#1054 chore(spec): retire #799 tracking claims fixed by #857

Why

The "Known-defect tracking issues are open" check fails on every PR. #799 closed on 2026-10-24, after #855 and #857 converged Retry-After parsing, but four registry rows still point at it.

What changed

• Remove the four #799 rows from spec/tracking-issues.yml.
• Restate the three sentences that said Python and Ruby still truncate or still differ. They now cite #857.

Scope

Comments and docs only. No behavior changes.

Verification

• scripts/check-known-defect-issues-open: all 5 referenced issues are open.
• Its self-test passes 42 cases. make doc-constants-check passes, and go build and go vet are clean.
• An independent GPT-6.1-sol review found nothing to fix.