Improve SET/ENUM validation

[morgo]

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Fixes #618 with a more complete fix.

[Copilot]

Pull request overview

This PR strengthens Spirit’s preflight validation for MySQL ENUM/SET changes to better handle reorder scenarios and to prevent unsafe type conversions in buffered migrations (per issue #618).

Changes:

• Update enumReorderCheck and setReorderCheck to treat non-ENUM/SET existing column types as type conversions (not reorders), avoiding false positives.
• Add a new preflight check (enumSetRemoval) to block ENUM/SET → non-ENUM/SET conversions in buffered mode to prevent ordinal-based corruption.
• Add/extend tests covering VARCHAR→ENUM/SET and buffered/unbuffered behavior, plus utility tests for isEnumOrSetType.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pkg/migration/check/setreorder.go	Skip reorder validation when existing type isn’t ENUM/SET (treat as conversion).
pkg/migration/check/setreorder_test.go	Add coverage for VARCHAR→SET conversions not being flagged as reorders.
pkg/migration/check/enumreorder.go	Skip reorder validation when existing type isn’t ENUM/SET (treat as conversion).
pkg/migration/check/enumreorder_test.go	Add coverage for VARCHAR→ENUM conversions not being flagged as reorders.
pkg/migration/check/enumsetutil.go	Introduce isEnumOrSetType helper.
pkg/migration/check/enumsetutil_test.go	Add tests for isEnumOrSetType.
pkg/migration/check/enumsetremoval.go	New preflight check to block ENUM/SET→non-ENUM/SET in buffered mode.
pkg/migration/check/enumsetremoval_test.go	Add tests ensuring buffered conversions fail and unbuffered conversions pass.

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[Copilot]

Pull request overview

This PR improves Spirit’s preflight validation around ENUM/SET schema changes to prevent unsafe buffered-mode migrations and avoid unavoidable checksum failures from SET member reordering (Issue #618).

Changes:

• Refines ENUM/SET reorder detection by extracting modified columns more generally and skipping reorder validation when the existing column wasn’t ENUM/SET (e.g., VARCHAR → ENUM/SET).
• Adds a new preflight check to block ENUM/SET → non-ENUM/SET type conversions in buffered mode (to prevent ordinal/bitmask replay corruption).
• Adds/extends test coverage for the new behaviors and documents test DB usage patterns in AGENTS.md.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pkg/migration/check/setreorder.go	Updates SET reorder check to identify SET via TiDB type and skip non-ENUM/SET existing-type conversions.
pkg/migration/check/setreorder_test.go	Adds coverage for VARCHAR → SET cases (should not be treated as reorders).
pkg/migration/check/enumreorder.go	Updates ENUM reorder check to identify SET via TiDB type and skip non-ENUM/SET existing-type conversions.
pkg/migration/check/enumreorder_test.go	Adds coverage for VARCHAR → ENUM cases (should not be treated as reorders).
pkg/migration/check/enumsetutil.go	Introduces isEnumOrSetType/isSetType and refactors altered-column extraction helpers.
pkg/migration/check/enumsetutil_test.go	Adds unit tests for isEnumOrSetType.
pkg/migration/check/enumsetremoval.go	New buffered-mode preflight check blocking ENUM/SET → non-ENUM/SET conversions.
pkg/migration/check/enumsetremoval_test.go	New integration tests for buffered vs unbuffered behavior on ENUM/SET → non-ENUM/SET conversions.
AGENTS.md	Updates guidance on when to use the default test DB vs unique test databases.

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[Copilot]

Pull request overview

Improves preflight validation around MySQL SET/ENUM schema changes to better handle reorders and to prevent unsafe buffered-mode type conversions that can corrupt data or guarantee checksum failures.

Changes:

• Make enumReorderCheck / setReorderCheck apply only when the existing column type is ENUM/SET respectively (avoids false failures on VARCHAR→ENUM/SET, etc.).
• Add enumSetRemovalCheck to block buffered-mode conversions from ENUM/SET to non-ENUM/SET, and ENUM↔SET cross-conversions.
• Add/extend integration tests for the new/adjusted behaviors and add small enum/set type-string helpers.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/migration/check/setreorder.go	Skip SET reorder validation when the existing column isn’t a SET (avoids false positives on cross-type conversions).
pkg/migration/check/setreorder_test.go	Adds coverage for VARCHAR→SET scenarios that should not be treated as reorders.
pkg/migration/check/enumreorder.go	Skip ENUM reorder validation when the existing column isn’t an ENUM (avoids false positives on cross-type conversions).
pkg/migration/check/enumreorder_test.go	Adds coverage for VARCHAR→ENUM scenarios that should not be treated as reorders.
pkg/migration/check/enumsetutil.go	Adds helpers to identify enum/set type strings; refactors ALTER parsing to expose all modified columns.
pkg/migration/check/enumsetutil_test.go	Adds tests for the new enum/set type-string helpers.
pkg/migration/check/enumsetremoval.go	New buffered-mode safety check preventing unsafe ENUM/SET removals and ENUM↔SET conversions.
pkg/migration/check/enumsetremoval_test.go	New tests covering buffered vs unbuffered behavior for unsafe conversions.
AGENTS.md	Updates documented testing patterns to reflect common usage in this repo.

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