docs: add Mermaid architecture diagrams

docs/contracts/workspace-evidence-v3.md

@@ -5,6 +5,21 @@ workspace descriptor. Evidence is optional: a valid v3 descriptor without it rem
 When present, `evidence` is strict: it contains `source` and a defaulted strict `policy`; every
 source variant and the policy reject unknown keys.
 
+```mermaid
+flowchart LR
+    REGISTRY["Workspace registry"] --> DESCRIPTOR["Evidence descriptor"]
+    DESCRIPTOR --> FILESYSTEM["Filesystem adapter"]
+    DESCRIPTOR --> HTTP["HTTP adapter"]
+    DESCRIPTOR --> S3["S3 adapter"]
+    FILESYSTEM --> CURATED["Curated markdown"]
+    HTTP --> CURATED
+    S3 --> CURATED
+    CURATED --> VALIDATE["Validate schema\nand provenance"]
+    VALIDATE --> PREPROCESS["Preprocess pinned\nrevision"]
+    PREPROCESS --> GENERATION["Versioned generation"]
+    GENERATION --> ACTIVE["Active corpus"]
+```
+
 ## Filesystem source
 
 A filesystem source uses the exact URI `<workspace.id>/evidence`. `patterns` is a nonempty list of