[zorn]

Closes #308

This enables pg_stat_statements on flick_prod, so LiveDashboard's Ecto Stats "outliers" and "calls" tabs can show which queries cost the most time. It follows the Ecto Stats rollout in #305.

The risk is a skipped extension, not a failed deploy

The migration runs at boot, so an error there would stop the deploy. To prevent that, the migration catches any error, rolls back, and logs pg_stat_statements skipped: <reason>. A revert followed by a rollback drops the extension. Nothing in Flick reads the extension, and the suite is unchanged at 193 passing.

Production preloads the library

A rolled-back dry run in a remote shell on flick_prod created the extension and read its view, returning {:error, :dry_run}. Render preloads the library, and the app role may create the extension.

The migration creates the extension, then reads its view once

The issue's plain CREATE EXTENSION broke Ecto Stats on any server that does not preload the library, which includes local and CI Postgres. A first version read shared_preload_libraries to decide, but only superusers can read that setting. The migration instead creates the extension and reads its view once. If either step raises, the block rolls back. I checked each path by hand on postgres:18:

Server	Result
Preloaded, superuser	Extension created, view readable
Not preloaded	Skipped with notice
Preloaded, plain owner role	Skipped with notice (permission denied)

Worth a reviewer's attention

• A skip is logged, not fatal. A diagnostics extension should never block a deploy, but a skip shows up only in the migration log.
• The check runs once. If a server starts preloading the library later, a new migration has to create the extension.
• The down step always drops the extension. Production had no extension before this migration, so this migration is what creates it.
• No automated test covers the preloaded path. CI's service container cannot pass -c shared_preload_libraries, so I verified it by hand.

[Copilot]

🟢 Approval recommended

The scoped migration handles the documented failure paths and rollback, with no blocking issues identified.

No open issues 🎉

What changed in this PR

Enables pg_stat_statements where supported so LiveDashboard’s Ecto Stats can report query costs, following the dashboard rollout in #305.

Changes:

• Adds a reversible migration that creates and probes the extension, skipping expected preload and permission failures with a notice.
• Documents the requirements for the “outliers” and “calls” tabs.

File	Description
priv/​repo/​migrations/​20261020164842_enable_pg_stat_statements.exs	Creates and checks the extension; drops it on rollback.
AGENTS.md	Documents preload requirements and local/CI skip behavior.

_{Review effort: Balanced}