Architecture Decisions

Key architectural decisions in the Amigo API design and their rationale.

Key architectural decisions in the Amigo AI API design and their rationale.

ADR-001: NDJSON for Classic API Streaming

Status: Accepted

Context: Conversation creation and interaction endpoints stream multiple events back to the client. The HTTP streaming protocol had to be chosen from Server-Sent Events (SSE), WebSocket, and Newline-Delimited JSON (NDJSON).

Decision: Use NDJSON (newline-delimited JSON) for Classic API conversation streaming endpoints (create conversation and interact). The Platform API made a different choice: its conversation turns endpoints stream Server-Sent Events (SSE, text/event-stream) - see the note below.

Platform API uses SSE for turns. The Platform API conversation turns endpoints stream SSE, not NDJSON. POST /turns returns an SSE stream when the request sends Accept: text/event-stream (and the synchronous JSON response otherwise), while POST /turns/stream always returns text/event-stream. Each frame is a typed TurnStreamEvent. New Platform API integrations should prefer POST /turns/stream.

Rationale:

Factor	NDJSON	SSE	WebSocket
Parsing complexity	Parse each line as JSON	Event ID management, retry logic, type field parsing	Full duplex protocol, framing
Client support	Works with any HTTP client	Requires EventSource API or polyfill	Requires WebSocket API
Content types	Standard application/x-ndjson	text/event-stream	Binary frames
Proxy compatibility	Passes through standard HTTP proxies	Some proxies buffer SSE streams	Requires upgrade
Error handling	Standard HTTP status codes	Limited to stream reconnection	Close codes
Binary data	Base64 in JSON fields	Text only	Native binary support

Key advantages for this use case:

• Simplicity. Each line is a self-contained JSON object. No event ID tracking or reconnection logic needed.
• Language agnostic. Works with any language that can read lines from an HTTP response body.
• Discriminated unions. Each event has a type field that maps directly to a typed discriminated union in both SDKs.
• Progressive parsing. Clients can process events as they arrive without buffering the entire response.

Consequences:

• Clients must handle newline-delimited parsing (both SDKs provide this via async generators).
• No built-in reconnection semantics (clients implement retry via the SDK retry middleware).
• WebSocket is used separately for the real-time voice endpoint where bidirectional streaming is required.

---

ADR-002: JWT over Session Tokens

Status: Accepted

Context: The API needs an authentication mechanism that works across multiple services, supports token refresh, and can be verified without database lookups.

Decision: Use JWT (JSON Web Token) bearer tokens obtained via API key exchange.

Authentication flow:

1. Client exchanges API key + API key ID for a JWT via POST /user/signin_with_api_key.
2. JWT is sent as Authorization: Bearer {token} on subsequent requests.
3. SDKs proactively refresh tokens 5 minutes before expiry.

Rationale:

Factor	JWT	Session Tokens	API Key Direct
Stateless verification	Yes (signature check)	No (DB lookup)	No (DB lookup)
Cross-service	Yes (signature verification)	No (service-specific)	Yes
Expiration	Built-in exp claim	Manual tracking	Never expires
Revocation	Requires token blacklist	Delete from DB	Requires rotation
Payload	Standard claims (sub, exp)	Opaque identifier	Opaque identifier
Token size	Larger (~1KB)	Small (~32 bytes)	Small (~64 bytes)

Key advantages:

• Stateless. API servers verify tokens without hitting a session store, which enables horizontal scaling.
• Standard claims. sub (user ID) and exp (expiration) are standard JWT fields that any JWT library can validate.
• Proactive refresh. The 5-minute refresh window in both SDKs keeps operation uninterrupted without 401 retry overhead.
• Separation of concerns. Long-lived API keys never travel over the wire after initial exchange. Short-lived JWTs limit exposure if intercepted.

Consequences:

• Tokens are larger than session IDs, which increases request overhead slightly.
• SDKs must implement token refresh logic (both SDKs implement safe concurrent token refresh).
• Token revocation requires additional infrastructure (not currently needed for API key-based auth).

---

ADR-003: service_hierarchical_state_machine Naming

Status: Accepted

Context: The platform documentation refers to "Context Graphs," the state-based architecture that structures agent reasoning and conversation flow. The API needs a field name for this entity.

Decision: Use service_hierarchical_state_machine as the API resource name.

Rationale:

The name was chosen to be technically precise about what the entity represents:

• service. Scoped to a service (the deployment unit that combines agent, state machine, and tools).
• hierarchical. States can be nested hierarchically (parent states containing child states).
• state_machine. The fundamental computational model: a finite set of states with defined transitions.

Why not context_graph?

Concern	Decision
Disambiguation	"Graph" is overloaded and could be confused with knowledge graphs, graph databases, or dependency graphs. "State machine" is unambiguous in computer science.
Implementation fidelity	The implementation IS a hierarchical state machine. Exit conditions define transitions. States have types (Action, Annotation, Decision, Recall, Reflection, ToolCall).
API stability	Technical names are less likely to change than marketing names. The platform docs can rename "Context Graph" without breaking the API.
Self-documenting	A developer seeing service_hierarchical_state_machine in a payload immediately understands the data structure without needing to read documentation.

Consequences:

• Verbose field name increases payload sizes slightly.
• Developers must learn the mapping between platform terminology ("Context Graph") and API names.
• The terminology mapping page bridges this gap. See Terminology Mapping.

See also: Terminology Mapping for the complete mapping between platform concepts and API names.