ARSN-648: replace archived level/level-sublevel with classic-level

[francoisferrand]

level@~5.0.1 and level-sublevel@~6.6.5 are archived, and drag in an equally old levelup/abstract-leveldown/bytewise stack carrying three advisories. Moving the file metadata backend onto maintained classic-level takes that to zero, and drops 47 transitive deps.

The risky part: on-disk compatibility

Deployed stores have to keep working, so the key layout must stay byte-identical. level-sublevel's encoding isn't what native abstract-level sublevels produce by nesting, so this reproduces it explicitly rather than relying on the new default.

Verified against a real legacy store: wrote one with level@5 + level-sublevel@6.6.5, then opened it with this code — root, bucket and nested recordLog sublevels, stream ordering, and new writes landing in the same namespace as the legacy ones. tests/unit/storage/metadata/file/levelUtils.spec.js pins the raw key bytes so this can't drift silently.

Scope

MetadataFileServer, RecordLog and level-net move onto the abstract-level API directly, with no compatibility facade left behind. What remains are helpers for our own contracts rather than the library's: the # flattened sublevel paths, the sublevel lookup cache, batch operations carrying a sublevel path across RPC rather than a handle, and the iterator to Readable bridge the RPC layer needs to pipe listings back.

lib/db.ts is left alone — IndexTransaction.commit() takes a caller-supplied handle, so changing it would be a public API break outside this ticket.

Also fixes a shadowed err in metadataAPI.batch that was silently swallowing createLogRecordOps failures.

Validation

Worth flagging: this backend's own coverage is thin (MetadataFileServer.initMetadataService at 6.5% function coverage, BucketFileInterface at 5%). Pre-existing and not made worse here, but it does mean the real net under this change is CloudServer's S3BACKEND=file functional suite rather than Arsenal's. Probably deserves a follow-up ticket.

Issue: ARSN-648

[bert-e]

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[codecov]

Codecov Report

❌ Patch coverage is 69.90291% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.87%. Comparing base (ca7b099) to head (12aabeb).

Files with missing lines	Patch %	Lines
lib/storage/metadata/file/MetadataFileServer.js	6.89%	27 Missing ⚠️
lib/storage/metadata/file/levelUtils.ts	91.66%	4 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           development/8.6    #2713      +/-   ##
===================================================
+ Coverage            74.80%   74.87%   +0.06%     
===================================================
  Files                  229      230       +1     
  Lines                18686    18729      +43     
  Branches              3909     3916       +7     
===================================================
+ Hits                 13978    14023      +45     
+ Misses                4703     4701       -2     
  Partials                 5        5              

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[bert-e]

Waiting for approval

The following approvals are needed before I can proceed with the merge:

• the author

• 2 peers

[delthas]

LGTM but would be easier to review with format changes moved into their own commit

[delthas]

Hm, I feel this commit mixes preexisting prettier file changes with actual changes. Would it be possible to move preexisting prettify into its own first commit?

[SylvainSenechal]

This is hard to understand, feels like its written from the pov of doing a migration (so having the context of level-sublevel) instead of focusing on what it is doing

[SylvainSenechal]

Ok I guess its easier to understand when knowing about leveldb

[SylvainSenechal]

One comment from claude might be relevant.

I think it could be nice to have a review from hopo team too