backend-code-structure.md

Backend Code Structure

This document describes package ownership for the Go backend. It defines where code belongs, how packages interact, and the architectural boundaries that keep the system maintainable.

Table of Contents

• Overview
• Architecture Layers
• Package-by-Package Ownership
• Interface Placement Rules
• Import Graph
• Adding New Code
• Examples

---

Overview

The backend is a layered hybrid architecture with clear separation between core business logic and external concerns:

graph TB
    subgraph CLI["CLI Layer"]
        CLI[internal/cli]
    end

    subgraph HTTP["HTTP Layer"]
        HTTPD[internal/httpd]
    end

    subgraph Services["Service Layer"]
        Project[internal/service/project]
        Session[internal/service/session]
        PR[internal/service/pr]
        Review[internal/service/review]
    end

    subgraph Core["Core Layer"]
        SessionMgr[internal/session_manager]
        Lifecycle[internal/lifecycle]
        Observe[internal/observe/*]
    end

    subgraph Data["Data Layer"]
        Domain[internal/domain]
        Ports[internal/ports]
        Storage[internal/storage/sqlite]
        CDC[internal/cdc]
    end

    subgraph Infra["Infrastructure Layer"]
        Terminal[internal/terminal]
        Adapters[internal/adapters/*]
        Daemon[internal/daemon]
        Config[internal/config]
    end

    CLI -->|calls| HTTPD
    HTTPD -->|calls| Services
    Services -->|calls| Core
    Services -->|uses| Data
    Core -->|uses| Data
    Core -->|uses| Infra
    HTTPD -->|uses| Data

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Key Architectural Principles

1. Domain stays pure — No infrastructure dependencies
2. Ports define contracts — Interfaces consumed by core, implemented by adapters
3. Services orchestrate — Controller-facing use cases over core and data
4. Adapters are leaves — Implement ports, don't import core
5. CLI/HTTP stay thin — Just protocol handling, all logic in daemon

---

Architecture Layers

Layer Interactions

flowchart LR
    Protocol[Protocol Layer<br/>CLI + HTTP] -->|uses| Services[Service Layer<br/>Use Cases]
    Services -->|commands| Core[Core Layer<br/>Session Manager + Lifecycle]
    Services -->|queries| Data[Data Layer<br/>Domain + Ports + Storage]
    Core -->|reads/writes| Data
    Core -->|invokes| Infra[Infrastructure<br/>Adapters + Terminal]
    Infra -->|implements| Ports

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Dependency Rules

graph TD
    Direction[Dependency Direction]
    Direction --> Down["Top-down only"]
    Direction --> No["No upward dependencies"]

    CLI[CLI] -->|OK| HTTP[HTTP]
    HTTP -->|OK| Services[Services]
    Services -->|OK| Core[Core]
    Services -->|OK| Storage[Storage]
    Core -->|OK| Adapters[Adapters]

    Bad1[Adapters] -.->|FORBIDDEN| Services
    Bad2[Storage] -.->|FORBIDDEN| HTTP
    Bad3[Core] -.->|FORBIDDEN| CLI

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---

Package-by-Package Ownership

internal/domain

Purpose: Shared product vocabulary and durable fact records. The single source of truth for domain concepts.

graph TD
    Domain[internal/domain] --> Contains[Contains]
    Contains --> IDs[Shared IDs<br/>ProjectID, SessionID, IssueID]
    Contains --> Enums[Status Enums<br/>SessionStatus, ActivityState]
    Contains --> Records[Durable Records<br/>SessionRecord, PRRecord]
    Contains --> Vocab[Product Vocabulary<br/>PR, Project, Review concepts]

    DoesNot[Does NOT Contain] --> HTTP[HTTP DTOs]
    DoesNot --> CLI[CLI Output]
    DoesNot --> Generated[sqlc Generated Rows]
    DoesNot --> External[External Payloads<br/>GitHub, Claude, etc.]

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Belongs here:

• Shared IDs: ProjectID, SessionID, IssueID
• Enums and status vocabulary
• Durable fact records used across packages
• PR, tracker, project, session vocabulary

Does NOT belong here:

• HTTP request/response DTOs
• CLI output shapes
• OpenAPI wrapper types
• sqlc generated rows
• External system payloads (GitHub, tmux, agent-specific)

Rule of thumb: If AO would still use the concept after replacing HTTP, CLI, SQLite, GitHub, tmux, and every agent adapter, it belongs in domain.

---

internal/ports

Purpose: Narrow capability interfaces that connect core code to replaceable external systems.

graph LR
    Core[Core Code] -->|consumes| Ports[Ports Interfaces]
    Adapters[Adapters] -->|implement| Ports

    Ports --> Examples[Examples]
    Examples --> Runtime[Runtime<br/>Create, Destroy, IsAlive, Attach]
    Examples --> Workspace[Workspace<br/>Create, Destroy, ValidatePath]
    Examples --> Agent[Agent<br/>GetLaunchCommand, GetAgentHooks]
    Examples --> SCM[SCM<br/>ListPRs, FetchPR, FetchChecks]
    Examples --> PR[PR<br/>WriteSCMObservation]

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Belongs here:

• Interfaces consumed by core packages, implemented by adapters
• Capability structs: RuntimeConfig, WorkspaceConfig, SpawnConfig
• Vocabulary at the boundary between core and adapters

Does NOT belong here:

• Resource read models (belongs in service/*)
• HTTP request/response DTOs (belongs in httpd)
• sqlc rows (belongs in storage/sqlite)
• One-off internal interfaces

Key Port Interfaces:

Port	Purpose	Implementations
Runtime	Process isolation	tmux, conpty
Workspace	Git worktree management	gitworktree
Agent	Agent launching	23+ agent adapters
SCM	PR/CI observation	github
Tracker	Issue tracking	github (adapter only)
AgentMessenger	Agent communication	Agent hooks
PRWriter	PR persistence	pr.Manager

---

internal/service/*

Purpose: Controller-facing application boundary. Owns product use cases and read-model assembly.

graph TD
    subgraph Services
        Project[project]
        Session[session]
        PR[pr]
        Review[review]
    end

    subgraph Responsibilities
        UseCases[Use Cases]
        ReadModels[Read Models]
        Validation[Validation]
        Errors[User-Facing Errors]
    end

    Project --> Responsibilities
    Session --> Responsibilities
    PR --> Responsibilities
    Review --> Responsibilities

    subgraph NotHere
        LowLevel[Low-level runtime control]
        RawSQL[Raw sqlc rows]
        HTTP[HTTP routing]
    end

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Current service packages:

graph LR
    Controllers[HTTP Controllers] -->|call| Services

    Services --> Project[internal/service/project<br/>Project CRUD]
    Services --> Session[internal/service/session<br/>Session read-model assembly]
    Services --> PR[internal/service/pr<br/>PR observation/actions]
    Services --> Review[internal/service/review<br/>Code review]

    Services -->|delegate to| SessionMgr[session_manager]
    Services -->|query| Store[storage stores]

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Belongs here:

• Resource use cases called by HTTP controllers and CLI
• Resource read models and command/result types
• Display-model assembly (e.g., session status derivation)
• Resource-specific validation and user-facing errors
• Small store interfaces consumed by the service

Does NOT belong here:

• Low-level runtime/workspace/agent process control
• Raw sqlc generated rows as public results
• HTTP routing, path parsing, status-code decisions
• Concrete external adapter details

Example: Project concepts live in internal/service/project, not in domain and not in internal/project.

---

internal/session_manager

Purpose: Internal session command engine. Owns multi-step session mutations and resource orchestration.

graph TD
    Service[service/session] -->|commands| Mgr[session_manager]
    Mgr -->|orchestrates| Resources[Resources]

    Resources --> Workspace[Workspace Adapter]
    Resources --> Runtime[Runtime Adapter]
    Resources --> Agent[Agent Adapter]
    Resources --> Storage[Storage Store]
    Resources --> Lifecycle[Lifecycle Manager]
    Resources --> Messenger[Agent Messenger]

    Mgr -->|owns| Operations[Operations]
    Operations --> Spawn[Spawn<br/>Create all resources]
    Operations --> Kill[Kill<br/>Teardown all resources]
    Operations --> Restore[Restore<br/>Relaunch terminated session]
    Operations --> Send[Send<br/>Message to agent]

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Belongs here:

• Multi-step session mutations with rollback
• Resource sequencing (workspace → runtime → agent)
• Resource teardown safety and cleanup
• Internal errors: not found, terminated, not restorable

Does NOT belong here:

• HTTP request decoding
• CLI formatting
• Controller-facing list/get read-model assembly
• Terminal WebSocket framing

Intentional split: service/session is the product/API boundary; session_manager is the internal command engine.

---

internal/lifecycle

Purpose: Canonical write path for durable session lifecycle facts. Reduces observations into minimal persisted state.

graph LR
    subgraph Inputs
        RuntimeObs[Runtime Observations<br/>from Reaper]
        ActivitySignals[Activity Signals<br/>from Agent Hooks]
        SCMObs[SCM Observations<br/>from SCM Observer]
    end

    subgraph Lifecycle
        LCM[Lifecycle Manager]
        Reducer[Fact Reducer]
        StateMachine[State Machine]
        Nudge[Agent Nudge Engine]
    end

    subgraph Outputs
        ActivityState[activity_state]
        IsTerminated[is_terminated]
        PRFacts[PR Facts]
        Nudges[Agent Nudges]
    end

    RuntimeObs --> LCM
    ActivitySignals --> LCM
    SCMObs --> LCM

    LCM --> Reducer
    Reducer --> StateMachine
    StateMachine --> ActivityState
    StateMachine --> IsTerminated

    SCMObs --> Nudge
    Nudge --> Nudges

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Belongs here:

• Updates to lifecycle-owned session facts
• Guardrails around runtime/activity observations
• Lifecycle-triggered agent nudges for actionable PR facts

Does NOT belong here:

• Display status persistence (use service layer instead)
• HTTP/CLI DTOs
• Direct adapter implementation details
• PR row persistence (use pr.Manager)

Key invariant: The UI status is derived at read time by service code. Do not store display status in lifecycle or SQLite.

---

internal/observe/*

Purpose: Observation loops that poll external state and report facts to lifecycle.

graph TD
    subgraph Observe
        SCM[observe/scm<br/>SCM Observer]
        Reaper[observe/reaper<br/>Runtime Reaper]
    end

    subgraph External
        GitHub[GitHub API]
        Runtimes[tmux/conpty]
    end

    subgraph Internal
        LCM[Lifecycle Manager]
        Store[SQLite Store]
    end

    SCM -->|polls| GitHub
    SCM -->|writes| Store
    SCM -->|notifies| LCM

    Reaper -->|probes| Runtimes
    Reaper -->|reports to| LCM

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Current observation packages:

• internal/observe/scm — SCM (GitHub) observer loop
• internal/observe/reaper — Runtime liveness observation loop

Belongs here:

• Polling loops and observation logic
• External state transformation into domain facts
• Observation error handling and retry logic

Does NOT belong here:

• Product workflow decisions (belongs in service layer)
• Direct storage writes (use lifecycle instead)

---

internal/storage/sqlite

Purpose: SQLite setup, migrations, queries, and store implementations.

graph TD
    Storage[storage/sqlite] --> Components[Components]

    Components --> Setup[Connection Setup<br/>PRAGMAs]
    Components --> Migrations[Goose Migrations]
    Components --> SQLC[sqlc Queries + Generated Code]
    Components --> Stores[Table-specific Stores]
    Components --> Trans[Transactions + CDC]

    Components -->|NOT| HTTP[HTTP Response Types]
    Components -->|NOT| CLI[CLI Formatting]
    Components -->|NOT| Product[Product Display Status Rules]

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Belongs here:

• Connection setup and PRAGMAs
• Goose migrations
• sqlc queries and generated code
• Table-specific store methods
• Transactions and CDC-triggered persistence behavior

Does NOT belong here:

• HTTP response types
• CLI output formatting
• Product display status rules
• External adapter logic

Rule: Generated sqlc types should stay behind store methods. Services should work with domain records or service read models, not generated rows.

---

internal/cdc

Purpose: Change-log polling and event broadcasting.

graph LR
    SQLite[(SQLite)] -->|triggers| ChangeLog[change_log]
    ChangeLog -->|tail| Poller[CDC Poller]
    Poller -->|Event| Broadcaster[Broadcaster]
    Broadcaster -->|fan-out| Subs[Subscribers]

    Subs --> SSE[SSE Writer]
    Subs --> Term[Terminal Fanout]
    Subs --> Cache[Cache Invalidation]

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Belongs here:

• Event type definitions for the CDC stream
• Poller and broadcaster logic
• Subscriber fan-out behavior

Does NOT belong here:

• Terminal byte streams (belongs in internal/terminal)
• Product workflow decisions (belongs in service layer)
• Database schema ownership (belongs in storage/sqlite)

---

internal/terminal

Purpose: Terminal session protocol and PTY attach management used by the HTTP terminal mux.

graph TD
    HTTP[httpd] -->|WebSocket| Terminal[terminal]
    Terminal -->|creates| Attach[Attach Streams]
    Attach -->|wraps| PTY[PTY Sessions]

    PTY --> Unix[Unix: tmux attach<br/>via ptyexec]
    PTY --> Windows[Windows: conpty<br/>loopback dial]

    Terminal -->|manages| State[Session States]
    State --> Liveness[Liveness gating]
    State --> Backoff[Re-attach backoff]

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Belongs here:

• Per-client attachment lifecycle
• Input/output framing independent of HTTP
• PTY-backed attach handling and terminal protocol tests

Does NOT belong here:

• HTTP-specific concerns (belongs in httpd)
• HTTP routing or WebSocket upgrade logic

Note: httpd adapts WebSocket connections to terminal interfaces. terminal should not import httpd.

---

internal/httpd

Purpose: HTTP protocol adapter. Handles routing, middleware, and request/response encoding.

graph TD
    HTTPD[httpd] --> Components[Components]

    Components --> Routing[Routing + Middleware]
    Components --> Decode[Request Decoding]
    Components --> Encode[Response Encoding]
    Components --> Errors[API Error Envelopes]
    Components --> OpenAPI[OpenAPI Generation]
    Components --> WS[WebSocket for Terminal]

    Components -->|calls| Services[service/*]

    Services -->|NOT| Adapters[Direct Adapter Access]
    Services -->|NOT| Storage[Direct SQLite Access]

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Belongs here:

• Routing and middleware
• HTTP request decoding and response encoding
• Path/query parameter handling
• Status-code mapping
• API error envelopes
• OpenAPI generation and serving
• WebSocket upgrade handling for terminal mux

Does NOT belong here:

• Direct adapter or SQLite store access
• Application read models shared with CLI (belongs in service/*)

Rule: Controllers call service managers and translate service results/errors into HTTP responses.

---

internal/cli

Purpose: User-facing ao command. Thin client over the daemon HTTP API.

graph LR
    CLI[cli] --> Operations[Operations]

    Operations --> Discover[Discover Daemon]
    Operations --> Call[Call HTTP API]
    Operations --> Format[Format Output]
    Operations --> Control[Process Control<br/>start/stop/status/doctor]

    Operations -->|NOT| Direct[Direct Storage/DB Access]
    Operations -->|NOT| Runtime[Direct Runtime Control]
    Operations -->|NOT| Adapters[Direct Adapter Calls]

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Belongs here:

• Daemon discovery
• HTTP API calls
• Command output formatting
• Process control: start/stop/status/doctor

Does NOT belong here:

• Duplicate daemon business logic (put in daemon service/API)
• Direct storage, runtime, or adapter access

Rule: If a command needs product behavior, put it in the daemon and have the CLI call that API path.

---

internal/adapters/*

Purpose: Concrete implementations of ports interfaces. Wraps external systems.

graph TD
    Ports[Ports Interfaces] -->|implemented by| Adapters[Adapters]

    Adapters --> Agent[agent/*<br/>23+ harnesses]
    Adapters --> Runtime[runtime/*<br/>tmux, conpty]
    Adapters --> Workspace[workspace/*<br/>gitworktree]
    Adapters --> SCM[scm/*<br/>github]
    Adapters --> Tracker[tracker/*<br/>github]

    Agent --> Codex[codex]
    Agent --> Claude[claude-code]
    Agent --> Cursor[cursor]
    Agent --> Aider[aider]
    Agent -->|... 20+| More[more agents]

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Adapter principles:

• Adapters are leaves in the import graph
• Adapters translate external behavior into AO ports/domain concepts
• Adapters should not own product workflows
• All adapter-written files must be gitignored

Good dependencies:

session_manager → ports.Runtime
adapters/runtime/tmux → ports + domain
adapters/workspace/gitworktree → ports + domain
daemon → adapters + services + storage

Avoid:

domain → adapters
service/session → adapters/runtime/tmux
httpd/controllers → storage/sqlite/store
adapters/* → httpd

---

internal/daemon

Purpose: Production composition root. Wires all dependencies together.

graph TD
    Daemon[daemon] --> Responsibilities[Responsibilities]

    Responsibilities --> Wire[Dependency Construction]
    Responsibilities --> Register[Adapter Registration]
    Responsibilities --> Startup[Startup Sequencing]
    Responsibilities --> Shutdown[Shutdown Sequencing]
    Responsibilities --> Cross[Cross-component Wiring]

    Responsibilities -->|NOT| Business[Business Logic<br/>(put in service/lifecycle)]
    Responsibilities -->|NOT| Adapter[Adapter Implementation<br/>(put in adapters/*)]

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Belongs here:

• Production dependency construction
• Adapter registration
• Startup/shutdown sequencing
• Cross-component wiring

Does NOT belong here:

• Business logic (belongs in service, lifecycle, or manager packages)
• Adapter implementation details (belongs in adapters/*)

---

internal/config

Purpose: Environment-based daemon configuration.

graph LR
    Config[config] --> Sources[Sources]

    Sources --> Env[Environment Variables]
    Sources --> Defaults[Built-in Defaults]
    Sources --> Validate[Validation]

    Config -->|provides| Settings[Settings]

    Settings --> Port[AO_PORT]
    Settings --> Timeout[AO_REQUEST_TIMEOUT]
    Settings --> DataDir[AO_DATA_DIR]
    Settings --> RunFile[AO_RUN_FILE]
    Settings --> Agent[AO_AGENT]

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Key environment variables:

• AO_PORT — HTTP bind port (default: 3001)
• AO_REQUEST_TIMEOUT — Per-request timeout (default: 60s)
• AO_SHUTDOWN_TIMEOUT — Graceful shutdown cap (default: 10s)
• AO_RUN_FILE — PID/port handshake (default: ~/.ao/running.json)
• AO_DATA_DIR — SQLite data directory (default: ~/.ao/data)
• AO_AGENT — Compatibility agent adapter (default: claude-code)
• GITHUB_TOKEN — GitHub authentication

---

Interface Placement Rules

graph TD
    Question{Where to define<br/>interface?}

    Question --> Single{Only one package<br/>consumes it?}
    Single -->|Yes| InPackage[Define in consuming<br/>package]
    Single -->|No| Multiple{Multiple core packages<br/>need it?}

    Multiple -->|Yes| Ports[Define in ports]
    Multiple -->|No| HTTP{HTTP controllers<br/>need it?}

    HTTP -->|Yes| Service[Define in service/*]
    HTTP -->|No| Concrete[Return concrete type<br/>from constructor]

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Rules:

1. Single consumer → Define in the consuming package (smallest interface)
2. Multiple core consumers → Define in ports (shared capability)
3. HTTP controllers need resource → Use service/* manager interface
4. Return from constructor → Return concrete type unless genuinely needed

Examples:

// Good: Interface near single consumer
type sessionGetter interface {
    GetSession(ctx context.Context, id SessionID) (SessionRecord, bool, error)
}

// Good: Shared capability in ports
type Runtime interface {
    Create(ctx context.Context, cfg RuntimeConfig) (RuntimeHandle, error)
    Destroy(ctx context.Context, handle RuntimeHandle) error
    IsAlive(ctx context.Context, handle RuntimeHandle) (bool, error)
}

// Good: Service interface for controllers
type Manager interface {
    List(ctx context.Context) ([]Project, error)
    Add(ctx context.Context, cfg Config) (Project, error)
    Remove(ctx context.Context, id string) error
}

---

Import Graph

graph TD
    CLI[cli] --> HTTPD[httpd]
    HTTPD --> Services[service/*]
    HTTPD --> Terminal[terminal]

    Services --> SessionMgr[session_manager]
    Services --> Lifecycle[lifecycle]
    Services --> Storage[storage/sqlite]
    Services --> Domain[domain]
    Services --> Ports[ports]

    SessionMgr --> Ports
    SessionMgr --> Adapters[adapters/*]
    SessionMgr --> Lifecycle

    Lifecycle --> Ports
    Lifecycle --> Storage
    Lifecycle --> Domain

    Observe[observe/*] --> Ports
    Observe --> Storage
    Observe --> Lifecycle

    Storage --> Domain
    Storage --> Ports

    Adapters --> Ports
    Adapters --> Domain

    CDC[cdc] --> Storage
    Terminal --> Ports

    Daemon[daemon] --> All[All packages]

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Key patterns:

• All arrows point downward (no cycles)
• Adapters and domain are leaves
• CLI and HTTPD don't touch storage directly
• Everything depends on ports and domain

---

Adding New Code

New HTTP Route

flowchart LR
    AddRoute[Add HTTP Route] --> Route[Register in httpd]
    Route --> Call[Call service/*]
    Call --> Update[Update OpenAPI]
    Update --> Test[Add tests]

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Steps:

1. Add controller in httpd/controllers/
2. Call a service/* package
3. Update OpenAPI generation
4. Add spec tests

New Product Resource

flowchart TD
    NewResource[New Resource] --> Domain[Add IDs/vocab to domain]
    Domain --> Service[Create service/resource]
    Service --> Storage[Add storage queries]
    Storage --> Ports[Add ports if needed]
    Ports --> Adapter[Implement adapter if needed]

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Steps:

1. Add shared IDs/vocabulary to domain
2. Create use cases in service/<resource>
3. Add storage in storage/sqlite
4. Add ports if external system needed
5. Implement adapter in adapters/<capability>/<impl>
6. Wire in daemon

New Adapter

flowchart LR
    NewAdapter[New Adapter] --> Port[Implement port interface]
    Port --> Hooks[Implement hooks if agent]
    Hooks --> Gitignore[Add .gitignore entries]
    Gitignore --> Wire[Wire in daemon]
    Wire --> Test[Add conformance tests]

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Steps:

1. Implement a ports interface under adapters/<capability>/<impl>
2. For agents: implement hooks with gitignored files
3. Wire in daemon
4. Add conformance tests

---

Examples

Example: Adding a Session Command

// In internal/service/session/service.go
func (s *Service) MyNewCommand(ctx context.Context, id SessionID) (Result, error) {
    // 1. Validate input
    // 2. Call session_manager
    // 3. Enrich result
    // 4. Return read model
}

// In internal/httpd/controllers/sessions.go
func (c *SessionsController) myNewCommand(w http.ResponseWriter, r *http.Request) {
    // 1. Decode request
    // 2. Call service
    // 3. Encode response
}

Example: Adding a Port Interface

// In internal/ports/myfeature.go
package ports

type MyFeature interface {
    DoSomething(ctx context.Context, cfg Config) (Result, error)
}

// In internal/adapters/myfeature/impl.go
package impl

import "github.com/aoagents/agent-orchestrator/backend/internal/ports"

type Impl struct { ... }

func (i *Impl) DoSomething(ctx context.Context, cfg ports.Config) (ports.Result, error) {
    // Implementation
}

Example: Service Layer Pattern

// In internal/service/myresource/service.go
package service

// Service is the controller-facing boundary
type Service struct {
    manager *manager.Manager  // Internal command engine
    store   Store             // Storage interface
}

// New constructs the service
func New(mgr *manager.Manager, store Store) *Service {
    return &Service{manager: mgr, store: store}
}

// List returns enriched read models
func (s *Service) List(ctx context.Context) ([]MyResource, error) {
    records, err := s.store.List(ctx)
    if err != nil {
        return nil, err
    }
    return s.enrich(records), nil
}

// Create performs a use case
func (s *Service) Create(ctx context.Context, cfg Config) (MyResource, error) {
    // Business logic
    result, err := s.manager.Create(ctx, cfg)
    if err != nil {
        return MyResource{}, err
    }
    return s.enrichOne(result), nil
}

---

Summary

Key takeaways:

1. Domain stays pure — shared vocabulary only
2. Ports define contracts — interfaces for external systems
3. Services orchestrate — controller-facing use cases
4. Adapters are leaves — implement ports, no core imports
5. CLI/HTTP stay thin — protocol handling only
6. Daemon wires it all — composition root

Always ask:

• Does this belong in domain (shared concept)?
• Does this belong in ports (shared capability)?
• Does this belong in service (use case)?
• Does this belong in adapters (external system)?

Never:

• Put HTTP types in domain
• Put display status in storage
• Put business logic in CLI
• Import core from adapters
• Import adapters from services