CI ladder: idle drafts, ci:draft / ci:spinel, four unit shards

[thomasklemm]

Summary

Single meta-PR for the CI cost ladder (not folded into rubys#451):

1. Draft idle by default — no selected jobs until ci:draft, ci:spinel, or ci:full is applied (plan still routes; fixture/unit are selection-gated).
2. ci:draft — fixture + unit only.
3. ci:spinel — Ruby floor + full Spinel suite; skips other-language SDKs, WASM, Writebook.
4. Ready / non-draft — existing path-selected Ruby floor (unchanged ownership rules); ci:full still expands everything.
5. Four unit shards — shorter unit critical path on every non-idle run.

Docs: docs/ci/README.md ladder table + label request section.

Labels to create (if missing on the repo)

• ci:draft
• ci:spinel
• ci:full (already exists)

Verification

• python3 -B tests/ci_plan_test.py — 50 passed
• cargo test --test ci_fixture_workflow
• cargo test --test ci_policy_workflow -- --skip resource_and_harness
• cargo test --test workflow_yaml_parses draft_transitions

Commits

1. Opt-in draft CI and add a ci:spinel lane
2. Widen unit CI to four parallel shards

Target times and remaining cost centers are in the agent report (internal/draft-pr-ci.md).

  

[coderabbitai]

Important

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