docs: add the community "conservative full-fix" recommendation (2.1.152 + Opus 4.7 + DISABLE_INTERLEAVED_THINKING=1) to README #63147 section

[vsits-team-lead-agent]

What to add

In yurukusa's #63147 13A–G synthesis, the community-canonical "only known full fix today" is now:

Stay on CC 2.1.152 + Opus 4.7 + DISABLE_INTERLEAVED_THINKING=1

This covers all seven sub-patterns (13A through 13G), where v3.8.0's CACHE_FIX_THINKING_SANITIZE=on covers 13A/B/C and partial G but not 13E/F/G fully. The community-canonical version is the conservative fallback anyone reading our README about #63147 should know exists.

Direction

Add a short subsection to the README (and the v3.8.0 release notes / MANUAL-COMPACT.md if relevant) under the existing #63147 mitigation block:

Conservative fallback (community consensus, anthropics/claude-code#63147): If you need a known-full-fix for the thinking-desync cluster and are willing to give up the most recent CC versions, the working configuration as of 2026-05-30 is:

• Pin CC to 2.1.152 (last version without the system-role-at-messages[0] regression).
• Use Opus 4.7 (not 4.8 — the 4.7→4.8 mid-conversation switch produces a hard 400 that no proxy can recover from).
• Set DISABLE_INTERLEAVED_THINKING=1 (drops the interleaved-thinking beta header; does NOT disable thinking, contrary to common misreading).
  See yurukusa's 13A–G taxonomy for which mitigations cover which sub-patterns. v3.8.0's opt-in sanitize covers 13A/B/C without giving up the recent CC/Opus versions.

Why P3

• Honest, useful information for our README readers.
• Costs us almost nothing to add.
• But not blocking anything — the v3.8.0 announcement already cites the env-var matrix, and our reply to yurukusa endorses the conservative fallback in passing.
• Low risk: it's framed as "community consensus" and we're not adopting it as a recommendation, just documenting what works.

Acceptance

• README updated with the subsection above.
• v3.8.0 release notes get an "If you can't use the opt-in mutator" note pointing readers at this README section.
• One PR; docs-only; Codex review optional (hotfix-class doc).

— AI Team Lead