Fix: Surface destructive schema changes on forward-only models during dev plans (#5719) by brucearctor · Pull Request #5732

Fix: Surface destructive schema changes on forward-only models during dev plans (#5719) by brucearctor · Pull Request #5732 · SQLMesh/sqlmesh

… dev plans (SQLMesh#5719)

Extend _check_destructive_additive_changes in PlanBuilder to also inspect
indirectly modified forward-only snapshots for destructive/additive schema
changes. Previously, only directly modified snapshots were checked, and the
evaluator-level check (MigrateSchemasStage) is skipped for dev plans.

Changes:
- Refactor schema diffing into reusable _check_schema_change helper
- Pass indirectly_modified mapping to _check_destructive_additive_changes
- Add loop to check indirectly modified forward-only snapshots
- Add 5 new tests for is_dev=True scenarios (ERROR/WARN/ALLOW modes,
  indirect modification, --forward-only flag)