Phase 4: Client-side routing for SX expression URLs

Add sx-url-to-path to router.sx that converts SX expression URLs to
old-style slash paths for route matching. find-matching-route now
transparently handles both formats — the browser URL stays as the SX
expression while matching uses the equivalent old-style path.

/(language.(doc.introduction)) → /language/docs/introduction for matching
but pushState keeps the SX URL in the browser bar.

- router.sx: add _fn-to-segment (doc→docs, etc.), sx-url-to-path
- router.sx: modify find-matching-route to convert SX URLs before matching
- Rebootstrap sx-browser.js and sx_ref.py

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

shared/sx/ref/router.sx

@@ -102,25 +102,64 @@
 
 (define find-matching-route :effects []
   (fn ((path :as string) (routes :as list))
-    (let ((path-segs (split-path-segments path))
-          (result nil))
-      (for-each
-        (fn ((route :as dict))
-          (when (nil? result)
-            (let ((params (match-route-segments path-segs (get route "parsed"))))
-              (when (not (nil? params))
-                (let ((matched (merge route {})))
-                  (dict-set! matched "params" params)
-                  (set! result matched))))))
-        routes)
-      result)))
+    ;; If path is an SX expression URL, convert to old-style for matching.
+    (let ((match-path (if (starts-with? path "/(")
+                        (or (sx-url-to-path path) path)
+                        path)))
+      (let ((path-segs (split-path-segments match-path))
+            (result nil))
+        (for-each
+          (fn ((route :as dict))
+            (when (nil? result)
+              (let ((params (match-route-segments path-segs (get route "parsed"))))
+                (when (not (nil? params))
+                  (let ((matched (merge route {})))
+                    (dict-set! matched "params" params)
+                    (set! result matched))))))
+          routes)
+        result))))
+
+
+;; --------------------------------------------------------------------------
+;; 6. SX expression URL → old-style path conversion
+;; --------------------------------------------------------------------------
+;; Converts /(language.(doc.introduction)) → /language/docs/introduction
+;; so client-side routing can match SX URLs against Flask-style patterns.
+
+(define _fn-to-segment :effects []
+  (fn ((name :as string))
+    (case name
+      "doc" "docs"
+      "spec" "specs"
+      "bootstrapper" "bootstrappers"
+      "test" "testing"
+      "example" "examples"
+      "protocol" "protocols"
+      "essay" "essays"
+      "plan" "plans"
+      "reference-detail" "reference"
+      :else name)))
+
+(define sx-url-to-path :effects []
+  (fn ((url :as string))
+    ;; Convert an SX expression URL to an old-style slash path.
+    ;; "/(language.(doc.introduction))" → "/language/docs/introduction"
+    ;; Returns nil for non-SX URLs (those not starting with "/(" ).
+    (if (not (and (starts-with? url "/(") (ends-with? url ")")))
+      nil
+      (let ((inner (slice url 2 (- (len url) 1))))
+        ;; "language.(doc.introduction)" → dots to slashes, strip parens
+        (let ((s (replace (replace (replace inner "." "/") "(" "") ")" "")))
+          ;; "language/doc/introduction" → split, map names, rejoin
+          (let ((segs (filter (fn (s) (not (empty? s))) (split s "/"))))
+            (str "/" (join "/" (map _fn-to-segment segs)))))))))
 
 
 ;; --------------------------------------------------------------------------
 ;; Platform interface — none required
 ;; --------------------------------------------------------------------------
 ;; All functions use only pure primitives:
-;;   split, slice, starts-with?, ends-with?, len, empty?,
-;;   map, for-each, for-each-indexed, nth, get, dict-set!, merge,
-;;   list, nil?, not, =
+;;   split, slice, starts-with?, ends-with?, len, empty?, replace,
+;;   map, filter, for-each, for-each-indexed, nth, get, dict-set!, merge,
+;;   list, nil?, not, =, case, join, str
 ;; --------------------------------------------------------------------------

shared/sx/ref/sx_ref.py

@@ -3973,4 +3973,4 @@ def render(expr, env=None):
 
 def make_env(**kwargs):
     """Create an environment with initial bindings."""
-    return _Env(dict(kwargs))
+    return _Env(dict(kwargs))