Enforce SX boundary contract via boundary.sx spec + runtime validation

Add boundary.sx declaring all 34 I/O primitives, 32 page helpers, and 9
allowed boundary types. Runtime validation in boundary.py checks every
registration against the spec — undeclared primitives/helpers crash at
startup with SX_BOUNDARY_STRICT=1 (now set in both dev and prod).

Key changes:
- Move 5 I/O-in-disguise primitives (app-url, asset-url, config,
  jinja-global, relations-from) from primitives.py to primitives_io.py
- Remove duplicate url-for/route-prefix from primitives.py (already in IO)
- Fix parse-datetime to return ISO string instead of raw datetime
- Add datetime→isoformat conversion in _convert_result at the edge
- Wrap page helper return values with boundary type validation
- Replace all SxExpr(f"...") patterns with sx_call() or _sx_fragment()
- Add assert declaration to primitives.sx

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

sx/sx/nav-data.sx

@@ -97,7 +97,8 @@
 
 (define bootstrappers-nav-items (list
   (dict :label "Overview" :href "/bootstrappers/")
-  (dict :label "JavaScript" :href "/bootstrappers/javascript")))
+  (dict :label "JavaScript" :href "/bootstrappers/javascript")
+  (dict :label "Python" :href "/bootstrappers/python")))
 
 ;; Spec file registry — canonical metadata for spec viewer pages.
 ;; Python only handles file I/O (read-spec-file); all metadata lives here.

sx/sx/specs.sx

@@ -268,9 +268,11 @@ boot.sx             depends on: cssx, orchestration, adapter-dom, render")))
               (td :class "px-3 py-2 text-green-600" "Live"))
             (tr :class "border-b border-stone-100"
               (td :class "px-3 py-2 text-stone-700" "Python")
-              (td :class "px-3 py-2 font-mono text-sm text-stone-400" "bootstrap_py.py")
-              (td :class "px-3 py-2 font-mono text-sm text-stone-400" "shared/sx/")
-              (td :class "px-3 py-2 text-stone-400" "Planned"))
+              (td :class "px-3 py-2 font-mono text-sm text-violet-700"
+                (a :href "/bootstrappers/python" :class "hover:underline"
+                   "bootstrap_py.py"))
+              (td :class "px-3 py-2 font-mono text-sm text-stone-500" "sx_ref.py")
+              (td :class "px-3 py-2 text-green-600" "Live"))
             (tr :class "border-b border-stone-100"
               (td :class "px-3 py-2 text-stone-700" "Rust")
               (td :class "px-3 py-2 font-mono text-sm text-stone-400" "bootstrap_rs.py")
@@ -320,6 +322,47 @@ boot.sx             depends on: cssx, orchestration, adapter-dom, render")))
           (pre :class "text-xs leading-relaxed whitespace-pre-wrap break-words"
             (code (highlight bootstrapped-output "javascript"))))))))
 
+;; ---------------------------------------------------------------------------
+;; Python bootstrapper detail
+;; ---------------------------------------------------------------------------
+
+(defcomp ~bootstrapper-py-content (&key bootstrapper-source bootstrapped-output)
+  (~doc-page :title "Python Bootstrapper"
+    (div :class "space-y-8"
+
+      (div :class "space-y-3"
+        (p :class "text-stone-600"
+          "This page reads the canonical " (code :class "text-violet-700 text-sm" ".sx")
+          " spec files, runs the Python bootstrapper, and displays both the compiler source and its generated Python output. "
+          "The generated code below is live — it was produced by the bootstrapper at page load time.")
+        (p :class "text-xs text-stone-400 italic"
+          "With SX_USE_REF=1, the server-side SX evaluator running this page IS the bootstrapped output. "
+          "This page re-runs the bootstrapper to display the source and result."))
+
+      (div :class "space-y-3"
+        (div :class "flex items-baseline gap-3"
+          (h2 :class "text-2xl font-semibold text-stone-800" "Bootstrapper")
+          (span :class "text-sm text-stone-400 font-mono" "bootstrap_py.py"))
+        (p :class "text-sm text-stone-500"
+          "The compiler reads " (code :class "text-violet-700 text-sm" ".sx")
+          " spec files (eval, primitives, render, adapter-html) "
+          "and emits a standalone Python module. Platform bridge functions (type constructors, environment ops) "
+          "are emitted as native Python implementations.")
+        (div :class "bg-stone-100 rounded-lg p-5 max-h-96 overflow-y-auto border border-stone-200"
+          (pre :class "text-xs leading-relaxed whitespace-pre-wrap break-words"
+            (code (highlight bootstrapper-source "python")))))
+
+      (div :class "space-y-3"
+        (div :class "flex items-baseline gap-3"
+          (h2 :class "text-2xl font-semibold text-stone-800" "Generated Output")
+          (span :class "text-sm text-stone-400 font-mono" "sx_ref.py"))
+        (p :class "text-sm text-stone-500"
+          "The Python below was generated by running the bootstrapper against the current spec files. "
+          "It is a complete server-side SX evaluator — eval, primitives, and HTML renderer.")
+        (div :class "bg-stone-100 rounded-lg p-5 max-h-96 overflow-y-auto border border-violet-300"
+          (pre :class "text-xs leading-relaxed whitespace-pre-wrap break-words"
+            (code (highlight bootstrapped-output "python"))))))))
+
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 ;; Not found
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