diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..abfa596
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,2 @@
+# host snapshots are uploaded as raw bytes (docs/updates.md §4.1)
+**/tinyui-host/*.txt text eol=lf
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 98a632f..2009bdf 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -28,7 +28,7 @@ jobs:
           git clone --depth 1 --branch "$version" https://github.com/HarlonWang/quickjs-kmp.git "$RUNNER_TEMP/quickjs-kmp"
           (cd "$RUNNER_TEMP/quickjs-kmp" && ./gradlew :library:buildNativeHostJni --no-daemon)
           echo "TINYUI_QUICKJS_HOST_JNI=$RUNNER_TEMP/quickjs-kmp/library/build/native/host-jni/lib" >> "$GITHUB_ENV"
-      - run: ./gradlew :compose:testAndroidHostTest :compose:apiCheck :sample:androidApp:assembleDebug --no-daemon
+      - run: ./gradlew :compose:testAndroidHostTest :compose:apiCheck :sample:shared:testAndroidHostTest :sample:androidApp:assembleDebug --no-daemon
 
   pnpm:
     runs-on: ubuntu-latest
diff --git a/compose/api/compose.klib.api b/compose/api/compose.klib.api
index 1af914e..fbc7e84 100644
--- a/compose/api/compose.klib.api
+++ b/compose/api/compose.klib.api
@@ -37,7 +37,7 @@ abstract fun interface app.tinyui/Config { // app.tinyui/Config|null[0]
 }
 
 abstract fun interface app.tinyui/HostCapability { // app.tinyui/HostCapability|null[0]
-    abstract suspend fun call(kotlin/String): kotlin/String? // app.tinyui/HostCapability.call|call(kotlin.String){}[0]
+    abstract suspend fun call(kotlin/String, app.tinyui/PageContext): kotlin/String? // app.tinyui/HostCapability.call|call(kotlin.String;app.tinyui.PageContext){}[0]
 }
 
 abstract fun interface app.tinyui/I18n { // app.tinyui/I18n|null[0]
@@ -153,6 +153,19 @@ sealed interface app.tinyui.schema/SizeValue { // app.tinyui.schema/SizeValue|nu
     }
 }
 
+final class <#A: kotlin/Any> app.tinyui/PageLocal { // app.tinyui/PageLocal|null[0]
+    constructor <init>() // app.tinyui/PageLocal.<init>|<init>(){}[0]
+
+    final fun provides(#A): app.tinyui/PageLocalValue<#A> // app.tinyui/PageLocal.provides|provides(1:0){}[0]
+}
+
+final class <#A: kotlin/Any> app.tinyui/PageLocalValue { // app.tinyui/PageLocalValue|null[0]
+    final val local // app.tinyui/PageLocalValue.local|{}local[0]
+        final fun <get-local>(): app.tinyui/PageLocal<#A> // app.tinyui/PageLocalValue.local.<get-local>|<get-local>(){}[0]
+    final val value // app.tinyui/PageLocalValue.value|{}value[0]
+        final fun <get-value>(): #A // app.tinyui/PageLocalValue.value.<get-value>|<get-value>(){}[0]
+}
+
 final class app.tinyui.node/Command { // app.tinyui.node/Command|null[0]
     constructor <init>(kotlin/String, kotlin.collections/Map<kotlin/String, kotlin/Any?>) // app.tinyui.node/Command.<init>|<init>(kotlin.String;kotlin.collections.Map<kotlin.String,kotlin.Any?>){}[0]
 
@@ -285,6 +298,15 @@ final class app.tinyui/Bundle { // app.tinyui/Bundle|null[0]
     }
 }
 
+final class app.tinyui/CapabilityRegistry { // app.tinyui/CapabilityRegistry|null[0]
+    constructor <init>() // app.tinyui/CapabilityRegistry.<init>|<init>(){}[0]
+
+    final val names // app.tinyui/CapabilityRegistry.names|{}names[0]
+        final fun <get-names>(): kotlin.collections/Set<kotlin/String> // app.tinyui/CapabilityRegistry.names.<get-names>|<get-names>(){}[0]
+
+    final fun register(kotlin/String, app.tinyui/HostCapability) // app.tinyui/CapabilityRegistry.register|register(kotlin.String;app.tinyui.HostCapability){}[0]
+}
+
 final class app.tinyui/EventBus { // app.tinyui/EventBus|null[0]
     constructor <init>() // app.tinyui/EventBus.<init>|<init>(){}[0]
 
@@ -300,10 +322,8 @@ final class app.tinyui/HostException : kotlin/Exception { // app.tinyui/HostExce
 }
 
 final class app.tinyui/HostServices { // app.tinyui/HostServices|null[0]
-    constructor <init>(app.tinyui/Navigator = ..., app.tinyui/Store = ..., app.tinyui/HttpClient = ..., app.tinyui/I18n = ..., app.tinyui/Config = ..., app.tinyui/EventBus = ..., kotlin.collections/Map<kotlin/String, kotlin/String> = ..., kotlin.collections/Map<kotlin/String, app.tinyui/HostCapability> = ...) // app.tinyui/HostServices.<init>|<init>(app.tinyui.Navigator;app.tinyui.Store;app.tinyui.HttpClient;app.tinyui.I18n;app.tinyui.Config;app.tinyui.EventBus;kotlin.collections.Map<kotlin.String,kotlin.String>;kotlin.collections.Map<kotlin.String,app.tinyui.HostCapability>){}[0]
+    constructor <init>(app.tinyui/Navigator = ..., app.tinyui/Store = ..., app.tinyui/HttpClient = ..., app.tinyui/I18n = ..., app.tinyui/Config = ..., app.tinyui/EventBus = ..., kotlin.collections/Map<kotlin/String, kotlin/String> = ..., kotlin.collections/List<app.tinyui/PageLocalValue<*>> = ...) // app.tinyui/HostServices.<init>|<init>(app.tinyui.Navigator;app.tinyui.Store;app.tinyui.HttpClient;app.tinyui.I18n;app.tinyui.Config;app.tinyui.EventBus;kotlin.collections.Map<kotlin.String,kotlin.String>;kotlin.collections.List<app.tinyui.PageLocalValue<*>>){}[0]
 
-    final val capabilities // app.tinyui/HostServices.capabilities|{}capabilities[0]
-        final fun <get-capabilities>(): kotlin.collections/Map<kotlin/String, app.tinyui/HostCapability> // app.tinyui/HostServices.capabilities.<get-capabilities>|<get-capabilities>(){}[0]
     final val config // app.tinyui/HostServices.config|{}config[0]
         final fun <get-config>(): app.tinyui/Config // app.tinyui/HostServices.config.<get-config>|<get-config>(){}[0]
     final val deviceInfo // app.tinyui/HostServices.deviceInfo|{}deviceInfo[0]
@@ -314,6 +334,8 @@ final class app.tinyui/HostServices { // app.tinyui/HostServices|null[0]
         final fun <get-http>(): app.tinyui/HttpClient // app.tinyui/HostServices.http.<get-http>|<get-http>(){}[0]
     final val i18n // app.tinyui/HostServices.i18n|{}i18n[0]
         final fun <get-i18n>(): app.tinyui/I18n // app.tinyui/HostServices.i18n.<get-i18n>|<get-i18n>(){}[0]
+    final val locals // app.tinyui/HostServices.locals|{}locals[0]
+        final fun <get-locals>(): kotlin.collections/List<app.tinyui/PageLocalValue<*>> // app.tinyui/HostServices.locals.<get-locals>|<get-locals>(){}[0]
     final val navigator // app.tinyui/HostServices.navigator|{}navigator[0]
         final fun <get-navigator>(): app.tinyui/Navigator // app.tinyui/HostServices.navigator.<get-navigator>|<get-navigator>(){}[0]
     final val store // app.tinyui/HostServices.store|{}store[0]
@@ -370,6 +392,13 @@ final class app.tinyui/LoadedPage { // app.tinyui/LoadedPage|null[0]
         final fun <get-sourceMaps>(): app.tinyui/SourceMaps // app.tinyui/LoadedPage.sourceMaps.<get-sourceMaps>|<get-sourceMaps>(){}[0]
 }
 
+final class app.tinyui/PageContext { // app.tinyui/PageContext|null[0]
+    final val name // app.tinyui/PageContext.name|{}name[0]
+        final fun <get-name>(): kotlin/String // app.tinyui/PageContext.name.<get-name>|<get-name>(){}[0]
+
+    final fun <#A1: kotlin/Any> get(app.tinyui/PageLocal<#A1>): #A1? // app.tinyui/PageContext.get|get(app.tinyui.PageLocal<0:0>){0§<kotlin.Any>}[0]
+}
+
 final class app.tinyui/PageError { // app.tinyui/PageError|null[0]
     constructor <init>(kotlin/String, kotlin/String, kotlin/String, kotlin/String, kotlin/String? = ..., kotlin/String? = ..., kotlin.collections/List<app.tinyui/StackFrame> = ..., kotlin/String? = ...) // app.tinyui/PageError.<init>|<init>(kotlin.String;kotlin.String;kotlin.String;kotlin.String;kotlin.String?;kotlin.String?;kotlin.collections.List<app.tinyui.StackFrame>;kotlin.String?){}[0]
 
@@ -405,10 +434,10 @@ final class app.tinyui/PageFailure { // app.tinyui/PageFailure|null[0]
 }
 
 final class app.tinyui/PageHost { // app.tinyui/PageHost|null[0]
-    constructor <init>(app.tinyui/RuntimeBundle, app.tinyui/PageModule, app.tinyui.schema/ComponentRegistry, app.tinyui/PageSink, app.tinyui/HostServices = ..., kotlin/String = ..., kotlin/Long = ..., app.tinyui/SourceMaps = ...) // app.tinyui/PageHost.<init>|<init>(app.tinyui.RuntimeBundle;app.tinyui.PageModule;app.tinyui.schema.ComponentRegistry;app.tinyui.PageSink;app.tinyui.HostServices;kotlin.String;kotlin.Long;app.tinyui.SourceMaps){}[0]
+    constructor <init>(app.tinyui/RuntimeBundle, app.tinyui/PageModule, app.tinyui/TinyUIHost, app.tinyui/HostServices = ..., kotlin/String = ..., kotlin/Long = ..., app.tinyui/SourceMaps = ...) // app.tinyui/PageHost.<init>|<init>(app.tinyui.RuntimeBundle;app.tinyui.PageModule;app.tinyui.TinyUIHost;app.tinyui.HostServices;kotlin.String;kotlin.Long;app.tinyui.SourceMaps){}[0]
 
-    final val registry // app.tinyui/PageHost.registry|{}registry[0]
-        final fun <get-registry>(): app.tinyui.schema/ComponentRegistry // app.tinyui/PageHost.registry.<get-registry>|<get-registry>(){}[0]
+    final val host // app.tinyui/PageHost.host|{}host[0]
+        final fun <get-host>(): app.tinyui/TinyUIHost // app.tinyui/PageHost.host.<get-host>|<get-host>(){}[0]
     final val tree // app.tinyui/PageHost.tree|{}tree[0]
         final fun <get-tree>(): app.tinyui.node/NodeTree // app.tinyui/PageHost.tree.<get-tree>|<get-tree>(){}[0]
 
@@ -491,6 +520,17 @@ final class app.tinyui/StoreValue { // app.tinyui/StoreValue|null[0]
         final fun <get-version>(): kotlin/Long // app.tinyui/StoreValue.version.<get-version>|<get-version>(){}[0]
 }
 
+final class app.tinyui/TinyUIHost { // app.tinyui/TinyUIHost|null[0]
+    constructor <init>(app.tinyui.schema/ComponentRegistry, app.tinyui/PageSink, app.tinyui/CapabilityRegistry = ...) // app.tinyui/TinyUIHost.<init>|<init>(app.tinyui.schema.ComponentRegistry;app.tinyui.PageSink;app.tinyui.CapabilityRegistry){}[0]
+
+    final val capabilities // app.tinyui/TinyUIHost.capabilities|{}capabilities[0]
+        final fun <get-capabilities>(): app.tinyui/CapabilityRegistry // app.tinyui/TinyUIHost.capabilities.<get-capabilities>|<get-capabilities>(){}[0]
+    final val components // app.tinyui/TinyUIHost.components|{}components[0]
+        final fun <get-components>(): app.tinyui.schema/ComponentRegistry // app.tinyui/TinyUIHost.components.<get-components>|<get-components>(){}[0]
+    final val sink // app.tinyui/TinyUIHost.sink|{}sink[0]
+        final fun <get-sink>(): app.tinyui/PageSink // app.tinyui/TinyUIHost.sink.<get-sink>|<get-sink>(){}[0]
+}
+
 sealed class app.tinyui.schema/PropSpec { // app.tinyui.schema/PropSpec|null[0]
     abstract val default // app.tinyui.schema/PropSpec.default|{}default[0]
         abstract fun <get-default>(): kotlin/Any? // app.tinyui.schema/PropSpec.default.<get-default>|<get-default>(){}[0]
@@ -616,9 +656,15 @@ final object app.tinyui.schema/Theme { // app.tinyui.schema/Theme|null[0]
     final fun textStyle(androidx.compose.material3/Typography, kotlin/String): androidx.compose.ui.text/TextStyle? // app.tinyui.schema/Theme.textStyle|textStyle(androidx.compose.material3.Typography;kotlin.String){}[0]
 }
 
+final object app.tinyui/HostSnapshot { // app.tinyui/HostSnapshot|null[0]
+    final fun render(app.tinyui/TinyUIHost, kotlin/String): kotlin/String // app.tinyui/HostSnapshot.render|render(app.tinyui.TinyUIHost;kotlin.String){}[0]
+}
+
 final object app.tinyui/TinyUI { // app.tinyui/TinyUI|null[0]
     final val engineVersion // app.tinyui/TinyUI.engineVersion|{}engineVersion[0]
         final fun <get-engineVersion>(): kotlin/String // app.tinyui/TinyUI.engineVersion.<get-engineVersion>|<get-engineVersion>(){}[0]
+    final val version // app.tinyui/TinyUI.version|{}version[0]
+        final fun <get-version>(): kotlin/String // app.tinyui/TinyUI.version.<get-version>|<get-version>(){}[0]
 
     final var debug // app.tinyui/TinyUI.debug|{}debug[0]
         final fun <get-debug>(): kotlin/Boolean // app.tinyui/TinyUI.debug.<get-debug>|<get-debug>(){}[0]
@@ -653,18 +699,23 @@ final val app.tinyui.schema/app_tinyui_schema_SizeValue_Wrap$stableprop // app.t
 final val app.tinyui.schema/app_tinyui_schema_Theme$stableprop // app.tinyui.schema/app_tinyui_schema_Theme$stableprop|#static{}app_tinyui_schema_Theme$stableprop[0]
 final val app.tinyui/app_tinyui_BuildManifest$stableprop // app.tinyui/app_tinyui_BuildManifest$stableprop|#static{}app_tinyui_BuildManifest$stableprop[0]
 final val app.tinyui/app_tinyui_Bundle$stableprop // app.tinyui/app_tinyui_Bundle$stableprop|#static{}app_tinyui_Bundle$stableprop[0]
+final val app.tinyui/app_tinyui_CapabilityRegistry$stableprop // app.tinyui/app_tinyui_CapabilityRegistry$stableprop|#static{}app_tinyui_CapabilityRegistry$stableprop[0]
 final val app.tinyui/app_tinyui_EventBus$stableprop // app.tinyui/app_tinyui_EventBus$stableprop|#static{}app_tinyui_EventBus$stableprop[0]
 final val app.tinyui/app_tinyui_HostException$stableprop // app.tinyui/app_tinyui_HostException$stableprop|#static{}app_tinyui_HostException$stableprop[0]
 final val app.tinyui/app_tinyui_HostServices$stableprop // app.tinyui/app_tinyui_HostServices$stableprop|#static{}app_tinyui_HostServices$stableprop[0]
+final val app.tinyui/app_tinyui_HostSnapshot$stableprop // app.tinyui/app_tinyui_HostSnapshot$stableprop|#static{}app_tinyui_HostSnapshot$stableprop[0]
 final val app.tinyui/app_tinyui_HttpClient_None$stableprop // app.tinyui/app_tinyui_HttpClient_None$stableprop|#static{}app_tinyui_HttpClient_None$stableprop[0]
 final val app.tinyui/app_tinyui_HttpRequest$stableprop // app.tinyui/app_tinyui_HttpRequest$stableprop|#static{}app_tinyui_HttpRequest$stableprop[0]
 final val app.tinyui/app_tinyui_HttpResponse$stableprop // app.tinyui/app_tinyui_HttpResponse$stableprop|#static{}app_tinyui_HttpResponse$stableprop[0]
 final val app.tinyui/app_tinyui_InMemoryStore$stableprop // app.tinyui/app_tinyui_InMemoryStore$stableprop|#static{}app_tinyui_InMemoryStore$stableprop[0]
 final val app.tinyui/app_tinyui_LoadedPage$stableprop // app.tinyui/app_tinyui_LoadedPage$stableprop|#static{}app_tinyui_LoadedPage$stableprop[0]
 final val app.tinyui/app_tinyui_Navigator_None$stableprop // app.tinyui/app_tinyui_Navigator_None$stableprop|#static{}app_tinyui_Navigator_None$stableprop[0]
+final val app.tinyui/app_tinyui_PageContext$stableprop // app.tinyui/app_tinyui_PageContext$stableprop|#static{}app_tinyui_PageContext$stableprop[0]
 final val app.tinyui/app_tinyui_PageError$stableprop // app.tinyui/app_tinyui_PageError$stableprop|#static{}app_tinyui_PageError$stableprop[0]
 final val app.tinyui/app_tinyui_PageFailure$stableprop // app.tinyui/app_tinyui_PageFailure$stableprop|#static{}app_tinyui_PageFailure$stableprop[0]
 final val app.tinyui/app_tinyui_PageHost$stableprop // app.tinyui/app_tinyui_PageHost$stableprop|#static{}app_tinyui_PageHost$stableprop[0]
+final val app.tinyui/app_tinyui_PageLocal$stableprop // app.tinyui/app_tinyui_PageLocal$stableprop|#static{}app_tinyui_PageLocal$stableprop[0]
+final val app.tinyui/app_tinyui_PageLocalValue$stableprop // app.tinyui/app_tinyui_PageLocalValue$stableprop|#static{}app_tinyui_PageLocalValue$stableprop[0]
 final val app.tinyui/app_tinyui_PageModule$stableprop // app.tinyui/app_tinyui_PageModule$stableprop|#static{}app_tinyui_PageModule$stableprop[0]
 final val app.tinyui/app_tinyui_RuntimeBundle$stableprop // app.tinyui/app_tinyui_RuntimeBundle$stableprop|#static{}app_tinyui_RuntimeBundle$stableprop[0]
 final val app.tinyui/app_tinyui_SourceMap_Position$stableprop // app.tinyui/app_tinyui_SourceMap_Position$stableprop|#static{}app_tinyui_SourceMap_Position$stableprop[0]
@@ -672,6 +723,7 @@ final val app.tinyui/app_tinyui_SourceMaps$stableprop // app.tinyui/app_tinyui_S
 final val app.tinyui/app_tinyui_StackFrame$stableprop // app.tinyui/app_tinyui_StackFrame$stableprop|#static{}app_tinyui_StackFrame$stableprop[0]
 final val app.tinyui/app_tinyui_StoreValue$stableprop // app.tinyui/app_tinyui_StoreValue$stableprop|#static{}app_tinyui_StoreValue$stableprop[0]
 final val app.tinyui/app_tinyui_TinyUI$stableprop // app.tinyui/app_tinyui_TinyUI$stableprop|#static{}app_tinyui_TinyUI$stableprop[0]
+final val app.tinyui/app_tinyui_TinyUIHost$stableprop // app.tinyui/app_tinyui_TinyUIHost$stableprop|#static{}app_tinyui_TinyUIHost$stableprop[0]
 
 final fun (app.tinyui.schema/ComponentRegistry).app.tinyui.components/registerBuiltins(): app.tinyui.schema/ComponentRegistry // app.tinyui.components/registerBuiltins|registerBuiltins@app.tinyui.schema.ComponentRegistry(){}[0]
 final fun (app.tinyui.schema/NodeScope).app.tinyui.schema/Commands(kotlin.coroutines/SuspendFunction1<app.tinyui.node/Command, kotlin/Unit>, androidx.compose.runtime/Composer?, kotlin/Int) // app.tinyui.schema/Commands|Commands@app.tinyui.schema.NodeScope(kotlin.coroutines.SuspendFunction1<app.tinyui.node.Command,kotlin.Unit>;androidx.compose.runtime.Composer?;kotlin.Int){}[0]
@@ -699,21 +751,26 @@ final fun app.tinyui.schema/app_tinyui_schema_SizeValue_Fixed$stableprop_getter(
 final fun app.tinyui.schema/app_tinyui_schema_SizeValue_Wrap$stableprop_getter(): kotlin/Int // app.tinyui.schema/app_tinyui_schema_SizeValue_Wrap$stableprop_getter|app_tinyui_schema_SizeValue_Wrap$stableprop_getter(){}[0]
 final fun app.tinyui.schema/app_tinyui_schema_Theme$stableprop_getter(): kotlin/Int // app.tinyui.schema/app_tinyui_schema_Theme$stableprop_getter|app_tinyui_schema_Theme$stableprop_getter(){}[0]
 final fun app.tinyui/PageFailureScreen(app.tinyui/PageFailure, androidx.compose.runtime/Composer?, kotlin/Int) // app.tinyui/PageFailureScreen|PageFailureScreen(app.tinyui.PageFailure;androidx.compose.runtime.Composer?;kotlin.Int){}[0]
-final fun app.tinyui/TinyUIPage(app.tinyui/RuntimeBundle, app.tinyui/PageModule, app.tinyui.schema/ComponentRegistry, app.tinyui/PageSink, app.tinyui/HostServices?, kotlin/String?, androidx.compose.ui/Modifier?, app.tinyui/SourceMaps?, kotlin/Function3<app.tinyui/PageFailure, androidx.compose.runtime/Composer, kotlin/Int, kotlin/Unit>?, kotlin/Function1<app.tinyui/PageHost, kotlin/Unit>?, androidx.compose.runtime/Composer?, kotlin/Int, kotlin/Int) // app.tinyui/TinyUIPage|TinyUIPage(app.tinyui.RuntimeBundle;app.tinyui.PageModule;app.tinyui.schema.ComponentRegistry;app.tinyui.PageSink;app.tinyui.HostServices?;kotlin.String?;androidx.compose.ui.Modifier?;app.tinyui.SourceMaps?;kotlin.Function3<app.tinyui.PageFailure,androidx.compose.runtime.Composer,kotlin.Int,kotlin.Unit>?;kotlin.Function1<app.tinyui.PageHost,kotlin.Unit>?;androidx.compose.runtime.Composer?;kotlin.Int;kotlin.Int){}[0]
+final fun app.tinyui/TinyUIPage(app.tinyui/RuntimeBundle, app.tinyui/PageModule, app.tinyui/TinyUIHost, app.tinyui/HostServices?, kotlin/String?, androidx.compose.ui/Modifier?, app.tinyui/SourceMaps?, kotlin/Function3<app.tinyui/PageFailure, androidx.compose.runtime/Composer, kotlin/Int, kotlin/Unit>?, kotlin/Function1<app.tinyui/PageHost, kotlin/Unit>?, androidx.compose.runtime/Composer?, kotlin/Int, kotlin/Int) // app.tinyui/TinyUIPage|TinyUIPage(app.tinyui.RuntimeBundle;app.tinyui.PageModule;app.tinyui.TinyUIHost;app.tinyui.HostServices?;kotlin.String?;androidx.compose.ui.Modifier?;app.tinyui.SourceMaps?;kotlin.Function3<app.tinyui.PageFailure,androidx.compose.runtime.Composer,kotlin.Int,kotlin.Unit>?;kotlin.Function1<app.tinyui.PageHost,kotlin.Unit>?;androidx.compose.runtime.Composer?;kotlin.Int;kotlin.Int){}[0]
 final fun app.tinyui/app_tinyui_BuildManifest$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_BuildManifest$stableprop_getter|app_tinyui_BuildManifest$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_Bundle$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_Bundle$stableprop_getter|app_tinyui_Bundle$stableprop_getter(){}[0]
+final fun app.tinyui/app_tinyui_CapabilityRegistry$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_CapabilityRegistry$stableprop_getter|app_tinyui_CapabilityRegistry$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_EventBus$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_EventBus$stableprop_getter|app_tinyui_EventBus$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_HostException$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_HostException$stableprop_getter|app_tinyui_HostException$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_HostServices$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_HostServices$stableprop_getter|app_tinyui_HostServices$stableprop_getter(){}[0]
+final fun app.tinyui/app_tinyui_HostSnapshot$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_HostSnapshot$stableprop_getter|app_tinyui_HostSnapshot$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_HttpClient_None$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_HttpClient_None$stableprop_getter|app_tinyui_HttpClient_None$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_HttpRequest$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_HttpRequest$stableprop_getter|app_tinyui_HttpRequest$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_HttpResponse$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_HttpResponse$stableprop_getter|app_tinyui_HttpResponse$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_InMemoryStore$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_InMemoryStore$stableprop_getter|app_tinyui_InMemoryStore$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_LoadedPage$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_LoadedPage$stableprop_getter|app_tinyui_LoadedPage$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_Navigator_None$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_Navigator_None$stableprop_getter|app_tinyui_Navigator_None$stableprop_getter(){}[0]
+final fun app.tinyui/app_tinyui_PageContext$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_PageContext$stableprop_getter|app_tinyui_PageContext$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_PageError$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_PageError$stableprop_getter|app_tinyui_PageError$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_PageFailure$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_PageFailure$stableprop_getter|app_tinyui_PageFailure$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_PageHost$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_PageHost$stableprop_getter|app_tinyui_PageHost$stableprop_getter(){}[0]
+final fun app.tinyui/app_tinyui_PageLocal$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_PageLocal$stableprop_getter|app_tinyui_PageLocal$stableprop_getter(){}[0]
+final fun app.tinyui/app_tinyui_PageLocalValue$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_PageLocalValue$stableprop_getter|app_tinyui_PageLocalValue$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_PageModule$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_PageModule$stableprop_getter|app_tinyui_PageModule$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_RuntimeBundle$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_RuntimeBundle$stableprop_getter|app_tinyui_RuntimeBundle$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_SourceMap_Position$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_SourceMap_Position$stableprop_getter|app_tinyui_SourceMap_Position$stableprop_getter(){}[0]
@@ -721,3 +778,4 @@ final fun app.tinyui/app_tinyui_SourceMaps$stableprop_getter(): kotlin/Int // ap
 final fun app.tinyui/app_tinyui_StackFrame$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_StackFrame$stableprop_getter|app_tinyui_StackFrame$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_StoreValue$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_StoreValue$stableprop_getter|app_tinyui_StoreValue$stableprop_getter(){}[0]
 final fun app.tinyui/app_tinyui_TinyUI$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_TinyUI$stableprop_getter|app_tinyui_TinyUI$stableprop_getter(){}[0]
+final fun app.tinyui/app_tinyui_TinyUIHost$stableprop_getter(): kotlin/Int // app.tinyui/app_tinyui_TinyUIHost$stableprop_getter|app_tinyui_TinyUIHost$stableprop_getter(){}[0]
diff --git a/compose/build.gradle.kts b/compose/build.gradle.kts
index c890f66..310ff5f 100644
--- a/compose/build.gradle.kts
+++ b/compose/build.gradle.kts
@@ -7,12 +7,27 @@ plugins {
     alias(libs.plugins.binaryCompatibilityValidator)
 }
 
+// TinyUI.version: the published version, so a host snapshot names the tinyui it was built against
+val generateVersion by tasks.registering {
+    val version = providers.gradleProperty("VERSION_NAME")
+    val out = layout.buildDirectory.dir("generated/tinyui-version")
+    inputs.property("version", version)
+    outputs.dir(out)
+    doLast {
+        out.get().file("app/tinyui/Version.kt").asFile.apply { parentFile.mkdirs() }
+            .writeText("package app.tinyui\n\ninternal const val VERSION = \"${version.get()}\"\n")
+    }
+}
+
 kotlin {
     android {
         namespace = "app.tinyui"
     }
 
     sourceSets {
+        commonMain {
+            kotlin.srcDir(generateVersion)
+        }
         commonMain.dependencies {
             api(libs.quickjs.kmp)
             implementation(compose.runtime)
diff --git a/compose/src/androidHostTest/kotlin/app/tinyui/BundleSmokeTest.kt b/compose/src/androidHostTest/kotlin/app/tinyui/BundleSmokeTest.kt
index 0fcfa86..423712c 100644
--- a/compose/src/androidHostTest/kotlin/app/tinyui/BundleSmokeTest.kt
+++ b/compose/src/androidHostTest/kotlin/app/tinyui/BundleSmokeTest.kt
@@ -49,7 +49,7 @@ class BundleSmokeTest {
                 if (request.url.endsWith("page=1")) HttpResponse(200, """{"items":[{"id":1,"title":"a","done":false}],"next":2}""")
                 else throw HostException("E_HTTP", "500")
         }
-        val host = PageHost(loaded.runtime, loaded.module, ComponentRegistry().registerBuiltins(), sink, HostServices(http = http), sourceMaps = loaded.sourceMaps)
+        val host = PageHost(loaded.runtime, loaded.module, TinyUIHost(ComponentRegistry().registerBuiltins(), sink), HostServices(http = http), sourceMaps = loaded.sourceMaps)
         host.start()
         try {
             // the list only exists once the first page has loaded; node ids are dense, so scan them
diff --git a/compose/src/commonMain/kotlin/app/tinyui/HostServices.kt b/compose/src/commonMain/kotlin/app/tinyui/HostServices.kt
index 511b3cc..1c9110a 100644
--- a/compose/src/commonMain/kotlin/app/tinyui/HostServices.kt
+++ b/compose/src/commonMain/kotlin/app/tinyui/HostServices.kt
@@ -4,7 +4,7 @@ import kotlin.concurrent.atomics.AtomicReference
 import kotlin.concurrent.atomics.ExperimentalAtomicApi
 import kotlin.concurrent.atomics.update
 
-/** What the host App provides to pages (docs/native-api.md); every part has a default that does nothing. */
+/** What the host provides to one mount (docs/native-api.md); every part has a default that does nothing. App-wide parts live in [TinyUIHost]. */
 class HostServices(
     val navigator: Navigator = Navigator.None,
     val store: Store = InMemoryStore(),
@@ -14,14 +14,9 @@ class HostServices(
     val events: EventBus = EventBus(),
     /** Extra values merged into `device.info` (docs/native-api.md §1). */
     val deviceInfo: Map<String, String> = emptyMap(),
-    /** J3 `host.call` by name (docs/native-api.md §7); names the framework already uses are rejected. */
-    val capabilities: Map<String, HostCapability> = emptyMap(),
+    /** This mount's objects that capabilities read through [PageContext] (docs/native-api.md §7). */
+    val locals: List<PageLocalValue<*>> = emptyList(),
 ) {
-    init {
-        val taken = capabilities.keys.filter { it in FrameworkCapabilities }
-        require(taken.isEmpty()) { "capabilities $taken are framework names" }
-    }
-
     companion object {
         /** One shared instance, so a page whose host passes nothing keeps a stable `remember` key. */
         val Default = HostServices()
@@ -83,11 +78,6 @@ class HttpResponse(val status: Int, val bodyJson: String)
 /** An E3 failure with one of the codes in docs/native-api.md §6. */
 class HostException(val code: String, message: String) : Exception(message)
 
-/** One host-defined J3 capability: [argsJson] is the object JS passed; returns JSON text, or null for `undefined`. Throw [HostException] for E3 codes. */
-fun interface HostCapability {
-    suspend fun call(argsJson: String): String?
-}
-
 /** Names the framework dispatches itself (J2 / J3 / J4), listed in the mount manifest ahead of the host's. */
 internal val FrameworkCapabilities = listOf("device.info", "i18n.t", "config.get", "store.get", "store.set", "navigation.push", "navigation.pop", "events.emit", "http.request", "timer.schedule")
 
diff --git a/compose/src/commonMain/kotlin/app/tinyui/HostSnapshot.kt b/compose/src/commonMain/kotlin/app/tinyui/HostSnapshot.kt
new file mode 100644
index 0000000..de9553b
--- /dev/null
+++ b/compose/src/commonMain/kotlin/app/tinyui/HostSnapshot.kt
@@ -0,0 +1,64 @@
+package app.tinyui
+
+import app.tinyui.schema.ComponentSchema
+import app.tinyui.schema.FieldSpec
+import app.tinyui.schema.PropSpec
+import kotlinx.serialization.json.JsonPrimitive
+
+/** The host snapshot `tinyui-host/<hostVersion>.txt` (docs/updates.md §4.1, format §6.4). */
+object HostSnapshot {
+    fun render(host: TinyUIHost, hostVersion: String): String {
+        require(hostVersion.matches(Regex("[1-9][0-9]*"))) { "hostVersion must be a positive integer, got \"$hostVersion\"" }
+        val components = host.components.schemas.filter { '.' in it.type }.associate { it.type to describe(it) }
+        return buildString {
+            append("hostVersion ").append(hostVersion).append('\n')
+            append("tinyui ").append(TinyUI.version).append("\n\n")
+            append("components\n")
+            section(components)
+            append("\ncapabilities\n")
+            section(host.capabilities.names.associateWith { "" })
+        }
+    }
+
+    private fun StringBuilder.section(items: Map<String, String>) {
+        val width = items.keys.maxOfOrNull { it.length } ?: 0
+        for ((name, rest) in items.entries.sortedBy { it.key }) {
+            append("  ").append(if (rest.isEmpty()) name else name.padEnd(width + 2) + rest).append('\n')
+        }
+    }
+
+    private fun describe(schema: ComponentSchema): String = listOfNotNull(
+        schema.props.entries.sortedBy { it.key }.joinToString(", ") { (name, spec) -> prop(name, spec) }.ifEmpty { null },
+        calls("events", schema.events),
+        calls("commands", schema.commands),
+        "children".takeIf { schema.children },
+        "layout".takeIf { schema.layout },
+    ).joinToString("; ")
+
+    private fun prop(name: String, spec: PropSpec): String = buildString {
+        append(name)
+        if (!spec.required) append('?')
+        append(": ").append(if (spec is PropSpec.Enum) spec.values.sorted().joinToString("|", "enum(", ")") else spec.kind)
+        spec.declared?.let { append(" = ").append(if (spec is PropSpec.Str) JsonPrimitive(it as String).toString() else literal(it)) }
+        if (spec.initial) append(" (initial)")
+    }
+
+    private fun calls(label: String, calls: Map<String, Map<String, FieldSpec>>): String? {
+        if (calls.isEmpty()) return null
+        return calls.entries.sortedBy { it.key }.joinToString(", ", "$label ") { (name, fields) ->
+            fields.entries.sortedBy { it.key }.joinToString(", ", "$name(", ")") { (field, type) -> "$field: ${type.typeName}" }
+        }
+    }
+
+    private val FieldSpec.typeName: String
+        get() = when (this) {
+            FieldSpec.Str -> "string"
+            FieldSpec.Num -> "number"
+            FieldSpec.Bool -> "boolean"
+        }
+
+    private fun literal(value: Any): String = when (value) {
+        is Double -> if (value % 1.0 == 0.0 && value > -1e15 && value < 1e15) value.toLong().toString() else value.toString()
+        else -> value.toString()
+    }
+}
diff --git a/compose/src/commonMain/kotlin/app/tinyui/PageHost.kt b/compose/src/commonMain/kotlin/app/tinyui/PageHost.kt
index 599b363..55ed1bd 100644
--- a/compose/src/commonMain/kotlin/app/tinyui/PageHost.kt
+++ b/compose/src/commonMain/kotlin/app/tinyui/PageHost.kt
@@ -82,14 +82,16 @@ class PageFailure(val error: PageError) {
 class PageHost(
     private val runtimeBundle: RuntimeBundle,
     private val page: PageModule,
-    val registry: ComponentRegistry,
-    private val sink: PageSink,
+    val host: TinyUIHost,
     private val services: HostServices = HostServices.Default,
     private val propsJson: String = "{}",
     /** K entries longer than this are interrupted and fail the page (docs/native-api.md §6). */
     private val entryTimeoutMs: Long = 5_000,
     private val sourceMaps: SourceMaps = SourceMaps.EMPTY,
 ) {
+    private val registry: ComponentRegistry get() = host.components
+    private val sink: PageSink get() = host.sink
+    private val context by lazy { PageContext(page.name, services.locals.associate { it.local to it.value }) }
     val tree = NodeTree(registry) { report("E5", it.reason, op = it.op) }
     var failure: PageFailure? by mutableStateOf(null)
         private set
@@ -129,7 +131,7 @@ class PageHost(
                     check(protocol == PROTOCOL) { "protocol $protocol from the runtime module, host implements $PROTOCOL" }
                     namespace.use { ns ->
                         (ns.get("default", ObjectTransport.REF) as JsRef).use { default ->
-                            e.call("mount", default, JsValue.Str(propsJson), JsValue.Str(registry.manifest(FrameworkCapabilities + services.capabilities.keys)))
+                            e.call("mount", default, JsValue.Str(propsJson), JsValue.Str(registry.manifest(FrameworkCapabilities + host.capabilities.names)))
                         }
                     }
                     e.call("flush")
@@ -264,9 +266,9 @@ class PageHost(
                 val response = services.http.request(request)
                 buildJsonObject { put("status", response.status); put("body", Json.parseToJsonElement(response.bodyJson)) }.toString()
             }
-            else -> when (val capability = services.capabilities[name]) {
+            else -> when (val capability = host.capabilities[name]) {
                 null -> scope.launch { reject(cbId, "E_UNSUPPORTED", "$name is not available") }
-                else -> settle(cbId) { capability.call(argsJson) ?: "" }
+                else -> settle(cbId) { capability.call(argsJson, context) ?: "" }
             }
         }
     }
diff --git a/compose/src/commonMain/kotlin/app/tinyui/TinyUI.kt b/compose/src/commonMain/kotlin/app/tinyui/TinyUI.kt
index c7d341a..2a64599 100644
--- a/compose/src/commonMain/kotlin/app/tinyui/TinyUI.kt
+++ b/compose/src/commonMain/kotlin/app/tinyui/TinyUI.kt
@@ -3,6 +3,9 @@ package app.tinyui
 import wang.harlon.quickjs.QuickJs
 
 object TinyUI {
+    /** This library's version, as published (`0.0.0-local` in a source build). */
+    val version: String get() = VERSION
+
     /** Version of the quickjs-kmp SDK this build links against. */
     val engineVersion: String get() = QuickJs.sdkVersion
 
diff --git a/compose/src/commonMain/kotlin/app/tinyui/TinyUIHost.kt b/compose/src/commonMain/kotlin/app/tinyui/TinyUIHost.kt
new file mode 100644
index 0000000..503aca8
--- /dev/null
+++ b/compose/src/commonMain/kotlin/app/tinyui/TinyUIHost.kt
@@ -0,0 +1,56 @@
+package app.tinyui
+
+import app.tinyui.schema.ComponentRegistry
+
+/**
+ * What one App gives every TinyUI page, built once at startup and not changed after (docs/native-api.md §7).
+ * Its components and capabilities are the host contract [HostSnapshot] renders.
+ */
+class TinyUIHost(
+    val components: ComponentRegistry,
+    val sink: PageSink,
+    val capabilities: CapabilityRegistry = CapabilityRegistry(),
+) {
+    init {
+        components.freeze()
+        capabilities.freeze()
+    }
+}
+
+/** App-level J3 `host.call` capabilities by name (docs/native-api.md §7). */
+class CapabilityRegistry {
+    private val entries = LinkedHashMap<String, HostCapability>()
+    private var frozen = false
+
+    val names: Set<String> get() = entries.keys
+
+    fun register(name: String, capability: HostCapability) {
+        require(name.isNotEmpty() && name.none(Char::isWhitespace)) { "capability name \"$name\" is empty or has whitespace" }
+        require(name !in FrameworkCapabilities) { "capability $name is a framework name" }
+        check(!frozen) { "capability $name registered after the registry went into a TinyUIHost" }
+        require(name !in entries) { "capability $name already registered" }
+        entries[name] = capability
+    }
+
+    internal operator fun get(name: String): HostCapability? = entries[name]
+
+    internal fun freeze() { frozen = true }
+}
+
+/** One host-defined J3 capability: [argsJson] is the object JS passed; returns JSON text, or null for `undefined`. Throw [HostException] for E3 codes. */
+fun interface HostCapability {
+    suspend fun call(argsJson: String, page: PageContext): String?
+}
+
+/** The mount a capability call came from: the page's module name and the objects its [HostServices.locals] provide. */
+class PageContext internal constructor(val name: String, private val locals: Map<PageLocal<*>, Any>) {
+    @Suppress("UNCHECKED_CAST")
+    operator fun <T : Any> get(local: PageLocal<T>): T? = locals[local] as T?
+}
+
+/** A typed key for an object one mount hands to capabilities, such as its screen's snackbar. */
+class PageLocal<T : Any> {
+    infix fun provides(value: T): PageLocalValue<T> = PageLocalValue(this, value)
+}
+
+class PageLocalValue<T : Any> internal constructor(val local: PageLocal<T>, val value: T)
diff --git a/compose/src/commonMain/kotlin/app/tinyui/TinyUIPage.kt b/compose/src/commonMain/kotlin/app/tinyui/TinyUIPage.kt
index 5883725..c9964db 100644
--- a/compose/src/commonMain/kotlin/app/tinyui/TinyUIPage.kt
+++ b/compose/src/commonMain/kotlin/app/tinyui/TinyUIPage.kt
@@ -14,7 +14,6 @@ import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.unit.dp
-import app.tinyui.schema.ComponentRegistry
 
 /**
  * Renders one TinyUI page; the host owns navigation and passes the page's bytecode (docs/app-model.md).
@@ -24,8 +23,7 @@ import app.tinyui.schema.ComponentRegistry
 fun TinyUIPage(
     runtime: RuntimeBundle,
     page: PageModule,
-    registry: ComponentRegistry,
-    sink: PageSink,
+    host: TinyUIHost,
     services: HostServices = HostServices.Default,
     propsJson: String = "{}",
     modifier: Modifier = Modifier,
@@ -33,20 +31,20 @@ fun TinyUIPage(
     error: @Composable (PageFailure) -> Unit = { PageFailureScreen(it) },
     onHost: (PageHost) -> Unit = {},
 ) {
-    val host = remember(runtime, page, registry, sink, services, propsJson, sourceMaps) {
-        PageHost(runtime, page, registry, sink, services, propsJson, sourceMaps = sourceMaps)
+    val pageHost = remember(runtime, page, host, services, propsJson, sourceMaps) {
+        PageHost(runtime, page, host, services, propsJson, sourceMaps = sourceMaps)
     }
-    DisposableEffect(host) {
-        onHost(host)
-        host.start()
-        onDispose { host.close() }
+    DisposableEffect(pageHost) {
+        onHost(pageHost)
+        pageHost.start()
+        onDispose { pageHost.close() }
     }
     Box(modifier) {
-        val failure = host.failure
+        val failure = pageHost.failure
         if (failure != null) {
             error(failure)
         } else {
-            for (child in host.tree.root.children) key(child.id) { host.Render(child) }
+            for (child in pageHost.tree.root.children) key(child.id) { pageHost.Render(child) }
         }
     }
 }
diff --git a/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentRegistry.kt b/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentRegistry.kt
index 0f63671..49b1eeb 100644
--- a/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentRegistry.kt
+++ b/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentRegistry.kt
@@ -16,18 +16,24 @@ class ComponentRegistry {
     private class Entry(val schema: ComponentSchema, val component: Component)
 
     private val entries = LinkedHashMap<String, Entry>()
+    private var frozen = false
 
     init {
         register(ComponentSchema(PLACEHOLDER, emptyMap(), emptyMap(), emptyMap(), children = false, layout = true)) { Placeholder(it) }
     }
 
     fun register(schema: ComponentSchema, component: Component) {
+        check(!frozen) { "component ${schema.type} registered after the registry went into a TinyUIHost" }
         require(schema.type !in entries) { "component ${schema.type} already registered" }
         entries[schema.type] = Entry(schema, component)
     }
 
     fun schema(type: String): ComponentSchema? = entries[type]?.schema
 
+    internal fun freeze() { frozen = true }
+
+    internal val schemas: List<ComponentSchema> get() = entries.values.map { it.schema }.filter { it.type != PLACEHOLDER }
+
     @Composable
     fun Render(type: String, scope: NodeScope) {
         (entries[type] ?: entries.getValue(PLACEHOLDER)).component.Render(scope)
diff --git a/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentSchema.kt b/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentSchema.kt
index 63eeaa6..bd1af6f 100644
--- a/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentSchema.kt
+++ b/compose/src/commonMain/kotlin/app/tinyui/schema/ComponentSchema.kt
@@ -24,47 +24,57 @@ sealed interface SizeValue {
 sealed class PropSpec(val kind: String, val required: Boolean, val initial: Boolean) {
     /** Typed default; `null` when the schema has none. */
     abstract val default: Any?
+    /** The default as schema/ declared it, for the host snapshot. */
+    internal abstract val declared: Any?
     abstract fun convert(value: JsonPrimitive): Any?
 
     class Str(default: String?, required: Boolean = false, initial: Boolean = false) : PropSpec("string", required, initial) {
         override val default: String? = default
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? = value.takeIf { it.isString }?.content
     }
 
     class Num(default: Double?, required: Boolean = false, initial: Boolean = false) : PropSpec("number", required, initial) {
         override val default: Double? = default
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? = value.takeUnless { it.isString }?.doubleOrNull
     }
 
     class Bool(default: Boolean?, required: Boolean = false, initial: Boolean = false) : PropSpec("boolean", required, initial) {
         override val default: Boolean? = default
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? = value.takeUnless { it.isString }?.booleanOrNull
     }
 
     class Dp(default: Double?, required: Boolean = false, initial: Boolean = false) : PropSpec("dp", required, initial) {
         override val default: androidx.compose.ui.unit.Dp? = default?.dp
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? = value.takeUnless { it.isString }?.doubleOrNull?.dp
     }
 
     class Sp(default: Double?, required: Boolean = false, initial: Boolean = false) : PropSpec("sp", required, initial) {
         override val default: TextUnit? = default?.sp
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? = value.takeUnless { it.isString }?.doubleOrNull?.sp
     }
 
     /** `#RRGGBB` / `#AARRGGBB`, or a theme token name (Theme.kt). */
     class ColorSpec(default: String?, required: Boolean = false, initial: Boolean = false) : PropSpec("color", required, initial) {
         override val default: ColorValue? = default?.let(::parseColorValue)
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? = value.takeIf { it.isString }?.content?.let(::parseColorValue)
     }
 
     /** Stored as the enum name; the composable maps it. */
     class Enum(val values: Set<String>, default: String?, required: Boolean = false, initial: Boolean = false) : PropSpec("enum", required, initial) {
         override val default: String? = default
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? = value.takeIf { it.isString }?.content?.takeIf { it in values }
     }
 
     class Size(default: String?, required: Boolean = false, initial: Boolean = false) : PropSpec("size", required, initial) {
         override val default: SizeValue? = default?.let(::parseSize)
+        override val declared: Any? = default
         override fun convert(value: JsonPrimitive): Any? =
             if (value.isString) parseSize(value.content) else value.doubleOrNull?.let { SizeValue.Fixed(it.dp) }
 
diff --git a/compose/src/commonTest/kotlin/app/tinyui/HostSnapshotTest.kt b/compose/src/commonTest/kotlin/app/tinyui/HostSnapshotTest.kt
new file mode 100644
index 0000000..e8f60fe
--- /dev/null
+++ b/compose/src/commonTest/kotlin/app/tinyui/HostSnapshotTest.kt
@@ -0,0 +1,99 @@
+package app.tinyui
+
+import app.tinyui.components.registerBuiltins
+import app.tinyui.schema.ComponentRegistry
+import app.tinyui.schema.ComponentSchema
+import app.tinyui.schema.FieldSpec
+import app.tinyui.schema.PropSpec
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+class HostSnapshotTest {
+    private val sink = object : PageSink {
+        override fun error(error: PageError) {}
+        override fun log(line: String) {}
+    }
+
+    private val icon = ComponentSchema(
+        type = "ta.Icon",
+        props = mapOf(
+            "name" to PropSpec.Str(default = null, required = true),
+            "tint" to PropSpec.ColorSpec(default = "primary"),
+            "size" to PropSpec.Dp(default = 24.0),
+            "label" to PropSpec.Str(default = "a; b\ncapabilities"),
+        ),
+        events = emptyMap(), commands = emptyMap(), children = false, layout = true,
+    )
+
+    private val rating = ComponentSchema(
+        type = "ta.Rating",
+        props = mapOf(
+            "value" to PropSpec.Num(default = null, required = true),
+            "style" to PropSpec.Enum(setOf("stars", "hearts"), default = "stars", initial = true),
+            "step" to PropSpec.Num(default = 0.5),
+        ),
+        events = mapOf("onChange" to mapOf("value" to FieldSpec.Num, "fromUser" to FieldSpec.Bool)),
+        commands = mapOf("reset" to emptyMap()),
+        children = true, layout = false,
+    )
+
+    private fun host(capabilities: CapabilityRegistry = CapabilityRegistry()) = TinyUIHost(
+        ComponentRegistry().registerBuiltins().apply {
+            register(rating) {}
+            register(icon) {}
+        },
+        sink,
+        capabilities,
+    )
+
+    @Test
+    fun listsDottedComponentsWithTheirSchemaAndCapabilityNamesSorted() {
+        val capabilities = CapabilityRegistry().apply {
+            register("coupon.apply") { _, _ -> null }
+            register("checkout.start") { _, _ -> null }
+        }
+        assertEquals(
+            """
+            hostVersion 3
+            tinyui ${TinyUI.version}
+
+            components
+              ta.Icon    label?: string = "a; b\ncapabilities", name: string, size?: dp = 24, tint?: color = primary; layout
+              ta.Rating  step?: number = 0.5, style?: enum(hearts|stars) = stars (initial), value: number; events onChange(fromUser: boolean, value: number); commands reset(); children
+
+            capabilities
+              checkout.start
+              coupon.apply
+
+            """.trimIndent(),
+            HostSnapshot.render(host(capabilities), "3"),
+        )
+    }
+
+    @Test
+    fun writesBothSectionsEvenWhenEmpty() {
+        val bare = TinyUIHost(ComponentRegistry().registerBuiltins(), sink)
+        assertEquals("hostVersion 1\ntinyui ${TinyUI.version}\n\ncomponents\n\ncapabilities\n", HostSnapshot.render(bare, "1"))
+    }
+
+    @Test
+    fun registriesRejectRegistrationOnceInAHost() {
+        val host = host()
+        assertFailsWith<IllegalStateException> { host.components.register(ComponentSchema("ta.Other", emptyMap(), emptyMap(), emptyMap(), children = false, layout = true)) {} }
+        assertFailsWith<IllegalStateException> { host.capabilities.register("late.one") { _, _ -> null } }
+    }
+
+    @Test
+    fun rejectsAHostVersionThatIsNotAPositiveInteger() {
+        for (bad in listOf("0", "1.2.0", "", "01")) assertFailsWith<IllegalArgumentException>(bad) { HostSnapshot.render(host(), bad) }
+    }
+
+    @Test
+    fun registryRejectsFrameworkDuplicateAndBlankNames() {
+        val registry = CapabilityRegistry().apply { register("a.b") { _, _ -> null } }
+        for (bad in listOf("a.b", "store.get", "", "a b")) {
+            assertFailsWith<IllegalArgumentException>(bad) { registry.register(bad) { _, _ -> null } }
+        }
+    }
+}
diff --git a/compose/src/commonTest/kotlin/app/tinyui/PageHostTest.kt b/compose/src/commonTest/kotlin/app/tinyui/PageHostTest.kt
index 78399bf..d18a5a6 100644
--- a/compose/src/commonTest/kotlin/app/tinyui/PageHostTest.kt
+++ b/compose/src/commonTest/kotlin/app/tinyui/PageHostTest.kt
@@ -64,15 +64,16 @@ class PageHostTest {
             override suspend fun request(request: HttpRequest): HttpResponse =
                 if (request.url == "/todos") HttpResponse(200, """[{"id":1}]""") else throw HostException("E_HTTP", "404")
         },
-        capabilities = mapOf(
-            "checkout.start" to HostCapability { args ->
-                if (args.contains("annual")) """{"url":"https://pay"}""" else throw HostException("E_INVALID", "no such plan")
-            },
-        ),
+        locals = listOf(Merchant provides "acme"),
     )
+    private val tinyui = TinyUIHost(ComponentRegistry().registerBuiltins(), sink, CapabilityRegistry().apply {
+        register("checkout.start") { args, page ->
+            if (args.contains("annual")) """{"url":"https://pay/${page[Merchant]}/${page.name}"}""" else throw HostException("E_INVALID", "no such plan")
+        }
+    })
 
     private fun host(props: String = "{}", maps: SourceMaps = SourceMaps.EMPTY) =
-        PageHost(RuntimeBundle(core, native), page, ComponentRegistry().registerBuiltins(), sink, services, props, sourceMaps = maps)
+        PageHost(RuntimeBundle(core, native), page, tinyui, services, props, sourceMaps = maps)
 
     // runTest's virtual time never advances the real engine thread: wait on a real dispatcher
     private suspend fun PageHost.await(check: () -> Boolean) =
@@ -178,7 +179,7 @@ class PageHostTest {
         host.dispatch(2, "onCapability", "{}")
         host.await { text()?.count { it == ';' } == 2 }
         assertEquals(
-            """ok 11 {"url":"https://pay"};rejected 12 {"code":"E_INVALID","message":"no such plan"};rejected 13 {"code":"E_UNSUPPORTED","message":"nobody.home is not available"}""",
+            """ok 11 {"url":"https://pay/acme/pages/counter"};rejected 12 {"code":"E_INVALID","message":"no such plan"};rejected 13 {"code":"E_UNSUPPORTED","message":"nobody.home is not available"}""",
             text(),
         )
         host.dispatch(2, "onSubscribe", "{}")
@@ -211,7 +212,7 @@ class PageHostTest {
     @Test
     fun protocolMismatchIsE6() = runTest {
         val badCore = module("tinyui-core", "globalThis.__tinyui = { protocol: 99 }; export const VERSION = 'x';")
-        val host = PageHost(RuntimeBundle(badCore, native), page, ComponentRegistry().registerBuiltins(), sink)
+        val host = PageHost(RuntimeBundle(badCore, native), page, tinyui)
         host.start()
         host.await { host.failure != null }
         assertEquals("E6", host.failure!!.kind)
@@ -222,3 +223,5 @@ class PageHostTest {
     private fun module(name: String, source: String): ByteArray =
         JsBytecode.compile(source.trimIndent(), name, module = true, strip = JsBytecode.Strip.SOURCE)
 }
+
+private val Merchant = PageLocal<String>()
diff --git a/docs/native-api.md b/docs/native-api.md
index 1b07ed6..e9e5fd0 100644
--- a/docs/native-api.md
+++ b/docs/native-api.md
@@ -2,7 +2,7 @@
 
 - 状态：已定（2026-09-16）；M2 的实现依据
 - 来源：ADR-002 §3.1（J2 白名单、J3 / J4）、[app-model.md](./app-model.md)（路由、store、事件）、ADR-004 §3.1（连续事件阈值）
-- 两侧：JS 的 `tinyui-native` 是 `__host_*` 的类型化封装；Kotlin 的 `HostServices` 是宿主 App 实现的接口组，交给 `TinyUIPage`
+- 两侧：JS 的 `tinyui-native` 是 `__host_*` 的类型化封装；Kotlin 侧宿主给页面的东西分两层：App 级的 `TinyUIHost`（组件注册表、能力注册表、`PageSink`，启动时建一次）与每次挂载的 `HostServices`（本节以下各接口），都交给 `TinyUIPage`
 
 ## 1. J2 白名单
 
@@ -87,7 +87,26 @@ J3 `http.request`，参数 `{ method, url, headers?, body?, timeout? }`；宿主
 const { url } = await host.call<{ url: string }>("checkout.start", { plan: "annual" });
 ```
 
-J3，一个名字一个能力，Kotlin 侧 `HostServices(capabilities = mapOf("checkout.start" to HostCapability { argsJson -> … }))`：suspend，收 JS 传的对象（JSON 文本），返回 JSON 文本（`null` 即 `undefined`）；抛 `HostException` 走 E3 码，其他异常按 `E_NET`。没注册的名字拒绝 `E_UNSUPPORTED`。名字不强制前缀，但不能与框架自己的十个名字（§1–§5）重合，重合在构造 `HostServices` 时就报错。挂载清单的 `capabilities` 列出框架名 + 宿主名，页面可据此判断宿主是否提供某能力。
+J3，一个名字一个能力。能力在 App 级注册一次，与组件同属宿主契约（2026-09-23 定，M6：契约要能在不跑 App 的情况下枚举出来生成宿主快照，updates.md §4.1）：
+
+```kotlin
+val Snackbar = PageLocal<SnackbarHostState>()
+
+val host = TinyUIHost(components, sink, CapabilityRegistry().apply {
+    register("checkout.start") { argsJson, page -> … }
+    register("ui.snackbar") { argsJson, page ->
+        val snackbar = page[Snackbar] ?: throw HostException("E_UNSUPPORTED", "no snackbar on ${page.name}")
+        …
+    }
+})
+
+TinyUIPage(runtime, module, host, HostServices(locals = listOf(Snackbar provides snackbarHostState)))
+```
+
+- `HostCapability.call(argsJson, page)`：suspend，收 JS 传的对象（JSON 文本），返回 JSON 文本（`null` 即 `undefined`）；抛 `HostException` 走 E3 码，其他异常按 `E_NET`。没注册的名字拒绝 `E_UNSUPPORTED`
+- 能力只依赖 App 级对象；依赖某一屏的东西（snackbar、当前屏的 ViewModel）由挂载方经 `HostServices.locals` 以 `PageLocal` 为键传入，能力从 `page[local]` 取，没有就自己决定报什么码。同一名字按屏给不同行为，也在实现里看 `page` 分派
+- 注册表启动时建好即不可变，放进 `TinyUIHost` 后再 `register`（组件同样）直接报错：不能在运行中增删能力（登录后才开放之类，在实现里判断后拒绝）。名字不强制前缀，但不能与框架自己的十个名字（§1–§5）重合，不能含空白，也不能重复注册，都在 `register` 时报错
+- 挂载清单的 `capabilities` 列出框架名 + 注册表里的全部名字，页面可据此判断宿主是否提供某能力
 
 不做 J4（火后不理）变体：不等 Promise 就是火后不理，省不下什么。能力的类型声明由宿主 JS 工程自己写一层封装（`ta.checkout.start(plan)`），框架不生成。
 
diff --git a/docs/updates-plan.md b/docs/updates-plan.md
index 78a3a71..528bdd3 100644
--- a/docs/updates-plan.md
+++ b/docs/updates-plan.md
@@ -112,14 +112,15 @@ M1 之后 M2 → M3 与 M4 并行；M5.1、M5.2 与 tinyui 0.3.0（npm 三包 +
 | 7 | 命名 | 包名 `trendingai`（页面 `trendingai/subscription`），线上 app id `trendingai`；宿主层面标识页面（深链、埋点页面名、日志）用 `tinyui:trendingai/subscription`，`navigation.push` 仍用不带前缀的 |
 | 8 | JS 侧填错目标宿主版本 | 发布前核对（updates.md §1.3）：`tinyui build` 把每页用到的能力名与宿主组件名写进 manifest 的 `requires`；`publish` 上传前从热下发服务读目标版本的宿主快照比对，不通过即拒绝发布（`bundle` 保持离线）。快照由宿主 CI 在发 App 版本时上传，每版本只写一次。铁律：`host.call` 的名字必须是字面量、宿主组件必须能静态解析（build-chain.md §5.1）。设备侧核对暂不做 |
 | 9 | 服务端凭据分层 | 在实例 `ADMIN_TOKEN` 与包的发布 token 之间补 app token：一个 app 的完整管理权（注册包、公钥、签发发布 token、上传宿主快照），暂不细分权限范围；宿主 CI 用它上传快照；本 app 的发布 token 可读快照。权限与 URL 挂在 app（一个宿主 App）上，不挂在租户（`org`，可改可转让）上（updates.md §6） |
+| 10 | 宿主契约怎么枚举 | 能力名的真值在宿主 Kotlin；能力像组件一样 App 级注册（`CapabilityRegistry`），`HostCapability.call(argsJson, page)` 经 `PageLocal` 拿某一屏的对象；组件注册表、能力注册表、`PageSink` 合成 App 级 `TinyUIHost` 交给 `TinyUIPage` / `UpdatesPage`（native-api.md §7）。快照由库的 `HostSnapshot.render` 生成，检查是宿主自己的 host 侧单元测试，`-Ptinyui.updateHostSnapshot` 写入；已发版本的冻结只靠服务端 409（updates.md §4.1） |
 
 交付：
 
-- **tinyui**：`tinyui build` 静态找出每页用到的能力与宿主组件写进 manifest 的 `requires`，违反 build-chain.md §5.1 即失败；`tinyui publish` 上传前读目标宿主版本的快照核对（updates.md §1.3，快照格式 §6.4）；宿主契约快照——导出宿主组件 schema、能力名、tinyui 版本为稳定排序的文本，存 `tinyui-host/<hostVersion>.txt`；检查任务（当前宿主与快照不符即失败）与生成任务（已随发版带出的版本拒绝覆盖），任务名做时定。前置：宿主能力能集中枚举（TrendingAI 现在散在各 Screen 里注册）。`tinyui:` 前缀约定写进 app-model.md
-- **trendingai-tinyui**：先恢复可构建——依赖从 `link:` 换成 npm 的 0.3.0，加 `tinyui.config.json`（`name: "trendingai"`，公钥），模块名 `pages/subscription` → `trendingai/subscription`；`keys generate`，私钥写进 GitHub secret 与 `HarlonWang/secrets` 的 `tinyui-updates/signing/trendingai/trendingai.pem`；CI：合 main → build → `bundle --host-version <值>` → `publish --channel staging`，`hostVersion` 取 workflow 里的一个变量（抄宿主仓当前值；抄错时由 `publish` 对照服务端的宿主快照拒绝发布，见拍板第 8 点）；`production` environment 设人工批准，手动 workflow 跑 `releases promote / rollback / rollout`
+- **tinyui**：`tinyui build` 静态找出每页用到的能力与宿主组件写进 manifest 的 `requires`，违反 build-chain.md §5.1 即失败；`tinyui publish` 上传前读目标宿主版本的快照核对（updates.md §1.3，快照格式 §6.4）；宿主契约快照——`TinyUIHost` 与 `HostSnapshot.render`（拍板第 10 点），sample 带一份 `HostSnapshotTest` 作宿主的写法样板。`tinyui:` 前缀约定写进 app-model.md
+- **trendingai-tinyui**：先恢复可构建——依赖从 `link:` 换成 npm 上与 TrendingAI 同版本的 tinyui 三包（0.4.0），加 `tinyui.config.json`（`name: "trendingai"`，公钥），模块名 `pages/subscription` → `trendingai/subscription`；`keys generate`，私钥写进 GitHub secret 与 `HarlonWang/secrets` 的 `tinyui-updates/signing/trendingai/trendingai.pem`；CI：合 main → build → `bundle --host-version <值>` → `publish --channel staging`，`hostVersion` 取 workflow 里的一个变量（抄宿主仓当前值；抄错时由 `publish` 对照服务端的宿主快照拒绝发布，见拍板第 8 点）；`production` environment 设人工批准，手动 workflow 跑 `releases promote / rollback / rollout`
 - **服务端代码**：app token 的签发与吊销、各管理端点改为认 app token（updates.md §6.3）；宿主快照的上传与读取端点（§6.4，每个 (app, hostVersion) 只写一次）；CLI 配套 `apps tokens`、`hosts upload`
 - **服务端（线上，不可逆，执行前列命令确认）**：`apps create trendingai --name TrendingAI`（`org` 留空）；签一枚 app token 给 TrendingAI 宿主 CI 上传快照；`packages create trendingai --app trendingai`（登记公钥）；两枚发布 token，CI 用的限 `staging`，production environment 用的限 `production`
-- **TrendingAI**：依赖升到 tinyui 0.3.0 并加 `tinyui-updates`；`TinyUIHost` 改用 `Updates(listOf(embedded), hostVersion = "1", dir, installId = getOrCreateInstallId(), fetch = ktor)`，base URL `https://updates.tinyui.app/trendingai/<channel>`；设置页隐藏的 channel 开关（持久化，切回即恢复 `production`）；订阅页改用 `UpdatesPage`，`PAGE = "trendingai/subscription"`；App 启动即 `check()`（先于任何 TinyUI 页挂载）；`onEvent` 接埋点；宿主能力集中注册，`shared/tinyui-host/1.txt` 与检查任务进 CI，发版时 CI 把快照上传到热下发服务；内置包改为发 App 时从服务端拉当时 `production` 的那一版进 `composeResources/files/tinyui/trendingai/`（`pnpm sync` 只再生成 `HostSchemas.kt`），脚本还是 CLI 子命令做时定
+- **TrendingAI**：依赖升到带 `TinyUIHost` 的 tinyui（0.4.0）并加 `tinyui-updates`；宿主的 TinyUI 入口改用 `Updates(listOf(embedded), hostVersion = "1", dir, installId = getOrCreateInstallId(), fetch = ktor)`，base URL `https://updates.tinyui.app/trendingai/<channel>`；设置页隐藏的 channel 开关（持久化，切回即恢复 `production`）；订阅页改用 `UpdatesPage`，`PAGE = "trendingai/subscription"`；App 启动即 `check()`（先于任何 TinyUI 页挂载）；`onEvent` 接埋点；五个能力搬进 App 级 `CapabilityRegistry`（`ui.snackbar` 经 `PageLocal` 取当前屏的 snackbar），`shared/tinyui-host/1.txt` 与快照测试进 CI，发版时 CI 把快照上传到热下发服务；内置包改为发 App 时从服务端拉当时 `production` 的那一版进 `composeResources/files/tinyui/trendingai/`（`pnpm sync` 只再生成 `HostSchemas.kt`），脚本还是 CLI 子命令做时定
 
 验收：合 main → CI 发 `staging` → 商店版 App 切到 staging 看到新文案 → 批准 workflow 晋级 `production` → 切回、重启看到；往 staging 发坏包 → 回退到内置并在埋点里看到 `RolledBack`；production workflow `rollback` → 重启回到上一版；宿主加一个能力而不加 `hostVersion` → 宿主 CI 失败。
 
@@ -139,5 +140,5 @@ M1 之后 M2 → M3 与 M4 并行；M5.1、M5.2 与 tinyui 0.3.0（npm 三包 +
 | M5.1 改名 `hostVersion` | 已完成（2026-09-23，tinyui PR #17、tinyui-updates-server PR #2，服务端已部署）：manifest 字段、Kotlin API、CLI `--host-version`、服务端路由与校验、文档全部改名；CLI、`Updates` 构造、服务端路径与 manifest 五处限定正整数；共用签名夹具换钥重签，Android host 与 iOS 模拟器两端验签通过 |
 | M5.2 `qjsc-kmp` 平台包 | 已完成（2026-09-23，quickjs-kmp PR #13 与 0.1.2、tinyui PR #18）：入口包 `qjsc-kmp` + `@qjsc-kmp/{darwin-arm64,darwin-x64,linux-x64,linux-arm64}`，Linux 为 musl 全静态；首版本地发布，之后随 quickjs-kmp 的 tag 经 OIDC 发布；`tinyui-cli` 依赖它并由测试钉住与 `quickjsKmp` 同版本，CI 不再现编 `qjsc-kmp` |
 | tinyui 0.3.0 | 已发（2026-09-23）：npm `tinyui-core` / `tinyui-native` / `tinyui-cli`，Maven `app.tinyui:tinyui` 与首发的 `app.tinyui:tinyui-updates`；`tinyui-cli` 带 `qjsc-kmp@0.1.2` |
-| M6 TrendingAI 接入 | 进行中：拍板八点（2026-09-23）；`tinyui build` 写 `requires` 已完成（PR #19，TrendingAI 订阅页实测 5 个能力、2 个宿主组件）；服务端 app token 与快照端点已上线（tinyui-updates-server PR #3），CLI 的 `apps tokens` / `hosts upload` 与 `publish` 核对已完成（PR #20，本地 `wrangler dev` 端到端验过）；下一步宿主侧快照生成工具（前置：宿主能力集中枚举），然后 TrendingAI / trendingai-tinyui 接入 |
+| M6 TrendingAI 接入 | 进行中：拍板八点（2026-09-23）；`tinyui build` 写 `requires` 已完成（PR #19，TrendingAI 订阅页实测 5 个能力、2 个宿主组件）；服务端 app token 与快照端点已上线（tinyui-updates-server PR #3），CLI 的 `apps tokens` / `hosts upload` 与 `publish` 核对已完成（PR #20，本地 `wrangler dev` 端到端验过）；宿主契约收进 App 级 `TinyUIHost`（能力 `CapabilityRegistry` + `PageLocal`）与 `HostSnapshot.render` 已完成（拍板第 10 点，PR #21，sample 带 `HostSnapshotTest` 样板）；下一步发 tinyui 0.4.0，然后 TrendingAI / trendingai-tinyui 接入 |
 | M7 第二个 App | 待开 |
diff --git a/docs/updates.md b/docs/updates.md
index fe91ad9..c84c197 100644
--- a/docs/updates.md
+++ b/docs/updates.md
@@ -151,6 +151,15 @@ class Updates(
 
 漏加的后果是旧宿主收到跑不了的页面（不崩溃的错误不会触发 §4.5 回退），多加的后果是更早的宿主从此收不到更新。漏加只可能发生在宿主仓，由宿主构建拦：宿主快照 `tinyui-host/<hostVersion>.txt`（宿主组件 schema、能力名、tinyui 版本）每个版本一份入库，当前宿主与当前版本的快照不符即构建失败；已随发版带出去的版本，其快照冻结不可改。快照覆盖不到已有能力的参数与行为变化，这部分按上面的规则由人判断。为什么是精确匹配而不是 `>=` 范围，见 ADR-006 §2.2。
 
+快照由 `HostSnapshot.render(host, hostVersion)` 从宿主的 `TinyUIHost` 生成（所以能力必须在 App 级注册，native-api.md §7），检查写成宿主自己的 host 侧单元测试，照 sample 的 `HostSnapshotTest`：
+
+- 当前 `hostVersion` 的快照文件不存在，或与 `render` 结果不同 → 失败，提示加 `hostVersion`
+- 加 `-Ptinyui.updateHostSnapshot` 跑同一个测试 → 写入当前结果。这等于人声明"这个版本还没随发版带出去"；本地不判断版本是否已发，冻结由服务端兜底：`hosts upload` 同版本不同字节得 409（§6.4），发版 CI 在那里失败
+- 快照文件在 `.gitattributes` 里固定 `eol=lf`：上传的是原始字节，CRLF 的副本会被当成另一份快照而得 409
+- `hostVersion` 在宿主里只写一处常量，`Updates(hostVersion = …)` 与这个测试都读它
+
+测试只构造 `TinyUIHost`、不执行任何能力与组件，所以能在 JVM 上跑；能力实现需要的仓库类对象在测试里传假的即可。
+
 **接入约定：`check()` 在任何 TinyUI 页面挂载之前调用**（App 启动即调）。指针回滚对已装上的用户生效靠的是下一次 `check()` 装上回退版本；页面若先于它崩溃，回滚永远送不到。进程级崩溃（native 段错误）不在 §4.5 的回退范围内，出口就是灰度 + 指针回滚 + 这条约定；挂载标记见 ADR-006 §4.3 推迟项。
 
 文件与 sha256 用 okio（`FileSystem` + `ByteString.sha256`），是本 artifact 独有的依赖，core 库不引入。ECDSA 验签走平台 API（§7）。
@@ -162,7 +171,7 @@ class Updates(
 | `fun current(pkg: String): Bundle` | 构造时按包定死（§4.4）；进程内只在 §4.5 回退后换回该包的内置 |
 | `suspend fun check(): Map<String, CheckResult>` | 全部包各跑一遍 §4.3，彼此独立并行，一包失败不影响其他；同一实例串行，重入直接返回进行中的结果 |
 | `suspend fun check(pkg: String): CheckResult` | 只查一个包 |
-| 顶层 `@Composable fun UpdatesPage(updates, name, registry, sink, services, propsJson, modifier, error, onHost)` | 与 `TinyUIPage` 同参外加 `updates`；`name` 是含包名的模块名，第一个 `/` 之前即包，`current(pkg).page(name)` → `TinyUIPage`；`error` 前先走 §4.5 的回退 |
+| 顶层 `@Composable fun UpdatesPage(updates, name, host, services, propsJson, modifier, error, onHost)` | 与 `TinyUIPage` 同参外加 `updates`；`name` 是含包名的模块名，第一个 `/` 之前即包，`current(pkg).page(name)` → `TinyUIPage`；`error` 前先走 §4.5 的回退 |
 
 `CheckResult`：`UpToDate` / `Installed(version)` / `Skipped(reason)` / `Failed(stage, cause)`。`UpdateEvent` 是同一组事实加 `Running` 与 `RolledBack`，给宿主打日志与埋点；**所有事件都带 `pkg`**。宿主的分析口径会依赖它，所以发布后字段同样只增不改：
 
@@ -247,7 +256,7 @@ manifest 一到手先验签再解析：签名不对的 manifest 里任何字段
 
 ## 5. 与既有契约的关系
 
-- `PageHost` / `TinyUIPage` / patch 协议 / schema / `PageSink` 不变；`Updates` 全部搭在 `Bundle` 与 `TinyUIPage` 之上
+- `PageHost` / `TinyUIPage` / patch 协议 / schema / `PageSink` 不因热下发而变（M6 把组件、能力、sink 收进 App 级 `TinyUIHost` 是为了宿主快照，见 native-api.md §7）；`Updates` 全部搭在 `Bundle` 与 `TinyUIPage` 之上
 - 引擎的 `JsEngineConfig.moduleLoader` 不接入：它服务页内 `import()`，不是页面级分发（ADR-006 §4.3）
 - `PageError` 不加字段：`buildId` 已能定位到具体 build，`RolledBack` 事件带 `pkg` 与 `version`
 - 跨包的 params / store / events 约定在 app-model.md §7，热下发只保证每个包内部一致
@@ -320,15 +329,21 @@ hostVersion 2
 tinyui 0.3.0
 
 components
-  ta.Icon     name: string, tint?: color, size?: dp
-  ta.Loading  color?: color, size?: dp
+  ta.Icon     name: string, size?: dp = 24, tint?: color = primary; layout
+  ta.Rating   value: number; events onChange(value: number); commands reset(); layout
 
 capabilities
   checkout.start
   coupon.apply
 ```
 
-前两行固定；`components` 与 `capabilities` 两段按此顺序各出现一次，没有条目也要写段名（缺段会被读成"什么都不提供"，所以一律拒绝）；每项缩进两格、一行一项、按名排序。`tinyui hosts upload` 先解析并核对首行的 `hostVersion` 与 `--host-version` 相符再上传——服务端只收第一份。**每行第一个词是名字**，其后供人阅读、供宿主侧检查判断 schema 是否变了，CLI 核对只看名字。宿主组件只列带点的，内置组件随 `tinyui` 版本。
+前两行固定；`components` 与 `capabilities` 两段按此顺序各出现一次，没有条目也要写段名（缺段会被读成"什么都不提供"，所以一律拒绝）；每项缩进两格、一行一项、按名排序，名字补空格对齐。`tinyui hosts upload` 先解析并核对首行的 `hostVersion` 与 `--host-version` 相符再上传——服务端只收第一份。**每行第一个词是名字**，CLI 核对只看名字；其后是给人看、也给宿主侧检查判断 schema 变没变的完整 schema，改哪一处都会让快照不同：
+
+- 各段以 `; ` 分隔，依次为 props、`events …`、`commands …`、`children`、`layout`，没有的段省略
+- prop 按名排序，`名字: 类型`；可选的名字后加 `?`，有默认值加 ` = 默认值`（`string` 的默认值写成 JSON 字符串，带引号与转义，免得换行或 `;` 弄乱一行一项），只在创建时读的加 ` (initial)`；枚举写 `enum(a|b)`，取值排序
+- 事件与命令按名排序，参数写在括号里，参数按名排序，类型为 `string` / `number` / `boolean`
+
+宿主组件只列带点的，内置组件随 `tinyui` 版本。
 
 | 请求 | 凭据 | 语义 |
 |---|---|---|
diff --git a/sample/shared/build.gradle.kts b/sample/shared/build.gradle.kts
index b8c2282..d5cc484 100644
--- a/sample/shared/build.gradle.kts
+++ b/sample/shared/build.gradle.kts
@@ -30,9 +30,19 @@ kotlin {
             implementation(compose.components.resources)
             implementation(libs.kotlinx.coroutines.core)
         }
+        getByName("androidHostTest").dependencies {
+            implementation(libs.kotlin.test)
+        }
     }
 }
 
+// HostSnapshotTest compares against tinyui-host/ here; -Ptinyui.updateHostSnapshot makes it write instead
+val updateHostSnapshot = providers.gradleProperty("tinyui.updateHostSnapshot")
+tasks.withType<Test>().configureEach {
+    inputs.files(layout.projectDirectory.dir("tinyui-host")).withPropertyName("hostSnapshots")
+    updateHostSnapshot.orNull?.let { systemProperty("tinyui.updateHostSnapshot", "true") }
+}
+
 // JS 侧：pnpm 编三个包 → tinyui build 把每个示例包的页面与运行时模块编成字节码 → 只把 .bin 与清单打成 Compose 资源
 // 两个包演示多包模型（docs/updates.md §0）：各自的 JS 工程、密钥、资源子目录
 val jsPackages = mapOf("sample" to rootDir.resolve("sample/js"), "sample-extra" to rootDir.resolve("sample/js-extra"))
diff --git a/sample/shared/src/androidHostTest/kotlin/app/tinyui/sample/HostSnapshotTest.kt b/sample/shared/src/androidHostTest/kotlin/app/tinyui/sample/HostSnapshotTest.kt
new file mode 100644
index 0000000..6288c75
--- /dev/null
+++ b/sample/shared/src/androidHostTest/kotlin/app/tinyui/sample/HostSnapshotTest.kt
@@ -0,0 +1,24 @@
+package app.tinyui.sample
+
+import app.tinyui.HostSnapshot
+import java.io.File
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+/** The host-side check of docs/updates.md §4.1; `-Ptinyui.updateHostSnapshot` writes the file instead. */
+class HostSnapshotTest {
+    @Test
+    fun hostMatchesTheSnapshotOfItsHostVersion() {
+        val file = File("tinyui-host/$HOST_VERSION.txt")
+        val current = HostSnapshot.render(tinyUIHost, HOST_VERSION)
+        if (System.getProperty("tinyui.updateHostSnapshot") != null) {
+            file.parentFile.mkdirs()
+            file.writeText(current)
+            return
+        }
+        val hint = "if $HOST_VERSION has not shipped yet, rerun with -Ptinyui.updateHostSnapshot; otherwise raise HOST_VERSION and do that"
+        assertTrue(file.exists(), "no ${file.path} for HOST_VERSION $HOST_VERSION; $hint")
+        assertEquals(file.readText(), current, "the host no longer matches ${file.path}; $hint")
+    }
+}
diff --git a/sample/shared/src/commonMain/kotlin/app/tinyui/sample/App.kt b/sample/shared/src/commonMain/kotlin/app/tinyui/sample/App.kt
index eececec..3130cb0 100644
--- a/sample/shared/src/commonMain/kotlin/app/tinyui/sample/App.kt
+++ b/sample/shared/src/commonMain/kotlin/app/tinyui/sample/App.kt
@@ -34,23 +34,11 @@ import app.tinyui.HostServices
 import app.tinyui.HttpClient
 import app.tinyui.HttpRequest
 import app.tinyui.HttpResponse
-import app.tinyui.PageError
-import app.tinyui.PageSink
 import app.tinyui.TinyUI
-import app.tinyui.components.registerBuiltins
 import app.tinyui.sample.res.Res
-import app.tinyui.schema.ComponentRegistry
 import app.tinyui.updates.Updates
 import app.tinyui.updates.UpdatesPage
 
-/** App-level, built once (docs/adr-003 §3.3). */
-private val registry = ComponentRegistry().registerBuiltins()
-
-private val sink = object : PageSink {
-    override fun error(error: PageError) = println("TinyUI $error")
-    override fun log(line: String) = println("TinyUI $line")
-}
-
 /** Stands in for a backend: three pages of todos, 300 ms each. */
 private object FakeTodos : HttpClient {
     override suspend fun request(request: HttpRequest): HttpResponse {
@@ -86,7 +74,7 @@ fun App(updatesDir: Path) {
             val bundles = packages.map { embedded(it) }
             // debug builds ship the maps (-Ptinyui.maps); stacks on the failure screen only when they came along
             TinyUI.debug = !bundles.first().page("sample/todos").sourceMaps.isEmpty
-            Updates(bundles, hostVersion = "1", dir = updatesDir, installId = "sample-install", fetch = { path -> httpGet(otaBaseUrl() + path) }) {
+            Updates(bundles, hostVersion = HOST_VERSION, dir = updatesDir, installId = "sample-install", fetch = { path -> httpGet(otaBaseUrl() + path) }) {
                 println("TinyUI updates $it")
             }
         }
@@ -102,7 +90,7 @@ fun App(updatesDir: Path) {
                     for (p in pages) TextButton(onClick = { page = p }) { Text(p.substringBefore('/')) }
                 }
                 val u = updates
-                if (u == null) Text("loading…", Modifier.padding(16.dp)) else UpdatesPage(u, page, registry, sink, services, modifier = Modifier.fillMaxSize())
+                if (u == null) Text("loading…", Modifier.padding(16.dp)) else UpdatesPage(u, page, tinyUIHost, services, modifier = Modifier.fillMaxSize())
             }
         }
     }
diff --git a/sample/shared/src/commonMain/kotlin/app/tinyui/sample/Host.kt b/sample/shared/src/commonMain/kotlin/app/tinyui/sample/Host.kt
new file mode 100644
index 0000000..4acd8b9
--- /dev/null
+++ b/sample/shared/src/commonMain/kotlin/app/tinyui/sample/Host.kt
@@ -0,0 +1,19 @@
+package app.tinyui.sample
+
+import app.tinyui.PageError
+import app.tinyui.PageSink
+import app.tinyui.TinyUIHost
+import app.tinyui.components.registerBuiltins
+import app.tinyui.schema.ComponentRegistry
+
+/** Raise when [tinyUIHost] changes what pages can use; `tinyui-host/<n>.txt` records each value (docs/updates.md §4.1). */
+internal const val HOST_VERSION = "1"
+
+/** App-level, built once (docs/native-api.md §7). */
+internal val tinyUIHost = TinyUIHost(
+    components = ComponentRegistry().registerBuiltins(),
+    sink = object : PageSink {
+        override fun error(error: PageError) = println("TinyUI $error")
+        override fun log(line: String) = println("TinyUI $line")
+    },
+)
diff --git a/sample/shared/tinyui-host/1.txt b/sample/shared/tinyui-host/1.txt
new file mode 100644
index 0000000..98a7759
--- /dev/null
+++ b/sample/shared/tinyui-host/1.txt
@@ -0,0 +1,6 @@
+hostVersion 1
+tinyui 0.0.0-local
+
+components
+
+capabilities
diff --git a/updates/api/updates.klib.api b/updates/api/updates.klib.api
index 9eac680..9d05fd9 100644
--- a/updates/api/updates.klib.api
+++ b/updates/api/updates.klib.api
@@ -279,7 +279,7 @@ final val app.tinyui.updates/app_tinyui_updates_UpdateEvent_UpToDate$stableprop
 final val app.tinyui.updates/app_tinyui_updates_Updates$stableprop // app.tinyui.updates/app_tinyui_updates_Updates$stableprop|#static{}app_tinyui_updates_Updates$stableprop[0]
 final val app.tinyui.updates/app_tinyui_updates_Updates_State_$serializer$stableprop // app.tinyui.updates/app_tinyui_updates_Updates_State_$serializer$stableprop|#static{}app_tinyui_updates_Updates_State_$serializer$stableprop[0]
 
-final fun app.tinyui.updates/UpdatesPage(app.tinyui.updates/Updates, kotlin/String, app.tinyui.schema/ComponentRegistry, app.tinyui/PageSink, app.tinyui/HostServices?, kotlin/String?, androidx.compose.ui/Modifier?, kotlin/Function3<app.tinyui/PageFailure, androidx.compose.runtime/Composer, kotlin/Int, kotlin/Unit>?, kotlin/Function1<app.tinyui/PageHost, kotlin/Unit>?, androidx.compose.runtime/Composer?, kotlin/Int, kotlin/Int) // app.tinyui.updates/UpdatesPage|UpdatesPage(app.tinyui.updates.Updates;kotlin.String;app.tinyui.schema.ComponentRegistry;app.tinyui.PageSink;app.tinyui.HostServices?;kotlin.String?;androidx.compose.ui.Modifier?;kotlin.Function3<app.tinyui.PageFailure,androidx.compose.runtime.Composer,kotlin.Int,kotlin.Unit>?;kotlin.Function1<app.tinyui.PageHost,kotlin.Unit>?;androidx.compose.runtime.Composer?;kotlin.Int;kotlin.Int){}[0]
+final fun app.tinyui.updates/UpdatesPage(app.tinyui.updates/Updates, kotlin/String, app.tinyui/TinyUIHost, app.tinyui/HostServices?, kotlin/String?, androidx.compose.ui/Modifier?, kotlin/Function3<app.tinyui/PageFailure, androidx.compose.runtime/Composer, kotlin/Int, kotlin/Unit>?, kotlin/Function1<app.tinyui/PageHost, kotlin/Unit>?, androidx.compose.runtime/Composer?, kotlin/Int, kotlin/Int) // app.tinyui.updates/UpdatesPage|UpdatesPage(app.tinyui.updates.Updates;kotlin.String;app.tinyui.TinyUIHost;app.tinyui.HostServices?;kotlin.String?;androidx.compose.ui.Modifier?;kotlin.Function3<app.tinyui.PageFailure,androidx.compose.runtime.Composer,kotlin.Int,kotlin.Unit>?;kotlin.Function1<app.tinyui.PageHost,kotlin.Unit>?;androidx.compose.runtime.Composer?;kotlin.Int;kotlin.Int){}[0]
 final fun app.tinyui.updates/app_tinyui_updates_CheckResult$stableprop_getter(): kotlin/Int // app.tinyui.updates/app_tinyui_updates_CheckResult$stableprop_getter|app_tinyui_updates_CheckResult$stableprop_getter(){}[0]
 final fun app.tinyui.updates/app_tinyui_updates_CheckResult_Failed$stableprop_getter(): kotlin/Int // app.tinyui.updates/app_tinyui_updates_CheckResult_Failed$stableprop_getter|app_tinyui_updates_CheckResult_Failed$stableprop_getter(){}[0]
 final fun app.tinyui.updates/app_tinyui_updates_CheckResult_Installed$stableprop_getter(): kotlin/Int // app.tinyui.updates/app_tinyui_updates_CheckResult_Installed$stableprop_getter|app_tinyui_updates_CheckResult_Installed$stableprop_getter(){}[0]
diff --git a/updates/src/commonMain/kotlin/app/tinyui/updates/UpdatesPage.kt b/updates/src/commonMain/kotlin/app/tinyui/updates/UpdatesPage.kt
index a0b1e86..2cce939 100644
--- a/updates/src/commonMain/kotlin/app/tinyui/updates/UpdatesPage.kt
+++ b/updates/src/commonMain/kotlin/app/tinyui/updates/UpdatesPage.kt
@@ -13,9 +13,8 @@ import app.tinyui.LoadedPage
 import app.tinyui.PageFailure
 import app.tinyui.PageFailureScreen
 import app.tinyui.PageHost
-import app.tinyui.PageSink
+import app.tinyui.TinyUIHost
 import app.tinyui.TinyUIPage
-import app.tinyui.schema.ComponentRegistry
 
 /**
  * [TinyUIPage] for a page of one of [updates]' packages: [name] is the module name, the part before the first
@@ -26,8 +25,7 @@ import app.tinyui.schema.ComponentRegistry
 fun UpdatesPage(
     updates: Updates,
     name: String,
-    registry: ComponentRegistry,
-    sink: PageSink,
+    host: TinyUIHost,
     services: HostServices = HostServices.Default,
     propsJson: String = "{}",
     modifier: Modifier = Modifier,
@@ -39,7 +37,7 @@ fun UpdatesPage(
     val loaded by produceState<LoadedPage?>(null, bundle, name) { value = bundle.page(name) }
     val page = loaded ?: return
     TinyUIPage(
-        page.runtime, page.module, registry, sink, services, propsJson, modifier, page.sourceMaps,
+        page.runtime, page.module, host, services, propsJson, modifier, page.sourceMaps,
         error = { failure ->
             // only the failures that mean the package cannot run here (docs/updates.md §4.5)
             if ((failure.kind == "E2" || failure.kind == "E6") && page.bundle !== updates.embedded(pkg)) {