User decision 2026-11-05: unified schema, rejecting the rehearsal
runtime column-union workaround and a ledger rename. One definition
(cloud.attempt_ledger.TASK_ATTEMPTS_DDL, 12 columns) shared by
cloud.attempts and cloud.db.POSTGRES_SCHEMA; ensure builds the
unified table fresh and migrates old resume, gap-3 ledger, and
rehearsal shapes in place with rows intact. aggregate counts
ledger rows only (outcome NULL = resume row, never counted).
SQLite verified by 8 new tests; Postgres real-DB upgrade path
explicitly NOT verified (see batch summary). Local commit only:
no merge, no push, no deploy.
