ci: decouple playwright/kani/rocq from needs:[test] (#299)

[avrabe]

Closes #299.

Summary

Phase 1 of the CI fan-out de-coupling proposed in #299. When the self-hosted rust-cpu pool saturates (rivet-core mutation testing held it for ~4 hours on 2026-05-17, smithy commit 70401cd), the entire downstream CI tree blocks because eight jobs chain off test. Three of those — playwright, kani, rocq — have their own ubuntu-latest runner capacity available and are independent of cargo-test status.

Acceptance criteria from #299

• Remove needs: [test] from playwright. .github/workflows/ci.yml line ~117. Replaced with a 4-line comment explaining the decoupling and back-referencing ci: decouple playwright/kani/rocq from needs:[test] to reduce blast radius of rust-cpu queue saturation #299. Playwright runs the release binary end-to-end via npx; cargo-test status is not a precondition.
• Remove needs: [test] from kani. Line ~511. Kani harnesses are bounded model checks against rivet-core source; they do not read cargo-test status.
• Remove needs: [test] from rocq. Line ~594. Rocq theorem proving runs against vendored .v files; it does not read cargo-test status.
• Keep needs: [test] on coverage. Verified at the remaining grep line — coverage re-runs the same suite under llvm-cov so the dependency is legitimate.
• Keep needs: [test] on mutants. Verified at the remaining grep line — mutants (lean-mem) mutation testing intentionally gates on a clean test baseline.
• verus deferred to Phase 2. Verus still gates on test; no change in this PR per the issue's "Defer verus to Phase 2" line.

After the change, only five needs: [test] references remain in ci.yml: vscode-extension (Phase 2 audit), coverage (kept), mutants (kept), verus (deferred), release-results (Phase 2 fan-in concern).

Out of scope (Phase 2, not in this PR)

• Auditing vscode-extension's dep on test.
• Reconsidering the 5-way release-results fan-in.
• Lowering cargo-mutants --jobs or sharding the rivet-core mutation suite.

Test plan

• grep -n "needs:" .github/workflows/ci.yml — only the five expected references remain (vscode-extension, coverage, mutants, verus, release-results).
• python3 -c "import yaml; yaml.safe_load(open('.github/workflows/ci.yml'))" — workflow is still valid YAML.
• yamllint config (default + project overrides at .yamllint.yml): comment lines ≤120 chars, 4-space comment indentation matching surrounding context, no flow-style maps.
• First post-merge CI run on main shows playwright, kani, rocq starting in parallel with test rather than queuing behind it. (Validated only after merge — that's the gate the issue describes.)

Commit traceability

ci type is exempt from artifact trailers per CLAUDE.md ("Exempt types (no trailer needed): chore, style, ci, docs, build."). No Implements: / Refs: lines required.

---

Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!