Phase 7a: affinity annotations + fix parser escape sequences

Add :affinity :client/:server/:auto annotations to defcomp, with
render-target function combining affinity + IO analysis. Includes
spec (eval.sx, deps.sx), tests, Python evaluator, and demo page.

Fix critical bug: Python SX parser _ESCAPE_MAP was missing \r and \0,
causing bootstrapped JS parser to treat 'r' as whitespace — breaking
all client-side SX parsing. Also add \0 to JS string emitter and
fix serializer round-tripping for \r and \0.

Reserved word escaping: bootstrappers now auto-append _ to identifiers
colliding with JS/Python reserved words (e.g. default → default_,
final → final_), so the spec never needs to avoid host language keywords.

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

shared/sx/ref/bootstrap_js.py

@@ -29,6 +29,20 @@ from shared.sx.types import Symbol, Keyword, NIL as SX_NIL
 # SX → JavaScript transpiler
 # ---------------------------------------------------------------------------
 
+# JS reserved words — SX parameter/variable names that collide get _ suffix
+_JS_RESERVED = frozenset({
+    "abstract", "arguments", "await", "boolean", "break", "byte", "case",
+    "catch", "char", "class", "const", "continue", "debugger", "default",
+    "delete", "do", "double", "else", "enum", "eval", "export", "extends",
+    "final", "finally", "float", "for", "function", "goto", "if",
+    "implements", "import", "in", "instanceof", "int", "interface", "let",
+    "long", "native", "new", "package", "private", "protected", "public",
+    "return", "short", "static", "super", "switch", "synchronized", "this",
+    "throw", "throws", "transient", "try", "typeof", "var", "void",
+    "volatile", "while", "with", "yield",
+})
+
+
 class JSEmitter:
     """Transpile an SX AST node to JavaScript source code."""
 
@@ -114,6 +128,7 @@ class JSEmitter:
             "component-closure": "componentClosure",
             "component-has-children?": "componentHasChildren",
             "component-name": "componentName",
+            "component-affinity": "componentAffinity",
             "macro-params": "macroParams",
             "macro-rest-param": "macroRestParam",
             "macro-body": "macroBody",
@@ -176,6 +191,7 @@ class JSEmitter:
             "sf-lambda": "sfLambda",
             "sf-define": "sfDefine",
             "sf-defcomp": "sfDefcomp",
+            "defcomp-kwarg": "defcompKwarg",
             "sf-defmacro": "sfDefmacro",
             "sf-begin": "sfBegin",
             "sf-quote": "sfQuote",
@@ -278,6 +294,7 @@ class JSEmitter:
             "for-each-indexed": "forEachIndexed",
             "index-of": "indexOf_",
             "component-has-children?": "componentHasChildren",
+            "component-affinity": "componentAffinity",
             # engine.sx
             "ENGINE_VERBS": "ENGINE_VERBS",
             "DEFAULT_SWAP": "DEFAULT_SWAP",
@@ -531,6 +548,7 @@ class JSEmitter:
             "transitive-io-refs": "transitiveIoRefs",
             "compute-all-io-refs": "computeAllIoRefs",
             "component-pure?": "componentPure_p",
+            "render-target": "renderTarget",
             # router.sx
             "split-path-segments": "splitPathSegments",
             "make-route-segment": "makeRouteSegment",
@@ -552,6 +570,9 @@ class JSEmitter:
         parts = result.split("-")
         if len(parts) > 1:
             result = parts[0] + "".join(p.capitalize() for p in parts[1:])
+        # Escape JS reserved words
+        if result in _JS_RESERVED:
+            result = result + "_"
         return result
 
     # --- List emission ---
@@ -1018,7 +1039,7 @@ class JSEmitter:
         return str(expr)
 
     def _js_string(self, s: str) -> str:
-        return '"' + s.replace("\\", "\\\\").replace('"', '\\"').replace("\n", "\\n").replace("\r", "\\r").replace("\t", "\\t") + '"'
+        return '"' + s.replace("\\", "\\\\").replace('"', '\\"').replace("\n", "\\n").replace("\r", "\\r").replace("\t", "\\t").replace("\0", "\\0") + '"'
 
 
 # ---------------------------------------------------------------------------
@@ -1995,12 +2016,13 @@ PREAMBLE = '''\
   }
   Lambda.prototype._lambda = true;
 
-  function Component(name, params, hasChildren, body, closure) {
+  function Component(name, params, hasChildren, body, closure, affinity) {
     this.name = name;
     this.params = params;
     this.hasChildren = hasChildren;
     this.body = body;
     this.closure = closure || {};
+    this.affinity = affinity || "auto";
   }
   Component.prototype._component = true;
 
@@ -2308,8 +2330,8 @@ PLATFORM_JS_PRE = '''
   function makeKeyword(n) { return new Keyword(n); }
 
   function makeLambda(params, body, env) { return new Lambda(params, body, merge(env)); }
-  function makeComponent(name, params, hasChildren, body, env) {
-    return new Component(name, params, hasChildren, body, merge(env));
+  function makeComponent(name, params, hasChildren, body, env, affinity) {
+    return new Component(name, params, hasChildren, body, merge(env), affinity);
   }
   function makeMacro(params, restParam, body, env, name) {
     return new Macro(params, restParam, body, merge(env), name);
@@ -2327,6 +2349,7 @@ PLATFORM_JS_PRE = '''
   function componentClosure(c) { return c.closure; }
   function componentHasChildren(c) { return c.hasChildren; }
   function componentName(c) { return c.name; }
+  function componentAffinity(c) { return c.affinity || "auto"; }
 
   function macroParams(m) { return m.params; }
   function macroRestParam(m) { return m.restParam; }