slim

Slim embed — reference consumer

This is the reference consumer for the slim-embed guarantee (docs/library-api-design.md, "Slim-embed guarantee"): a single-file host service embedding exactly one mast control loop in-process — a SingleTurn classifier feeding one Task specialist over in-memory sessions — and nothing else.

host process
  └─ ADK runner
       └─ slim_triage (workflow graph root)
            START → classify (SingleTurn) → run_triage (Task specialist)

What matters here is what this program imports, not what it serves. The loop runs over hardcoded sample inputs because the point is the dependency graph, not the transport.

Run it

go run ./examples/deploy/slim

No credentials, no network: the loop runs on mast's offline echo model. Swapping in a real model is one ADK import (google.golang.org/adk/v2/model/gemini) — see the comment in main.go.

Pay for what you import

The slim slice this example pulls:

What it must not pull — enforced in CI by scripts/check-slim-deps.sh, which fails any PR whose changes grow this example's transitive dependency graph:

• pkg/inject (HTTP inject/resume/abort server)
• pkg/observability (Prometheus registry, OTel SDK wiring) — and with it github.com/prometheus/..., the OTel SDK, and the OTLP exporters
• pkg/mcp — and with it github.com/modelcontextprotocol/go-sdk
• pkg/graph, pkg/router (workload dispatch shapes)
• pkg/config (.agents/ discovery)

One honest caveat: the OTel API (go.opentelemetry.io/otel, /trace, /metric) is in the graph regardless, because ADK v2's model path (google.golang.org/genai) imports it directly. Those are no-op stubs unless an SDK is installed; the SDK and exporters stay out. The CI check denylists the heavy parts and documents this.

The upgrade path is additive

Each subsystem you later need is one import plus a config value — not a migration:

• Durability: swap session.InMemoryService() for ADK's session/database service over SQLite in the same runner.Config field.
• Budgets: already here — pkg/budget is part of the slim slice.
• Metrics / traces: import pkg/observability, register the fixed metric families, observe the same runner events this loop already iterates.
• HITL pauses: emit RequestInput interrupts from the workflow nodes (see pkg/graph for the full pattern) and feed operator verdicts back through the runner.
• An operator surface: import pkg/inject and mount its inject/resume/abort endpoints in your existing HTTP mux.
• MCP tools: import pkg/mcp and add toolsets to the specialists' BuildOptions.

That is the strategic point of the guarantee: slim consumers start inside mast and grow by adding imports, not by migrating off a side-car framework. If you don't need any of mast's governance or durability and never will, use raw ADK v2 — see the routing note in docs/positioning.md, "Smaller agents, slim embeds".