[ElanHasson]

Stacked on #15 (pgx v5 / tern v2 upgrade) — merge that first; this PR's diff against main includes it until then.

Story: MARSOHS-1643 (under epic MARSOHS-1585).

Motivation

tester serve runs the tern migrations at startup, i.e. inside the web container's health-check window on App Platform:

• a slow migration (e.g. an index build on the 15 GB tests table) makes the deploy look unhealthy and roll back mid-migration;
• multiple web replicas serialize on tern's advisory lock;
• the worker component rolls independently, so it can start against a not-yet-migrated schema.

A PRE_DEPLOY job runs once, to completion, before any component of the new deployment starts.

What changed

• tester migrate (cmd/tester/migrate.go): connects with --pg-dsn / MIGRATE_PG_DSN, falling back to SERVE_PG_DSN so the job can reuse the web service's env verbatim; applies pending migrations; exits 0 (non-zero on failure). It does not read config.json — the DSN is the only thing it needs (in this repo the DSN is a serve flag/env, not a config-file field).
• Migration logging: Migrator.OnStart is wired in (*db.PG).migrator, so both migrate and serve log every migration they apply (db: applying migration 5 "..." (up)).
• serve --migrate-on-start flag / SERVE_MIGRATE_ON_START env (bool, default true, so current behaviour is unchanged; same pattern as --pg-dsn / SERVE_PG_DSN). When false, serve skips Init and calls the new (*db.PG).CheckSchema, which compares tern's current version to len(pgMigrations) and fails with database schema is at version N, this binary expects M: run tester migrate`` if behind — so a misordered deploy fails fast rather than serving a stale schema. A newer schema is tolerated so the image can be rolled back. It is a flag rather than a config.json field so the `web` component can be switched over with an app-spec edit, no e2e image rebuild. `serve` uses the concrete `*db.PG`, so the `db.DB` interface and `db_mock.go` are unchanged.
• README: documents tester migrate, --migrate-on-start, an App Platform PRE_DEPLOY snippet, and the rollout order.
• Tests: TestPG_CheckSchema (current → rolled back one migration → re-migrated → ahead) against real Postgres; TestServe_migrateOnStart (default true, env overrides default, flag overrides env).

Rollout order

1. Deploy an image containing this change with --migrate-on-start at its default (true). No behaviour change.
2. Add the PRE_DEPLOY job to the e2e app spec. Both the job and the server now migrate; the server's is a no-op.
3. On the web component, set SERVE_MIGRATE_ON_START=false in envs (or run_command: tester serve --migrate-on-start=false ...). No image rebuild. The server now only verifies the schema.

App spec snippet (goes in digitalocean/e2e, separate manual step, not in this PR)

jobs:
  - name: migrate
    kind: PRE_DEPLOY
    image:                    # same image reference as the web/worker components
      registry_type: DOCR
      registry: do-e2e-canaries
      repository: <e2e image repository>
      tag: <same tag as web/worker>
    run_command: tester migrate
    envs:
      - key: SERVE_PG_DSN     # same DB env as web; MIGRATE_PG_DSN also works
        scope: RUN_TIME
        value: ${db.DATABASE_URL}

The binary is /bin/tester in the image (Dockerfile), invoked the same way serve/run are today.

Verification

gofmt -l ., go vet ./..., go generate ./... && git diff --exit-code db/db_mock.go, PG_DSN=... go test -race ./... all pass locally against postgres:16. Also exercised the built binary: serve --migrate-on-start=false and SERVE_MIGRATE_ON_START=false serve against an empty DB both exit 1 with the version message; migrate (via SERVE_PG_DSN) applies 5 migrations and exits 0; serve with the env set then starts; default serve on a fresh DB applies the 5 migrations itself.

[semgrep-code-digitalocean]

Use github.com/jackc/pgx/v5 or newer instead of other postgres driver libraries

🥳 Fixed in commit f251d49 🥳

[ElanHasson]

Resolved by upgrading the whole repo to github.com/jackc/pgx/v5 + github.com/jackc/tern/v2 in #15, which this PR is now stacked on. cmd/tester/migrate.go imports github.com/jackc/pgx/v5/pgxpool as of f251d49; pgx/v4, jackc/pgconn, tern v1 and lib/pq are gone from go.mod.