fix(core): commit generated migration for session directory index #243

Description

unit (linux) is red on dev itself (the "declared schema has no ungenerated migrations" check in packages/core/test/database-migration.test.ts). Root cause: session_directory_time_created_id_idx is already declared in packages/core/src/database/schema.ts, but the generated migration for it (schema.json, schema.gen.ts, migration.gen.ts, and the migration file itself) was never committed.

Reproduced locally on a clean dev checkout: bun test test/database-migration.test.ts fails with "Core schema has ungenerated database migrations."

Fix

Ran bun script/migration.ts from packages/core to generate the missing migration. The diff is purely the new index's generated migration entry — no other schema changes.

How to verify

• bun test test/database-migration.test.ts from packages/core: 16 pass, 0 fail (was 1 fail before).
• Full packages/core suite: 1135 pass; 2 pre-existing failures in util.flock/util.effect-flock are unrelated (caused by running tests as root, not by this change).