Add newcomer guide, agent guide, and sample app files

DIACHRON.md explains the framework to newcomers joining a
diachron-based project.  diachron/AGENTS.md helps AI coding
agents work with the framework conventions and commands.
backend/types.ts and backend/services.ts are sample starting
points for application-specific types and services.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

DIACHRON.md

@@ -0,0 +1,168 @@
+# What is diachron?
+
+diachron is a web framework for TypeScript and Node.js.  It uses a Go-based
+master process that handles file watching, building, process management, and
+request proxying.  The application code is TypeScript running on Express.js.
+
+If you're joining a project that uses diachron, this document will orient you.
+
+## Why diachron exists
+
+diachron was built around a few frustrations with mainstream web frameworks:
+
+- **No dev/prod split.**  Most frameworks behave differently in development and
+  production.  diachron doesn't.  The master process watches files, rebuilds,
+  and manages workers the same way everywhere.  There is no `NODE_ENV`.
+
+- **Managed tooling.**  Node.js, pnpm, and other tools are downloaded and
+  pinned to exact versions inside the project.  You don't install them
+  system-wide.  Everyone on the team runs the same binaries.
+
+- **PostgreSQL, directly.**  No ORM, no database abstraction layer.  You write
+  SQL (via Kysely for type safety) and talk to PostgreSQL.  If you need
+  MySQL or SQLite support, this is not the framework for you.
+
+- **Debuggability over magic.**  Everything is explicit and inspectable.
+  Logging and observability are first-class concerns, not afterthoughts.
+
+diachron is inspired by the
+[Taking PHP Seriously](https://slack.engineering/taking-php-seriously/) essay
+from Slack Engineering.  It's designed for small to medium systems (what we
+call "Ring 0 and Ring 1") -- not heavy-compliance or banking-scale
+applications.
+
+## How it works
+
+When you run `./master`, the following happens:
+
+1. The Go master process starts and watches your TypeScript source files.
+2. It builds the backend using `@vercel/ncc`, producing a single bundled JS
+   file.
+3. It starts one or more Node.js worker processes running your Express app.
+4. It proxies HTTP requests from port 8080 to the workers.
+5. When you edit a source file, it rebuilds and restarts the workers
+   automatically.
+6. If a worker crashes, it restarts automatically.
+
+There is no separate "dev server" or "hot module replacement."  The master
+process is the only way to run the application.
+
+## Project structure
+
+A diachron project looks like this:
+
+```
+.
+├── DIACHRON.md      # This file (framework overview for newcomers)
+├── master/          # Go master process (framework-owned)
+├── logger/          # Go logging service (framework-owned)
+├── diachron/        # Managed binaries, shims, framework library
+│   ├── AGENTS.md    # Guide for AI coding agents
+│   ├── binaries/    # Downloaded Node.js, pnpm (gitignored)
+│   ├── cmd.d/       # Commands available via ./cmd
+│   ├── shims/       # Wrappers that use managed binaries
+│   └── ...
+├── backend/         # Your application code
+│   ├── app.ts       # Entry point
+│   ├── routes.ts    # Route definitions
+│   ├── handlers.ts  # Route handlers
+│   ├── services.ts  # Service layer
+│   ├── types.ts     # Application types
+│   ├── config.ts    # Application configuration
+│   └── diachron/    # Framework library code (framework-owned)
+├── cmd              # Run managed commands (./cmd pnpm install, etc.)
+├── develop          # Development-only commands (./develop reset-db, etc.)
+├── mgmt             # Management commands safe for production
+├── sync.sh          # Install/update all dependencies
+├── master           # The compiled master binary (after sync)
+└── docker-compose.yml
+```
+
+### File ownership
+
+There are two owners of files in a diachron project:
+
+- **You own** everything in `backend/` (except `backend/diachron/`), plus
+  `docker-compose.yml`, `package.json`, and anything else you create.
+- **The framework owns** `master/`, `logger/`, `diachron/`,
+  `backend/diachron/`, and the top-level scripts (`cmd`, `develop`, `mgmt`,
+  `sync.sh`, `check.sh`).
+
+Don't modify framework-owned files.  This separation keeps framework upgrades
+clean.
+
+## Getting started
+
+```bash
+# Install dependencies and build the master process
+./sync.sh
+
+# Start the application
+./master
+```
+
+The app will be available at `http://localhost:8080`.
+
+You need Linux or macOS on x86_64.  For the full stack (database, Redis,
+etc.), you also need `docker compose`.
+
+## The command system
+
+diachron has three types of commands, separated by intent and safety:
+
+- **`./cmd <command>`** -- Run managed tools (node, pnpm, tsx, etc.).  These
+  use the project's pinned versions, not whatever is installed on your system.
+
+  ```bash
+  ./cmd pnpm install
+  ./cmd pnpm test
+  ```
+
+- **`./mgmt <command>`** -- Management commands that are safe to run in
+  production.  Migrations, user management, that sort of thing.
+
+  ```bash
+  ./mgmt migrate
+  ./mgmt add-user
+  ```
+
+- **`./develop <command>`** -- Development commands that may be destructive.
+  Database resets, fixture loading, etc.  These are gated in production.
+
+  ```bash
+  ./develop reset-db
+  ./develop db           # Open a database shell
+  ```
+
+The rule of thumb: if you'd run it at 3am while tired and worried, it's a
+`mgmt` command.  If it destroys data on purpose, it's a `develop` command.
+
+## Key concepts
+
+### Call and Result
+
+diachron wraps Express's `Request` and `Response` in its own types called
+`Call` and `Result`.  This avoids shadowing and keeps the framework's
+interface distinct from Express internals.  Your handlers receive a `Call`
+and return a `Result`.
+
+### Routes
+
+Routes are defined as data (arrays of `Route` objects in `routes.ts`), not
+through decorators or method chaining.  The framework processes them into
+Express handlers.
+
+### No environment variables for behavior
+
+There is no `NODE_ENV`, no `DEBUG`, no mode switching.  Configuration that
+must vary between deployments (database URLs, secrets) lives in
+configuration files, but the application's behavior doesn't branch on
+environment.
+
+## Further reading
+
+- `README.md` -- Project introduction and requirements
+- `diachron/AGENTS.md` -- Guide for AI coding agents
+- `docs/` -- Design documents and philosophy
+- `docs/commands.md` -- Detailed explanation of the command system
+- `docs/concentric-circles.md` -- What diachron is (and isn't) designed for