sx-host plan steps 1-2: defhelper + SX config + SXTP spec + nav tools

Step 1 — defhelper: SX-defined page data helpers replace Python helpers.
(defhelper name (params) body) in .sx files, using existing IO primitives
(query, action, service). Loaded into OCaml kernel as pure SX defines.

Step 2 — SX config: app-config.sx replaces app-config.yaml with (defconfig)
form. (env-get "VAR") resolves secrets from environment. Kebab-to-underscore
aliasing ensures backward compatibility with all 174 config consumers.

Also: SXTP protocol spec (applications/sxtp/spec.sx), docs article,
sx_nav move/delete modes, reactive-runtime moved to geography.

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

shared/sx/ocaml_bridge.py

@@ -308,14 +308,30 @@ class OcamlBridge:
             return
         self._helpers_injected = True
         try:
-            from .pages import get_page_helpers
+            from .pages import get_page_helpers, get_sx_helpers
             import inspect
-            helpers = get_page_helpers("sx")
-            if not helpers:
-                self._helpers_injected = False
-                return
             count = 0
+
+            # 1. Inject SX-defined helpers (defhelper) — pure SX, no Python bridge
+            #    Load from all services since they're pure SX defines.
+            sx_helpers: dict[str, str] = {}
+            from .pages import _SX_HELPERS
+            for svc_helpers in _SX_HELPERS.values():
+                sx_helpers.update(svc_helpers)
+            for name, sx_source in sx_helpers.items():
+                try:
+                    await self._send_command(f'(load-source "{_escape(sx_source)}")')
+                    await self._read_until_ok(ctx=None)
+                    count += 1
+                except OcamlBridgeError:
+                    _logger.warning("Failed to inject SX helper: %s", name)
+
+            # 2. Inject Python helpers — wrapped as (helper "name" ...) IO bridge calls
+            helpers = get_page_helpers("sx")
             for name, fn in helpers.items():
+                # Skip if already defined by defhelper (SX takes priority)
+                if name in sx_helpers:
+                    continue
                 if callable(fn) and not name.startswith("~"):
                     try:
                         sig = inspect.signature(fn)
@@ -333,7 +349,12 @@ class OcamlBridge:
                         count += 1
                     except OcamlBridgeError:
                         pass
-            _logger.info("Injected %d page helpers into OCaml kernel", count)
+
+            if not count and not helpers and not sx_helpers:
+                self._helpers_injected = False
+                return
+            _logger.info("Injected %d page helpers into OCaml kernel (%d SX, %d Python)",
+                         count, len(sx_helpers), count - len(sx_helpers))
         except Exception as e:
             _logger.warning("Helper injection failed: %s", e)
             self._helpers_injected = False