Remove the --strict flag

[morgo]

Fixes #909.

Summary

Removes the --strict migration flag (and the Migration.Strict field) entirely. This is the strict-removal portion of #879, forked out into its own change so it can land independently of the status-API work in that PR.

With --strict gone, a failed resume-from-checkpoint always logs the reason and falls back to a fresh migration — Spirit's default best-effort behavior. The flag was already documented as not-recommended and had a surprising gap (it does not hard-fail on a checkpoint-table schema mismatch), so it was a footgun rather than a safety net. See #909 for the full rationale.

Changes

• Remove the --strict CLI flag / Migration.Strict field (pkg/migration/migration.go)
• Remove the strict branch in setup() and update a stale comment (pkg/migration/runner.go)
• Remove the WithStrict() test helper (pkg/migration/helpers_test.go) and the four TestResumeFromCheckpoint*Strict* tests (pkg/migration/resume_test.go)
• Remove the --strict documentation in docs/migrate.md and pkg/migration/resume-from-checkpoint.md
• Drop the WithStrict() reference in AGENTS.md

The typed status.Err* resume errors (ErrMismatchedAlter, ErrBinlogNotFound, ErrCheckpointTooOld, ErrCheckpointCollision) are retained — they are still produced and logged internally; only the strict consumer of them is removed.

Breaking change

Anyone passing --strict will now get a Kong error on the unknown flag.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Removes Spirit’s --strict migration mode end-to-end (CLI surface, Migration config, runner behavior branch, tests, and documentation) so resume-from-checkpoint is always best-effort: on any resume failure, Spirit logs the reason and falls back to starting a fresh migration.

Changes:

• Deleted the --strict CLI flag and Migration.Strict field, and removed the strict-only error-return branch in Runner.setup().
• Removed strict-mode test helper and strict-only resume tests; adjusted remaining resume tests/comments to match best-effort semantics.
• Updated docs to remove strict-mode guidance and describe the single fallback behavior.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/migration/runner.go	Removes strict-mode branching in setup and updates resume-related comments.
pkg/migration/resume-from-checkpoint.md	Updates checkpoint resume docs to reflect always-best-effort behavior and removes strict-mode section.
pkg/migration/resume_test.go	Deletes strict-mode resume tests and updates remaining test comments accordingly.
pkg/migration/migration.go	Removes the Strict field / --strict flag definition from the migration config struct.
pkg/migration/helpers_test.go	Removes WithStrict() test helper.
docs/migrate.md	Removes --strict documentation and updates resume-related text to match new behavior.
AGENTS.md	Removes WithStrict() from the documented test runner options list.

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