DB migration failure at startup panicked via .expect() (main.rs:223),
dumping a raw backtrace for what is usually just "PostgreSQL isn't running
yet". Worse, the 1.6s runtime retry budget was reused at startup, so it
almost always failed against a cold/slow DB (docker-compose without
healthchecks, local Postgres not started, etc.).
Changes:
- pool: extract build_pg_config() (returns Result, no panic); add
validate_database_url() so URL-format / DB_POOL_SIZE errors surface as
friendly exit(1) instead of hitting the LazyLock's unreachable .expect()
- pool: add get_conn_for_startup() — a startup-only retry loop with a
configurable total-duration window (MIGRATE_STARTUP_TIMEOUT_SECS,
default 30s, 500ms interval), separate from the runtime get_conn()
anti-avalanche fast retry (untouched)
- migrate: split run() into run_on_conn(&mut conn) so callers control the
connection-acquisition strategy; main.rs pairs this with the startup
retry. Advisory-lock release comment updated: exit(1) terminates the
process just like panic, so the session-level lock is still freed
- main: startup fatal errors (bad URL, DB unreachable, migration failed)
now each emit tracing::error! + eprintln! ERROR + targeted HINT, then
exit(1) — no panic, no backtrace nudge
- .env.example / AGENTS.md: document MIGRATE_STARTUP_TIMEOUT_SECS
No runtime behavior change: get_conn() and its ~40 call sites are
unchanged. Advisory-lock safety preserved (documented in migrate.rs).
