Make capabilities real: declaration and runtime fail-fast

[aniketwattamwar]

Problem

capabilities is a dead field. The runtime validates it is an object and then ignores it. Nothing is ever declared and nothing ever reads it.

Concrete cost: a manifest with tool_usage graders run against an agent that cannot report tool calls fails with "No tool_calls present" on every step. That is indistinguishable from an agent that legitimately used no tools — one is a broken integration, the other a real test failure, and we report them identically.

Proposal

Presence of a key means supported; the value is an options object.

Capability	Runtime behaviour when absent
tool_calls	Fail fast if the manifest has tool_usage graders
evaluation_context	Fail fast if a grader targets that field
usage	Report audit usage as unavailable, not zero
reset	Warn that scenario isolation is not guaranteed
multi_turn	Warn on multi-step scenarios

Unknown keys MUST be ignored — that is what makes minor versions additive. Vendor extensions use x-<vendor>.<name>.

Acceptance criteria

• SDK declares capabilities from registered hooks
• Runtime fails before running when a manifest needs a missing capability
• Error message names the capability and the offending grader