trust-systems-meta-model

Capability Negotiation Model

Capability negotiation separates what a system advertises from what a requester is allowed to use. This is the key governance move in agentic systems: a published capability is not an authorization decision.

TSMM v0.19.0 generalizes the A2A Skill and extension declaration pattern into a reusable capability-governance contract. The model applies to agents, registries, verifiers, orchestration layers, and any service that exposes policy-bound actions.

Capability layers

Layer	Meaning	Governance question
Advertised capability	Provider claims it can do something	Is the claim visible and attributable?
Discoverable capability	Requester may see the capability	Is disclosure authorized?
Negotiated capability	Parties agree on modes and extensions	Are input/output modes and extensions compatible?
Authorized capability	Policy permits use in context	Does the requester have authority for this effect?
Executed capability	Capability is invoked	Was execution bounded by the negotiated contract?
Evidenced capability	Evidence exists for audit/replay	Can the decision and output be inspected?

Extension negotiation

A2A demonstrates an important pattern: extensions are identified by URI, can be required or optional, and require explicit client opt-in. TSMM generalizes this into requestedExtensions, acceptedExtensions, rejectedExtensions, and requiredExtensionsMissing.

Normative requirements

• Capability negotiation MUST identify requester, provider, skill or capability reference, policy scope, and decision reference.
• Required extensions that are missing MUST result in rejected or review-required.
• Accepted modes MUST be a subset of requested modes or be explained through a constraint.
• Negotiation outcomes SHOULD produce evidence references suitable for audit.
• Capability acceptance MUST NOT be interpreted as permission to perform downstream effects unless an authorization decision also exists.

Schema and example

• Schema: schemas/tsmm-capability-negotiation.schema.json
• Example: examples/capability-negotiation-instance.json
• Valid vector: validation/test_vectors/valid/capability-negotiation-valid.json
• Invalid vector: validation/test_vectors/invalid/capability-negotiation-required-extension-missing.json

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