Add tx_write_set column to the Coordinator table

[brfrn169]

Description

This PR adds a new tx_write_set (BLOB) column to the Coordinator table schema. The column is the first piece of an upcoming feature that records the write set of each transaction in the Coordinator table, which will enable proactive recovery of orphan PREPARED records (rather than relying solely on per-record lazy recovery) and lay the groundwork for future backup-based recovery.

The column is added unconditionally on the master branch. Existing Coordinator tables created with earlier versions are migrated automatically by Admin.upgrade(), which detects the missing column and adds it via ALTER TABLE. The runtime logic that populates the column will be added in a follow-up PR.

Related issues and/or PRs

N/A

Changes made

• Added Attribute.WRITE_SET = "tx_write_set" constant.
• Added the tx_write_set (BLOB) column to Coordinator.TABLE_METADATA.
• Included Attribute.WRITE_SET in ConsensusCommitAdmin.upgradeCoordinatorTable()'s potentialMissingColumnNames so existing tables receive the column during Admin.upgrade().
• Updated the unit test in ConsensusCommitAdminTestBase to verify that both tx_child_ids and tx_write_set are added when missing (test method renamed to upgrade_CoordinatorTableExistsButMissingChildIdsAndWriteSetColumns_ShouldAddMissingColumns).
• Updated the comment in SchemaLoaderIntegrationTestBase.upgrade_WithOldCoordinatorTableSchema_ShouldProperlyUpdateTheSchema to reflect that both columns are part of the upgrade migration.

Checklist

• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation to reflect the changes.
• I have considered whether similar issues could occur in other products, components, or modules if this PR is for bug fixes.
• Any remaining open issues linked to this PR are documented and up-to-date (Jira, GitHub, etc.).
• Tests (unit, integration, etc.) have been added for the changes.
• My changes generate no new warnings.
• Any dependent changes in other PRs have been merged and published.

Additional notes (optional)

The follow-up PR will add the proto definitions and the runtime logic that populates the new column on commit/abort.

Release notes

Added a tx_write_set column to the Coordinator table to lay the groundwork for proactive transaction recovery. The column is added automatically to existing Coordinator tables when Admin.upgrade() is run.

[gemini-code-assist]

Code Review

This pull request introduces a tx_write_set column to the coordinator table for the consensus commit transaction manager. The changes include updating the Attribute class, table metadata, and upgrade logic, with corresponding test updates. Feedback suggests moving the new column to the end of the metadata definition to maintain consistent column ordering across fresh and upgraded installations.

[Copilot]

Pull request overview

This PR extends the Consensus Commit coordinator table schema by adding a new tx_write_set column (BLOB) and updates the upgrade path so existing coordinator tables are automatically migrated via Admin.upgrade().

Changes:

• Added Attribute.WRITE_SET ("tx_write_set") and included it in Coordinator.TABLE_METADATA as a BLOB column.
• Updated ConsensusCommitAdmin.upgradeCoordinatorTable() to detect and add the missing tx_write_set column (alongside tx_child_ids) during upgrades.
• Updated unit/integration tests to validate the upgrade behavior when both columns are missing.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
integration-test/src/main/java/com/scalar/db/schemaloader/SchemaLoaderIntegrationTestBase.java	Updates the old-schema test comment to reflect both missing columns for upgrade coverage.
core/src/test/java/com/scalar/db/transaction/consensuscommit/ConsensusCommitAdminTestBase.java	Renames/extends the upgrade test to verify both tx_child_ids and tx_write_set columns are added.
core/src/main/java/com/scalar/db/transaction/consensuscommit/Coordinator.java	Adds tx_write_set (BLOB) to the coordinator table metadata.
core/src/main/java/com/scalar/db/transaction/consensuscommit/ConsensusCommitAdmin.java	Extends coordinator-table upgrade logic to include the new column.
core/src/main/java/com/scalar/db/transaction/consensuscommit/Attribute.java	Introduces the WRITE_SET attribute constant.

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