[lucasfang]

Purpose

Closes #506.

Add 25 focused regression tests and extend existing tests for storage edge cases identified by the coverage report:

• Cover local parent paths, prefetch reader forwarding/metrics/batch lifecycle, realtime commit replay, snapshot statistics across schema changes, and conflict checks for snapshot bounds, row ranges, and write columns.
• Synchronize concurrent credential callers so both observe an expired token, then verify that only one refresh occurs and both receive the refreshed credentials.
• Cover snapshot time retention, snapshots and index manifests disappearing during expiration, deleted and out-of-order tags, unreadable tagged manifests preserving data, retained statistics, and empty-directory cleanup.
• Cover global system-table discovery and schema loading, catalog options, schema discovery without schema-0, and ignored drops of incomplete table directories.
• Exercise cleaner option replacement with a caller-provided memory pool and executor, string-predicate dispatch through actual bitmap-index matches, and Parquet sequential fallback for missing or malformed offset indexes while preserving selected rows and the streaming schema.

Improve coverage collection with atomic C/C++ gcov counters, isolate coverage flags from bundled dependencies, and enable Jindo, OSS, S3, Lumina, Lucene, full-text, and REST alongside the existing formats.

Tests

The following focused suites passed on the final binaries:

Command	Result
./build/debug/paimon-fs-test --gtest_filter='LocalFileTest.*'	8 passed
./build/debug/paimon-common-test --gtest_filter='*PrefetchFileBatchReader*'	59 passed, 2 existing cases skipped because the read-ahead cache is disabled
./build/debug/paimon-core-test --gtest_filter='FileStoreCommitImplTest.*:ConflictDetectionTest.*'	145 passed
./build/debug/paimon-rest-test --gtest_filter='RestCredentialProviderTest.*:RestTokenFileSystemTest.*'	30 passed
./build/debug/paimon-core-test --gtest_filter='ExpireSnapshotsTest.*:FileSystemCatalogTest.*:OrphanFilesCleanerTest.*'	61 passed
./build/debug/paimon-common-test --gtest_filter='BitmapGlobalIndexTest.*'	7 passed
./build/debug/paimon-parquet-format-test --gtest_filter='PageFilteredRowGroupReaderTest.*'	50 passed

The new credential concurrency test also passed 100 repetitions. Changed-file pre-commit checks and git diff --check passed. The coverage script passed bash -n; isolated compiler/CMake probes verified atomic counters and third-party flag isolation, and a stubbed coverage-script smoke test verified its component options and command sequence.

Rerunning the four newly covered suites with an isolated GCOV_PREFIX verified 63 of the 64 requested business lines: REST 1/1, expiration 19/20, catalog 18/18, cleaner 9/9, Parquet 8/8, and predicate dispatch 8/8. The remaining expiration line 355 is a defensive continue for a missing hierarchy key; the producer always inserts contiguous keys starting at zero, so normal inputs cannot reach it. The full coverage HTML report was not regenerated; these are targeted execution counts, not a new overall coverage percentage.

The normal CMake build remains blocked by Vortex selecting stable Rust 1.67.1, below its dependency requirements. The changed C++ test objects were freshly compiled and the REST, core, common, and Parquet Debug test binaries were relinked using Ninja's generated commands with existing dependency artifacts. This does not claim a successful full dependency rebuild.

API and Format

No public API, storage format, or protocol changes.

Documentation

No new user-facing feature documentation is required. The coverage script contains the expanded component configuration.

Generative AI tooling

Generated-by: OpenAI Codex 0.166.0

[lxy-9602]

+1