Assigning conn.isolation_level commits any pending transaction as a side
effect, so entering the context manager with a transaction open silently
committed the caller's work and made a later rollback() a no-op. All
internal callers already ensure no transaction is open; the public API
now enforces it, matching enable_wal() and disable_wal().
Refs https://github.com/simonw/sqlite-utils/issues/769#issuecomment-4900034150
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
A dedicated sqlite_utils.db.TransactionError exception is clearer
to catch than a generic RuntimeError, and gives future
transaction-state guards a home.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UnLnhsH25Nnv7LHhekUfPd
Changing the journal mode assigns conn.isolation_level, which
commits any open transaction as a side effect - silently breaking
the rollback guarantee of atomic() blocks and of user-managed
transactions. Both methods now raise RuntimeError if a transaction
is open. Calling them when the database is already in the requested
mode remains a no-op.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UnLnhsH25Nnv7LHhekUfPd
