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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

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"]
        ELEVATEFILES["elevatefiles.go\nelevation 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"]
        ELEVATE["elevate/\nelevation 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 --> ELEVATE

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.

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.

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:

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

New

Creates the Agent struct from AgentConfig:

Sweeps stale tmpdirs from previous crashes
Stores the provided Runtime (or creates an empty one)
Sets the backend model if ModelName is specified
Creates /tmp/ollie/{sessionID} for this session
Sets up the plan file reader
Wires the turnError hook with a detached context
Pushes OLLIE_SESSION_ID and OLLIE_AGENT_ID into the runner env
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

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:

Classify each tool call via ClassifyTool(name) (reads readOnly from .meta file)
Batch consecutive parallel-read-safe calls into a group
Fan out the batch concurrently with deduplication (identical calls share one execution)
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:

Flatten tool call/result pairs to plain text
Send full history + compaction prompt to the LLM
Parse structured JSON response into TaskState
Rebuild history as cold + warm + hot zones
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):

Built-in table in toolsrv/tier.go (defaultColdTools)
tier field in the tool's .meta sidecar file
Default: hot

Persistence

Sessions are saved as PersistedSession 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]`
`/help`	Show command help

Agent Switching

When /agent <name> is issued:

Load the new agent config JSON
Create a fresh runner via newToolServer()
Call BuildRuntime with the new config
If the config specifies a backend/model, switch those too
Replace the entire Runtime pointer on the agent struct
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):

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:

{
  "cmd": "...",
  "timeout": 30,
  "sandbox": "default",
  "elevated": 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.

Elevation

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

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:

Open SSH connection to target host
Send bootstrap script over stdin
Bootstrap checks for cached ollie-remote binary (by SHA-256 hash)
If not cached: receive binary over stdin (gzipped + base64)
Launch ollie-remote with the working directory
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:

Execute the HTTP request
Classify response status into typed errors
Spawn a goroutine that parses SSE/NDJSON into StreamEvent channel
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

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

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:

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.

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