Clarify independent nested plugins

docs/plugin-architecture.md

@@ -624,6 +624,11 @@ For Sai VN:
 - ABI fixture proving `describe`, `validate`, `project`, `lower`, `measure`,
   and `apply` publish the expected contract shape without direct imports.
 
+The Norn and TeX slots are composition evidence, not Sai-owned plugin
+semantics. A Sai surface may reserve space for `embed.norn` or `embed.tex` when
+those plugin advertisements are available, but Norn and TeX keep their own ABI,
+capability claims, conformance packs, and owner repos.
+
 The parity manifest should be extended so runtimes declare plugin support:
 
 ```json
@@ -661,4 +666,5 @@ Recommended path:
 
 Absorbing Sai into Eve is the fallback if the plugin boundary fails. It should
 not be the first move. The cleaner machine is Eve as kernel, Sai as VN plugin,
-Aetheria as provider, and renderer clients as separate bodies.
+Norn and TeX as independent plugins, Aetheria as provider, and renderer clients
+as separate bodies.

web/fixtures/sai-vn-surface.conformance.json

@@ -8,7 +8,7 @@
     "transport": "local-json",
     "path": "web/fixtures/sai-vn-surface.json"
   },
-  "purpose": "Proves Sai visual-novel semantics with Norn and TeX embedded plugin surfaces before the plugins graduate.",
+  "purpose": "Proves Sai visual-novel semantics and optional nested placement of independently-owned Norn and TeX plugin surfaces before the plugins graduate.",
   "exitCriteria": "Move to Sai when VN/Ink story state, story commands, projection fixtures, and plugin ABI cases stabilize.",
   "asserts": [
     "vn.stage component",

web/fixtures/sai-vn.provider-advertisement.json

@@ -27,7 +27,7 @@
     {
       "kind": "plugin-fixture",
       "ref": "web/fixtures/sai-vn-surface.json",
-      "summary": "Advertisement-shaped provider entry for the Sai/Norn/TeX plugin conformance fixture."
+      "summary": "Advertisement-shaped provider entry for a Sai VN fixture that may nest independently-owned Norn and TeX plugin surfaces."
     },
     {
       "kind": "owner-repo",