feat(roadmap): stage requires workflow contract tests for workflow changes #4083

Problem or Motivation

The stage planning job permits a task group to change a workflow file under .github/workflows/ without requiring a workflow contract test in tests/invariants/test_workflow_contracts.py.

In issue #2163 (pull request #4031), the stage planner placed the .github/workflows/ci.yml edit in Group 2 with the verification command uv run devops ci --check --only actionlint,zizmor, and deferred the contract test to Group 3.
This design has two defects:

1. It breaks the test-first rule of AGENTS.md (Rule 4: "Test new behavior first"): Group 2 modified behavior without an executable test proving the change.
2. The verification command uv run devops ci --check --only actionlint,zizmor is vacuous for validating the added step because it passes on the base before the change and only verifies syntax, not step configuration or existence.

Proposed Solution & Architectural Design

1. Extend path_problems in src/devops_cli/roadmap/stage/stage_paths.py:
   • When a task group lists a workflow file (.github/workflows/*.yml) in changes, require that the same group (or change) lists tests/invariants/test_workflow_contracts.py in changes.
2. Update the stage planner prompt (src/devops_cli/ai/tasks/roadmap_stage_change.md) to instruct the model that workflow changes require an invariant contract test in the same group.
3. This prevents vacuous verification commands on workflow modifications and ensures test-driven implementation for CI automation.

Target Subsystem

AI & Agentic Review Pipeline

Existing Tool Considered

path_problems in src/devops_cli/roadmap/stage/stage_paths.py. The change extends existing path validation rules: approximately 8,000 tokens to build and test.

Standards Compliance

• I confirm this proposal aligns with AGENTS.md engineering principles (cyclomatic complexity <= 10, nesting <= 5, zero bare exceptions, tests that cover the changed lines).
• I am willing to submit a pull request implementing this feature with accompanying tests.

Source: #4031