ollie-core/ARCHITECTURE.md

ollie Architecture

Philosophy

ollie is a small, extensible core library for building agentic systems. It has no binary of its own — frontends and consumers live in separate repos and import ollie as a dependency. The internal surface area is kept minimal; everything a consumer needs is exported under pkg/.

Package Layout

pkg/
  agent/         — Core interface, agent loop, session and context management
  backend/       — Backend interface + implementations
  config/        — Agent config struct and loader
  mcp/           — MCP client (concrete)
  tools/         — Server and Dispatcher interfaces, tool definitions (builtin.go)
  tools/execute/ — execute.Server: execute_code, execute_tool, execute_pipe
  tools/file/    — file.Server: file_read, file_write

internal/
  sandbox/       — landrun sandbox config and command wrapper

Why internal/sandbox?

The sandbox package is an implementation detail of pkg/tools/execute. It has no stable public API and no reason to be imported by consumers directly. Keeping it internal prevents accidental coupling.

Why pkg/mcp is concrete (not interfaced)

pkg/mcp exposes a concrete Client rather than an interface. MCP is a well-defined protocol; the client is a thin transport layer and there is currently no need for consumers to swap implementations. This may be revisited.

Extension Points

Consumers extend ollie by implementing or composing its interfaces:

• backend.Backend — swap or add LLM backends
• tools.Server — add a new tool server (built-in or MCP-backed); all servers are equal
• tools.Dispatcher — replace the tool router entirely (e.g. remote dispatcher, mock)
• agent.Core — the agent's public API; frontends drive it without knowing internals

All tool servers implement the same tools.Server interface regardless of whether they are built-in or backed by MCP. There is no special "builtin" concept — execute.Server and file.Server are registered by name the same way MCP servers are, and are torn down and recreated on /agent switches just like MCP connections.

Each built-in server package exports a Decl function (func Decl(...) func() tools.Server) — a parameterized factory that produces a fresh server instance. tools.NewDispatcherFunc takes a map of name→Decl result and returns a func() tools.Dispatcher suitable for agent.AgentCoreConfig.NewDispatcher. tools.NewServer(client) wraps an mcp.Client as a tools.Server.

execute.Decl(workdir string) accepts a working directory that is set as cmd.Dir for sandboxed commands and used to expand {CWD} in the sandbox config. Pass "" to fall back to os.Getwd().

Adding a new tool server:

1. Implement tools.Server in a new package under pkg/tools/
2. Export func Decl(...) func() tools.Server
3. Add tool definitions to pkg/tools/builtin.go (avoids import cycles)
4. Register the Decl result by name in tools.NewDispatcherFunc — no frontend changes needed

Data Flow

Frontend
  └── agent.Core.Submit(prompt)
        └── loop.run()
              ├── backend.ChatStream()              — LLM call
              └── tools.Dispatcher.Dispatch(...)   — tool dispatch
                    ├── "execute" → tools.Server
                    │       execute_code / execute_tool / execute_pipe
                    ├── "file"    → tools.Server
                    │       file_read / file_write
                    └── "<servername>"  → tools.Server

All tool calls go through one tools.Dispatcher.Dispatch path. Every registered server is a tools.Server; the dispatcher routes by name and is agnostic to how any server is implemented.

Built-in Tools

Five tools are registered across two servers:

Server	Tool	What it does
execute	execute_code	Runs inline bash in a landrun sandbox
execute	execute_tool	Reads a named script from OLLIE_TOOLS_PATH and runs it sandboxed
execute	execute_pipe	Chains steps, piping stdout of each into stdin of the next
file	file_read	Reads a file with line numbers (required before file_write)
file	file_write	Writes or patches a file by line range

Tool definitions (ExecuteDefs, FileDefs) live in pkg/tools/builtin.go to avoid import cycles — the subpackages import pkg/tools, so pkg/tools cannot import them back.

OLLIE_TOOLS_PATH defaults to ~/.local/share/ollie/tools. The directory can be a symlink or a mountpoint — execute_tool treats it as an ordinary filesystem path.

Typical Consumer Setup

newDispatcher := tools.NewDispatcherFunc(map[string]func() tools.Server{
    "execute": execute.Decl(workdir),  // "" falls back to os.Getwd()
    "file":    file.Decl,
})

env := agent.BuildAgentEnv(cfg, newDispatcher(), workdir)  // also connects MCP servers from cfg

core := agent.NewAgentCore(agent.AgentCoreConfig{
    Backend:       be,
    WorkDir:       workdir,
    Env:           env,
    NewDispatcher: newDispatcher,
    // ...
})

BuildAgentEnv adds MCP servers from the config on top of the pre-registered servers. On /agent switches, NewDispatcher is called to produce a fresh dispatcher — all servers (built-in and MCP) are torn down and recreated for the new agent config. WorkDir is preserved across switches.

Session and Context

agent.Session owns the message history. A contextBuilder enforces a rolling window to prevent unbounded prompt growth. When the window fills, older messages are either evicted (with a compaction notice injected) or proactively summarized via /compact.

Sandboxing

internal/sandbox wraps commands with landrun (Landlock LSM). Configuration is layered:

1. Global defaults (~/.config/ollie/sandbox.yaml)
2. Named sandbox overlay (~/.config/ollie/sandbox/<name>.yaml)

If superpowerd is running, commands are additionally wrapped with superpowers run-session for privilege scoping (optional, detected at runtime).

Frontends

The reference frontend is ollie-tui: a readline-based terminal UI that imports ollie as a library. It is the only consumer of agent.Core today, but the interface is intentionally frontend-agnostic.