fix(ci): make direct tests portable for non-root runners

[artem-korolev]

Summary

• make the v0.8.1 OCI acceptance helper library own its standard temp-root fallback (OCI_V081_MATRIX_TEMP_ROOT, then TMPDIR, then /tmp)
• add a regression that sources the library directly with the private override absent and verifies scratch cleanup
• add least-privilege PR/main CI that runs direct non-root npm test and rejects generated/tracked-file drift
• add contract coverage for CI triggers, permissions, immutable Action pins, pinned Node, and the absent workaround
• preserve generated-SDK-aware type-checking in the established Dagger self-check

Root cause and impact

The production matrix runner initialized the private temp-root variable, but one direct test sourced the helper library without the runner. Under root this accidentally created root-level /rush-delivery-v081-* scratch files; under an ordinary user it failed. The defect was isolated to the repository test harness and does not change Rush Delivery consumer configuration or runtime behavior.

Clean-checkout tooling decision

The first GitHub run confirmed direct non-root npm test passed, then showed that standalone root yarn typecheck is not a valid clean-checkout command: the generated sdk directory is intentionally ignored. The workflow therefore does not invent a second SDK bootstrap. The clean Dagger self-check remains the authoritative type-check path because it injects the current generated SDK before running yarn typecheck.

Validation

• pre-fix clean non-root run: 446 passed / 1 failed (447 total)
• post-fix clean non-root run with both OCI_V081_MATRIX_TEMP_ROOT and TMPDIR initially absent: 448/448 passed
• focused OCI/CI/documentation contract suites: 30/30 passed
• yarn install --frozen-lockfile
• generated-SDK-aware yarn typecheck
• repository-wide Trunk checks, shell syntax validation, and git diff --check
• npm run self-check:clean: 448/448 passed on the corrected implementation HEAD
• final GitHub-hosted CI: run 31094043572

Release compatibility

This is release-neutral QA hardening. It does not modify versions, schemas, provenance, site-version data, release artifacts, consumer .dagger configuration, or the immutable v0.9.1 tag.