Begin the Great S4 Massacre

[isomorphisms]

What this adds

• Great S4 massacre/fixtures/ with a reference S4 corpus covering construction/defaults, slot access, validity, inheritance, single dispatch, multiple dispatch, and coercion
• Great S4 massacre/converter scripts/scan_s4.R to inventory S4 machinery without executing the source
• Great S4 massacre/converter scripts/extract_contract.R to extract literal class/generic/method/coercion declarations into a conservative neutral migration contract
• Great S4 massacre/tests/run_compliance.R with self-contained reference-R compliance checks
• the requested README/manifesto framing S4 removal as architectural reworking rather than semantic amnesia

Design constraint

The scripts intentionally do not emit guessed IR object syntax yet. Unsupported/dynamic declarations remain visible instead of being silently mistranslated. Once the IR object surface is settled, the neutral contract can feed an emitter and the same fixtures can become differential compliance tests.

Verification

The branch is one commit ahead of ir and changes only the new Great S4 massacre/ tree. The R compliance runner still needs execution in an R-capable environment/CI before this should leave draft.

[isomorphisms]

Reference-R gate executed on the PR head in an R-capable GitHub Actions runner (R 4.6.1).

• Exact gate: Rscript 'Great S4 massacre/tests/run_compliance.R'
• Result: Great S4 massacre: 22 compliance checks passed.
• Scanner probe: passed on fixtures/reference_s4.R
• Contract extractor probe: passed on fixtures/reference_s4.R
• Run: https://github.com/isomorphisms/ir/actions/runs/33115912730
• Evidence artifact: https://github.com/isomorphisms/ir/actions/runs/33115912730/artifacts/9664484891

The first run isolated two mechanical defects: R 4.6.1 encoded spaces in the runner's --file= argument, and both converter walkers descended into missing-argument markers. Those were corrected without adding or choosing any IR object syntax. The gate now preserves Rscript's exit status through tee.