docs(self-scan): validate m4 (3/3) and scheme (partial) ledger shapes

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Summary

• Investigates and validates the entire m4 tri-comparison ledger backlog plus scheme's original recall-gap shape, via the tri-comparison-ledger-sweep skill.
• m4/function/existence/agree[ctags]_vs[gitgalaxy] (79): clean ctags-side limitation, not a GitGalaxy defect -- every sampled occurrence is a real AC_DEFINE/AC_DEFINE_UNQUOTED autoconf helper call (emits a C preprocessor #define at build time), not an M4 macro definition. ctags' M4 parser heuristically over-tags these as function definitions; documented in ctags_reader.py alongside the existing C RICHCMP_WRAPPER precedent.
• m4/function/existence/agree[gitgalaxy]_vs[ctags] (1): real GitGalaxy false positive (func_start captured the AC_DEFUN keyword itself as a function name), fixed in fix(m4): func_start captures the real macro name, not the defun keyword #1927.
• m4/class/existence/agree[gitgalaxy]_vs[ctags] (4): real GitGalaxy false positive -- m4's class_start is None but detector.py's class-extraction fallback doesn't check that, so it matches raw C struct declarations embedded as text inside autoconf feature-test macro arguments. Filed as detector.py's class fallback doesn't skip languages with class_start=None, causing false-positive class extraction (confirmed: m4) #1925 (broader gap, 18 other class_start=None languages not yet checked), not fixed in this sweep.
• scheme/function/existence/agree[ctags]_vs[gitgalaxy] (92): confirmed catastrophic GitGalaxy engine defect (100% function recall loss for the whole language), root-caused and fixed in fix(scheme): _slice_by_braces checks dead lang_id "lisp", causing 100% recall loss #1929. A smaller residual gap remains post-fix (58/92 found) and a new, legitimate GitGalaxy-alone shape it surfaces (real nested define forms ctags' parser misses) is left unvalidated for a future sweep pass.
• Also filed yacc corpus: both real .y files silently excluded from file_data by statistical_auditor.py despite successful extraction #1926 (yacc: both real corpus files silently excluded by statistical_auditor.py's anomaly sweep, likely an n=2 degenerate-cohort Z-score issue -- not root-caused to the exact triggering check, flagged for follow-up).

Regenerated tri_comparison_chart.svg and tri_comparison_points_of_interest.md; diff confirmed scoped to m4 (asterisks fully cleared) and scheme (0→58/92 found, still asterisked since the residual gap is real and not yet fully closed).

Related PRs/issues

• fix(m4): func_start captures the real macro name, not the defun keyword #1927 (m4 func_start fix), fix(scheme): _slice_by_braces checks dead lang_id "lisp", causing 100% recall loss #1929 (scheme _slice_by_braces fix) -- code fixes this ledger validation depends on/references.
• detector.py's class fallback doesn't skip languages with class_start=None, causing false-positive class extraction (confirmed: m4) #1925 (class_start=None fallback bug), yacc corpus: both real .y files silently excluded from file_data by statistical_auditor.py despite successful extraction #1926 (yacc statistical_auditor exclusion) -- filed, not fixed in this sweep.

Test plan

• Doc/ledger-only change -- no parsing logic touched directly in this PR (the code fixes are in the linked PRs above)
• Chart diff verified scoped to expected cells only

🤖 Generated with Claude Code

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