Keeps #983's known_mismatches.toml guard next to the archive guards in
check-frozen-archives.sh, and both sides' wording in AGENTS.md and
plan/findings/README.md. split_archives.py leaves the issues archive's own
"Frozen archive" notice (3 lines, dead relative link) out of the README; the
check lists those lines and compares the rest.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QaDuBSC1mqS9DnQoEsr7LJ
scripts/split_archives.py (run with python3 -I) splits the frozen plan/findings.md
(425 `## ` sections) and plan/upstream-issues.md (436 `#### ` entries) into one file
per record under plan/findings/ and plan/upstream-issues/, moves the archives' intro
and "Note: duplicate IDs" text into the READMEs, and deletes the archives.
`split_archives.py check` proves the split lossless against the archives at 4fe6f4d51.
site/build.py reads issues only from the directory (intro from its README);
check-frozen-archives.sh now fails if either archive comes back.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QaDuBSC1mqS9DnQoEsr7LJ
bherbruck