Add canonical SX language spec reference to CLAUDE.md

Points AI and developers to shared/sx/ref/ as the authoritative
source for SX semantics — eval rules, type system, rendering modes,
component calling convention, and platform interface.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -52,6 +52,65 @@ artdag/
   test/      # Integration & e2e tests
 ```
 
+## SX Language — Canonical Reference
+
+The SX language is defined by a self-hosting specification in `shared/sx/ref/`. **Read these files for authoritative SX semantics** — they supersede any implementation detail in `sx.js` or Python evaluators.
+
+### Specification files
+
+- **`shared/sx/ref/eval.sx`** — Core evaluator: types, trampoline (TCO), `eval-expr` dispatch, special forms (`if`, `when`, `cond`, `case`, `let`, `and`, `or`, `lambda`, `define`, `defcomp`, `defmacro`, `quasiquote`), higher-order forms (`map`, `filter`, `reduce`, `some`, `every?`, `for-each`), macro expansion, function/lambda/component calling.
+- **`shared/sx/ref/parser.sx`** — Tokenizer and parser: grammar, string escapes, dict literals `{:key val}`, quote sugar (`` ` ``, `,`, `,@`), serializer.
+- **`shared/sx/ref/primitives.sx`** — All ~80 built-in pure functions: arithmetic, comparison, predicates, string ops, collection ops, dict ops, format helpers, CSSX style primitives.
+- **`shared/sx/ref/render.sx`** — Three rendering modes: `render-to-html` (server HTML), `render-to-sx`/`aser` (SX wire format for client), `render-to-dom` (browser). HTML tag registry, void elements, boolean attrs.
+- **`shared/sx/ref/bootstrap_js.py`** — Transpiler: reads the `.sx` spec files and emits `sx-ref.js`.
+
+### Type system
+
+```
+number, string, boolean, nil, symbol, keyword, list, dict,
+lambda, component, macro, thunk (TCO deferred eval)
+```
+
+### Evaluation rules (from eval.sx)
+
+1. **Literals** (number, string, boolean, nil) — pass through
+2. **Symbols** — look up in env, then primitives, then `true`/`false`/`nil`, else error
+3. **Keywords** — evaluate to their string name
+4. **Dicts** — evaluate all values recursively
+5. **Lists** — dispatch on head:
+   - Special forms (`if`, `when`, `cond`, `case`, `let`, `lambda`, `define`, `defcomp`, `defmacro`, `quote`, `quasiquote`, `begin`/`do`, `set!`, `->`)
+   - Higher-order forms (`map`, `filter`, `reduce`, `some`, `every?`, `for-each`, `map-indexed`)
+   - Macros — expand then re-evaluate
+   - Function calls — evaluate head and args, then: native callable → `apply`, lambda → bind params + TCO thunk, component → parse keyword args + bind params + TCO thunk
+
+### Component calling convention
+
+```lisp
+(defcomp ~card (&key title subtitle &rest children)
+  (div :class "card"
+    (h2 title)
+    (when subtitle (p subtitle))
+    children))
+```
+
+- `&key` params are keyword arguments: `(~card :title "Hi" :subtitle "Sub")`
+- `&rest children` captures positional args as `children`
+- Component body evaluated in merged env: `closure + caller-env + bound-params`
+
+### Rendering modes (from render.sx)
+
+| Mode | Function | Expands components? | Output |
+|------|----------|-------------------|--------|
+| HTML | `render-to-html` | Yes (recursive) | HTML string |
+| SX wire | `aser` | No — serializes `(~name ...)` | SX source text |
+| DOM | `render-to-dom` | Yes (recursive) | DOM nodes |
+
+The `aser` (async-serialize) mode evaluates control flow and function calls but serializes HTML tags and component calls as SX source — the client renders them. This is the wire format for HTMX-like responses.
+
+### Platform interface
+
+Each target (JS, Python) must provide: type inspection (`type-of`), constructors (`make-lambda`, `make-component`, `make-macro`, `make-thunk`), accessors, environment operations (`env-has?`, `env-get`, `env-set!`, `env-extend`, `env-merge`), and DOM/HTML rendering primitives.
+
 ## Tech Stack
 
 **Web platform:** Python 3.11+, Quart (async Flask), SQLAlchemy (asyncpg), Jinja2, HTMX, PostgreSQL, Redis, Docker Swarm, Hypercorn.
@@ -110,11 +169,11 @@ cd artdag/l1 && mypy app/types.py app/routers/recipes.py tests/
 
 ### SX Rendering Pipeline
 
-The SX system renders component trees defined in s-expressions. The same AST can be evaluated in different modes depending on where the server/client rendering boundary is drawn:
+The SX system renders component trees defined in s-expressions. Canonical semantics are in `shared/sx/ref/` (see "SX Language" section above). The same AST can be evaluated in different modes depending on where the server/client rendering boundary is drawn:
 
-- `render_to_html(name, **kw)` — server-side, produces HTML. Used by route handlers returning full HTML.
+- `render_to_html(name, **kw)` — server-side, produces HTML. Maps to `render-to-html` in the spec.
-- `render_to_sx(name, **kw)` — server-side, produces SX wire format. Component calls stay **unexpanded** (serialized for client-side rendering by sx.js).
+- `render_to_sx(name, **kw)` — server-side, produces SX wire format. Maps to `aser` in the spec. Component calls stay **unexpanded**.
-- `render_to_sx_with_env(name, env, **kw)` — server-side, **expands the top-level component** then serializes children as SX wire format. Used by layout components that need Python context (auth state, fragments, URLs) resolved server-side.
+- `render_to_sx_with_env(name, env, **kw)` — server-side, **expands known components** then serializes as SX wire format. Used by layout components that need Python context.
 - `sx_page(ctx, page_sx)` — produces the full HTML shell (`<!doctype html>...`) with component definitions, CSS, and page SX inlined for client-side boot.
 
 See the docstring in `shared/sx/async_eval.py` for the full evaluation modes table.