diff --git a/conformance/agent/direct_json/compiler.yaml b/conformance/agent/direct_json/compiler.yaml
index 413374c044..9bc24e815f 100644
--- a/conformance/agent/direct_json/compiler.yaml
+++ b/conformance/agent/direct_json/compiler.yaml
@@ -58,6 +58,9 @@
 # v1.0. A case states no version of its own: the version it runs under is the
 # one its catalog document declares.
 
+# A compile case checks the block on its own, as `validate_payload` does: a
+# surface that the block updates without creating is assumed to exist.
+
 - name: test_compile_json_message_list
   description: A well formed message list compiles to those messages.
   action: compile
diff --git a/conformance/agent/direct_json/decompiler.yaml b/conformance/agent/direct_json/decompiler.yaml
index 0f9c7c8187..e04e296efe 100644
--- a/conformance/agent/direct_json/decompiler.yaml
+++ b/conformance/agent/direct_json/decompiler.yaml
@@ -36,6 +36,9 @@
 # v1.0. A case states no version of its own: the version it runs under is the
 # one its catalog document declares.
 
+# A round trip checks the recompiled block on its own, as `validate_payload`
+# does: a surface that the block updates without creating is assumed to exist.
+
 - name: test_decompile_json_messages
   description: Messages are written back out as the JSON a model would have emitted, and compiling that returns them.
   action: decompile
diff --git a/conformance/agent/direct_json/response_parser.yaml b/conformance/agent/direct_json/response_parser.yaml
index 569bef689b..b4b057ef82 100644
--- a/conformance/agent/direct_json/response_parser.yaml
+++ b/conformance/agent/direct_json/response_parser.yaml
@@ -56,6 +56,9 @@
 # v1.0. A case states no version of its own: the version it runs under is the
 # one its catalog document declares.
 
+# A response is parsed as one chat turn, against a renderer that holds no
+# surfaces yet, so a case that updates a surface also creates it.
+
 # --- Unwrapping a response ---
 
 - name: test_unwrap_text_before_between_and_after_blocks
@@ -213,11 +216,15 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
   input: |-
     Here is the surface.
-    <a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": "Hello"}]}}]</a2ui-json>
+    <a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}, {"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": "Hello"}]}}]</a2ui-json>
     Tell me if you want it changed.
   expect:
     - text: "Here is the surface."
     - a2ui:
+        - version: "v1.0"
+          createSurface:
+            surfaceId: "s1"
+            catalogId: "conformance/simplified"
         - version: "v1.0"
           updateComponents:
             surfaceId: "s1"
diff --git a/conformance/agent/direct_json/response_streaming.yaml b/conformance/agent/direct_json/response_streaming.yaml
index 6f4724a33d..9e433981fc 100644
--- a/conformance/agent/direct_json/response_streaming.yaml
+++ b/conformance/agent/direct_json/response_streaming.yaml
@@ -102,6 +102,11 @@
 # version" run them against v0.8, v0.9 and v1.0 catalogs alike. The v0.8 and
 # v0.9 cases use `streaming_catalog_v0_8.json` and `streaming_catalog_v0_9.json`.
 
+# A stream is read as one chat turn, against a renderer that holds no surfaces
+# yet. A case that updates a surface it does not create starts with a block
+# that creates it, since a renderer rejects an update to a surface it does not
+# hold.
+
 # --- Text as it arrives ---
 
 - name: test_chunk_text_emitted_as_it_arrives
@@ -125,6 +130,13 @@
     format: direct_json
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: |
         Here is the surface.
       expect:
@@ -231,6 +243,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1",'
       expect: []
     - input: ' "components": [{"id": "root", "component": "Text", "text": "Hello"}]}}]</a2ui-json>'
@@ -253,6 +272,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["greeting"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateDataModel": {"surfaceId": "s1", "value": {"greeting": "Hel'
       expect:
         - a2ui:
@@ -278,6 +304,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": "Hello", "variant": "cap'
       expect: []
     - input: 'tion"}]}}]</a2ui-json>'
@@ -301,6 +334,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["value"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateDataModel": {"surfaceId": "s1", "path": "/greeting", "value": "Hel'
       expect:
         - a2ui:
@@ -326,6 +366,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": "Hel'
       expect: []
     - input: 'lo"'
@@ -352,6 +399,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Card", "child": "body"}, {"id": "body", "component": "Text", "text": "Hel'
       expect:
         - a2ui:
@@ -410,6 +464,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": "Hel'
       expect: []
     - input: 'lo"}]}}]</a2ui-json>'
@@ -432,6 +493,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": "</a2ui'
       expect: []
     - input: '-json>"}]}}]</a2ui-json>'
@@ -453,6 +521,13 @@
     format: direct_json
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: |
         First the greeting.
       expect:
@@ -548,6 +623,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": {"@path": "/user'
       expect: []
     - input: '/name"}}]}}]</a2ui-json>'
@@ -571,6 +653,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Te'
       expect: []
     - input: 'xt", "text": "Hello"}]}}]</a2ui-json>'
@@ -593,6 +682,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Card", "child": "bo'
       expect: []
     - input: 'dy"}, {"id": "body", "component": "Text", "text": "Hello"}]}}]</a2ui-json>'
@@ -618,6 +714,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Column", "children": ["one", "tw'
       expect: []
     - input: 'o"]}, {"id": "one", "component": "Text", "text": "One"}, {"id": "two", "component": "Text", "text": "Two"}]}}]</a2ui-json>'
@@ -646,6 +749,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: ["text"]
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Column", "children": {"componentId": "row"'
       expect: []
     - input: ', "path": "/items"}}, {"id": "row", "component": "Text", "text": "Item"}]}}]</a2ui-json>'
@@ -744,6 +854,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateDataModel": {"surfaceId": "s1", "value": {"items": {'
       expect:
         - a2ui:
@@ -783,6 +900,13 @@
     catalog: "test_data/catalogs/simplified_catalog_v1_0.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v1.0", "createSurface": {"surfaceId": "s1", "catalogId": "conformance/simplified"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v1.0"
+              createSurface:
+                surfaceId: "s1"
+                catalogId: "conformance/simplified"
     - input: '<a2ui-json>[{"version": "v1.0", "updateDataModel": {"surfaceId": "s1", "value": {"title": "Top", "items": {"item1"'
       expect: []
     - input: ': {"name": "Item 1"}}}}}]</a2ui-json>'
@@ -1289,7 +1413,7 @@
                 root: "root"
 
 - name: test_stream_update_before_create_surface_fails_v09
-  description: An updateComponents before its surface's createSurface is emitted while the block arrives, and the block raises a validation error when it closes, since the surface did not exist yet.
+  description: An updateComponents for a surface that does not exist yet is held back, since a renderer would reject it, and the block raises a validation error when it closes.
   action: parse_chunk
   args:
     format: direct_json
@@ -1299,15 +1423,7 @@
     - input: "<a2ui-json>["
       expect: []
     - input: '{"version": "v0.9", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": "hi"}]}}, '
-      expect:
-        - a2ui:
-            - version: "v0.9"
-              updateComponents:
-                surfaceId: "s1"
-                components:
-                  - id: "root"
-                    component: "Text"
-                    text: "hi"
+      expect: []
     - input: '{"version": "v0.9", "createSurface": {"catalogId": "test_catalog", "surfaceId": "s1"}}]</a2ui-json>'
       expect_error:
         category: "ValidationError"
@@ -3061,7 +3177,7 @@
                           path: "/name"
 
 - name: test_stream_data_model_before_create_surface_fails_v09
-  description: An updateDataModel before its surface's createSurface is emitted while the block arrives, and the block raises a validation error when it closes.
+  description: An updateDataModel for a surface that does not exist yet is held back, since a renderer would reject it, the messages after it wait with it, and the block raises a validation error when it closes.
   action: parse_chunk
   args:
     format: direct_json
@@ -3071,20 +3187,9 @@
     - input: "<a2ui-json>["
       expect: []
     - input: '{"version": "v0.9", "updateDataModel": {"surfaceId": "s1", "value": {"name": "Alice"}}}, '
-      expect:
-        - a2ui:
-            - version: "v0.9"
-              updateDataModel:
-                surfaceId: "s1"
-                value:
-                  name: Alice
+      expect: []
     - input: '{"version": "v0.9", "createSurface": {"catalogId": "test_catalog", "surfaceId": "s1"}}, '
-      expect:
-        - a2ui:
-            - version: "v0.9"
-              createSurface:
-                surfaceId: "s1"
-                catalogId: "test_catalog"
+      expect: []
     - input: '{"version": "v0.9", "updateComponents": {"surfaceId": "s1", "components": [{"id": "root", "component": "Text", "text": {"path": "/name"}}]}}]</a2ui-json>'
       expect_error:
         category: "ValidationError"
@@ -3428,6 +3533,13 @@
     catalog: "test_data/catalogs/streaming_catalog_v0_9.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v0.9", "createSurface": {"surfaceId": "default", "catalogId": "test_catalog"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v0.9"
+              createSurface:
+                surfaceId: "default"
+                catalogId: "test_catalog"
     - input: '<a2ui-json>[ {"version": "v0.9", "updateDataModel": {"surfaceId": "default", "value": {"name": "John", "incomplete": '
       expect: []
     - input: '"done"}}}]</a2ui-json>'
@@ -3484,6 +3596,13 @@
     catalog: "test_data/catalogs/streaming_catalog_v0_9.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v0.9", "createSurface": {"surfaceId": "default", "catalogId": "test_catalog"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v0.9"
+              createSurface:
+                surfaceId: "default"
+                catalogId: "test_catalog"
     - input: '<a2ui-json>[ {"version": "v0.9", "updateDataModel": {"surfaceId": "default", "value": {"infoLink": "[More Info](x)", "rat'
       expect: []
     - input: 'ing": "5 star"'
@@ -3549,6 +3668,13 @@
     catalog: "test_data/catalogs/streaming_catalog_v0_9.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v0.9", "createSurface": {"surfaceId": "default", "catalogId": "test_catalog"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v0.9"
+              createSurface:
+                surfaceId: "default"
+                catalogId: "test_catalog"
     - input: "<a2ui-json>["
       expect: []
     - input: '{"version": "v0.9", "updateDataModel": {"surfaceId": "default", "value": {"title": "Top Restaurants", "items": {'
@@ -3596,6 +3722,13 @@
     catalog: "test_data/catalogs/streaming_catalog_v0_9.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v0.9", "createSurface": {"surfaceId": "default", "catalogId": "test_catalog"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v0.9"
+              createSurface:
+                surfaceId: "default"
+                catalogId: "test_catalog"
     - input: '<a2ui-json>[ {"version": "v0.9", "updateDataModel": {"surfaceId": "default", "value": {"title": "Top Restaurants","items": {"item1": {"name": "Food", "detail": "Spicy", "imageUrl":'
       expect: []
     - input: ' "https://example.com/food.png"}}}}}]</a2ui-json>'
@@ -3633,6 +3766,13 @@
     catalog: "test_data/catalogs/streaming_catalog_v0_9.json"
     progressive_keys: []
   steps:
+    - input: '<a2ui-json>[{"version": "v0.9", "createSurface": {"surfaceId": "default", "catalogId": "test_catalog"}}]</a2ui-json>'
+      expect:
+        - a2ui:
+            - version: "v0.9"
+              createSurface:
+                surfaceId: "default"
+                catalogId: "test_catalog"
     - input: '<a2ui-json>[ {"version": "v0.9", "updateDataModel": {"surfaceId": "default", "value": {"title": "Top Restaurants","items": {"item2": {"name": "Han Dynasty", "imageUrl": "http://localhost:10002/static/mapotofu.jpeg", "broken":'
       expect: []
     - input: '"x"}}}}}]</a2ui-json>'
diff --git a/conformance/agent/express/compiler.yaml b/conformance/agent/express/compiler.yaml
index f1240830fd..1424b4d8ae 100644
--- a/conformance/agent/express/compiler.yaml
+++ b/conformance/agent/express/compiler.yaml
@@ -101,6 +101,9 @@
 # v1.0. A case states no version of its own: the version it runs under is the
 # one its catalog document declares.
 
+# A compile case checks the block on its own, as `validate_payload` does: a
+# surface that the block updates without creating is assumed to exist.
+
 - name: test_compile_express_minimal_root
   description: A block that assigns root compiles to one createSurface carrying that component.
   action: compile
diff --git a/conformance/agent/express/decompiler.yaml b/conformance/agent/express/decompiler.yaml
index e9bced6eb9..c8261a62e8 100644
--- a/conformance/agent/express/decompiler.yaml
+++ b/conformance/agent/express/decompiler.yaml
@@ -50,6 +50,9 @@
 # v1.0. A case states no version of its own: the version it runs under is the
 # one its catalog document declares.
 
+# A round trip checks the recompiled block on its own, as `validate_payload`
+# does: a surface that the block updates without creating is assumed to exist.
+
 - name: test_decompile_express_components
   description: A createSurface writes back out as the surface line and the component assignments it came from.
   action: decompile