instructions about new columns

Author: ericallam

.claude/rules/database-safety.md

@@ -7,6 +7,7 @@ paths:
 
 - When adding indexes to **existing tables**, use `CREATE INDEX CONCURRENTLY IF NOT EXISTS` to avoid table locks. These must be in their own separate migration file (one index per file).
 - Indexes on **newly created tables** (same migration as `CREATE TABLE`) do not need CONCURRENTLY.
+- When indexing a **new column on an existing table**, split into two migrations: first `ADD COLUMN IF NOT EXISTS`, then `CREATE INDEX CONCURRENTLY IF NOT EXISTS` in a separate file.
 - After generating a migration with Prisma, remove extraneous lines for: `_BackgroundWorkerToBackgroundWorkerFile`, `_BackgroundWorkerToTaskQueue`, `_TaskRunToTaskRunTag`, `_WaitpointRunConnections`, `_completedWaitpoints`, `SecretStore_key_idx`, and unrelated TaskRun indexes.
 - Never drop columns or tables without explicit approval.
 - New code should target `RunEngineVersion.V2` only.

internal-packages/database/CLAUDE.md

@@ -49,6 +49,10 @@ When adding indexes to **existing tables**:
 
 Indexes on **newly created tables** (in the same migration as `CREATE TABLE`) do not need CONCURRENTLY and can be in the same migration file.
 
+When adding an index on a **new column on an existing table**, use two migrations:
+1. First migration: `ALTER TABLE ... ADD COLUMN IF NOT EXISTS ...` (the column)
+2. Second migration: `CREATE INDEX CONCURRENTLY IF NOT EXISTS ...` (the index, in its own file)
+
 See `README.md` in this directory and `ai/references/migrations.md` for the full index workflow.
 
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