ci: keep validation fresh and preserve failed-shard reports (#2210)

Run the existing README consistency and Python producer guards from their
CI owners. Execute full local validation fresh while preserving cached
preparation, and permit scoped reuse of earlier portable build entries.

Collect failed-shard diagnostics before enforcing success and publish
compact, portable timing history only after a complete successful merge.
Preserve installer truncation failure across supported Bash versions.

Keep cancellation tests focused on the called MCP tool, observe server
progress before timing target readiness, and retain delayed-startup,
cancellation, cleanup, and live follow-up request assertions.

Validation: all 32 CI jobs and the separate Go lane passed; 935 files,
9,630 cases, 9,544 passed, 86 skipped, zero failed. Controlled regressions
and fault/restoration probes are recorded in PR #2210.

Refs #2190.

Assisted-by: Kogasa (gensokyo-skills:kogasa-surprise-testing)

CONTRIBUTING.md

@@ -182,6 +182,10 @@ CI diagnosis. Packaging/setup/distribution changes additionally require
 `npm run verify:package` and `npm pack --dry-run`; provider changes require the
 matching real-provider lane. State which host/provider workflows ran.
 
+`check:pr` reuses build and static-check outputs while executing the test suite
+fresh, including the fast Python producer checks. `docs:check` also runs the
+onboarding example consistency suite for README-only changes.
+
 Pre-commit formats and lints staged files; pre-push runs `check:fast`.
 
 ### Generated files and command ownership