[Slach]

Fix #1562

Antalya metadata_type=cas disks keep parts as content-addressed objects in the pool. system.disks.path for such a disk is a bucket prefix with no local directory behind it.

Problem

• create_remote with use_embedded_backup_restore: true failed in checkDisksConsistency:
  disk "cas" (type "s3") path "/var/lib/clickhouse/<prefix>/" is not exists locally
• after that was fixed, restore_remote failed in fixEmbeddedMetadata → getObjectDisksCredentials:
  unsupported <metadata_type>cas</metadata_type>, because credentials are parsed for every server disk

Changes

• checkDisksConsistency skips CAS disks when use_embedded_backup_restore: true. Without embedded mode it now reports an explicit error: FREEZE on CAS publishes shadow refs inside the pool, so there are no local files to hardlink.
• credentialsFromDiskArgs accepts metadata_type=cas, which uses the same connection settings as other object storage disks.
• new Disk.IsCAS()

Tests

• unit: TestCheckDisksConsistency (CAS with and without embedded), CAS case in TestCredentialsFromDiskArgs_XMLAndSQLParity
• integration: TestAntalyaCASDisk runs embedded create_remote → DROP → restore_remote for a table on cas + cas_cache disks (the reporter's layout), then checks the row count and that the restored parts are back on the CAS disks.
  It runs only on the Antalya image and is skipped elsewhere. Passes locally with:

  CLICKHOUSE_IMAGE=altinity/clickhouse-server CLICKHOUSE_VERSION=26.6.8.20002.altinityantalya RUN_TESTS=TestAntalyaCASDisk ./test/integration/run.sh
  

  MinIO OSS fails the CAS mount capability probe, so the test disk uses skip_access_check=true, the same as the reporter's config.

The CI integration matrix has no Antalya image yet, so TestAntalyaCASDisk is skipped in CI.

🤖 Generated with Claude Code

[coveralls]

Coverage Report for CI Build 40926125661

Coverage increased (+0.02%) to 70.568%

Details

• Coverage increased (+0.02%) from the base build.
• Patch coverage: 8 of 8 lines across 3 files are fully covered (100%).
• 17 coverage regressions across 7 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

17 previously-covered lines in 7 files lost coverage.

File	Lines Losing Coverage	Coverage
pkg/backup/upload.go	4	74.06%
pkg/backup/freezes.go	3	72.95%
pkg/backup/list.go	2	70.26%
pkg/clickhouse/clickhouse.go	2	81.56%
pkg/backup/create_remote.go	2	66.8%
pkg/storage/general.go	2	70.27%
pkg/backup/backuper.go	2	79.93%

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Coverage Stats

Relevant Lines:	29726
Covered Lines:	20977
Line Coverage:	70.57%
Coverage Strength:	34498.2 hits per line

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💛 - Coveralls