docs: make schema v3 the only workspace contract

docs/workspace-diagnostic-protocol.md

@@ -7,9 +7,10 @@ response body belongs in the descriptor, generated `.env.example` files, or diag
 
 ## Scope and safety rules
 
-- The operational descriptor is schema version 3.
-- Schema-v1/v2 descriptors are readable only and remain `migration_required` until an explicit
-  reviewed migration writes schema version 3.
+- Schema v3 is the only accepted workspace descriptor format.
+- Schema v1 and v2 descriptors are rejected before diagnostics run. There is no in-product
+  migrator or automatic conversion; the Git repository must already contain reviewed v3
+  descriptors.
 - One workspace owns one Qdrant collection.
 - Qdrant and Ollama are internal services. Operators do not bind external vector or embedding
   transports for active manuals or supported diagnostics.