Implement cascade_rules.sole_stateful_step_exemption from runner-output-contract 2.1.0

[bokelley]

Context

adcontextprotocol/adcp#4058 adds a new normative cascade_rules section to runner-output-contract.yaml (bumping it 2.0.0 → 2.1.0). The TS SDK already conforms (adcp-client#1146, #1545). This Python SDK runner needs to catch up.

What changed in the contract

A new MUST: when a phase contains a sole stateful step that grades not_applicable, missing_tool, or missing_test_controller, and no same-phase peer declares provides_state_for, downstream phases MUST evaluate independently (i.e., the cascade is suppressed).

default_cascade enumerates the trigger set (passed:false, prerequisite_failed, unsatisfied_contract, peer_branch_taken) and the non-trigger set (peer_substituted, plus the new exemption).

Why it matters

Until this Python runner implements the exemption, the same storyboard graded against the same adopter via TS vs Python produces different cascade outcomes for sole-stateful-step skips. Vendors running comply through both runners will see grade divergence on this edge case.

Acceptance criteria

• Cascade engine consumes cascade_rules from the contract YAML
• Sole-stateful-step exemption suppresses cascade for the three skip reasons listed
• Cascade still fires for passed:false, prerequisite_failed, unsatisfied_contract, peer_branch_taken (no regression)
• peer_substituted continues to not cascade (no regression)
• Test fixtures cover both branches: sole-stateful-step skip → downstream graded; same step but with provides_state_for peer → cascade still fires
• Contract version: 2.1.0 accepted by parser

References

• feat(compliance): add cascade_rules section to runner-output-contract.yaml adcp#4058 — spec PR
• adcp-client#1146 — TS SDK leader implementation
• adcp-client#1545 — TS SDK follow-on

[bokelley]

Triage

Classification: Feature request
Bucket(s): cross-repo (implements adcontextprotocol/adcp spec artifact; no matching bucket label found — gap flagged in run summary)
Status: ready-for-human

What the experts said:

• ad-tech-protocol-expert: The cascade_rules logic may be entirely internal to the TS runner engine; if so, the Python SDK needs zero changes and the issue may be misfiled. Key unresolved question: does adcp#4058 change the comply_test_controller wire protocol at all, or is the exemption runner-opaque?
• code-reviewer: Epic-shaped if a Python runner is required (four net-new subsystems: contract YAML loader, phase/step data model, cascade engine, peer-declaration scanner). Non-breaking if isolated to a new module. Blocked on runner-output-contract.yaml 2.1.0 being available in the repo or at a canonical URL before implementation.

My take: The Python SDK has no storyboard runner (adcp storyboard run is the TS CLI; the Python server is the entity under test). Both experts flag that building this from scratch is epic-shaped and potentially misfiled if the exemption logic is TS-runner-internal.

Three concrete questions before proceeding:

1. Does adcp#4058 change the comply_test_controller wire protocol (new fields sent to the Python server), or is cascade_rules evaluation entirely internal to the TS runner? If the latter, no Python SDK changes are needed and this issue should be closed or retargeted.
2. Where does runner-output-contract.yaml 2.1.0 live after adcp#4058 merges — fetchable URL or bundled path? Without it, a Python implementation has no spec to conform against.
3. Is the intent a full Python storyboard runner (new adcp storyboard CLI subcommand, mirroring @adcp/client) or a narrower contract-validation helper?

If Q1 is "wire protocol unchanged," this closes. If Q1 is "wire protocol changed," the scope collapses to a bounded server-side change and I can execute.

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Triaged by Claude Code. Session: https://claude.ai/code/session_01Rr2A3PPg8aEKbZnEeyXHfX

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Generated by Claude Code

[bokelley]

Closing as not-needed. adcp-client-python has no storyboard runner — adcp storyboard run is the TS @adcp/client CLI; this repo is the server-side entity under test (see src/adcp/server/test_controller.py, the comply_test_controller skill implementation). cascade_rules is runner-internal grading logic, so the Python SDK has nothing to catch up to.

Filed in error after a reviewer note on adcontextprotocol/adcp#4058 cross-referenced "adcp-client-python#550" — that number is the merged ProposalManager v1.5 PR, not a cascade-engine tracker. No such tracker is needed.

If a Python storyboard runner is ever scoped, it would be its own epic, not a contract catch-up.