Add restructure plan for spec/hosts/web/sx separation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

RESTRUCTURE_PLAN.md

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+# Restructure Plan
+
+Reorganise from flat `shared/sx/ref/` to layered `spec/` + `hosts/` + `web/` + `sx/`.
+
+Recovery point: commit `1a3d7b3` on branch `macros`.
+
+## Phase 1: Directory structure
+Create all directories. No file moves.
+```
+spec/tests/
+hosts/python/
+hosts/javascript/
+web/adapters/
+web/tests/
+web/platforms/python/
+web/platforms/javascript/
+sx/platforms/python/
+sx/platforms/javascript/
+```
+
+## Phase 2: Spec files (git mv)
+Move from `shared/sx/ref/` to `spec/`:
+- eval.sx, parser.sx, primitives.sx, render.sx
+- cek.sx, frames.sx, special-forms.sx
+- continuations.sx, callcc.sx, types.sx
+Move tests to `spec/tests/`:
+- test-framework.sx, test.sx, test-eval.sx, test-parser.sx
+- test-render.sx, test-cek.sx, test-continuations.sx, test-types.sx
+Remove boundary-core.sx from spec/ (it's a contract doc, not spec)
+
+## Phase 3: Host files (git mv)
+Python host - move from `shared/sx/ref/` to `hosts/python/`:
+- bootstrap_py.py → hosts/python/bootstrap.py
+- platform_py.py → hosts/python/platform.py
+- py.sx → hosts/python/transpiler.sx
+- boundary_parser.py → hosts/python/boundary_parser.py
+- run_signal_tests.py, run_cek_tests.py, run_cek_reactive_tests.py,
+  run_continuation_tests.py, run_type_tests.py → hosts/python/tests/
+
+JS host - move from `shared/sx/ref/` to `hosts/javascript/`:
+- run_js_sx.py → hosts/javascript/bootstrap.py
+- bootstrap_js.py → hosts/javascript/cli.py
+- platform_js.py → hosts/javascript/platform.py
+- js.sx → hosts/javascript/transpiler.sx
+
+Generated output stays in place:
+- shared/sx/ref/sx_ref.py (Python runtime)
+- shared/static/scripts/sx-browser.js (JS runtime)
+
+## Phase 4: Web framework files (git mv)
+Move from `shared/sx/ref/` to `web/`:
+- signals.sx → web/signals.sx
+- engine.sx, orchestration.sx, boot.sx → web/
+- router.sx, deps.sx, forms.sx, page-helpers.sx → web/
+Move adapters to `web/adapters/`:
+- adapter-dom.sx → web/adapters/dom.sx
+- adapter-html.sx → web/adapters/html.sx
+- adapter-sx.sx → web/adapters/sx.sx
+- adapter-async.sx → web/adapters/async.sx
+Move web tests to `web/tests/`:
+- test-signals.sx, test-aser.sx, test-engine.sx, etc.
+Move boundary-web.sx to `web/boundary.sx`
+Move boundary-app.sx to `web/boundary-app.sx`
+
+## Phase 5: Platform bindings
+Web platforms:
+- Extract DOM/browser primitives from platform_js.py → web/platforms/javascript/
+- Extract IO/server primitives from platform_py.py → web/platforms/python/
+App platforms:
+- sx/sxc/pages/helpers.py → sx/platforms/python/helpers.py
+- sx/sxc/init-client.sx.txt → sx/platforms/javascript/init.sx
+
+## Phase 6: Update imports
+- All Python imports referencing shared.sx.ref.*
+- Bootstrapper paths (ref_dir, _source_dirs, _find_sx)
+- Docker volume mounts in docker-compose*.yml
+- Test runner paths
+- CLAUDE.md paths
+
+## Phase 7: Verify
+- Both bootstrappers build
+- All tests pass
+- Dev container starts
+- Website works
+- Remove duplicate files from shared/sx/ref/
+
+## Notes
+- Generated files (sx_ref.py, sx-browser.js) stay where they are
+- The runtime imports from shared.sx.ref.sx_ref — that doesn't change
+- Only the SOURCE .sx files and bootstrapper tools move
+- Each phase is a separate commit for safe rollback