# 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
  tools/execute/   — execute.Server: execute_code, execute_tool, execute_pipe
  tools/file/      — file.Server: file_read, file_write, file_edit, file_glob, file_grep
  tools/memory/    — memory.Server: memory_remember, memory_recall
  tools/reasoning/ — reasoning.Server: reasoning_think
  tools/task/      — task.Server: task_plan, task_complete

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. Includes `Close()` to release session resources (tmpdir under `/tmp/ollie/`).

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(cwd string)` and `file.Decl(cwd string)` accept a working directory. Pass `""` to fall back to `os.Getwd()`.

`task.Decl(planDir string)` accepts the directory where plan files are written.

**Adding a new tool server:**
1. Implement `tools.Server` in a new package under `pkg/tools/`
2. Export `func Decl(...) func() tools.Server`
3. 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 / file_edit / file_glob / file_grep
                    ├── "memory"    → tools.Server
                    │       memory_remember / memory_recall
                    ├── "reasoning" → tools.Server
                    │       reasoning_think
                    ├── "task"      → tools.Server
                    │       task_plan / task_complete
                    └── "<servername>"  → tools.Server (MCP)
```

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

Twelve tools across five 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 from the filesystem |
| `file` | `file_write` | Writes a file to the filesystem |
| `file` | `file_edit` | Edits a file with precise string replacement |
| `file` | `file_glob` | Finds files by glob pattern |
| `file` | `file_grep` | Searches file contents by regex |
| `memory` | `memory_remember` | Saves a persistent memory to a flat markdown file |
| `memory` | `memory_recall` | Searches saved memories by keyword |
| `reasoning` | `reasoning_think` | Externalizes intermediate reasoning (no-op, recorded in history) |
| `task` | `task_plan` | Decomposes a goal into ordered steps; saves a markdown checklist to pl/ |
| `task` | `task_complete` | Marks a plan step complete; returns remaining steps |

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

`OLLIE_MEMORY_PATH` defaults to `~/.config/ollie/memory`. Memory files use denote naming: `YYYYMMDDTHHmmss__{slug}--{tag1}-{tag2}.md`.

## Planning

`task_plan` saves a markdown checklist to the plan directory (`pl/` in ollie-9p) as a `__todo.md` file. The agent then:

1. Renames `__todo` → `__wip` when work begins (`file_edit` or shell)
2. Calls `task_complete` after each step finishes — marks `[ ]` → `[x]`, returns remaining steps
3. Uses `file_*` tools to add, remove, or revise steps as the plan evolves
4. Renames `__wip` → `__done` when the goal is realized

`task_complete` takes the plan filename and a step title (substring match, case-insensitive). It errors if no matching unchecked step is found, so silent skips are caught.

Everything else — listing plans, inspecting a specific step, bulk operations — goes through `file_*` or `execute_code`. The task server handles only creation and step completion.

## Typical Consumer Setup

```go
newDispatcher := tools.NewDispatcherFunc(map[string]func() tools.Server{
    "execute":   execute.Decl(cwd),  // "" falls back to os.Getwd()
    "file":      file.Decl(cwd),
    "memory":    memory.Decl(),
    "reasoning": reasoning.Decl(),
    "task":      task.Decl(planDir),
})

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

core := agent.NewAgentCore(agent.AgentCoreConfig{
    Backend:       be,
    CWD:           cwd,
    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. `CWD` is preserved across switches.

`Core.ListServers()` returns all registered tool servers and their tools, grouped by server name. Accessible via the `/mcp` command or `ollie/s/{sid}/mcp` in ollie-9p.

## Session Lifecycle

`NewAgentCore` creates `/tmp/ollie/{sessionID}` when a session starts. `Core.Close()` removes it recursively. Callers (e.g. olliesrv's `killSession`) must call `Close()` when tearing down a session. `SetSessionID` renames the tmpdir atomically alongside the persisted session files.

`!<cmd>` shell commands run in the session's current working directory (`Core.CWD()`), not the process working directory.

## 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](https://github.com/landlock-lsm/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](https://github.com/lneely/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.