fix: preserve original error in IcebergIterator._seek_to_usable_file

[mengw15]

What changes were proposed in this PR?

IcebergIterator._seek_to_usable_file previously swallowed every error during file-scan setup:

except Exception:
    print("Could not read iceberg table:\n")
    raise Exception

The bare raise Exception (no args, no from) constructs a fresh Exception with empty str() and no __cause__. Callers that do except Exception as e: log.error(str(e)) see only an empty class name — the original error type, message, and traceback are all lost. The print also bypasses the project logger.

This PR replaces the bare re-raise with a true re-raise of the original exception and routes the diagnostic message through loguru, matching the existing except Exception as err: logger.exception(err) pattern used in data_processor.py:125, main_loop.py:422, and input_port_materialization_reader_runnable.py:169:

except Exception as err:
    logger.exception(err)
    raise

Callers now see the actual underlying exception (catalog auth failure, S3 IO error, manifest corruption, etc.) with its full class name, message, and traceback.

Any related issues, documentation, discussions?

Closes #5091.

How was this PR tested?

Added amber/src/test/python/core/storage/iceberg/test_iceberg_iterator_error_paths.py, a slim mocked regression test: it patches load_table_metadata to return a Mock whose refresh() raises RuntimeError("Catalog auth failure: token expired"), drives next(IcebergIterator(...)), and asserts the caller observes the original RuntimeError (via pytest.raises(RuntimeError, match=...)). Locks in the contract that the except clause must not swallow the underlying exception's type/message.

Run locally:

python -m pytest amber/src/test/python/core/storage/iceberg/test_iceberg_iterator_error_paths.py -v

Result: 1 passed.

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (claude-opus-4-7)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.15%. Comparing base (e27b98a) to head (094d060).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5092   +/-   ##
=========================================
  Coverage     43.15%   43.15%           
  Complexity     2209     2209           
=========================================
  Files          1045     1045           
  Lines         40260    40261    +1     
  Branches       4250     4250           
=========================================
+ Hits          17373    17376    +3     
+ Misses        21815    21813    -2     
  Partials       1072     1072           

Flag	Coverage Δ		*Carryforward flag
access-control-service	39.53% <ø> (ø)		Carriedforward from e27b98a
agent-service	33.72% <ø> (ø)		Carriedforward from e27b98a
amber	43.80% <ø> (ø)		Carriedforward from e27b98a
computing-unit-managing-service	0.00% <ø> (ø)		Carriedforward from e27b98a
config-service	0.00% <ø> (ø)		Carriedforward from e27b98a
file-service	32.18% <ø> (ø)		Carriedforward from e27b98a
frontend	34.05% <ø> (ø)		Carriedforward from e27b98a
python	90.49% <100.00%> (+0.05%)	⬆️
workflow-compiling-service	56.81% <ø> (ø)		Carriedforward from e27b98a

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[Copilot]

Pull request overview

This PR updates Iceberg table scan error handling so _seek_to_usable_file logs failures through Loguru and re-raises the original exception instead of replacing it with an empty generic Exception.

Changes:

• Adds loguru.logger import to iceberg_document.py.
• Replaces print(...) and raise Exception with logger.exception(err) and bare raise.

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