runtime schema repair must record DDL changes in the migration ledger

[EtanHey]

Problem

BrainLayer's runtime schema-ensure path can create or replace FTS objects without writing a corresponding schema_migrations or migration_events record.

During the M1 outage, the index job reported missing/mismatched chunks_fts_* objects. Hours later the 21-object runtime contract passed, but:

• the latest schema_migrations entry predated the repair by weeks;
• migration_events was empty.

This made the exact repair time and actor impossible to establish.

Expected

Every runtime path that mutates DDL should leave an atomic, queryable event containing at least:

• timestamp;
• actor/path;
• prior and resulting schema fingerprint;
• affected objects;
• success/failure.

Acceptance

• Regression test performs a runtime FTS/schema repair and asserts a ledger event.
• No event is written for a read-only validation.
• Failed repairs record failure without claiming the resulting fingerprint.
• Existing explicit migrations remain compatible.