docs: add some basic info to readme

README.md

@@ -1,11 +1,110 @@
 # Thespian
+
 Fast & flexible actors for Zig, C & C++ applications
 
 To build:
+
 ```
-./zig build
+zig build
 ```
 
 See `tests/*` for many interesting examples.
 
+To run the tests:
+```
+zig build test
+```
+
+---
+
+## Architecture Overview
+
+Thespian is an actor framework where concurrent units ("instances")
+communicate exclusively via message passing, with no shared mutable state.
+Messages are encoded using **CBOR** (Concise Binary Object Representation).
+
+The library has three layers:
+
+1. **C++ core** - the primary implementation (`src/instance.cpp`, `src/executor_asio.cpp`, `src/hub.cpp`)
+2. **C API** - a thin wrapper layer in `src/c/` exposing the C++ core to other languages
+3. **Zig module** - `src/thespian.zig` wraps the C API into idiomatic Zig types with comptime features
+
+---
+
+## Key Concepts
+
+**`context`** - the runtime environment. You create one, spawn actors into
+it, then call `run()`. It owns the executor thread pool.
+
+**`instance` / actor** - each spawned actor is a `behaviour` (a
+`std::function<result()>`) that registers a `receiver` to handle incoming
+messages. Actors run on an executor. Currently the only executor provided
+in this repo is one backed by ASIO.
+
+**`handle` / `pid`** - a reference to a live actor. In C++ this is
+`thespian::handle`; in Zig it is `pid` (owned) or `pid_ref` (borrowed).
+Sending to an expired handle is safe and fails gracefully.
+
+**`message`** - a CBOR-encoded byte buffer. Pattern matching uses
+`extract`/`match` with a composable matcher DSL (`string`, `array`, `any`,
+`more`, etc.).
+
+**`hub`** - a pub/sub broadcast actor. Subscribers receive all broadcasts;
+supports filtering and Unix socket-based IPC.
+
+---
+
+## I/O Primitives
+
+| Primitive                        | Purpose                                          |
+| -------------------------------- | ------------------------------------------------ |
+| `timeout`                        | One-shot timer                                   |
+| `metronome`                      | Repeating timer                                  |
+| `signal`                         | OS signal handling                               |
+| `tcp_acceptor` / `tcp_connector` | TCP networking                                   |
+| `unx_acceptor` / `unx_connector` | Unix domain sockets                              |
+| `socket`                         | Raw FD-backed socket I/O                         |
+| `file_descriptor`                | Async wait on arbitrary file descriptors (posix) |
+| `file_stream`                    | Async read/write on file handles (win32)         |
+| `subprocess`                     | Child process management (platform-specific)     |
+
+### ⚠️ I/O Primitive Ownership - Critical Rule
+
+**Every I/O primitive is owned by the actor that was executing at the time
+it was created.** Async completion messages from a primitive are delivered
+only to that owning actor. There is no way to transfer ownership or
+redirect delivery to a different actor after construction.
+
+A common mistake is to create an I/O primitive in one actor and then spawn
+a separate "handler" actor, passing the primitive (or its handle) to it.
+The handler will never receive any events - they will continue to be
+delivered to the original actor that created the primitive.
+
+**The correct pattern:** the actor responsible for handling a primitive's
+events must be the one that creates it. If you need a dedicated handler
+actor, have it create its own primitives from within its own behaviour.
+
+---
+
+## Ownership & Lifecycle
+
+- Zig's `pid` is `Owned` (must call `deinit()`); `pid_ref` is `Wrapped`
+  (borrowed, no deinit required)
+- Actors can `trap()` exit signals and `link()` to other actors for supervision
+- `spawn_link` ties an actor's lifetime to its parent
+
+---
+
+## Build System
+
+- **Zig 0.15.2+** required
+- Dependencies: `cbor` (CBOR codec), `asio` (ASIO network executor),
+  `tracy` (optional profiling via `-Denable_tracy=true`)
+- Produces a static library `libthespian` and a Zig module
+- Tests live in `test/` and cover both the C++ and Zig APIs
+
+---
+
+## Misc
+
 See DeepWiki for more documentation: [![Ask DeepWiki](https://deepwiki.com/badge.svg)](https://deepwiki.com/neurocyte/thespian)