Step 16: Fix client routing — prefix-agnostic SX URL matching

The /sx/ prefix mismatch: defpage declares paths like /language/docs/<slug>
but browser URLs are /sx/(language.(doc.slug)). find-matching-route used
starts-with? "/(", missing the /sx/ prefix entirely.

Fix: find-matching-route now uses (index-of path "/(") to detect the SX
URL portion regardless of prefix. Works for /sx/, /myapp/, any prefix.
No hardcoded paths.

Also fixed deps-satisfied?: nil deps (unknown) now returns false instead
of true, preventing client-side eval of pages with unresolved components.
Correctly falls back to server fetch.

Verified with Playwright: clicking "Getting Started" on the docs page now
shows "sx:route deps miss for docs-page" → "sx:route server fetch" instead
of the old "sx:route no match (51 routes)".

2 new router tests for prefix stripping. 2914/2914 total, zero failures.

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

web/tests/test-router.sx

@@ -208,16 +208,34 @@
 ;; find-matching-route with SX URLs
 ;; --------------------------------------------------------------------------
 
-(defsuite "find-matching-route-sx-urls"
-  (deftest "SX URL auto-converts for matching"
-    (let ((routes (list
-            {:pattern "/language/docs/<slug>"
-             :parsed (parse-route-pattern "/language/docs/<slug>")
-             :name "docs-page"})))
-      (let ((result (find-matching-route "/(language.(doc.introduction))" routes)))
+(defsuite
+  "find-matching-route-sx-urls"
+  (deftest
+    "SX URL auto-converts for matching"
+    (let
+      ((routes (list {:parsed (parse-route-pattern "/language/docs/<slug>") :pattern "/language/docs/<slug>" :name "docs-page"})))
+      (let
+        ((result (find-matching-route "/(language.(doc.introduction))" routes)))
         (assert-true (not (nil? result)))
         (assert-equal "docs-page" (get result "name"))
-        (assert-equal "introduction" (get (get result "params") "slug"))))))
+        (assert-equal "introduction" (get (get result "params") "slug")))))
+  (deftest
+    "SX URL with /sx/ prefix auto-converts"
+    (let
+      ((routes (list {:parsed (parse-route-pattern "/language/docs/<slug>") :pattern "/language/docs/<slug>" :name "docs-page"})))
+      (let
+        ((result (find-matching-route "/sx/(language.(doc.introduction))" routes)))
+        (assert-true (not (nil? result)))
+        (assert-equal "docs-page" (get result "name"))
+        (assert-equal "introduction" (get (get result "params") "slug")))))
+  (deftest
+    "SX URL with custom prefix auto-converts"
+    (let
+      ((routes (list {:parsed (parse-route-pattern "/geography/") :pattern "/geography/" :name "geo-index"})))
+      (let
+        ((result (find-matching-route "/myapp/(geography)" routes)))
+        (assert-true (not (nil? result)))
+        (assert-equal "geo-index" (get result "name"))))))
 
 
 ;; ==========================================================================