Phase 3: Client-side routing with SX page registry + routing analyzer demo

Add client-side route matching so pure pages (no IO deps) can render
instantly without a server roundtrip. Page metadata serialized as SX
dict literals (not JSON) in <script type="text/sx-pages"> blocks.

- New router.sx spec: route pattern parsing and matching (6 pure functions)
- boot.sx: process page registry using SX parser at startup
- orchestration.sx: intercept boost links for client routing with
  try-first/fallback — client attempts local eval, falls back to server
- helpers.py: _build_pages_sx() serializes defpage metadata as SX
- Routing analyzer demo page showing per-page client/server classification
- 32 tests for Phase 2 IO detection (scan_io_refs, transitive_io_refs,
  compute_all_io_refs, component_pure?) + fallback/ref parity
- 37 tests for Phase 3 router functions + page registry serialization
- Fix bootstrap_py.py _emit_let cell variable initialization bug
- Fix missing primitive aliases (split, length, merge) in bootstrap_py.py

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

sx/sxc/pages/docs.sx

@@ -416,6 +416,9 @@
     "bundle-analyzer" (~bundle-analyzer-content
       :pages pages :total-components total-components :total-macros total-macros
       :pure-count pure-count :io-count io-count)
+    "routing-analyzer" (~routing-analyzer-content
+      :pages pages :total-pages total-pages :client-count client-count
+      :server-count server-count :registry-sample registry-sample)
     :else (~plan-isomorphic-content)))
 
 (defpage bundle-analyzer
@@ -432,6 +435,20 @@
     :pages pages :total-components total-components :total-macros total-macros
     :pure-count pure-count :io-count io-count))
 
+(defpage routing-analyzer
+  :path "/isomorphism/routing-analyzer"
+  :auth :public
+  :layout (:sx-section
+    :section "Isomorphism"
+    :sub-label "Isomorphism"
+    :sub-href "/isomorphism/"
+    :sub-nav (~section-nav :items isomorphism-nav-items :current "Routing Analyzer")
+    :selected "Routing Analyzer")
+  :data (routing-analyzer-data)
+  :content (~routing-analyzer-content
+    :pages pages :total-pages total-pages :client-count client-count
+    :server-count server-count :registry-sample registry-sample))
+
 ;; ---------------------------------------------------------------------------
 ;; Plans section
 ;; ---------------------------------------------------------------------------

sx/sxc/pages/helpers.py

@@ -22,6 +22,7 @@ def _register_sx_helpers() -> None:
         "read-spec-file": _read_spec_file,
         "bootstrapper-data": _bootstrapper_data,
         "bundle-analyzer-data": _bundle_analyzer_data,
+        "routing-analyzer-data": _routing_analyzer_data,
     })
 
 
@@ -342,6 +343,82 @@ def _bundle_analyzer_data() -> dict:
     }
 
 
+def _routing_analyzer_data() -> dict:
+    """Compute per-page routing classification for the sx-docs app."""
+    from shared.sx.pages import get_all_pages
+    from shared.sx.parser import serialize as sx_serialize
+    from shared.sx.helpers import _sx_literal
+
+    pages_data = []
+    full_content: list[tuple[str, str, bool]] = []  # (name, full_content, has_data)
+    client_count = 0
+    server_count = 0
+
+    for name, page_def in sorted(get_all_pages("sx").items()):
+        has_data = page_def.data_expr is not None
+        content_src = ""
+        if page_def.content_expr is not None:
+            try:
+                content_src = sx_serialize(page_def.content_expr)
+            except Exception:
+                pass
+
+        full_content.append((name, content_src, has_data))
+
+        # Determine routing mode and reason
+        if has_data:
+            mode = "server"
+            reason = "Has :data expression — needs server IO"
+            server_count += 1
+        elif not content_src:
+            mode = "server"
+            reason = "No content expression"
+            server_count += 1
+        else:
+            mode = "client"
+            reason = ""
+            client_count += 1
+
+        pages_data.append({
+            "name": name,
+            "path": page_def.path,
+            "mode": mode,
+            "has-data": has_data,
+            "content-expr": content_src[:80] + ("..." if len(content_src) > 80 else ""),
+            "reason": reason,
+        })
+
+    # Sort: client pages first, then server
+    pages_data.sort(key=lambda p: (0 if p["mode"] == "client" else 1, p["name"]))
+
+    # Build a sample of the SX page registry format (use full content, first 3)
+    total = client_count + server_count
+    sample_entries = []
+    sorted_full = sorted(full_content, key=lambda x: x[0])
+    for name, csrc, hd in sorted_full[:3]:
+        page_def = get_all_pages("sx").get(name)
+        if not page_def:
+            continue
+        entry = (
+            "{:name " + _sx_literal(name)
+            + "\n :path " + _sx_literal(page_def.path)
+            + "\n :auth " + _sx_literal("public")
+            + " :has-data " + ("true" if hd else "false")
+            + "\n :content " + _sx_literal(csrc)
+            + "\n :closure {}}"
+        )
+        sample_entries.append(entry)
+    registry_sample = "\n\n".join(sample_entries)
+
+    return {
+        "pages": pages_data,
+        "total-pages": total,
+        "client-count": client_count,
+        "server-count": server_count,
+        "registry-sample": registry_sample,
+    }
+
+
 def _attr_detail_data(slug: str) -> dict:
     """Return attribute detail data for a specific attribute slug.