AI Assistant Rules for pg_exporter

# AI Assistant Rules for pg_exporter

Follow all guidelines in `.github/copilot-instructions.md` and `CONTRIBUTING.md`.

## Critical: Zero Tolerance for Panics
- Always use `try_get()`, never `get()`
- Always cast SQL numeric types explicitly (`::bigint`, `::double precision`)
- Always check denominators before division
- Always check extension availability with `fetch_optional()`

## Code Quality Standards
- **Formatting**: `cargo fmt --all -- --check`
- **Linting**: `cargo clippy --all-targets --all-features`
- **Testing**: `just test` (runs clippy, fmt, and all tests)

## Required Tests for New Collectors
1. Registration test
2. Extension availability test
3. NULL value handling test
4. Type conversion test
5. Realistic workload test

## Before Committing
```bash
just postgres                      # Start PostgreSQL
./scripts/setup-local-test-db.sh  # Verify test database
just test                          # Run all checks
```

## Code Style
- Minimal comments - code should be self-documenting
- Use `anyhow::Result` for error handling
- Use `warn!()` for non-critical issues, `debug!()` for verbose info
- Never panic in production code

## Documentation
See `CONTRIBUTING.md` for complete development guide and safe coding patterns.

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**Remember**: Every production panic is a test we didn't write.