837 backend pg pool created without max idle connection statement timeout settings

[jotel-dev]

Description

This PR addresses issue #837 by ensuring pg.Pool is constructed with environment-configurable settings for maximum pool size, connection timeouts, idle timeouts, and statement execution timeouts. Previously, pg.Pool was instantiated with no explicit tuning, using node-postgres defaults (max 10 connections, no statement timeout), which risked connection pool exhaustion and unbound slow query execution under load.

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ⚡ Performance improvement
• 📚 Documentation update
• 🧪 Test addition or update

Related Issues

Closes #837

Changes Made

• backend/src/lib/pg-pool.ts:
  • Implemented createPgPoolConfig with sane default fallbacks:
    • PG_POOL_MAX: 10
    • PG_IDLE_TIMEOUT_MS: 30000 (30s)
    • PG_CONNECTION_TIMEOUT_MS: 5000 (5s)
    • PG_STATEMENT_TIMEOUT_MS: 30000 (30s)
  • Updated createPgPoolConfig and createPgPool to accept optional Partial<pg.PoolConfig> overrides.
• backend/.env.example:
  • Documented all 4 PostgreSQL pool environment variables with comments and default values.
• backend/src/lib/prisma.ts & backend/prisma/seed.ts:
  • Ensured pool instantiation uses createPgPool().
• backend/tests/pg-pool.test.ts & backend/tests/integration/stream-lifecycle.test.ts:
  • Added unit test cases covering configuration defaults, environment variable overrides, invalid input fallbacks, and custom pool overrides.
  • Updated integration tests to initialize database pools via createPgPool({ connectionString }).

Testing

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Test Steps

1. Run backend unit tests: npm test from backend/ directory. All 51 test files pass, and pg-pool.ts reaches 100% test coverage.
2. Verify env variable overrides by setting PG_POOL_MAX=25, PG_STATEMENT_TIMEOUT_MS=15000, etc., in .env and running createPgPoolConfig().
3. Verify invalid env variable fallbacks (e.g. PG_POOL_MAX=invalid falls back to default 10).

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published
• I have checked for breaking changes and documented them if applicable