fix: consolidate boundary ownership and cleanup failure paths (#477)

docs/architecture.mermaid

@@ -29,7 +29,7 @@ graph TD
     end
 
     subgraph "Provider Process Foundation"
-        PROCESS["src/process/<br/>owned process groups, private roots<br/>deadlines, bounded diagnostics, cleanup"]
+        PROCESS["src/process/<br/>owned process groups, private roots<br/>deadlines, bounded file reads and diagnostics, cleanup"]
     end
 
     subgraph "Contracts Layer"