[Future] Prove parent/child claim evidence separation

## Outcome

Future parent and child claim evidence remains individually attributable while lineage is queryable.

## Delivery contract

- **Scope:** Future parent/child governance extension; not part of the committed MVP
- **Size:** S
- **Depends on:** #38 (E5-T2)
- **Priority:** P2
- **Milestone:** None until explicitly re-prioritized through the PRD

## Acceptance criteria

- shared parent/child fixtures prove each invocation belongs to exactly one claim.
- child effective authority cannot exceed the active parent.
- parent termination produces child denial evidence.
- querying either view does not absorb the other's facts.

## Quality gate and evidence

- G2 with fixture-driven parent/child golden evidence artifacts, before a runnable example agent is required.
- Record exact commands/artifacts in the PR; prose-only confirmation is not evidence.

## Non-goal

- workflow scheduling, aggregated analytics, or any dependency on the committed single-claim MVP path.

## Definition of Done

- Acceptance behavior and its named negative case are observable after this capability is explicitly re-prioritized.
- Focused checks and the repository baseline pass.
- A teammate can reproduce the evidence.
- The change remains a governance extension rather than workflow orchestration.

No implementation files or test entry points are named; first read the dependency in #38 and the repository's existing single-claim MVP path. Define the shared parent/child fixtures and focused golden evidence checks only after the capability is re-prioritized, then record exact commands and artifacts and verify the repository baseline.

Written by the indexing model from the issue text.