[ENH] Add the schema for Rust Log Service in Spanner.

[rescrv]

Description of changes

This PR is the schema for the replicated log.

Test plan

CI

Migration plan

N/A

Observability plan

N/A

Documentation Changes

N/A

[github-actions]

Reviewer Checklist

Please leverage this checklist to ensure your code review is thorough before approving

Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
• Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
• Should any logging, debugging, tracing information be added or removed?
• Are error messages user-friendly?
• Have all documentation changes needed been made?
• Have all non-obvious changes been commented?

System Compatibility

• Are there any potential impacts on other parts of the system or backward compatibility?
• Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• Is this code of a unexpectedly high quality (Readability, Modularity, Intuitiveness)

[propel-code-bot]

Introduce Spanner schema for Rust log service

Adds the initial Cloud Spanner schema for the Rust log service, covering manifests, fragments, and fragment regions. Updates the migration manifest sums so the new migration set is tracked with running SHA checksums and refreshed CLI regeneration instructions.

Key Changes

• Create manifests, fragments, and fragment_regions tables with primary keys scoped by log_id
• Interleave fragments under manifests and fragment_regions under fragments to collocate hierarchical rows
• Regenerate rust/spanner-migrations/log_migrations/log_migrations.sum to include the new files and adjust checksum annotations

Affected Areas

• rust/spanner-migrations/log_migrations
• rust/spanner-migrations/migrations

This summary was automatically generated by @propel-code-bot

[sanketkedia]

I thought you were not in favor of keeping an explicit enumeration_offset since it incurs an update to this table for every write?

[rescrv]

This design is the one we benchmarked most recently. The alternative is to do a query across all fragments which is worse.

[propel-code-bot]

[Logic] The path column length of 64 characters is insufficient for the paths generated by wal3.

In rust/wal3/src/lib.rs, unprefixed_fragment_path generates paths like:
log/Bucket={:016x}/FragmentSeqNo={:016x}.parquet

Counting the characters:

• log/ (4)
• Bucket= (7)
• 16 hex digits (16)
• / (1)
• FragmentSeqNo= (14)
• 16 hex digits (16)
• .parquet (8)

Total = 66 characters. This exceeds the STRING(64) limit and will cause insertion failures for SeqNo-based fragments.

Increase the column size to at least 128 to be safe.

Context for Agents

The `path` column length of 64 characters is insufficient for the paths generated by `wal3`.

In `rust/wal3/src/lib.rs`, `unprefixed_fragment_path` generates paths like:
`log/Bucket={:016x}/FragmentSeqNo={:016x}.parquet`

Counting the characters:
- `log/` (4)
- `Bucket=` (7)
- 16 hex digits (16)
- `/` (1)
- `FragmentSeqNo=` (14)
- 16 hex digits (16)
- `.parquet` (8)

Total = 66 characters. This exceeds the `STRING(64)` limit and will cause insertion failures for SeqNo-based fragments.

Increase the column size to at least 128 to be safe.

File: rust/spanner-migrations/log_migrations/0002-create_fragments_table.spanner.sql
Line: 4

[rescrv]

UUID-based fragments don't have the added chars