fix(rollback): plan rollback from selected apply

[aparajon]

Summary

Rollback is now planned from the apply the operator selected, after validating that it is the current completed schema change for the PR/database/type/environment. schemabot rollback <apply-id> rebuilds declarative schema files from that source plan's captured original_files, and stores a new rollback plan for review.

The PR comment flow now pins that reviewed rollback plan to the database lock, and rollback-confirm consumes the lock-pinned plan instead of re-planning. That keeps rollback deterministic when newer plans exist or concurrent comment deliveries occur, while still rejecting stale apply IDs instead of rolling back an older schema change.

╭──────────────────────╮     ╭──────────────────────╮     ╭──────────────────────╮
│ rollback <apply-id>  │────▶│ validate current     │────▶│ plan from source     │
│ from PR comment      │     │ completed apply      │     │ plan original_files  │
╰──────────────────────╯     ╰──────────────────────╯     ╰──────────┬───────────╯
                                                                      │
                                                                      ▼
                                                           ╭──────────────────────╮
                                                           │ pin rollback plan    │
                                                           │ to database lock     │
                                                           ╰──────────┬───────────╯
                                                                      │
                                                                      ▼
                                                           ╭──────────────────────╮
                                                           │ rollback-confirm     │
                                                           │ applies pinned plan  │
                                                           ╰──────────────────────╯

The rollback path is now engine-agnostic over captured files: MySQL table files and Vitess artifacts such as vschema.json are both carried through original_files. Unsafe cases still fail closed: older applies without captured original files are rejected, rollback plans cannot be consumed by apply-confirm, and confirmation validates the pinned plan still matches the target database, type, and environment.

Generated with Amp

[Copilot]

Pull request overview

This PR updates rollback planning to be based on the requested apply’s captured pre-apply schema, routes rollback planning through the normal Plan flow so local and gRPC clients share behavior, and extends Tern plan responses to include the captured “original schema” for later rollback planning and remote plan storage.

Changes:

• Add original_schema to SchemaChange in the Tern proto and propagate it through LocalClient Plan responses and SchemaBot plan storage.
• Replace the prior client-level RollbackPlan flow with service-level rollback planning (ExecuteRollbackPlanForApply) that calls the standard Plan path and stores the resulting plan.
• Update webhook/API rollback handlers and tests to use apply-scoped rollback planning.

Reviewed changes

Copilot reviewed 12 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pkg/webhook/rollback.go	Rollback plan generation now uses the requested apply; rollback-confirm re-plans via the service.
pkg/tern/local_control.go	Removes LocalClient RollbackPlan implementation (no longer needed).
pkg/tern/local_client.go	Attaches stored OriginalSchema to plan response schema changes.
pkg/tern/local_client_integration_test.go	Asserts OriginalSchema is present in Plan responses.
pkg/tern/grpc_client.go	Removes unsupported RollbackPlan method.
pkg/tern/client.go	Removes RollbackPlan from the tern.Client interface.
pkg/proto/tern.proto	Adds original_schema field to SchemaChange.
pkg/proto/ternv1/tern.pb.go	Regenerated protobuf bindings for original_schema.
pkg/proto/ternv1/tern_grpc.pb.go	Regenerated gRPC bindings (version bump).
pkg/api/rollback_plan_integration_test.go	Integration test ensuring rollback uses the requested apply’s original schema and stores rollback plan original schema.
pkg/api/proto_helpers.go	Persists SchemaChange.OriginalSchema into stored plan namespaces.
pkg/api/plan_handlers.go	Introduces ExecuteRollbackPlanForApply, factors out storePlanResponse, adds latest-completed-apply lookup.
pkg/api/handlers_test.go	Enhances mock Tern client to capture/return Plan requests/responses.
pkg/api/control_handlers.go	Rollback plan endpoint now plans from the requested apply (apply-scoped).

Files not reviewed (2)

• pkg/proto/ternv1/tern.pb.go: Language not supported
• pkg/proto/ternv1/tern_grpc.pb.go: Language not supported

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