fusion-harness
Canonical agent harness kernel for the Fusion ecosystem: budget funnels, lifecycle hooks, permission engine, and context compaction. Pure stdlib, zero dependencies.
Consumers
- fusion-agent-studio and fusion-cowork import this package directly
(hard dependency —
pip install -e fusion-harness; no in-tree fallback copies). - fusion-code (TypeScript) keeps its own implementation held to the same kernel contract by parity tests — cross-language runtime sharing is not the goal; contract conformance is.
The behavior contract for all runtimes lives in docs/contract.md.
Modules
fusion_harness.funnels—LLMFunnel,ToolFunnel,LifecycleBus(budget enforcement + lifecycle events)fusion_harness.permissions—PermissionEngine(deny-first permission checks)fusion_harness.hooks—HookEngine(lifecycle hook registry + dispatch)fusion_harness.compactor—Compactor(context window compaction with retention)
Security defaults (0.2.0, breaking)
Permission enforcement is fail-closed by default: a ToolFunnel without a
wired PermissionEngine denies every tool call. Headless/CI deployments opt out
explicitly:
export FUSION_FUNNEL_PERMISSIONS=off # or FUSION_FUNNEL_REQUIRE_PERMISSIONS=0
Every call skipped this way logs permission enforcement DISABLED via ... — no
deployment is silently unarmed. See docs/contract.md §5 for
the full environment variable table.
Install
From PyPI:
pip install fusion-harness
From source (development):
pip install -e ".[test]"
Releases are published by CI on tag push (.github/workflows/release.yml) via
PyPI trusted publishing.
Usage
from fusion_harness import Compactor, LLMFunnel, LifecycleBus, PermissionEngine, ToolFunnel
Test
pytest tests/ # unit coverage per module: funnels, permissions, hooks, compactor
The suite is the executable form of the contract: dangerous-pattern denies, layered rule precedence, fail-closed hook semantics, compaction levels, and the enforcement default flip. Consumer repos' CI (agent-studio, cowork) is the downstream detector for hidden passthrough assumptions.
License
Same license as the fusion monorepo.
1 maintainer
Metadata
1 maintainer
Release files for fusion-harness 0.2.1
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| File | Size | Uploaded | Provenance | |
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| fusion_harness-0.2.1.tar.gz | 25.4 kB | With provenance | Details |
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| fusion_harness-0.2.1-py3-none-any.whl | Python 3 | none | any | Details |
Total release size: 47.4 kB
Release files / fusion_harness-0.2.1.tar.gz
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