Application resources - Fused

Use lifecycle resources for database pools, service clients, caches, and other application-owned dependencies. From the agent root, create an invocation-scoped provider starter:

harnest add context catalog

Use --project <agent-root> when running the command from elsewhere. Add @lifecycle.resource when the value should be created once for the application instead of once per invocation.

from harnest import context, lifecycle
from harnest.lib.catalog import CatalogClient


@lifecycle.resource
@context.provider("catalog")
async def catalog():
    client = CatalogClient()
    try:
        yield client
    finally:
        await client.close()

Resource properties

Decorator	Lifetime	Visible to agent code?
`@lifecycle.resource`	Application	No
Both decorators	Application	Yes
`@context.provider("name")`	Invocation	Yes

Harnest starts application resources by ascending order, then source location, and closes them in reverse order.

Read a resource

from harnest import context


def search_catalog(query: str):
    catalog = context.resource("catalog")
    return catalog.search(query)

Rule	Result
Unique name	Duplicate context resources fail compilation
Active invocation	Access outside an invocation fails
Root ownership	SubAgents use the root binding
No credentials	Resolve secrets through `context.credentials`

Resource or tool?

Need	Choose
Dependency used by trusted Python	Resource
Capability the model can invoke	Agent Tool
Downstream secret or user token	Credential provider
Session or checkpoint persistence	Storage factory

Agent Tools

Expose typed capabilities to the model.

Auth and credentials

Resolve private credentials inside an invocation.