Add shared command path primitives

docs/roadmap/implementation.md

@@ -266,6 +266,11 @@ literal quotes/backslashes, invalid option components, empty declarations,
 root lookup, and a single argv token containing whitespace. Existing routing
 and help tests remain green.
 
+**Completed:** Added shared command-path parsing, validation, relations, keys,
+formatting, and token-copy helpers. Core command validation and path diagnostics,
+plus adapter route comparison and exact help lookup, now use the shared package.
+Verified with `go test ./internal/commandpath ./internal/cobra .`.
+
 ## Stage 2: Model deterministic prefix rewriting
 
 **Work**