config: organize scenario stacks into method sections

[hubunt]

Summary

Reorganize scenario stacks into the four well-defined sections proposed in #1064: common, standalone, modelservice, and fma.

Common settings are expanded into the effective configuration inherited by every standup method, while method-specific modelservice settings can be nested under modelservice. The resolved config.yaml remains flat for existing templates and execution steps.

Motivation

Fixes #1064.

Scenario stacks currently mix shared settings such as model, storage, and vllmCommon with method-specific settings such as prefill, decode, and inferenceExtension. This makes the scope of each field unclear and forces scenario files to rely on comment headers instead of an explicit YAML structure.

What changed

• Added normalization for per-stack common sections before defaults, shared settings, and stack overrides are merged.
• Extended modelservice nesting to support common, prefill, decode, inferenceExtension, and multinode in addition to the existing gateway/router sections.
• Preserved override precedence: defaults < shared < stack < treatment/CLI.
• Added clear validation errors when stack.common or shared.common is not a mapping.
• Updated early workspace discovery to read common.workDir.
• Reorganized the FMA example and OCP CI scenario using the sectioned layout.
• Documented the new structure and backward-compatible flat spelling.
• Added regression coverage for common inheritance, method-specific normalization, multi-stack sibling metadata, invalid structures, and end-to-end scenario rendering.

Testing

• python -m pytest tests -q
  • 674 passed, 31 skipped.
• python -m pytest tests/test_scenario_sections.py tests/test_hoist_modelservice_sections.py tests/test_config_schema.py -q
  • 62 passed.
• pre-commit run
  • Byte compilation, full unit tests, changed-scenario dry-run rendering, secret scan, Ruff lint, and Ruff format all passed.
• Rendered both migrated scenarios and compared their effective config.yaml dictionaries with the versions from upstream main.
  • config/scenarios/examples/fma.yaml: identical.
  • config/scenarios/cicd/ocp.yaml: identical.
• git diff --check

Backward Compatibility

Legacy flat scenario keys remain supported and render unchanged. If both a legacy flat key and its sectioned spelling are present in the same scenario layer, the sectioned value wins. Treatment and CLI overrides continue to take final precedence.

The modelservice Helm chart's own common values can be written as modelservice.common, avoiding ambiguity with the stack-level common section.

Checklist

• My changes follow the style guidelines of this project.
• I have performed a self-review of my changes.
• I confirm that pre-commit run was run and all checks passed.
• I have updated the documentation accordingly.

[Vezio]

Pretty good intentions here to solve that issue, tagging as DNM for now until we can go through a bit more testing to ensure existing functionality doesn't break. Thank you for these changes, this is an amazing step forward to reduce redundant configurations.

[Vezio]

In the meantime, can you resolve some of the conflicts being reported above?

[hubunt]

Conflicts are resolved and the branch is rebased onto current main. The updated signed head is 04aeb0d. I preserved the upstream OCP scenario additions (maxModelLen, blockSize, and vLLM flags) inside the new common section. Full tests pass: 674 passed, 31 skipped.