fix(storage): refuse to overwrite a collection record this version cannot parse (follow-up to #194)

[CaffeinatedCoder]

Follow-up to the #194 review (#187).

Changes

• Records that don't parse are refused. SaveCollectionMetadata and DeleteCollectionMetadata now throw NotSupportedException when the collection's stored record cannot be parsed. The message names the collection and this version, and the record is left unchanged. Before, TryReadRecord swallowed every exception, so the feature check was skipped and the record was overwritten. Such a record also makes GetCollectionMetadata return null, so a dynamic open saved a fresh, empty record over it.
  • EnsureCanReplaceRecord replaces TryReadRecord in the same place: right after FindMetadataRecord, before the in-place step.
  • The delete guard now finds the record with LoadMetadataChain/FindMetadataRecord instead of GetCollectionMetadata, which skips records it cannot parse.
• Index-type rule, documented accurately (CollectionFeatures remarks). The rule only protects a new index type if the older release that rewrote the record kept the index entry. Typed collections and saves that start from the stored record keep it. 5.2.3's DynamicCollection.PersistIndexMetadata doesn't: it rebuilds the index list from the indexes it loaded, on every dynamic index create/drop and on a vacuum with RebuildIndexes, and so drops the entry together with the feature section.
• Format rule (CollectionFeatures and ReadCollectionMetadata): new per-index data goes only in trailing sections, never inline in the index list. An older version reads the list by position. Unexpected bytes there make the record fail to parse; GetCollectionMetadata then returns null, a dynamic open saves a fresh record, and the feature refusal never runs.
• Version in the refusal message: checked. versionize bumps <Version>, and nuget-publish.yml passes -p:Version=<tag>. A build with -p:Version=5.3.0-beta.1 has assembly version 5.3.0.0, so the message says "BLite 5.3.0".

Tests

RecordThisVersionCannotParse_IsNeitherOverwrittenNorDropped: a record is cut right after its name.

• SaveCollectionMetadata and DeleteCollectionMetadata throw.
• GetOrCreateCollection throws.
• Another collection stays readable and writable.
• The stored bytes are unchanged.

The test fails with main's guard, and also with only the Delete guard reverted. RequiredFeaturesTests + MetadataChainTests: 18/18. BLite.Core builds for net10.0 and netstandard2.1 with no warnings. Full suite: 2519 passed; the 5 failures were lock timeouts under heavy parallel load, and each passed when rerun on its own. BLite.NetStandard21.Tests couldn't run locally (it needs the net6.0 runtime).

Release notes (suggestion)

Collections can now record features they depend on. From this release on, a BLite version that does not know such a feature refuses to open or modify the collection, with an error naming the feature and the version that supports it, instead of damaging it.

Do not open a database with BLite < 5.3 for writing once it has been used by 5.3 or later. Older releases cannot refuse, and they drop the recorded features when they rewrite a collection's metadata. In those releases, a dynamic index create or drop, or a vacuum that rebuilds indexes, also drops index entries of types they don't know.

BLiteEngine.ListCollections now also lists collections this version cannot open; GetOrCreateCollection throws NotSupportedException for them.

A collection whose stored metadata this version cannot parse is no longer overwritten or dropped; opening or modifying it throws NotSupportedException.

🤖 Generated with Claude Code

[mrdevrobot]

Thanks. Refusing to overwrite or drop a record this version can't parse closes the gap where TryReadRecord swallowed the error and a dynamic open saved an empty record over it. The format rule in CollectionFeatures and ReadCollectionMetadata is a good thing to have written down. Note for the release notes: a collection whose metadata record is damaged can now no longer be opened or dropped either; the message says so, which is fine. Verified together with #218 and #215 on top of main: full suite green.