Add comparison selection and format flags

docs/roadmap/implementation.md

@@ -163,11 +163,18 @@ without prematurely constructing application inputs or shared state.
    `--path` remains explain-only; against flags remain diff-only. Keep ordinary
    format defaults and singleton flag behavior unchanged.
 
-**Completion evidence:** the roadmap's inheritance table, including explicit
-empty and single-field overrides; default/explicit YAML and unsupported execution
-formats; unknown/all/unsupported scopes failing before factories. Verify against
-flags appear in diff help, not other operations. Successful pair preparation is
-completed in Stage 4; acquisition and delivery remain for Stage 8.
+**Completion evidence — complete:** right-side configuration and overlay fields
+inherit independently with their supplied state, while explicit empty overrides
+remain supplied. The `diff` command defaults to YAML, accepts explicit YAML, and
+rejects text and unsupported formats. Its help exposes both right-side flags;
+validate, show, sources, and explain do not, and `--path` remains explain-only.
+Comparison scope preflight defaults to `app` and rejects `all`, unknown, and
+unsupported scopes before suite factories run. Valid comparison preparation
+stores the resolved right selection without constructing application input or
+shared state. The existing show default and other operation defaults remain
+unchanged. Focused tests and the full ckconfig and dependent ckp suites pass.
+Separate typed pair preparation remains in Stage 4; acquisition and delivery
+remain in Stage 8.
 
 ## Stage 4: Prepare separate typed inputs for the selected pair