# ollie-core: Detailed Architecture

This document covers the internal design of the Go library — the packages that implement the agent engine. It is the dependency imported by all consumers (olliesrv, frontends, tests).

## Package Map

```mermaid
flowchart TB
    subgraph Agent["agent/ package"]
        AGENT["agent.go\nAgent struct, New()"]
        LOOP["loop.go\nrun() — agent loop"]
        HISTORY["history.go\nHistory, TaskState, compaction"]
        TURN["turn.go\nper-turn state machine"]
        HOOKS["hooks.go\nlifecycle callbacks"]
        CMDS["commands.go\n/command dispatch"]
        BUILD["build_runtime.go\nBuildRuntime()"]
        PROMPT["prompt_resolver.go\nsystem prompt assembly"]
        STATE["state.go\nResultTier, toolResult"]
        COST["cost.go\npricing table"]
        FIFO["fifo.go\nprompt queue"]
        COMPLETE["complete.go\ncode completion"]
        CONFIG["agent_config.go\nConfig schema"]
        CONFIG_PATHS["config_paths.go\nXDG config discovery"]
        RUNTIME["runtime.go\nRuntime struct"]
        NEW["new.go\nNew() factory"]
        USAGE["usage_log.go\nusage tracking"]
    end

    subgraph Backend["backend/ package"]
        BACKEND["backend.go\nBackend interface"]
        OPENAI["openai.go"]
        ANTHROPIC["anthropic.go"]
        OLLAMA["ollama.go"]
        GEMINI["gemini.go"]
        COPILOT["copilot.go"]
        CW["codewhisperer.go"]
        POOL["pool.go\nbackend pool"]
    end

    subgraph Toolsrv["toolsrv/ package"]
        SERVER["server.go\nServer struct"]
        SHELL["shell.go\nshell execution"]
        TOOLS["tools.go\nRunner interface"]
        REGISTRY["registry.go\ntool discovery"]
        DISCOVER["discover.go\ntool script scanning"]
        SCHEMA["schema.go\nJSON Schema parsing"]
        TIER["tier.go\nresult tiering"]
        SKILLS["skills.go\nskill management"]
        STREAM["stream.go\noutput streaming"]
        REMOTE["remote.go\nRemoteServer"]
        DIAL["dial.go\nSSH bootstrap"]
        ACCESSORS["accessors.go\nIsParallelRead, ResultTier"]
        BOOTSTRAP["bootstrap.sh\nSSH bootstrap script"]
    end

    subgraph Session["session/ package"]
        SESS["session.go\nSession, Config"]
    end

    subgraph Fs["fs/ package"]
        TREE["tree.go\n*Tree"]
        NEWROOT["newroot.go\nNewRoot()"]
        LIFECYCLE["lifecycle.go\nCreate/Kill/Rename"]
        SESSFILES["sessionfiles.go\nsession file handlers"]
        AGENTFILES["agentfiles.go\nagent file handlers"]
        ROOTFILES["rootfiles.go\nroot file handlers"]
        BYPASSFILES["bypassfiles.go\nbypass handlers"]
        PROCFILES["procfiles.go\nprocess handlers"]
        PERSIST["persist.go\nsession persistence"]
        FS_GO["fs.go\n9P File/FileConfig"]
        FORMAT["format.go\nevent formatting"]
        TYPES["types.go\nSession struct"]
        SPEC["spec.go\nEDSL namespace declaration"]
        BUILDER["builder.go\nBuildTree"]
        FSNODE["fsnode.go\nFsNodeDecl"]
    end

    subgraph Support["Supporting Packages"]
        DETACH["detach/\nprocess management"]
        BYPASS["bypass/\nbypass broker"]
        SANDBOX["sandbox/\nLandlock config"]
        ENV["env/\nenvironment"]
        LOG["log/\nstructured logging"]
        PATHS["paths/\nXDG resolution"]
    end

    Agent --> Backend
    Agent --> Toolsrv
    Agent --> Session
    Fs --> Session
    Toolsrv --> SANDBOX
    Toolsrv --> DETACH
    Toolsrv --> BYPASS
```

## The Agent Struct (`agent/agent.go`)

`Agent` is the boundary between the engine and any consumer. It is a concrete struct, not an interface — the interface was removed during the Great Flattening because no consumer ever implemented it independently.

```go
type Agent struct {
    history        *History
    runtime        *Runtime
    cfg            agentConfig
    profileName    string
    agentID        string
    displayName    string
    agentsDir      string
    baseLayers     []string
    promptEnvExtra []string
    newToolServer  func() toolsrv.Runner
    newBackend     func(string) (backend.Backend, error)
    currentAction  atomic.Pointer[actionHandle]
    // ... execution state, sync primitives, session metadata
}

func New(cfg AgentConfig) *Agent
```

All output flows through the event bus as `Event{Role, Name, Content}` values. Roles include: `assistant`, `tool`, `call`, `info`, `exec`, `error`, `usage`, `reasoning`, `limitretry`.

## Agent Construction (`agent/new.go`)

### AgentConfig

The full construction config:

| Field | Purpose |
|---|---|
| `History` | Pre-existing session history to restore (nil = new) |
| `Runtime` | Pre-built *Runtime (tools, hooks, prompt, params) |
| `Profile` | Name of the active agent configuration profile |
| `ID` | Immutable agent ID (`uname`) |
| `Name` | Mutable display name |
| `AgentsDir` | Path to agent JSON directory |
| `SessionsDir` | Path to persisted session files |
| `SessionID` | Unique session identifier |
| `AgentID` | Immutable agent principal |
| `CWD` | Working directory for tools and prompt |
| `NewToolServer` | Factory for fresh toolsrv.Runner on agent switch |
| `NewBackend` | Factory for backend by name |
| `Log` | Logger instance |
| `MaxSteps` | Override agent config's maxSteps |
| `ReadPlanStep` | Function to read next unchecked plan step |
| `ListHandlers` | Additional list handlers |

### Runtime

The `Runtime` struct holds all per-agent configuration that changes on an `/agent` switch but remains stable across turns. The agent struct stores a pointer to the active Runtime; switching agents replaces it atomically.

```go
type Runtime struct {
    Backend      backend.Backend
    Runner       toolsrv.Runner
    Hooks        Hooks
    Preamble     string              // compiled system prompt
    Tools        []backend.Tool
    ClassifyTool func(string) bool   // parallelism check
    ClassifyTier func(string, json.RawMessage) string
    GenParams    backend.GenerationParams
    MaxSteps           int
    ToolResultMaxBytes int
    CfgBackend   string
    CfgModel     string
    Messages     []string            // non-fatal warnings
}
```

### BuildRuntime

`BuildRuntime(cfg, runner, cwd, env)` wires everything together:

1. Lists all tools from the runner
2. Resolves the system prompt by executing the config's `prompt` commands
3. Extracts generation parameters from the config
4. Builds the tool executor closure (routes calls through the runner)
5. Extracts parallelism and tier classifiers
6. Applies tool/executor restrictions if configured
7. Returns a `*Runtime` struct ready for `New`

### New

Creates the `Agent` struct from `AgentConfig`:
1. Sweeps stale tmpdirs from previous crashes
2. Stores the provided `Runtime` (or creates an empty one)
3. Sets the backend model if `ModelName` is specified
4. Creates `/tmp/ollie/{sessionID}` for this session
5. Sets up the plan file reader
6. Wires the `turnError` hook with a detached context
7. Pushes `OLLIE_SESSION_ID` and `OLLIE_AGENT_ID` into the runner env
8. Sets the flock directory for parallel coordination

## The Agent Loop (`agent/loop.go`)

The `run()` function is the core execution engine. It takes an `agentConfig` and a `state` interface, and loops until the model stops calling tools.

### Per-Iteration Flow

```mermaid
flowchart TB
    START["Start turn"]
    GATE["Context gate:\nstrip cold material\nif over budget"]
    BUILD["Build message history:\nsystem prompt + task state + hot tail"]
    STREAM["Stream from backend\n(with retry logic)"]
    CHECK{"Tool calls\nin response?"}
    EXEC["Execute tool calls\n(serial or parallel)"]
    UPDATE["Update state:\nappend messages + results"]
    INFER["Infer TaskState\nupdates"]
    SAFETY["Safety checks:\nerror limits, stall,\nreplan, max steps"]
    COMPACT["Auto-compact\nif needed"]
    DONE["Turn complete"]

    START --> GATE --> BUILD --> STREAM --> CHECK
    CHECK -- yes --> EXEC --> UPDATE --> INFER --> SAFETY --> COMPACT --> BUILD
    CHECK -- no --> DONE
```

### Streaming & Retry

The streaming loop handles three failure modes:

| Failure | Detection | Recovery |
|---|---|---|
| Rate limit (429) | `*RateLimitError` | Exponential backoff (5x2^attempt seconds), up to 3 retries |
| Transient (5xx, network) | `*TransientError` | Same retry logic |
| Stream drop | `Done` never received, channel closes | Retry with 2x2^attempt second delay |
| Context overflow | `*ContextOverflowError` | Trigger compaction, retry |
| Tool unsupported | `*ToolUnsupportedError` | Propagate to turnError hook |

On the first error, the `turnError` hook fires. If it exits 0 (handled), the loop returns immediately — the hook is responsible for recovery (e.g., switching models via `freeloader`).

### Tool Execution

Tool calls are dispatched with parallelism awareness:

1. **Classify** each tool call via `ClassifyTool(name)` (reads `readOnly` from `.meta` file)
2. **Batch** consecutive parallel-read-safe calls into a group
3. **Fan out** the batch concurrently with deduplication (identical calls share one execution)
4. **Serial** calls run one at a time

Per-call lifecycle:
```
preTool hook → execute → postTool hook → inject check → truncation → cache (if read-safe)
```

- `preTool` exit 2 blocks execution
- `postTool` exit 2 replaces the result
- Results exceeding `ToolResultMaxBytes` are hard-truncated
- Read-safe results are cached in a `sync.Map` for the duration of the turn

### Safety Mechanisms

| Mechanism | Threshold | Action |
|---|---|---|
| Consecutive errors (soft) | 5 rounds | Inject nudge: "try a different approach" |
| Consecutive errors (hard) | 10 rounds | Abort the turn |
| Replan gate | 8 rounds without PLAN: block | Inject replan nudge |
| Stall detection | 5 rounds with same LastAction | Inject stall nudge |
| Max steps | Configurable per-agent | Soft exit with nudge |
| Plan re-injection | Every 10 tool rounds | Re-inject task state |

### TaskState Inference

After each tool round, `inferTaskStateUpdate` updates the structured overlay:
- `LastAction` ← most recent tool call + truncated result
- `PlanStep` ← next unchecked item from the plan file (or heuristic from assistant text)

## Session & Context (`agent/history.go`)

### Message History

`History` holds a flat `[]backend.Message` slice. No rolling window — grows until compaction.

**Checkpoint**: `History.Checkpoint(ts TaskState)` forks the session — returns a new History that inherits the given TaskState but starts with a clean message history. Used for narrow-context sub-agents that know what to do without inheriting parent message noise.

Token tracking per session:
- `TotalInputTokens`, `TotalOutputTokens`, `TotalRequests`
- `TotalCachedInputTokens`, `TotalCacheCreationTokens`
- Per-turn accumulators reset at turn start
- `LastTurnCostUSD`, `SessionCostUSD`

### Compaction

Triggered when estimated tokens reach 50% of model context length.

**Three-zone strategy:**

| Zone | Content | Size |
|---|---|---|
| Cold | Structured TaskState JSON | 1 message |
| Warm | One-line decision index | ~10 messages |
| Hot | Verbatim recent messages | 8 messages |

Process:
1. Flatten tool call/result pairs to plain text
2. Send full history + compaction prompt to the LLM
3. Parse structured JSON response into TaskState
4. Rebuild history as cold + warm + hot zones
5. Write pre-compaction snapshot to `{id}.compaction.jsonl` for recovery

### Result Tiers

Tool results are classified at execution time:

| Tier | Behavior | Examples |
|---|---|---|
| Hot | Stays verbatim in messages | `file_write`, `file_edit`, `reasoning_think` |
| Warm | Summarized on next compaction | (custom tools) |
| Cold | Immediately collapsed to one-line summary | `file_read`, `memory_recall`, `lsp_*` |

Classification sources (in priority order):
1. Built-in table in `toolsrv/tier.go` (`defaultColdTools`)
2. `tier` field in the tool's `.meta` sidecar file
3. Default: hot

### Persistence

Sessions are saved as `PersistedSession` JSON:
```json
{
  "id": "1716300000000-abc123",
  "agent": "coding",
  "messages": [...],
  "taskState": {...}
}
```

Saved after every tool round (`saveSession` callback) and on clean exit.

## Hooks (`agent/hooks.go`)

Hooks are shell commands executed with:
- **stdin**: JSON payload with context (session_id, cwd, model, error, etc.)
- **env**: `OLLIE_*` variables derived from the payload map
- **timeout**: 60 seconds (configurable in tests)
- **process group**: `Setpgid=true` for clean kill on timeout

### Exit Code Semantics

| Code | Meaning |
|---|---|
| 0 | Success. Stdout appended to context. |
| 2 | Block. Stops the action (e.g., blocks a tool call, prevents compaction). |
| Other | Non-blocking warning. Execution continues. |

### Hook Execution Order

Multiple commands per hook run sequentially. If any exits 2, execution stops immediately and returns `Blocked=true`.

## Commands (`agent/commands.go`)

`Submit()` first checks for commands before starting an agent turn:

| Prefix | Dispatch |
|---|---|
| `!<cmd>` | Shell command in session CWD |
| `/backend [name]` | Show or switch LLM backend |
| `/model [name]` | Show or switch model |
| `/models` | List available models |
| `/agent [name]` | Show or switch agent config (rebuilds Runtime) |
| `/agents` | List available agents |
| `/maxsteps [n]` | Get/set max steps (0 = unlimited) |
| `/compact` | Manual compaction |
| `/context` | Show context size and message breakdown |
| `/usage` | Show token usage and context percentage |
| `/cost` | Show last turn and session cost |
| `/history` | Dump bounded message history |
| `/sessions` | List saved sessions |
| `/clear` | Clear session (reset context) |
| `/kill` | Kill session |
| `/rn <name>` | Rename session |
| `/cwd [path]` | Show or change working directory |
| `/skills` | List available skills |
| `/tools` | List available tools |
| `/sp` | Show rendered system prompt |
| `/i <prompt>` | Inject into running turn |
| `/irw <prompt>` | Inject-rewrite |
| `/queued [pop|clear]` | Manage queued prompts |
| `/help` | Show command help |

### Agent Switching

When `/agent <name>` is issued:
1. Load the new agent config JSON
2. Create a fresh runner via `newToolServer()`
3. Call `BuildRuntime` with the new config
4. If the config specifies a backend/model, switch those too
5. Replace the entire `Runtime` pointer on the agent struct
6. Clear the session (fresh context for the new persona)

## Tool System (`toolsrv/`)

### Runner Interface

The `Runner` is the minimal interface satisfied by any tool server (local or remote):

```go
type Runner interface {
    ListTools() ([]ToolInfo, error)
    CallTool(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error)
}
```

### Server

The concrete `Server` struct implements `Runner` and provides:
- **shell**: sandboxed bash command execution
- **tool registry**: `tool_load`, `tool_list` — lazy tool discovery
- **skill registry**: `skill_load`, `skill_list` — skill management

#### shell

Runs a single bash command in a sandbox.

**Input schema:**
```json
{
  "cmd": "...",
  "timeout": 30,
  "sandbox": "default",
  "bypass": false
}
```

### Code Validation

Before execution, inline code is checked against dangerous patterns:

- **Universal**: `mkfs`, `dd if=/dev/`, `sudo/su`, `/etc/shadow`
- **Bash**: recursive force-delete of system paths, fork bombs, `/dev/sd` writes, eval injection
- **Python**: `shutil.rmtree("/")`, subprocess rm -rf, os.remove of system paths
- **Perl**: system/exec rm -rf, backtick rm, unlink system paths
- **Lua**: os.execute rm -rf, os.remove system paths

Validation failures are rate-limited: 5 failures within 1 minute triggers a 5-minute block.

### Parallelism & Locking

Tool scripts declare their concurrency class via their `.meta` sidecar file:

| `.meta` field | Lock Class | Behavior |
|---|---|---|
| `"readOnly": true` | Read | Shared lock (LOCK_SH); concurrent with other reads |
| `"readOnly": false` (default) | Write | Exclusive lock (LOCK_EX); serialized |

Lock files live in `/tmp/ollie/{sessionID}/` and are acquired via `flock(2)`.

### Result Tier Classification (`toolsrv/tier.go`)

Built-in cold tools (results consumed immediately, don't need verbatim retention):
- `file_read`, `memory_recall`, `web_fetch`, `web_search`
- `lsp_definition`, `lsp_references`, `lsp_hover`

Custom tools declare their tier via `"tier": "cold|warm|hot"` in their `.meta` file.

### Bypass

Steps marked `bypass: true` bypass the sandbox entirely. They are dispatched to the bypass backend (`x/bypass`) which runs outside landrun. Only bash is supported for bypass steps.

### Remote Execution

When a session is configured with `remote=user@host`, the runner is a `RemoteServer` that forwards tool calls over SSH to an `ollie-remote` binary:

```go
type RemoteServer struct {
    conn *rpc.Conn  // JSON-RPC over SSH stdin/stdout
}

func (r *RemoteServer) CallTool(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
    return r.conn.Call(ctx, "execute", tool, args)
}
```

The agent loop doesn't know or care whether execution is local or remote. The `NewToolServer` factory returns a `RemoteServer` instead of a local `Server` when the session is configured for remote execution.

SSH bootstrap:
1. Open SSH connection to target host
2. Send bootstrap script over stdin
3. Bootstrap checks for cached `ollie-remote` binary (by SHA-256 hash)
4. If not cached: receive binary over stdin (gzipped + base64)
5. Launch `ollie-remote` with the working directory
6. Switch to JSON-RPC over stdin/stdout

## Backend System (`backend/`)

### Shared Types

| Type | Purpose |
|---|---|
| `Message` | Conversation turn (role, content, tool_calls, tool_call_id) |
| `Tool` | Function declaration (name, description, JSON Schema params) |
| `ToolCall` | Model's request to invoke a function |
| `StreamEvent` | Incremental streaming delta (content, reasoning, tool_calls, done, usage) |
| `Usage` | Token counts + optional cost |
| `GenerationParams` | Unified sampling parameters |

### Error Types

| Error | HTTP Code | Loop Behavior |
|---|---|---|
| `RateLimitError` | 429 | Retry with backoff |
| `TransientError` | 5xx, network | Retry with backoff |
| `ContextOverflowError` | 400 (specific) | Compact and retry |
| `ToolUnsupportedError` | 400/422 (specific) | Propagate to turnError hook |

### streamRequest

Shared HTTP streaming infrastructure used by all backends:
1. Execute the HTTP request
2. Classify response status into typed errors
3. Spawn a goroutine that parses SSE/NDJSON into `StreamEvent` channel
4. Return the channel for the loop to consume

### Backend Implementations

**OllamaBackend** (`/api/chat`):
- Local inference, no API key
- Context length from `/api/show` (cached)
- Model list from `/api/tags`
- NDJSON streaming

**OpenAIBackend** (`/v1/chat/completions`):
- Works with OpenAI, OpenRouter, any compatible API
- Configurable base URL, name, extra headers
- Context length from model list endpoint (cached)
- SSE streaming (`data: {...}` lines)
- Handles both `tool_calls` and legacy `function_call`

**AnthropicBackend** (`/v1/messages`):
- Extended thinking (reasoning budget via `ThinkingBudget`)
- Prompt caching (cache_control blocks)
- 200k context window (hardcoded)
- SSE streaming with content_block_delta events

**GeminiBackend** (Gemini API):
- Google Gemini models

**CopilotBackend** (GitHub Copilot API):
- Copilot Chat integration

**CodeWhispererBackend** (AWS CodeWhisperer API):
- AWS CodeWhisperer integration

## Config System (`agent/`)

### Agent Config Schema

```go
type Config struct {
    Hooks               map[string]HookCmds
    Prompt              Prompt
    Backend             string
    Model               string
    Tools               *bool
    AllowExecutors      []string
    AllowTools          []string
    MaxTokens           int
    MaxCompletionTokens int
    MaxSteps            int
    Temperature         *float64
    TopP, TopK, MinP, TopA  *float64/*int
    FrequencyPenalty    *float64
    PresencePenalty     *float64
    RepetitionPenalty   *float64
    Reasoning           int
    ReasoningEffort     string
    IncludeReasoning    *bool
    ResponseFormat      string
    Stop                []string
    Verbosity           string
}
```

### Prompt Type

Dual-mode unmarshaling:
- **JSON string**: treated as literal text (with `!command`, file path, or env expansion)
- **JSON array**: each element is a shell command; stdout concatenated

The array form is preferred — it enables composable prompt assembly from template fragments.

### HookCmds Type

Dual-mode: a single string `"cmd"` or an array `["cmd1", "cmd2"]`. Multiple commands run sequentially.

## Prompt Resolution (`agent/prompt_resolver.go`)

Two paths based on `Prompt.IsExec`:

**Exec mode** (array):
- Each command runs via `sh -c` with 30s timeout
- CWD set to session working directory
- Extra env vars injected (OLLIE_SESSION_ID, OLLIE mount path)
- Non-zero exit skips that command (no error propagation)
- All stdout concatenated with newlines

**String mode** (legacy):
- Environment variables expanded
- If contains newline: literal text
- If starts with `!`: execute as shell command
- If names an existing file: read file contents
- Otherwise: use as-is

## Cost Tracking (`agent/cost.go`)

When the backend doesn't report cost directly (only OpenRouter does), cost is computed from a built-in pricing table:

- Matches model name prefix (case-insensitive)
- Covers Anthropic Claude, OpenAI GPT/o-series, Google Gemini
- Cached input tokens charged at discount (10% Anthropic, 50% others)
- Cache creation tokens charged at 125% of input rate
- Unknown/local models return zero cost

## Sandbox (`sandbox/`)

### Config Format

```yaml
general:
  best_effort: true
  log_level: ""

filesystem:
  ro:  ["/usr", "/lib", "/etc"]
  rox: ["/usr/bin", "/usr/local/bin"]
  rw:  ["{CWD}", "{TMPDIR}"]
  rwx: []

network:
  enabled: true
  unrestricted: true
  bind_tcp: []
  connect_tcp: []

env: []

advanced:
  ldd: false
  add_exec: false
```

### Template Variables

| Variable | Expansion |
|---|---|
| `{CWD}` | Session working directory |
| `{HOME}` | User home directory |
| `{TMPDIR}` | Temp directory (default: /tmp) |
| `{XDG_CONFIG_HOME}` | XDG config (default: ~/.config) |
| `{XDG_DATA_HOME}` | XDG data (default: ~/.local/share) |
| `{XDG_CACHE_HOME}` | XDG cache (default: ~/.cache) |
| `{XDG_STATE_HOME}` | XDG state (default: ~/.local/state) |
| `{XDG_RUNTIME_DIR}` | XDG runtime (default: /run/user/UID) |
| `{OLLIE_CFG_PATH}` | ollie config directory |
| `{OLLIE_DATA_PATH}` | ollie data directory |

## Event System

The agent communicates exclusively through events published on a `pubsub.Bus`:

```go
type Event struct {
    Role    string
    Name    string
    Content string
}
```

| Role | When |
|---|---|
| `assistant` | Streaming text delta from the model |
| `reasoning` | Thinking/reasoning delta |
| `call` | Tool call initiated (Name=tool, Content=args JSON) |
| `tool` | Tool result returned (Name=tool, Content=result) |
| `info` | Informational message (command output, status) |
| `exec` | Shell command output (`!cmd`) |
| `error` | Error message |
| `usage` | Token usage report |
| `limitretry` | Rate limit retry initiated |

Consumers subscribe to the `"event"` topic on the bus. The 9P server's session manager subscribes to build the chat log; frontends subscribe to render output.

## Concurrency Model

- **One turn at a time**: `submitMu` serializes `Submit()` calls
- **Interrupt**: `currentAction` holds a `CancelCauseFunc`; `Interrupt()` calls it
- **Queue drain**: after each turn completes, queued prompts are drained sequentially
- **State observation**: `WaitChange()` uses a condition variable (`changeCond`) that broadcasts on any state/usage/cwd change
- **Tool parallelism**: within a turn, read-safe tools fan out via goroutines with `sync.Map` caching and `flock` coordination

## Session ID Format

```
<unix-nanoseconds>-<6-hex-chars>
```

Lexicographically sortable by creation time. Unique even within the same nanosecond due to the random suffix.