Spec explorer data endpoint, spec file finder, browser render test (failing)

- Add spec-explorer-data-by-slug helper with _SPEC_SLUG_MAP
- _find_spec_file searches spec/, web/, shared/sx/ref/ directories
- defpage specs-explore-page uses :data for server-side data fetch
- test_evaluator_renders_in_browser: failing test for client-side rendering
  (client re-evaluates defpage content, find-spec unavailable — pre-existing)

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

sx/sxc/pages/helpers.py

@@ -159,18 +159,35 @@ def _reference_data(slug: str) -> dict:
     return build_reference_data(slug, raw, detail_keys)
 
 
-def _read_spec_file(filename: str) -> str:
-    """Read a spec .sx file from the ref directory. Pure I/O — metadata lives in .sx."""
+def _find_spec_file(filename: str) -> str | None:
+    """Find a spec .sx file across spec/, web/, shared/sx/ref/ directories."""
     import os
-    ref_dir = os.path.join(os.path.dirname(__file__), "..", "..", "shared", "sx", "ref")
-    if not os.path.isdir(ref_dir):
-        ref_dir = "/app/shared/sx/ref"
-    filepath = os.path.join(ref_dir, filename)
+    base = os.path.join(os.path.dirname(__file__), "..", "..")
+    search_dirs = [
+        os.path.join(base, "spec"),
+        os.path.join(base, "web"),
+        os.path.join(base, "shared", "sx", "ref"),
+        "/app/spec",
+        "/app/web",
+        "/app/shared/sx/ref",
+    ]
+    for d in search_dirs:
+        path = os.path.join(d, filename)
+        if os.path.isfile(path):
+            return path
+    return None
+
+
+def _read_spec_file(filename: str) -> str:
+    """Read a spec .sx file. Pure I/O — metadata lives in .sx."""
+    filepath = _find_spec_file(filename)
+    if not filepath:
+        return ";; spec file not found: " + filename
     try:
         with open(filepath, encoding="utf-8") as f:
             return f.read()
-    except FileNotFoundError:
-        return ";; spec file not found"
+    except (FileNotFoundError, TypeError):
+        return ";; spec file not found: " + filename
 
 
 # ---------------------------------------------------------------------------
@@ -332,7 +349,7 @@ def _collect_symbols(expr) -> set[str]:
 
 _SPEC_SLUG_MAP = {
     "parser": ("parser.sx", "Parser", "Tokenization and parsing"),
-    "evaluator": ("eval.sx", "Evaluator", "Tree-walking evaluation"),
+    "evaluator": ("evaluator.sx", "Evaluator", "CEK machine evaluator"),
     "primitives": ("primitives.sx", "Primitives", "Built-in pure functions"),
     "render": ("render.sx", "Renderer", "Three rendering modes"),
     "special-forms": ("special-forms.sx", "Special Forms", "Special form dispatch"),
@@ -374,10 +391,9 @@ def _spec_explorer_data(filename: str, title: str = "", desc: str = "") -> dict
         return None
 
     # Read the raw source
-    ref_dir = os.path.join(os.path.dirname(__file__), "..", "..", "shared", "sx", "ref")
-    if not os.path.isdir(ref_dir):
-        ref_dir = "/app/shared/sx/ref"
-    filepath = os.path.join(ref_dir, filename)
+    filepath = _find_spec_file(filename)
+    if not filepath:
+        return None
     try:
         with open(filepath, encoding="utf-8") as f:
             source = f.read()