alembic asked for confirmation on a destructive downgrade and the agent's run stalled with zero output for 10 minutes

TL;DR: Alembic itself runs headless - the prompt is almost certainly coming from a custom env.py hook or a wrapper script, not from alembic core. Find the prompt's source, review the downgrade SQL offline first with the --sql flag, then answer the prompt programmatically or parameterize the hook. Never let a destructive downgrade wait on a human in an unattended run.

alembic asked for confirmation on a destructive downgrade and the agent's run stalled with zero output for 10 minutes

1. Confirm the prompt exists and find its wording: run the same downgrade command interactively in a terminal.

Expected: you see the actual confirmation question and can read which step asks it.

1. Find the prompt's source: search env.py and any wrapper scripts for interactive input calls.

Expected: you locate the hook or wrapper that asks for confirmation - alembic core has no such prompt.

1. Review what the downgrade would do before answering anything: run alembic downgrade [target-revision] --sql and read the generated SQL.

Expected: the full SQL of the downgrade printed without touching the database.

1. Decide the policy: if the hook is a safety guard, keep it for interactive use but give the agent a non-interactive path (an explicit flag or environment switch that records the approval). If it is leftover scaffolding, remove it.

Expected: the agent's run has a deterministic, prompt-free path to the downgrade.

1. Add a stdin guard to the harness: any step that blocks on stdin with no tty fails fast.

Expected: future prompt-waits become immediate errors, not 10-minute stalls.

Use this when

• an alembic downgrade (or any alembic run) stalls with zero output
• a confirmation prompt appears that alembic's own docs do not mention
• a destructive downgrade must run in an unattended agent session

Not for this skill when

• the downgrade fails with a SQL error - fix the migration
• you are unsure the downgrade is safe - stop and review it with a human first
• the stall has output (logs, progress) - that is a slow migration, not a prompt

Variant phrasings

• alembic downgrade hangs waiting for confirmation
• alembic run stalls with no output on destructive downgrade
• headless alembic blocked on interactive prompt

Why it happens

Alembic's command line is fully non-interactive by design - upgrades and downgrades never ask questions. Teams often add confirmation hooks into env.py or wrap the CLI in a script that prompts before destructive operations. Those additions work fine for a developer at a keyboard and freeze solid in an agent sandbox with no tty: the process blocks on input that will never arrive, producing zero output for as long as the harness lets it wait.

Edge cases

• Reviewing with --sql shows the SQL but not data-loss consequences - a DROP COLUMN looks innocent in SQL and destroys data. Read it as a human would.
• If the hook reads from the real stdin even with the bypass flag set, fix the hook - a bypass that does not bypass is worse than no bypass.
• Downgrades that drop tables cannot be undone by re-running upgrade - take a backup or snapshot before any destructive downgrade, attended or not.
• An agent that can self-approve destructive downgrades needs that authority stated explicitly in its runbook, not implied.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_Ls2S6lLvjX5WYnlEqCx79Q