# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project Overview

MCDSL (Metacircular Dynamics Standard Library) is the shared Go library for the Metacircular platform. It extracts common patterns from production services into reusable, tested packages. MCDSL is not a deployed service — it is imported by other services.

**Module path:** `git.wntrmute.dev/kyle/mcdsl`

## Build Commands

```bash
make all          # vet -> lint -> test -> build
make build        # go build ./...
make test         # go test ./...
make vet          # go vet ./...
make lint         # golangci-lint run ./...
make clean        # go clean ./...
```

Run a single test:
```bash
go test ./auth/ -run TestCacheExpiry
```

## Packages

| Package | Purpose |
|---------|---------|
| `auth` | MCIAS token validation with 30s SHA-256 cache |
| `db` | SQLite setup (WAL, foreign keys, busy timeout), migration runner, VACUUM INTO snapshots |
| `config` | TOML loading with env var overrides, Base config struct with standard sections |
| `httpserver` | TLS 1.3 HTTP server with chi, logging middleware, JSON helpers, graceful shutdown |
| `grpcserver` | gRPC server with TLS, auth/admin interceptors, default-deny for unmapped methods |
| `csrf` | HMAC-SHA256 double-submit cookie CSRF protection |
| `web` | Session cookies, auth middleware, template rendering for htmx UIs |
| `health` | REST and gRPC health check handlers |
| `archive` | tar.zst snapshots with SQLite-aware backup (VACUUM INTO) |

## Import Pattern

Services import individual packages with aliased imports:

```go
import (
    mcdslauth   "git.wntrmute.dev/kyle/mcdsl/auth"
    mcdsldb     "git.wntrmute.dev/kyle/mcdsl/db"
    mcdslconfig "git.wntrmute.dev/kyle/mcdsl/config"
    "git.wntrmute.dev/kyle/mcdsl/httpserver"
    "git.wntrmute.dev/kyle/mcdsl/grpcserver"
)
```

## Inter-Package Dependencies

```
archive --> db
auth --> (mcias client library)
config --> auth (for auth.Config type)
csrf --> (stdlib only)
db --> (modernc.org/sqlite)
grpcserver --> auth, config
health --> db
httpserver --> config
web --> auth, csrf
```

No circular dependencies. Each package can be imported independently except where noted.

## Key Design Decisions

- **No global state, no init().** Explicit construction, explicit errors.
- **Stdlib-compatible types.** Functions accept and return `*sql.DB`, `http.Handler`, `*slog.Logger`, `context.Context` — not custom wrappers.
- **TLS 1.3 minimum is non-configurable.** `httpserver` and `grpcserver` enforce this unconditionally.
- **Default-deny for unmapped gRPC methods.** A method not in the MethodMap is rejected, not allowed. This is the most important safety property.
- **Cookie security flags are non-configurable.** Session cookies are always `HttpOnly`, `Secure`, `SameSite=Strict`.
- **Extract, don't invent.** Every package comes from patterns proven across multiple services. No speculative abstractions.
- **Optional composition.** Services import only the packages they need.

## Critical Rules

- No CGo — all builds use `CGO_ENABLED=0`, SQLite via `modernc.org/sqlite`
- Testing uses stdlib `testing` only, real SQLite in `t.TempDir()`, no mocks for databases
- Token cache keys are SHA-256 of the raw token (never use raw token as map key)
- CSRF secrets must come from `crypto/rand`, unique per service instance
- Database file permissions are always `0600`
- Verify changes with `go build ./...` and `go test ./...` before claiming resolution

## Key Documents

- `ARCHITECTURE.md` — Full library specification with all package APIs
- `README.md` — Usage examples and quick start
- `PROJECT_PLAN.md` — Implementation phases
- `PROGRESS.md` — Development status
- `../engineering-standards.md` — Platform-wide standards (authoritative reference)