata with nil arguments; call that directly.
No behavior change beyond the 500 message, which now reads err.Error()
like every other manager error rather than carrying its own prefix.
Chris Lu