Evidence is an opt-in, bounded tool loop on a Hustle definition. Its binding is read-only by construction and is distinct from Loop tools, delegation, gates, workspace mutation, and session control.

Definition and limits

policy := hustle.EvidenceToolPolicy{
	Revision: "evidence-v1",
	Limits: hustle.ToolLoopLimits{
		MaxRounds: 4, MaxCalls: 12, MaxCallsPerRound: 4,
		MaxResultBytes: 64 << 10, MaxEvidenceBytes: 256 << 10,
	},
	Definitions: []tool.Definition{readOnlyTool},
}
reviewer, err := hustle.Define(
	hustle.WithName("permission.review"),
	hustle.WithParticipation(hustle.ParticipationBlocking),
	hustle.WithTimeout(10*time.Second),
	hustle.WithLimits(hustle.Limits{InputBytes: 1 << 20, OutputBytes: 1 << 20}),
	hustle.WithCurrentLoopModel(),
	hustle.WithSystemPrompt("Review the supplied evidence.", "prompt-v1"),
	hustle.WithPolicyRevision("review-v1"),
	hustle.WithOutputSchema(schema),
	hustle.WithEvidenceTools(policy),
)
_ = reviewer
_ = err

An evidence policy must have a revision, a bounded definition catalog, bounded round/call/result/evidence limits, structured output, and blocking participation. The definition and produced-tool-name digests are part of the descriptor.

Proof: evidence policy definition and evidence option tests.

Read-only binding

The exact invocation binding is:

// package hustle
type EvidenceBindings struct {
	SessionID     uuid.UUID
	LoopID        uuid.UUID
	ReadWorkspace *tool.ReadWorkspaceBinding
}

tool.ReadWorkspaceBinding supplies only a canonical root. The binding cannot carry mutation permits, observation invalidation, delegation, gates, grants, session controllers, or loop control. Tool definitions are copied at option creation and bound per invocation.

Proof: EvidenceBindings and read-only capability and tool binding types.

Bounded evidence loop

The internal runtime enforces maximum rounds, total calls, calls per round, individual result bytes, and aggregate evidence bytes. Unknown or unprepared tools, forbidden capability kinds, containment or access refusal, cancellation, deadline, and bound exhaustion become redacted EvidenceError reasons. Raw tool arguments and results do not enter Hustle audit events.

%%{init: {"theme":"dark"}}%%
flowchart LR
    I[input] --> C[read-only catalog]
    C --> R[bounded model round]
    R --> D{tool call?}
    D -->|yes| V[capability and containment checks]
    V --> B[bounded result]
    B --> R
    D -->|no| O[structured terminal output]

Proof: evidence runtime and evidence failure tests.

Definition and limits

Read-only binding

Bounded evidence loop

Source and proof