Add migration for branched_from_task_id column

Add database migration to support task branching feature:
- Add branched_from_task_id UUID column to tasks table
- Create index for efficient lookups
- FK constraint with ON DELETE SET NULL for referential integrity

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/makima/migrations/20250121000000_add_branched_from.sql b/makima/migrations/20250121000000_add_branched_from.sql
new file mode 100644
index 0000000..bbb395b
--- /dev/null
+++ b/makima/migrations/20250121000000_add_branched_from.sql
@@ -0,0 +1,10 @@
+-- Add branched_from_task_id column to tasks table for task branching support.
+-- This allows creating new tasks that branch from an existing task's conversation,
+-- enabling "what if" exploration of different approaches from the same starting point.
+
+ALTER TABLE tasks
+ADD COLUMN IF NOT EXISTS branched_from_task_id UUID REFERENCES tasks(id) ON DELETE SET NULL;
+
+CREATE INDEX IF NOT EXISTS idx_tasks_branched_from ON tasks(branched_from_task_id);
+
+COMMENT ON COLUMN tasks.branched_from_task_id IS 'Source task ID when this task was branched from another task conversation';