# Python API — Application Layer

This page documents the **application layer** of the CleverAgents Python package:
application services, the dependency injection (DI) container, domain models,
and key protocols.  For module-level API documentation (exceptions, registries,
adapters) see the [Module Index](index.md).

See [ADR-001](../adr/ADR-001-layered-architecture.md) (layered architecture) and
[ADR-003](../adr/ADR-003-dependency-injection.md) (dependency injection) for
design rationale.

---

## Architecture Overview

CleverAgents follows a strict layered architecture:

```
Entry Points (CLI / TUI / A2A server)
    ↓
Application Layer  ← this page
    ↓
Domain Layer       (models, value objects, domain services)
    ↓
Infrastructure     (database, file system, external services)
    ↓
Integration        (LangChain/LangGraph, MCP, LSP adapters)
    ↓
Core               (exceptions, retry, circuit breaker, async cleanup)
```

All cross-layer dependencies flow **downward only**.  The DI container wires
everything together at startup.

---

## Dependency Injection Container

**Module:** `cleveragents.application.container`

CleverAgents uses [dependency-injector](https://python-dependency-injector.ets-labs.org/)
for IoC.  The `CleverAgentsContainer` is the root container; all application
services are registered as providers and resolved lazily.

```python
from cleveragents.application.container import CleverAgentsContainer

container = CleverAgentsContainer()
container.config.from_dict({"provider": "openai", ...})
container.wire(modules=[__name__])

# Resolve services
plan_service = container.plan_service()
registry_service = container.registry_service()
session_service = container.session_service()
invariant_service = container.invariant_service()
```

### Key Providers

| Provider | Type | Description |
|----------|------|-------------|
| `container.settings` | `Singleton` | Application `Settings` instance |
| `container.event_bus` | `Singleton` | In-process event bus |
| `container.plan_service` | `Singleton` | `PlanLifecycleService` |
| `container.registry_service` | `Singleton` | `RegistryService` |
| `container.session_service` | `Singleton` | `SessionService` |
| `container.invariant_service` | `Singleton` | `InvariantService` |
| `container.actor_registry` | `Singleton` | `ActorRegistry` |
| `container.tool_registry` | `Singleton` | `ToolRegistry` |
| `container.skill_registry` | `Singleton` | `SkillRegistry` |
| `container.provider_registry` | `Singleton` | `ProviderRegistry` |
| `container.mcp_registry` | `Singleton` | `McpRegistry` |
| `container.lsp_registry` | `Singleton` | `LSPRegistry` |
| `container.resource_registry` | `Singleton` | `ResourceRegistry` |
| `container.a2a_facade` | `Singleton` | `A2aLocalFacade` |

> **Tip:** Always obtain services via the container rather than constructing
> them directly.  This ensures correct lifecycle management and dependency
> resolution.

---

## PlanLifecycleService

**Module:** `cleveragents.application.services.plan_service`

The central application service for the plan lifecycle.  Orchestrates the
four phases (Action → Strategize → Execute → Apply) and coordinates actors,
tools, resources, and invariants.

```python
from cleveragents.application.services.plan_service import PlanLifecycleService

service: PlanLifecycleService = container.plan_service()

# Create a plan from an action
plan = await service.create_plan(
    action_name="local/refactor",
    project_names=["my-project"],
    args={"target": "src/"},
    automation_profile="review",
)

# Execute the plan (Strategize + Execute phases)
result = await service.execute_plan(plan.plan_id)

# Apply the sandbox changeset
await service.apply_plan(plan.plan_id)
```

### Key Methods

| Method | Returns | Description |
|--------|---------|-------------|
| `create_plan(action_name, project_names, args, ...)` | `Plan` | Instantiate a plan from an action |
| `execute_plan(plan_id)` | `PlanExecutionResult` | Run Strategize and Execute phases |
| `apply_plan(plan_id)` | `PlanApplyResult` | Merge sandbox changeset into real resources |
| `get_plan(plan_id)` | `Plan` | Retrieve a plan by ID |
| `list_plans(filters)` | `list[Plan]` | List plans with optional filters |
| `cancel_plan(plan_id, reason)` | `Plan` | Cancel a running plan |
| `rollback_plan(plan_id, checkpoint_id)` | `Plan` | Roll back to a checkpoint |
| `get_plan_diff(plan_id)` | `PlanDiff` | Get the sandbox diff for a plan |
| `correct_decision(decision_id, mode, guidance)` | `CorrectionAttempt` | Correct a decision and recompute |
| `get_decision_tree(plan_id)` | `DecisionTree` | Retrieve the full decision tree |

---

## RegistryService

**Module:** `cleveragents.application.services.registry_service`

Unified CRUD service for all registry entities: actions, actors, skills,
tools, resources, projects, LSP servers, and automation profiles.

```python
from cleveragents.application.services.registry_service import RegistryService

service: RegistryService = container.registry_service()

# Register an action from a YAML file
action = await service.register_action(Path("examples/actions/refactor.yaml"))

# List all tools
tools = await service.list_tools(namespace="local", source="mcp")

# Register a resource
resource = await service.register_resource(
    type_name="git-checkout",
    name="local/my-repo",
    args={"url": "https://github.com/org/repo.git"},
)
```

### Key Methods

| Method | Description |
|--------|-------------|
| `register_action(path, update=False)` | Register or update an action from YAML |
| `list_actions(namespace, state, regex)` | List actions |
| `get_action(name)` | Get an action by name |
| `archive_action(name)` | Archive an action |
| `register_actor(path, update=False)` | Register or update an actor from YAML |
| `list_actors()` | List all actors |
| `get_actor(name)` | Get an actor by name |
| `register_skill(path, update=False)` | Register or update a skill from YAML |
| `list_skills(namespace, source)` | List skills |
| `register_tool(path, update=False)` | Register or update a tool from YAML |
| `list_tools(namespace, source, type)` | List tools |
| `register_resource(type_name, name, args)` | Register a resource |
| `list_resources(type, include_stopped)` | List resources |
| `get_resource(name)` | Get a resource by name |
| `create_project(name, description, resources, invariants)` | Create a project |
| `list_projects(namespace, regex)` | List projects |
| `link_resource_to_project(project, resource, read_only)` | Link a resource to a project |

---

## SessionService

**Module:** `cleveragents.application.services.session_service`

Manages conversation sessions — creation, retrieval, message history,
export, and import.

```python
from cleveragents.application.services.session_service import SessionService

service: SessionService = container.session_service()

# Create a session
session = await service.create_session(actor="openai/gpt-4o")

# Send a message
response = await service.send_message(
    session_id=session.session_id,
    content="What is the current plan status?",
)

# Export as JSON
export_data = await service.export_session(session.session_id)

# Export as Markdown transcript
md = await service.export_session_markdown(session.session_id)
```

### Key Methods

| Method | Description |
|--------|-------------|
| `create_session(actor)` | Create a new session |
| `get_session(session_id)` | Retrieve a session |
| `list_sessions()` | List all sessions |
| `delete_session(session_id)` | Delete a session |
| `send_message(session_id, content, stream)` | Send a message and get a response |
| `export_session(session_id)` | Export session as a JSON-serializable dict |
| `export_session_markdown(session_id)` | Export session as a Markdown transcript |
| `import_session(data)` | Import a session from a previously exported dict |

---

## InvariantService

**Module:** `cleveragents.application.services.invariant_service`

See [`cleveragents.core` — Invariant Service](core.md#invariant-service) for
the full API reference.  The service is registered as a Singleton in the DI
container:

```python
invariant_service = container.invariant_service()
```

---

## Domain Models

**Module:** `cleveragents.domain.models`

All domain models inherit from `DomainBaseModel` (see [Core Utilities](core.md#domain-base-model)).

### Plan

```python
from cleveragents.domain.models.core.plan import Plan, PlanPhase, PlanState

class Plan(DomainBaseModel):
    plan_id: str              # ULID
    name: str | None          # namespaced name (top-level plans only)
    action_name: str          # action this plan was instantiated from
    project_names: list[str]  # bound projects
    phase: PlanPhase          # Action | Strategize | Execute | Apply
    state: PlanState          # running | applied | errored | cancelled | ...
    automation_profile: str
    created_at: datetime
    updated_at: datetime
    parent_plan_id: str | None
```

**`PlanPhase`** enum: `ACTION`, `STRATEGIZE`, `EXECUTE`, `APPLY`

**`PlanState`** enum: `RUNNING`, `APPLIED`, `CONSTRAINED`, `ERRORED`, `CANCELLED`

### Action

```python
from cleveragents.domain.models.core.action import Action

class Action(DomainBaseModel):
    name: str                    # namespaced name
    description: str
    definition_of_done: str
    strategy_actor: str | None
    execution_actor: str | None
    estimation_actor: str | None
    invariant_actor: str | None
    args: list[ActionArgument]
    invariants: list[str]
    state: str                   # "active" | "archived"
```

### Decision

```python
from cleveragents.domain.models.core.decision import Decision, DecisionType

class Decision(DomainBaseModel):
    decision_id: str        # ULID
    plan_id: str
    type: DecisionType
    question: str
    chosen_option: str
    alternatives: list[str]
    confidence: float       # 0.0–1.0
    rationale: str
    phase: PlanPhase
    created_at: datetime
    superseded_by: str | None
```

**`DecisionType`** enum: `PROMPT_DEFINITION`, `INVARIANT_ENFORCED`,
`STRATEGY_CHOICE`, `SUBPLAN_SPAWN`, `SUBPLAN_PARALLEL_SPAWN`, …

### Resource

```python
from cleveragents.domain.models.core.resource import Resource

class Resource(DomainBaseModel):
    resource_id: str        # ULID
    name: str               # namespaced name
    type_name: str          # e.g. "git-checkout", "sqlite"
    description: str | None
    is_physical: bool
    parent_ids: list[str]
    child_ids: list[str]
    state: str              # "active" | "stopped"
    created_at: datetime
```

### Project

```python
from cleveragents.domain.models.core.project import Project

class Project(DomainBaseModel):
    name: str               # namespaced name (sole identifier — no ULID)
    description: str | None
    resource_links: list[ResourceLink]
    invariants: list[str]
    context_policy: ContextPolicy | None
    created_at: datetime
```

### Session

```python
from cleveragents.domain.models.core.session import Session

class Session(DomainBaseModel):
    session_id: str
    actor: str
    messages: list[Message]
    linked_plan_ids: list[str]
    created_at: datetime
    updated_at: datetime

    def as_export_markdown(self) -> str:
        """Render a human-readable Markdown transcript (lossy, not importable)."""
```

### Invariant

```python
from cleveragents.domain.models.core.invariant import Invariant, InvariantScope

class Invariant(DomainBaseModel):
    invariant_id: str       # ULID
    text: str
    scope: InvariantScope   # GLOBAL | PROJECT | ACTION | PLAN
    source_name: str        # project/action/plan name, or "global"
    active: bool
    non_overridable: bool   # global invariants only
    created_at: datetime
```

**`InvariantScope`** enum: `GLOBAL`, `PROJECT`, `ACTION`, `PLAN`

---

## Key Protocols and Interfaces

### `AIProviderInterface`

**Module:** `cleveragents.providers.interface`

Protocol that all AI provider implementations must satisfy.

```python
class AIProviderInterface(Protocol):
    @property
    def name(self) -> str: ...

    @property
    def model_id(self) -> str: ...

    async def generate(
        self,
        messages: list[Message],
        tools: list[ToolSpec] | None = None,
        stream: bool = False,
    ) -> GenerationResult: ...
```

### `ResourceHandler`

**Module:** `cleveragents.resource.handlers.base`

Protocol for resource handler implementations.

```python
class ResourceHandler(Protocol):
    async def read(self, resource_id: str, context: ...) -> Any: ...
    async def write(self, resource_id: str, data: Any, context: ...) -> None: ...
    async def delete(self, resource_id: str, context: ...) -> None: ...
    async def list_children(self, resource_id: str, context: ...) -> list[str]: ...
    async def diff(self, resource_id: str, other_id: str, context: ...) -> str: ...
    async def checkpoint(self, resource_id: str) -> str: ...
    async def rollback(self, resource_id: str, checkpoint_id: str) -> None: ...
    async def create_sandbox(self, resource_id: str) -> "Sandbox": ...
```

### `LLMCaller`

**Module:** `cleveragents.tool`

Protocol for calling an LLM.  Implement this to plug in a custom provider
into the tool-calling runtime.

```python
class LLMCaller(Protocol):
    async def call(
        self,
        messages: list[Message],
        tools: list[ToolSpec],
    ) -> LLMResponse: ...
```

---

## End-to-End Example

The following example shows how to use the Python API to create and execute
a plan programmatically:

```python
import asyncio
from cleveragents.application.container import CleverAgentsContainer

async def main():
    # Bootstrap the container
    container = CleverAgentsContainer()
    container.config.from_env("CLEVERAGENTS_")

    plan_service = container.plan_service()
    registry_service = container.registry_service()

    # Register a resource
    await registry_service.register_resource(
        type_name="git-checkout",
        name="local/my-repo",
        args={"url": "https://github.com/org/repo.git", "path": "/workspace/repo"},
    )

    # Create a project
    await registry_service.create_project(
        name="my-project",
        description="Main application project",
        resources=["local/my-repo"],
    )

    # Instantiate a plan
    plan = await plan_service.create_plan(
        action_name="local/refactor",
        project_names=["my-project"],
        args={"target": "src/"},
        automation_profile="review",
    )
    print(f"Plan created: {plan.plan_id}")

    # Execute the plan
    result = await plan_service.execute_plan(plan.plan_id)
    print(f"Execution result: {result.state}")

    # Review the decision tree
    tree = await plan_service.get_decision_tree(plan.plan_id)
    for decision in tree.decisions:
        print(f"  [{decision.type}] {decision.question[:60]}…")

    # Apply if satisfied
    await plan_service.apply_plan(plan.plan_id)
    print("Plan applied successfully.")

asyncio.run(main())
```

---

## Event Bus

**Module:** `cleveragents.application.events`

The in-process event bus enables loose coupling between application services.
Services emit events; subscribers react without direct dependencies.

```python
from cleveragents.application.events import EventBus, EventType

bus: EventBus = container.event_bus()

# Subscribe to plan phase transitions
@bus.on(EventType.PLAN_PHASE_CHANGED)
async def on_phase_change(event):
    print(f"Plan {event.plan_id} moved to {event.new_phase}")

# Emit an event (done internally by services)
await bus.emit(EventType.PLAN_PHASE_CHANGED, plan_id="01JXYZ...", new_phase="execute")
```

### Key Event Types

| Event | Description |
|-------|-------------|
| `PLAN_CREATED` | A new plan was instantiated |
| `PLAN_PHASE_CHANGED` | A plan advanced to a new phase |
| `PLAN_APPLIED` | A plan was successfully applied |
| `PLAN_CANCELLED` | A plan was cancelled |
| `PLAN_ERRORED` | A plan encountered an unrecoverable error |
| `DECISION_RECORDED` | A new decision was added to the decision tree |
| `INVARIANT_VIOLATED` | An invariant was not satisfied |
| `INVARIANT_ENFORCED` | An invariant enforcement record was created |
| `INVARIANT_RECONCILED` | Invariant reconciliation completed for a phase |
| `TOOL_EXECUTED` | A tool invocation completed |
| `SESSION_CREATED` | A new session was created |
| `SESSION_MESSAGE_ADDED` | A message was added to a session |